Biology subjects

Mayali, X.

Publications and source records attributed to Mayali, X..

At least 19 recordsLinked to original sources

bioRxiv2026

Phycosphere-associated bacteria differentially impact accessibility of dust-bound iron to model diatom Phaeodactylum tricornutum

In marine ecosystems, phytoplankton growth is frequently limited by iron, a micronutrient, due to its poor solubility from major sources such as atmospheric dust. Many phytoplankton cannot access dust-bound iron independently, and processes that solubilize this iron remain poorly understood. Here, we investigated whether bacterial partners can enhance phytoplankton growth under iron-limited conditions by facilitating utilization of dust-bound iron. Our study focused on Phaeodactylum tricornutum, a model diatom that is adapted to low iron growth conditions, grown in co-culture with bacteria isolated from its phycosphere. In iron-limited experiments using mineral dust as the sole iron source, the addition of Marinobacter significantly enhanced diatom growth compared to axenic controls, whereas Stappia significantly suppressed it. However, under iron-replete conditions, neither bacterium affected growth. These results indicated that under low-iron conditions, Marinobacter actively alleviates iron deficiency. Co-cultured bacterial cell abundances remained at least an order of magnitude lower than diatom cells. Marinobacter also enhanced algal growth within days of dust addition to established Fe-limited co-cultures, indicating its beneficial effect on P. tricornutum was not unique to a system in which it was newly introduced. Exometabolomic profiling comparing the axenic diatom and co-cultures revealed a suite of condensed aromatic organosulfur and peptide-like compounds associated with bacterial presence, as well as compounds that appeared to be unique to each co-culture, hinting at a molecular underpinning of each strains impact. Our findings demonstrate that low-abundance members of the phycosphere community can have a significant impact on host growth by modulating the accessibility of dust-bound Fe.

microbiology↗

bioRxiv2026

Oxidative stress reshapes diatom-microbiome interactions by shifting benefits from mutualistic to opportunistic bacteria

The roles of reactive oxygen species (ROS) as signaling molecules and inhibitors of phytoplankton growth are well documented. While phytoplankton physiological mechanisms for ROS detoxification are well characterized, the role of heterotrophic bacterial partners in ROS alleviation and outcomes for these bacteria remain poorly understood. Here, we examined how extracellular hydrogen peroxide (H2O2) shapes nutrient exchange between the diatom Phaeodactylum tricornutum and two phycosphere bacteria. From an initial screen of 20 bacteria, we identified a "helper" (Muricauda sp.) that enabled P. tricornutum to survive acute H2O2 stress and a "non-helper" (Algoriphagus sp.) that did not. Using nanoscale secondary ion mass spectrometry (nanoSIMS), we tracked diatom-derived carbon and nitrogen (13C and 15N) transfer to each bacterial partner under ROS stress. Oxidative stress disrupted diatom metabolism and altered nutrient transfer: diatom-derived carbon and nitrogen incorporation was significantly reduced in the helper but increased in the non-helper under H2O2 stress. Growth assays revealed that the helper preferentially utilized exudates from healthy, intact hosts, whereas the non-helper did not grow on exudates but thrived on lysates from damaged or lysed cells. Together, these findings indicate the helper was better adapted to accessing resources from living hosts, while the non-helper relied on nutrients released through ROS-induced host damage. Our results highlight oxidative stress as a key driver of algal-bacterial interactions and suggest that bacterial resource-acquisition strategy underlies host protection: bacteria utilizing healthy-host exudates are more likely to protect hosts from oxidative stress, while those benefiting from host damage are not, despite retaining ROS detoxification capacity.

microbiology↗

bioRxiv2026

Iron limitation alters diatom carbon flow through shifts in microbiome exometabolite consumption

Iron is required for photosynthesis, and thus affects biogeochemical cycling in widespread regions where its availability is limited. Turnover of aquatic photosynthetically-derived carbon is largely constrained by bacterial activity, but we lack a mechanistic understanding of how iron limitation influences this activity. We examined a bacterial enrichment community dependent on carbon from the diatom Phaeodactylum tricornutum to investigate how iron limitation alters the flow of carbon to bacteria, and exometabolite and community composition. Using stable isotope tracing, we quantified diatom exudate incorporation with single-cell-resolution. We identified a population of bacteria under iron limitation with high metabolic activity yet low incorporation of newly-fixed diatom carbon, indicating a shift in metabolism relative to the iron-replete control. Ultra-high-resolution exometabolomics revealed bacterial consumption of aromatics, lipid-like compounds, and purines and pyrimidines occurred under iron-limitation, when these compounds also exhibited increased exudation. We identified gene pathways for utilization of these compounds in taxa with increased abundance under iron limitation which may be responsible for carbon flow shifts. These results provide a mechanistic link between iron-limitation driven shifts in exudate composition and flow of carbon to the microbiome. This has important implications for predicting carbon flow in surface oceans and manipulating algal-bacterial interactions in engineered systems.

microbiology↗

bioRxiv2025

Marine bacteria cross-feeding controls the fate of extracellular glycolate carbon

Glycolate is a major product of phytoplankton photorespiration, but its fate in the microbial food web is not well constrained. Here, we used stable isotope probing and mass spectrometry combined with genomic analyses and microscopy to quantify glycolate metabolism by a taxonomically diverse set of heterotrophic marine bacteria. We found that 9 of 16 tested strains with the genomic capability to metabolize glycolate directly assimilated and respired glycolate carbon in monoculture. We next co-cultivated glycolate-incorporating strains with non-incorporating strains and found that several cross-feeders incorporated more glycolate carbon into their biomass than direct incorporators. Carbon use efficiency, reflecting proportional differences in movement of glycolate carbon into biomass versus into carbon dioxide, were distinct across co-cultures and ranged from 0.01 -3.15% depending on the strain mixtures. These results suggest that the fate of glycolate carbon is not limited to microbial taxa with the genetic capability for direct assimilation, and that bacterial metabolic interactions via cross-feeding play a critical role in influencing the efficiency of carbon transfer. Such information is critical to refine conceptual and numerical models of heterotrophic processing and transfer of organic carbon in an era of global change with predicted increases in photorespiration.

microbiology↗

bioRxiv2024

Spatially structured competition and cooperation alters algal carbon flow to bacteria

Microbial communities regulate the transformations of carbon in aquatic systems through metabolic interactions and food-web dynamics that can alter the balance of photosynthesis and respiration. Direct competition for resources is thought to drive microbial community assembly in algal systems, but other interaction modes that may shape communities are more challenging to isolate. Through untargeted metabolomics and metabolic modeling, we predicted the degree of resource competition between bacterial pairs when growing on model diatom Phaeodactylum tricornutum-derived substrates. In a subsequent sequential media experiment, we found that pairwise interactions were consistently more cooperative than predicted based on resource competition alone, indicating an unexpected role for cooperation in algal carbon processing. To link this directly to algal carbon fate, we chose a representative cooperative and competitive influencer isolate and a model recipient and applied single-cell isotope tracing in a custom porous microplate cultivation system. In the presence of live algae, the recipient drew down more algal carbon in the presence of the cooperative influencer compared to the competitive influencer, supporting the sequential experiment results. We also found that total carbon assimilation into bacterial biomass, integrated over influencer and recipient, was significantly higher for the cooperative interaction. Our findings support the notion that non-competitive interactions are critical for predicting algal carbon fate. Significance StatementMicrobial interactions have widely been studied in the context of host resources but testing and measuring direct interactions in a lab has been particularly challenging. By combining untargeted metabolomics, sequential/(co-)culture, and metabolic modeling, we demonstrate that the presence of an unexpected interaction mode in a live system and show how it impacts the flow of host-derived resources. This top-down approach can help identify novel bacterial interactions that play a crucial role in microbial community-host ecosystems, which may have an impact in holobiont phenotypes including alga, fungal, or plant systems.

microbiology↗

bioRxiv2024

Coastal bacteria and protists assimilate viral carbon and nitrogen

Free viruses are the most abundant type of biological particles in the biosphere, but the lack of quantitative knowledge about their consumption by heterotrophic protists and bacterial degradation has hindered the inclusion of virovory in biogeochemical models. Here, using isotope-labeled viruses added to three independent microcosm experiments with natural microbial communities followed by isotope measurements with single-cell resolution and flow cytometry, we quantified the flux of viral C and N into virovorous protists and bacteria and compared the loss of viruses due to abiotic vs biotic factors. We found that some protists can obtain most of their C and N requirements from viral particles and that viral C and N get incorporated into bacterial biomass. We found that bacteria and protists were responsible for increasing the daily removal rate of viruses by 33% to 85%, respectively, compared to abiotic processes alone. Our laboratory incubation experiments showed that abiotic processes removed roughly 50% of the viruses within a week, and adding biotic processes led to a removal of 83% to 91%. Our data provide direct evidence for the transfer of viral C and N back into the microbial loop through protist grazing and bacterial breakdown, representing a globally significant flux that needs to be investigated further to better understand and predictably model the C and N cycles of the hydrosphere.

ecology↗

bioRxiv2024

Volatile Organic Compound Specialists in the Phycosphere

Labile dissolved organic carbon (LDOC) in the oceans accounts for [~][1/4] of marine primary production and turns over with a half-life of seconds to days, fueling one of the largest engines of microbial heterotrophic production on the planet. Volatile organic compounds (VOCs) are poorly constrained components of LDOC. Here, we detected 78 m/z signals, corresponding to unique VOCs, including petroleum hydrocarbons, totaling 18.5 nM in the culture medium of a model diatom. In five cocultures with bacteria adapted to grow with this diatom, 1 to 66 VOCs were depleted. Two of the most active VOC consumers, Marinobacter and Roseibium, contained more genes encoding VOC oxidation proteins, and attached to the diatom, suggesting VOC specialism. With NanoSIMS and stable isotope labeling, we confirmed that Marinobacter incorporated carbon from benzene, one of the depleted VOCs detected in the co-culture. Diatom gross carbon production increased by up to 29% in the presence of VOC consumers, indicating that VOC consumption by heterotrophic bacteria in the phycosphere - a region of rapid organic carbon oxidation that surrounds phytoplankton cells - could impact global rates of gross primary production.

microbiology↗

bioRxiv2024

An algicidal bacterium shapes the microbiome during outdoor diatom cultivation collapse

Biogeochemistry and productivity of algae-dominated environments is fundamentally influenced by the diversity and activity of bacteria. Namely, algicidal bacteria that prey on algal hosts can control elemental cycling and host populations within outdoor algal ponds used for biofuel production. In this study, we describe the genomic and proteomic signatures of a putative algicidal bacterium, Kordia sp. (family Flavobacteriaceae), that bloomed during a population-wide crash of the biofuel diatom, Phaeodactylum tricornutum. This Kordia sp. bloom occurred after 29 days of cultivation in outdoor algal raceway ponds inoculated with P. tricornutum, but not in parallel ponds inoculated with Microchloropsis salina. Several signatures of antagonism expressed by Kordia during diatom demise highlights previously unexplored mechanisms that may aid in algicidal activity or bacterial competition, including the type VI secretion system and hydrogen peroxide production. Analysis of accompanying downstream microbiota (primarily of the Rhodobacteraceae family) provides evidence that cross-feeding is important in supporting microbial diversity during algal demise. Specifically, in situ and laboratory data suggest that Kordia acts as a primary degrader of biopolymers during algal demise, and co-occurring Rhodobacteraceae exploit degradation molecules or scavenge metabolic byproducts for carbon. Further, targeted analysis of 30 Rhodobacteraceae metagenome assembled genomes suggest algal pond Rhodobacteraceae commonly harbor pathways for carbon monoxide oxidation, a potential strategy to persist under competition. Collectively, these observations further constrain the role of algicidal bacteria in the aquatic ecosystem.

microbiology↗

bioRxiv2024

Scarcity of fixed carbon transfer in a model microbial phototroph-heterotroph interaction

Although the green alga Chlamydomonas reinhardtii has long served as a reference organism, few studies have interrogated its role as a primary producer in microbial interactions. Here, we quantitatively investigated C. reinhardtiis capacity to support a heterotrophic microbe using the established coculture system with Mesorhizobium japonicum, a vitamin B12-producing -proteobacterium. Using stable isotope probing and nanoscale secondary ion mass spectrometry (nanoSIMS), we tracked the flow of photosynthetic fixed carbon and consequent bacterial biomass synthesis under continuous and diurnal light with single-cell resolution. We found that more 13C fixed by the alga was taken up by bacterial cells under continuous light, invalidating the hypothesis that the algas fermentative degradation of starch reserves during the night would boost M. japonicum heterotrophy. 15NH4 assimilation rates and changes in cell size revealed that M. japonicum cells reduced new biomass synthesis in coculture with the alga but continued to divide - a hallmark of nutrient limitation often referred to as reductive division. Despite this sign of starvation, the bacterium still synthesized vitamin B12 and supported the growth of a B12-dependent C. reinhardtii mutant. Finally, we showed that bacterial proliferation could be supported solely by the algal lysis that occurred in coculture, highlighting the role of necromass in carbon cycling. Collectively, these results reveal the scarcity of fixed carbon in this microbial trophic relationship (particularly under environmentally relevant light regimes), demonstrate B12 exchange even during bacterial starvation, and underscore the importance of quantitative approaches for assessing metabolic coupling in algal-bacterial interactions.

microbiology↗

bioRxiv2024

A toxic environment selects for specialist microbiome in poison frogs

Shifts in microbiome community composition can have large effects on host health. It is therefore important to understand how perturbations, like those caused by the introduction of exogenous chemicals, modulate microbiome community composition. In poison frogs within the family Dendrobatidae, the skin microbiome is exposed to the alkaloids that the frogs sequester from their diet and use for defense. Given the demonstrated antimicrobial effects of these poison frog alkaloids, these compounds may be structuring the skin microbial community. To test this, we first characterized microbial communities from chemically defended and closely related non-defended frogs from Ecuador. Then we conducted a laboratory experiment to monitor the effect of the alkaloid decahydroquinoline (DHQ) on the microbiome of a single frog species. In both the field and lab experiments, we found that alkaloid-exposed microbiomes are more species rich and phylogenetically diverse, with an increase in rare taxa. To better understand the strain-specific behavior in response to alkaloids, we cultured microbial strains from poison frog skin and found the majority of strains exhibited either enhanced growth or were not impacted by the addition of DHQ. Additionally, stable isotope tracing coupled to nanoSIMS suggests that some of these strains are able to metabolize DHQ. Taken together, these data suggest that poison frog chemical defenses open new niches for skin-associated microbes with specific adaptations, including the likely metabolism of alkaloids, that enable their survival in this toxic environment. This work helps expand our understanding of how exposure to exogenous compounds like alkaloids can impact host microbiomes.

microbiology↗

bioRxiv2023

THE DUAL ROLE OF THE MICROCYSTIS AERUGINOSA MICROBIOME ON CYANOTOXIN PRODUCTION: COMPETITION FOR AND REMINERALIZATION OF ORGANIC NITROGEN

Nutrient-induced blooms of the globally abundant freshwater toxic cyanobacterium Microcystis are the cause of worldwide public and ecosystem health concerns. The response of Microcystis growth and toxin production to new and recycled nitrogen (N) inputs, and the impact of heterotrophic bacteria in the Microcystis phycosphere on these processes are not well understood. Here, using microbiome transplant experiments, cyanotoxin analysis, and stable isotope tracing to measure N incorporation and exchange at single cell resolution, we monitored the growth, cyanotoxin production, and microbiome community structure of several Microcystis strains grown on amino acids and proteins as the sole N source. We demonstrate that 1) organic N availability shapes the microbiome community structure in the Microcystis phycosphere; 2) external organic N input leads to lower bacterial colonization of the phycosphere; 3) certain Microcystis strains can directly uptake amino acids, but with lower rates than heterotrophic bacteria; 4) biomass-specific microcystin production is not impacted by N source (i.e., nitrate, amino acids and protein) but rather by total N availability; and 5) some bacterial communities compete with Microcystis for organic N, but others remineralize organic N, in the process producing bio-available N for Microcystis. We conclude that organic N input can support Microcystis blooms and toxin production, and Microcystis-associated microbial communities play critical roles by influencing cyanobacterial succession through either decreasing (via competition) or increasing (via remineralization) N availability, especially under inorganic N scarcity.

microbiology↗

bioRxiv2023

Differential substrate affinity and catabolite repression enable preferential use of urea by ammonia-oxidizing bacteria

Four distinct lineages of ammonia-oxidizing microorganisms (AOM) collectively contribute to one of the largest nitrogen fluxes in the global nitrogen budget. AOM possess widely different specific affinities for ammonia, thought to determine their niche differentiation. Nevertheless, ammonia-oxidizing archaea and bacteria (AOA, AOB), and complete ammonia oxidizers (comammox) co-occur in soils, freshwater sediments, and aquifers, suggesting that other factors must drive their coexistence. Here, we show that representatives of four AOM lineages employ distinct regulatory strategies for ammonia or urea utilization, thereby minimizing direct competition for either substrate. The tested AOA and comammox species preferentially used ammonia over urea, while beta-proteobacterial AOB favored urea utilization, repressed ammonia transport in the presence of urea, and showed higher affinity for urea than ammonia, whereas gamma-proteobacterial AOB co-utilized both substrates. Stable isotope tracing, kinetics, and transcriptomics experiments revealed that both assimilation and oxidation of ammonia are transport-dependent. These results reveal novel mechanisms of nitrogen metabolism regulation and transporter-based affinity underlying the contrasting niche adaptation and coexistence patterns among the major AOM lineages.

microbiology↗

bioRxiv2022

The Western Lake Erie Culture Collection: A promising resource for evaluating the physiological and genetic diversity of Microcystis and its associated microbiome

Cyanobacteria harmful algal blooms (cyanoHABs) dominated by Microcystis spp. have significant public health and economic implications in freshwater bodies around the world. These blooms are capable of producing a variety of cyanotoxins, including microcystins, that affect fishing and tourism industries, human and environmental health, and access to drinking water. In this study, we isolated and sequenced the genomes of 21 unialgal Microcystis cultures collected from western Lake Erie between 2017-2019. While some cultures isolated in different years have a high degree of genetic similarity (Average Nucleotide Identity >99%), genomic data shows that these cultures also represent much of the breadth of known Microcystis diversity in natural populations. Only 5 isolates contained all the genes required for microcystin synthesis while 2 isolates contained a previously described partial mcy operon. Microcystin production within cultures was also assessed using Enzyme-Linked Immunosorbent Assay (ELISA) and supported genomic results with high concentrations (up to 900 g L-1) in cultures with complete mcy operons and no or low toxin detected otherwise. These xenic cultures also contained a substantial diversity of bacteria associated with Microcystis, which has become increasingly recognized as an essential component of cyanoHAB community dynamics. These results highlight the genomic diversity among Microcystis strains and associated bacteria in Lake Erie, and their potential impacts on bloom development, toxin production, and toxin degradation. This collection significantly increases the availability of environmentally relevant Microcystis strains from temperate North America, which is changing rapidly due to climate change. HighlightsO_LITwenty one xenic Microcystis cultures were isolated from western Lake Erie and capture the diversity of Microcystis strains observed in natural populations as well as their associated bacteria C_LIO_LIMicrocystis strains show variability in core and accessory gene content, and genetically similar strains produce varying concentrations and congeners of microcystins C_LIO_LIThis collection is a valuable resource for studying strain diversity and interactions between Microcystis and associated bacteria C_LIO_LIOur collection increases the availability of environmentally relevant strains from temperate North America, which is historically underrepresented in culture collections. C_LI

microbiology↗

bioRxiv2022

Single cell carbon and nitrogen incorporation and remineralization profiles are uncoupled from phylogenetic groupings of diatom-associated bacteria

Bacterial remineralization of algal organic matter is thought to fuel algal growth, but this has not been quantified. Consequently, we cannot currently predict whether some bacterial taxa may provide more remineralized nutrients to algae than others, nor whether this is linked their incorporation. We quantified bacterial incorporation of algal-derived complex dissolved organic C (DOC) and N (DON) and net algal incorporation of remineralized C and N at the single cell level using isotope tracing and NanoSIMS for fifteen bacterial co-cultures growing with the diatom Phaeodactylum tricornutum. We found unexpected variability in the net C and N fluxes between algae and bacteria, including non-ubiquitous complex DON utilization and remineralization. We identified three distinct functional categories of metabolic interactions, which we termed macromolecule remineralizers, macromolecule users, and small-molecule users, the latter exhibiting efficient growth under low carbon availability. The functional categories were not linked to phylogeny and could not be elucidated strictly from metabolic capacity as predicted by comparative genomics. Using comparative proteogenomic analyses, we show that a complex DON incorporating strain expressed proteins related to growth and peptide transport, and a non-incorporator prioritized reactive oxygen species scavenging and inorganic nutrient uptake. Our analysis suggests that phylogeny does not predict the extent of algae-bacteria metabolite exchange, and activity-based measurements are indispensable to classify the high diversity of microbes into functional groups. These categorizations are useful for conceptual understanding and mechanistic numerical modeling to ultimately predict the fate of elemental cycles in response to environmental change.

microbiology↗

bioRxiv2022

Dynamic Phaeodactylum tricornutum Exometabolites Shape Surrounding Bacterial Communities

The roles of exometabolites in mediating algal-bacterial interactions and regulating microbial community composition are not well understood. Here, we identified specific exometabolites from the model diatom Phaeodactylum tricornutum affecting abundance of specific bacterial taxa in isolation and in a community setting. We examined the response of a P. tricornutum-adapted enrichment community and found that both algal exudates and algal presence drove similar changes in community composition compared to controls. Using LC-MS/MS, we identified 50 metabolites produced by axenic P. tricornutum and found that different exometabolites accumulated during different algal growth phases. Profiling growth of 12 bacterial isolates representative of the enrichment community uncovered two algal exometabolites (out of 12 tested) which supported growth of a subset of isolates as a primary carbon source. We compared enrichment community response with and without the addition of two contrasting metabolites: 4-hydroxybenzoic acid, which supported isolate growth, and lumichrome, which did not. Exogenous metabolite additions did promote increased abundances of taxa that were able to utilize the metabolite in the isolate study, but also revealed the importance of factors relating to algal presence in regulating community composition. Collectively, this work demonstrates the influence of specific algal exometabolites in driving microbial community composition.

microbiology↗

bioRxiv2022

A proton pump enhancing photosynthesis links phagocytosis to marine phytoplankton symbiogenesis

Diatoms, dinoflagellates, and coccolithophorids are the dominant groups of marine eukaryotic phytoplankton collectively responsible for the majority of primary production in the ocean1. These phytoplankton contain additional intracellular membranes around their chloroplasts derived from ancestral engulfment of red microalgae by unicellular heterotrophic eukaryotes that led to secondary endosymbiosis2. This symbiogenesis hypothesis for the origin of modern secondary endosymbiotic phytoplankton is supported by a wealth of palaeontologic, morphologic, and genomic evidence3-6. However, the selectable evolutionary advantage of these membranes and the physiological significance for extant phytoplankton are unknown. We report that the proton-pumping enzyme V-type H+-ATPase (VHA), ubiquitously used in eukaryotic intercellular digestion, is localized around the chloroplasts of centric diatoms and that VHA-activity significantly enhances photosynthesis over a wide range of oceanic irradiances. Similar results in pennate diatoms, dinoflagellates, and coccolithophorids, but not green or red microalgae, imply a mechanism resulting from the co-option of phagocytic VHA activity into a carbon concentrating mechanism that is common to secondary endosymbiotic phytoplankton. Furthermore, analogous VHA-dependent mechanisms in extant photosymbiotic marine invertebrates7-9 provide functional evidence for an adaptive advantage throughout the transition from endosymbiosis to symbiogenesis. Our results suggest that VHA-dependent enhancement of photosynthesis contributes at least 7% of primary production in the ocean, providing an example of a symbiosis-derived evolutionary innovation with global environmental implications.

evolutionary biology↗

bioRxiv2021

Identification of effector metabolites using exometabolite profiling of diverse microalgae

Dissolved exometabolites mediate algal interactions in aquatic ecosystems, but microalgal exometabolomes remain understudied. We conducted an untargeted metabolomic analysis of non-polar exometabolites exuded from four phylogenetically and ecologically diverse eukaryotic microalgal strains grown in the laboratory: freshwater Chlamydomonas reinhardtii, brackish Desmodesmus sp., marine Phaeodactylum tricornutum, and marine Microchloropsis salina, to identify released metabolites based on relative enrichment in the exometabolomes compared to cell pellet metabolomes. Exudates from the different taxa were distinct, but we did not observe clear phylogenetic patterns. We used feature based molecular networking to explore the identities of these metabolites, revealing several distinct di- and tripeptides secreted by each of the algae, lumichrome, a compound that is known to be involved in plant growth and bacterial quorum sensing, and novel prostaglandin-like compounds. We further investigated the impacts of exogenous additions of eight compounds selected based on exometabolome enrichment on algal growth. Of the these, five (lumichrome, 5-S-methyl-5-thioadenosine, 17-phenyl trinor prostaglandin A2, dodecanedioic acid, and aleuritic acid) impacted growth in at least one of the algal cultures. Two of these (dodecanedioic acid and aleuritic acid) produced contrasting results, increasing growth in some algae and decreasing growth in others. Together, our results reveal new groups of microalgal exometabolites, some of which could alter algal growth when provided exogenously, suggesting potential roles in allelopathy and algal interactions. IMPORTANCEMicroalgae are responsible for nearly half of primary production on earth and play an important role in global biogeochemical cycling as well as in a range of industrial applications. Algal exometabolites are important mediators of algal-algal and algal-bacterial interactions that ultimately affect algal growth and physiology. In this study we characterize exometabolomes across marine and freshwater algae to gain insights into the diverse metabolites they release into their environments ("exudates"). We observe that while phylogeny can play a role in exometabolome content, environmental conditions or habitat origin (freshwater vs marine) are also important. We also find that several of these compounds can influence algal growth (as measured by chlorophyll production) when provided exogenously, highlighting the importance of characterization of these novel compounds and their role in microalgal ecophysiology.

microbiology↗

bioRxiv2021

Bacterial response to spatial gradients of algal-derived nutrients in a porous microplate

AO_SCPLOWBSTRACTC_SCPLOWPhotosynthetic microalgae are responsible for 50% of the global atmospheric CO2 fixation into organic matter and hold potential as a renewable bioenergy source. Their metabolic interactions with the surrounding microbial community (the algal microbiome) play critical roles in carbon cycling, but due to methodological limitations, it has been challenging to examine how community is developed by spatial proximity to their algal host. Here we introduce a hydrogel-based porous microplate to co-culture algae and bacteria, where metabolites are constantly exchanged between the microorganisms while maintaining physical separation. In the microplate we found that the diatom Phaeodactylum tricornutum accumulated to cell abundances ~20 folds higher than under normal batch conditions due to constant replenishment of nutrients through the hydrogel. We also demonstrate that algal-associated bacteria, both single isolates and complex communities, responded to inorganic nutrients away from their host as well as organic nutrients originating from the algae in a spatially predictable manner. These experimental findings coupled with a mathematical model suggest that host proximity and algal culture growth phase impact bacterial community development in a taxon-specific manner through organic and inorganic nutrient availability. Our novel system presents a useful tool to investigate universal metabolic interactions between microbes in aquatic ecosystems.

ecology↗