Biology subjects

Landry, Z.

Publications and source records attributed to Landry, Z..

6 recordsLinked to original sources

bioRxiv2025

GUARDIANS OF THE CELL: COCCOSPHERE PREVENTS OPPORTUNISTIC BACTERIA ATTACK IN HEAVY CALCIFYING COCCOLITHOPHORE

Coccolithophores are responsible for 40-60% of marine calcium carbonate production. This occurs through the biomineralization of extracellular calcium carbonate plates that encase the cell in a structure called the coccosphere. Despite its central role in ocean biogeochemistry, the function of coccolithophore calcification remains unresolved. One hypothesis is that the coccosphere acts as a physical shield, deterring predators and microbes. While its protective role has been investigated against grazers and viruses, its function in bacterial defense remains untested. Here, we investigate the interaction between heavily calcified Coccolithus braarudii and the bacterial pathogen Phaeobacter inhibens, known for its lethal Jekyll and Hyde relationship with the bloom-forming Gephyrocapsa huxleyi. We find that in C. braarudii, no P. inhibens pathogenicity is observed--unless the algae are decalcified. Upon decalcification, the relationship with P. inhibens becomes pathogenic, leading to algal cell death. Mortality of decalcified cells is specific to interactions with P. inhibens and is attachment-mediated: no toxicity is observed when cells are exposed to P. inhibens supernatant or to growth-inhibiting concentrations of indole-3-acetic acid-- identified in the P. inhibens-G. huxleyi system. Attachment requirement is further supported by scanning electron microscopy, which reveals extensive bacterial colonization on decalcified but not on calcified C. braarudii with P. inhibens. These findings provide the first experimental evidence that the coccosphere acts as a physical barrier against bacterial attack, underscoring its defensive role in coccolithophores.

microbiology↗

bioRxiv2025

Risk-reward trade-off in motility endurance generates dichotomy in search strategies among copiotrophic marine bacteria

Coptiotrophic marine bacteria contribute significantly to carbon storage in the ocean by remineralizing organic carbon present in nutrient-rich hotspots amidst oligotrophic waters. Motility is both highly beneficial and costly in such environments, presenting copiotrophs with a risk-reward trade-off in search behavior. Here we studied the motility endurance of 26 marine isolates using video microscopy and cell tracking over two days of carbon starvation. We found that this cost-benefit trade-off results in a distinct dichotomy among marine bacteria: risk-averse copiotrophs ceased motility within hours ( limostatic), whereas risk-prone copiotrophs converted 10% of their biomass per day into energy to retain motility for the two days of observation ( limokinetic). We identified a genomic component of this dichotomy, sufficiently robust to predict the response of additional species with 83% accuracy and the prevalence of both strategies in the ocean. This dichotomy can facilitate the incorporation of the bacterial contribution in ocean carbon cycle models.

microbiology↗

bioRxiv2025

Extracellular polymeric substance degradation shapes microbial community diversity

Competition for and exchange of nutrients play crucial roles in shaping microbial community function and dynamics. Although cross-feeding of small metabolites is known to drive carbon exchange among species, the importance of self-produced extracellular polymeric substances (EPS)-- which include proteins, polysaccharides, DNA, and humic-like substances-- remains less understood. Utilizing chitin-degrading microbial isolates and natural seawater communities, we found that 4-7% of the carbon from chitin degradation is converted into EPS, accounting for nearly a quarter of the exuded carbon. Different sources of EPS were found to select for distinct microbial communities. Through enzyme assays and untargeted metabolomics, we demonstrated that secreted enzymes degrade EPS in multiple steps that influence community diversity: larger oligomers are initially utilized by specialized degraders, while the subsequent breakdown into smaller oligomers, monosaccharides, and amino acids supports non-specialized consumers. These findings highlight the role of EPS as a significant carbon source exchanged between microbes, fueling metabolically diverse populations and enriching our understanding of carbon-mediated microbial interactions.

microbiology↗

bioRxiv2025

Growth in Low Carbon Conditions Reveals Amino-Acid-Coupled Iron Uptake

Bacteria in nature encounter substrates at widely varying concentrations, yet studies of bacterial physiology have focused more on nutrient type than concentration, partly due to challenges in maintaining low concentrations. We developed a Millifluidic Continuous Culture Device (MCCD) to culture bacteria under precisely controlled nutrient conditions, including very low concentrations, in a manner suitable for proteomic analysis. Using the MCCD, we cultured Escherichia coli with a mixture of amino acids as the sole carbon source at three concentrations supporting growth rates spanning a fivefold range. Surprisingly, at the lowest concentration, cells exhibited proteomic signatures of iron shortage despite equal iron levels across conditions. We observed the uptake of labeled iron-histidine and iron-cysteine complexes, indicating that amino acids facilitated iron acquisition and that amino-acid-bound iron is bioavailable to E. coli. These findings reveal a previously unknown mechanism of bacterial iron acquisition that emerged under the flow imposed by the MCCD, which likely diluted the siderophore pool and reduced their efficacy. This work highlights the importance of studying bacterial physiology under low nutrient concentrations and demonstrates how physical conditions, such as flow, shape microbial nutrient acquisition strategies.

microbiology↗

bioRxiv2023

High-throughput profiling of metabolic responses to exogenous nutrients in Synechocystis sp. PCC 6803

Cyanobacteria fix carbon dioxide and release carbon-containing compounds into the wider ecosystem, yet they are sensitive to small metabolites that may impact their growth and physiology. Several cyanobacteria can grow mixotrophically, but we currently lack a molecular understanding of how specific nutrients may alter the compounds they release, limiting our knowledge of how environmental factors might impact primary producers and the ecosystems they support. In this study, we develop a high-throughput phytoplankton culturing platform and identify how the model cyanobacterium Synechocystis sp. PCC 6803 responds to nutrient supplementation. We assess growth responses to 32 nutrients at two concentrations, identifying 15 that are utilized mixotrophically. Seven nutrient sources significantly enhance growth, while 19 elicit negative growth responses at one or both concentrations. High-throughput exometabolomics indicates that oxidative stress limits PCC 6803s growth, but may be alleviated by antioxidant metabolites. Furthermore, glucose and valine induce strong changes in metabolite exudation in a possible effort to correct pathway imbalances or maintain intracellular elemental ratios. This study sheds light on the flexibility and limits of cyanobacterial physiology and metabolism, as well as how primary production and trophic food webs may be modulated by exogenous nutrients. ImportanceCyanobacteria capture and release carbon compounds to fuel microbial food webs, yet we lack a comprehensive understanding of how external nutrients modify their behavior and what they produce. We developed a high throughput culturing platform to evaluate how the model cyanobacterium Synechocystis sp. PCC 6803 responds to a broad panel of externally supplied nutrients. We found that growth may be enhanced by metabolites that protect against oxidative stress, and that growth and exudate profiles are altered by metabolites that interfere with central carbon metabolism and elemental ratios. This work contributes a holistic perspective of the versatile response of PCC 6803 to externally supplied nutrients, which may alter carbon flux into the wider ecosystem.

microbiology↗

bioRxiv2019

Pangenomics reveal diversification of enzyme families and niche specialization in globally abundant SAR202 bacteria

It has been hypothesized that abundant heterotrophic ocean bacterioplankton in the SAR202 clade of the phylum Chloroflexi evolved specialized metabolism for the oxidation of organic compounds that are resistant to microbial degradation via common metabolic pathways. Expansions of paralogous enzymes were reported and implicated in hypothetical metabolism involving monooxygenase and dioxygenase enzymes. In the metabolic schemes proposed, the paralogs serve the purpose of diversifying the range of organic molecules that cells can utilize. To further explore this question, we reconstructed SAR202 single amplified genomes and metagenome-assembled genomes from locations around the world, including the deepest ocean trenches. In analyses of 122 SAR202 genomes that included six subclades spanning SAR202 diversity, we observed additional evidence of paralog expansions that correlated with evolutionary history, and further evidence of metabolic specialization. Consistent with previous reports, families of flavin-dependent monooxygenases were observed mainly in the Group III SAR202, in the proposed class Monstramaria and expansions of dioxygenase enzymes were prevalent in Group IV. We found that Group I SAR202 encode expansions of racemases in the enolase superfamily, which we propose evolved for the degradation of compounds that resist biological oxidation because of chiral complexity. Supporting the conclusion that the paralog expansions indicate metabolic specialization, fragment recruitment and fluorescence in situ hybridization with phylogenetic probes showed that SAR202 subclades are indigenous to different ocean depths and geographical regions. Surprisingly, some of the subclades were abundant in surface waters and contained rhodopsin genes, altering our understanding of the ecological role of SAR202 in stratified water columns.\n\nImportanceThe oceans contain an estimated 662 Pg C of dissolved organic carbon (DOC). Information about microbial interactions with this vast resource is limited, despite broad recognition that DOM turnover has a major impact on the global carbon cycle. To explain patterns in the genomes of marine bacteria we propose hypothetical metabolic pathways for the oxidation of organic molecules that are resistant to oxidation via common pathways. The hypothetical schemes we propose suggest new metabolism and classes of compounds that could be important for understanding of the distribution of organic carbon throughout the biosphere. These genome-based schemes will remain hypothetical until evidence from experimental cell biology can be gathered to test them, but until then they provide a perspective that directs our attention to the biochemistry of resistant DOM metabolism. Our findings also fundamentally change our understanding of the ecology of SAR202, showing that metabolically diverse variants of these cells occupy niches spanning all depths, and are not relegated to the dark ocean.

genomics↗