Biology subjects

Becker, J. W.

Publications and source records attributed to Becker, J. W..

7 recordsLinked to original sources

bioRxiv2025

ProSynTaxDB: A curated protein database and workflow for taxonomic classification of Prochlorococcus and Synechococcus in metagenomes

Prochlorococcus and Synechococcus are abundant marine picocyanobacteria that contribute significantly to ocean primary production. Recent genome sequencing efforts, including those presented here, have yielded a large number of high-quality reference genomes, enabling the classification of these picocyanobacteria in marine metagenomic sequence data at high phylogenetic resolution. When combined with environmental data, these classifications can guide cluster/clade/grade assignments and offer insights into niche differentiation within these populations. Here we present ProSynTax, a curated protein sequence dataset and accompanying workflow aimed at enhancing the taxonomic resolution of Prochlorococcus and Synechococcus classification. ProSynTax includes proteins from 1,260 genomes of Prochlorococcus and Synechococcus, including single-amplified genomes, high-quality draft genomes, and newly closed genomes. Additionally, ProSynTax incorporates proteins from 41,753 genomes of marine heterotrophic bacteria, archaea, and viruses to assess microbial and viral communities surrounding Prochlorococcus and Synechococcus. This resource enables accurate classification of picocyanobacterial clusters/clades/grades in metagenomic data - even when present at 0.15% of reads for Prochlorococcus or 0.03% of reads for Synechococcus.

bioinformatics↗

bioRxiv2024

Global niche partitioning of purine and pyrimidine cross-feeding among ocean microbes

Cross-feeding involves microbes consuming the exudates of other surrounding microbes, mediating elemental cycling. Characterizing the diversity of cross-feeding pathways in ocean microbes illuminates evolutionary forces driving self-organization of ocean ecosystems. Here, we uncover a purine and pyrimidine cross-feeding network in globally abundant groups. The cyanobacterium Prochlorococcus exudes both compound classes, which metabolic reconstructions suggest follows synchronous daily genome replication. Co-occurring heterotrophs differentiate into purine- and pyrimidine-using generalists, or specialists that use compounds for different purposes. The most abundant heterotroph, SAR11, is a specialist that uses purines as sources of energy, carbon and/or nitrogen, with subgroups differentiating along ocean-scale gradients in the supply of energy and nitrogen, in turn producing putative cryptic nitrogen cycles that link many microbes. Finally, in a SAR11 subgroup that dominates where Prochlorococcus is abundant, adenine additions to cultures inhibit DNA synthesis, poising cells for replication. We argue this subgroup uses inferred daily adenine pulses from Prochlorococcus to synchronize to the daily photosynthate supply from surrounding phytoplankton.

ecology↗

bioRxiv2023

Novel isolates expand the physiological diversity of Prochlorococcus and illuminate its macroevolution

Prochlorococcus is a diverse picocyanobacterial genus and the most abundant phototroph on Earth. Its photosynthetic diversity divides it into high- or low-light adapted groups representing broad phylogenetic grades - each composed of several monophyletic clades. Here we physiologically characterize four new Prochlorococcus strains isolated from below the deep chlorophyll maximum in the North Pacific Ocean and combine this information with genomic and evolutionary analyses. The isolates belong to deeply-branching low-light adapted clades that have no other cultivated representatives and display some unusual characteristics. For example, despite its otherwise low-light adapted physiological characteristics, strain MIT1223 has low chl b2 content similar to high-light adapted strains. Isolate genomes revealed that each strain contains a unique arsenal of pigment biosynthesis and binding alleles that have been horizontally acquired, contributing to the observed physiological diversity. Comparative genomic analysis of all picocyanobacteria reveals that Pcb, the major pigment carrying protein in Prochlorococcus, greatly increased in copy number and diversity per genome along a branch that coincides with the loss of facultative particle attachment. Collectively, these observations add support to the current macroevolutionary model of picocyanobacteria, where niche constructing radiations allowed ancestral lineages to transition from a particle-attached to planktonic lifestyle and broadly colonize the water column, followed by adaptive radiations near the surface that pushed ancestral lineages deeper in the euphotic zone resulting in modern depth-abundance profiles. Originality-Significance StatementThe marine cyanobacterium, Prochlorococcus, is among the Earths most abundant organisms, and much of its genetic and physiological diversity remains uncharacterized. While field studies help reveal the scope of diversity, cultured isolates allow us to link genomic potential to physiological processes, illuminate eco-evolutionary feedbacks, and test theories arising from comparative genomics of wild cells. Here, we report the isolation and characterization of novel low-light (LL) adapted Prochlorococcus strains that fill in multiple evolutionary gaps. These new strains are the first cultivated representatives of the LLVII and LLVIII paraphyletic grades of Prochlorococcus, which are broadly distributed in the lower regions of the ocean euphotic zone. Each of these grades is a unique, highly diverse section of the Prochlorococcus tree that separates distinct ecological groups: the LLVII grade branches between monophyletic clades that have facultatively particle-associated and constitutively planktonic lifestyles, while the LLVIII grade lies along the branch that leads to all high-light (HL) adapted clades. Characterizing strains and genomes from these grades yields insights into the large-scale evolution of Prochlorococcus. The new LLVII and LLVIII strains are adapted to growth at very low irradiance levels and possess unique light-harvesting gene signatures and pigmentation. The LLVII strains represent the most basal Prochlorococcus group with a major expansion in photosynthetic antenna genes. Further, a strain from the LLVIII grade challenges the paradigm that all LL-adapted Prochlorococcus exhibit high ratios of chl b:a2. These findings provide insights into major transitions in Prochlorococcus evolution, from the benthos to a fully planktonic lifestyle and from growth at low irradiances to the rise of the HL-adapted clades that dominate the modern ocean.

microbiology↗

bioRxiv2022

Metabolite diversity among Prochlorococcus strains belonging to divergent ecotypes

Primary AbstractThe euphotic zone of the surface ocean contains distinct physical-chemical regimes that vary inversely in light and nutrient concentrations as a function of depth. The most numerous phytoplankter of the mid- and low-latitude ocean is the picocyanobacterium Prochlorococcus, which consists of ecologically distinct subpopulations (i.e., "ecotypes"). Ecotypes have different temperature, light and nutrient optima and display distinct relative abundances along gradients of these niche dimensions. As a primary producer, Prochlorococcus fixes and releases organic carbon to neighboring microbes as part of the microbial loop. However, little is known about the specific molecules Prochlorococcus accumulates and releases or how these processes vary among its ecotypes. Here we characterize metabolite diversity of Prochlorococcus by profiling three ecologically-distinct cultured strains: MIT9301, representing a high-light adapted ecotype dominating shallow tropical and sub-tropical waters, MIT0801, representing a low-light adapted ecotype found throughout the euphotic zone and MIT9313, representing a low-light adapted ecotype relatively most abundant at the base of the euphotic zone. In both intracellular and extracellular metabolite profiles, we observe striking differences across strains in the accumulation and release of molecules. Some differences reflect variable genome content across the strains, while others likely reflect variable regulation of genetically-conserved pathways. In the extracellular profiles, we identify molecules that may serve as currencies in Prochlorococcus interactions with neighboring microbes and therefore merit further investigation. ImportanceApproximately half of the annual carbon fixation on Earth occurs in the surface ocean through the photosynthetic activities of phytoplankton such as the ubiquitous picocyanobacterium Prochlorococcus. Ecologically-distinct subpopulations of Prochlorococcus (or ecotypes) are central conduits of organic substrates into the ocean microbiome, thus playing important roles in surface ocean production. By measuring the chemical profile of three cultured ecotype strains, we observed striking differences in the likely chemical impact of Prochlorococcus subpopulations on their surroundings. Subpopulations differ along gradients of temperature, light and nutrient concentrations, suggesting that these chemical differences could affect carbon cycling in different ocean strata and should be considered in models of Prochlorococcus physiology and marine carbon dynamics.

microbiology↗

bioRxiv2020

Bacterial quorum sensing signal arrests phytoplankton cell division and protects against virus-induced mortality

Interactions between phytoplankton and heterotrophic bacteria fundamentally shape marine ecosystems. These interactions are driven by the exchange of compounds, however, linking these chemical signals, their mechanisms of action, and resultant ecological consequences remains a fundamental challenge. The bacterial signal 2-heptyl-4-quinolone (HHQ), induces immediate cellular stasis in the coccolithophore, Emiliania huxleyi, however, the mechanism responsible remains unknown. Here, we show that HHQ exposure leads to the accumulation of DNA damage in phytoplankton and prevents its repair. While this effect is reversible, HHQ-exposed phytoplankton are also protected from viral mortality, ascribing a new role of quorum sensing signals in regulating multi-trophic interactions. Further results demonstrate global HHQ production potential and the first in situ measurements of HHQ which coincide with areas of enhanced micro- and nanoplankton biomass. Our results support bacterial communication signals as emerging players, providing a new mechanistic framework for how compounds may contribute to structure complex marine microbial communities.

microbiology↗

bioRxiv2019

Toward a genetic system in the marine cyanobacterium Prochlorococcus

As the smallest and most abundant primary producer in the oceans, the cyanobacterium Prochlorococcus is of interest to diverse branches of science. For the past 30 years, research on this minimal phototroph has led to a growing understanding of biological organization across multiple scales, from the genome to the global ocean ecosystem. Progress in understanding drivers of its diversity and ecology, as well as molecular mechanisms underpinning its streamlined simplicity, has been hampered by the inability to manipulate these cells genetically.\n\nMultiple attempts have been made to develop an efficient genetic transformation method for Prochlorococcus over the years; all have been unsuccessful to date, despite some success with their close relative, Synechococcus. To avoid the pursuit of unproductive paths, we report here what has not worked in our hands, as well as our progress developing a method to screen the most efficient electroporation parameters for optimal DNA delivery into Prochlorococcus cells. We also report a novel protocol for obtaining axenic colonies and a new method for differentiating live and dead cells. The electroporation method can be used to optimize DNA delivery into any bacterium, making it a useful tool for advancing transformation systems in other genetically recalcitrant microorganisms.

microbiology↗

bioRxiv2018

Co-culture and biogeography of Prochlorococcus and SAR11

Prochlorococcus and SAR11 are among the smallest and most abundant organisms on Earth. With a combined global population of about 2.7 x 1028 cells, they numerically dominate bacterioplankton communities in oligotrophic ocean gyres and yet they have never been grown together in vitro. Here we describe co-cultures of Prochlorococcus and SAR11 isolates representing both high- and low-light adapted clades. We examined: (1) the influence of Prochlorococcus on the growth of SAR11 and vice-versa, (2) whether Prochlorococcus can meet specific nutrient requirements of SAR11, and (3) how co-culture dynamics vary when Prochlorococcus is grown with SAR11 compared with sympatric copiotrophic bacteria. SAR11 grew as much as 70% faster in the presence of Prochlorococcus, while the growth of the latter was unaffected. When Prochlorococcus populations entered stationary phase, SAR11 abundances decreased dramatically. In parallel experiments with copiotrophic bacteria however, the heterotrophic partner increased in abundance as Prochlorococcus densities leveled off. The presence of Prochlorococcus was able to meet SAR11s central requirement for organic carbon, but not reduced sulfur. Prochlorococcus strain MIT9313, but not MED4, could meet the unique glycine requirement of SAR11, likely due to production and release of glycine betaine by MIT9313. Evidence suggests that Prochlorococcus MIT9313 may also compete with SAR11 for the uptake of 3-dimethylsulfoniopropionate (DMSP). To place our results in context, we assessed the relative contribution of Prochlorococcus and SAR11 genome equivalents to those of identifiable bacteria and archaea in over 800 marine metagenomes. At many locations, more than half of the identifiable genome equivalents in the euphotic zone belonged to Prochlorococcus and SAR11 - highlighting the biogeochemical potential of these two groups.

microbiology↗