Biology subjects

Teeling, H.

Publications and source records attributed to Teeling, H..

4 recordsLinked to original sources

bioRxiv2023

Novel laminarin-binding CBMs in multimodular proteins of marine Bacteroidota feature prominently in phytoplankton blooms

The {beta}-(1,3)-glucan laminarin functions as storage polysaccharide in marine stramenophiles such as diatoms. Laminarin is abundant, water-soluble and structured simply, making it an attractive substrate for marine bacteria. As a consequence, many marine bacteria have developed competitive strategies to scavenge and decompose laminarin, which involves carbohydrate-binding modules (CBMs) as key players. We therefore functionally and structurally characterized two yet unassigned domains as laminarin-binding CBMs in multimodular proteins from our model bacterium Christiangramia forsetii KT0803T, hereby unveiling the novel laminarin-binding CBM families CBMxx and CBMyy (official CAZy numbering will be provided upon acceptance of the manuscript in a peer-reviewed journal). We discovered four CBMxx repeats in a surface glycan-binding protein (SGBP) and a single CBMyy combined with a glycoside hydrolase module from family 16 (GH16_3). Our analyses revealed that both modular proteins have an elongated shape, and that the GH16_3 displayed a higher flexibility than the SGBP. While motility of both polypeptide chains may facilitate recognition and/or degradation of laminarin, constraints in the SGBP may support docking of laminarin onto the bacterial surface. The exploration of bacterial metagenome-assembled genomes (MAGs) from phytoplankton blooms in the North Sea revealed that both laminarin-binding CBM families are widely distributed among marine Bacteroidota, illustrating the high adaptability of modularity in sugar-binding and -degrading proteins. High expression of CBMxx- and CBMyy-containing proteins during phytoplankton blooms further underpins their importance in marine laminarin usage.

biochemistry↗

bioRxiv2022

Grazers affect the composition of dissolved storage glycans and thereby bacterioplankton composition during a biphasic North Sea spring algae bloom

Blooms of marine microalgae play a pivotal role in global carbon cycling. Such blooms entail successive blooms of specialized clades of planktonic bacteria that remineralize algal biomass. We investigated the bacterioplankton response to a bloom in the German Bight in spring 2020. Metagenome sequencing at 30 time-points allowed reconstruction of 251 metagenome-assembled genomes (MAGs), 245 representing as yet uncultured species, while corresponding metatranscriptome sequencing highlighted 50 particularly active MAGs. Together with algae, copepod, protist and bacteria diversity and abundance data in combination with physico-chemical data and antibody-based saccharide measurements, we demonstrate (i) how dissolved primary photoassimilated algal and secondary bacterial storage glycans shape the bacterioplankton community composition, and (ii) how grazing on higher trophic levels determines the release of these abundant glycans. We thus elucidate principles governing how bacterioplankton clades respond to algal blooms and collectively remineralize gigatons of carbon annually on a global scale.

ecology↗

bioRxiv2022

Transcriptomics sheds light on N2-fixation strategies employed by a thermophilic member of the Methanococcales

Some marine thermophilic methanogens are able to perform energy-consuming nitrogen fixation despite deriving only little energy from hydrogenotrophic methanogenesis. We studied this process in Methanothermococcus thermolithotrophicus DSM 2095, a methanogenic archaeon of the order Methanococcales, that contributes to the nitrogen pool in some marine environments. We successfully grew this archaeon under diazotrophic conditions in both batch and fermenter cultures, reaching the highest cell density reported so far. Diazotrophic growth depended strictly on molybdenum and, in contrast to other diazotrophs, was not inhibited by tungstate or vanadate. This suggests an elaborate control of metal uptake and a specific metal recognition system for the insertion into the nitrogenase cofactor. Differential transcriptomics of M. thermolithotrophicus grown under diazotrophic conditions with ammonium-fed cultures as controls revealed upregulation of the nitrogenase machinery including chaperones, regulators, and molybdate-importers, as well as simultaneous upregulation of an ammonium-transporter and a putative pathway for nitrate/nitrite utilization. The organism thus employs multiple synergistic strategies for uptake of nitrogen nutrients during the early exponential growth phase without altering transcription levels for genes involved in methanogenesis. As a counterpart, genes coding for transcription and translation processes were downregulated, highlighting the maintenance of an intricate metabolic balance to deal with energy constraints and nutrient limitations imposed by diazotrophy. This switch in the metabolic balance included unexpected processes, such as upregulation of the CRISPR-Cas system, probably caused by drastic changes in transcription levels of putative mobile and virus-like elements. ImportanceThe thermophilic anaerobic archaeon, M. thermolithotrophicus, is a particularly suitable model organism to study the coupling of methanogenesis to diazotrophy. Likewise, its capability to simultaneously reduce N2/CO2 into NH3/CH4 with H2 makes it a viable target for biofuel production. We optimized M. thermolithotrophicus cultivation, resulting in considerably higher cell yields and enabling the successful establishment of N2-fixing bioreactors. Improved understanding of the N2-fixation process would provide novel insights into metabolic adaptations that allow this energy-limited extremophile to thrive under diazotrophy, for instance by investigating its physiology and uncharacterized nitrogenase. We demonstrate that diazotrophic growth of M. thermolithotrophicus is exclusively dependent on molybdenum, and complementary transcriptomics corroborated the expression of the molybdenum nitrogenase system. Further analyses of differentially expressed genes during diazotrophy across three cultivation time points revealed insights into the response to nitrogen limitation and the coordination of core metabolic processes.

microbiology↗

bioRxiv2022

Sulfate reducing bacteria associated to diatoms during a spring phytoplankton bloom

Phytoplankton blooms fuel marine food webs with labile dissolved carbon, but also lead to the formation of particulate organic matter composed of living and dead algal cells. These particles contribute to carbon sequestration, yet are also sites of intense algal-bacterial interactions and provide diverse niches for microbes to thrive. We analyzed 16S and 18S ribosomal RNA gene amplicon sequences obtained from 51 time points and metaproteomes from 3 time points during a spring phytoplankton bloom in the North Sea. Particulate fractions larger than 10 {micro}m diameter were collected at near daily intervals between early March and late May in 2018. Network analysis identified two major modules representing bacteria co-occurring with diatoms and with dinoflagellates, respectively. The diatom network module included known sulfate-reducing Desulfobacterota as well as potentially sulfur-oxidizing Ectothiorhodospiraceae. Metaproteome analyses confirmed presence of key enzymes involved in dissimilatory sulfate reduction, a process known to occur in sinking particles at greater depths. Our results indicate the presence of sufficiently anoxic niches in the particle fraction of an active phytoplankton bloom to sustain sulfate reduction, which may have implications for algal-bacterial interactions and carbon export during blooms.

ecology↗