Distinct capabilities of different Gammaproteobacterial strains on utilizing small peptides in seawater

Abstract

Proteins and peptides account for 20-75% of marine biota biomass, of which a major fraction is metabolized by bacteria, thus deciphering interactions between bacteria and peptides is important in understanding marine carbon and nitrogen cycling. To better understand capabilities of different bacterial strains on peptide decomposition, four Gammaproteobacteria (Pseudoalteromonas atlantica, Alteromonas sp., Marinobacterium jannaschii, Amphritea japonica) were incubated in autoclaved seawater amended with tetrapeptide alanine-valine-phenylalanine-alanine (AVFA), a fragment of RuBisCO. While AVFA was decomposed greatly by Pseudoalteromonas atlantica and Alteromonas sp, it remained nearly intact in the Marinobacterium jannaschii and Amphritea japonica incubations. Pseudoalteromonas and Alteromonas decomposed AVFA mainly through extracellular hydrolysis pathway, releasing 71-85% of the AVFA as hydrolysis products to the surrounding seawater. Overall, this study showed that Gammaproteobacterial strains differ greatly in their capabilities of metabolizing peptides physiologically, providing insights into interactions of bacteria and labile organic matter in marine environments.The microbial loop plays a significant role in shaping the temporal and spatial distributions and pathways of bioelements such as C, N, P, and Fe in seawater 1 . The microbial loop converts organic matter from dissolved to particulate phase through the buildup of microbial biomass that is further passed to higher trophic levels via grazing, thus the interaction between bacteria and dissolved organic matter (DOM) is one of the major factors determining carbon flux in the ocean 2 . Labile organic matter, such as proteins and peptides in either dissolved or particulate phases, turns over rapidly in seawater, supporting a major fraction of bacterial growth 3,4 . To be available for bacteria, proteins and peptides need to be first cleaved into small peptides (ca. <600 Da) outside cell membrane by extracellular hydrolysis 5 . Therefore, it is important to study decomposition efficiency and pathways of small peptides in order to understand C and N cycling rates and factors controlling the bacteria-DOM interactions in seawater 6-8 .Knowing "who is doing what" is a fundamental question in the field of microbial ecology, and identifying biogeochemical function of different bacteria is key to understanding their ecological niche in the environment and their contribution to biological processes. Previously, differentiating the capability of different bacteria on labile DOM decomposition is mainly based on examining the change of bacterial community structures. Copiotrophic bacteria often dominate bacterial community after labile DOM is introduced to seawater incubations 9-15 . For example, Alphaproteobacteria (including Roseobacter), Gammaproteobacteria (including Alteromonas), Flavobacteria/ Sphingobacteria, Bacteroidetes, and Verrucomicrobia can outcompete other bacterial taxa and dominate bacterial community structure in incubations after specific labile co...

Prokaryotic Diversity and Distribution Along Physical and Nutrient Gradients in the Tunisian Coastal Waters (South Mediterranean Sea)

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Significance of Viral Activity for Regulating Heterotrophic Prokaryote Community Dynamics along a Meridional Gradient of Stratification in the Northeast Atlantic Ocean

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Linkages Among Dissolved Organic Matter Export, Dissolved Metabolites, and Associated Microbial Community Structure Response in the Northwestern Sargasso Sea on a Seasonal Scale

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