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

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.