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.

Figure 1

Changes of AVFA concentrations with incubation time in (a) four bacterial strain treatments (data points were presented as average ± standard deviation of duplicates) and (b) seawater without bacterial strain.

Figure 2

Changes of bacterial abundance with incubation time in each bacterial strain treatments and their corresponding control (CTR) treatments (without AVFA amendment). Data points were presented as average ± standard deviation of duplicates.

Figure 3

(a,b) Changes of concentrations of peptide fragments and amino acids with incubation time in the Pseudoalteromonas and Alteromonas treatments; (c,d) changes of amino acid concentrations with incubation time in the Pseudoalteromonas and Alteromonas control (no AVFA amendment) treatments. Data points were presented as average ± standard deviation of duplicates.

Figure 4

Changes of ammonium concentrations with incubation time in four bacterial strain and their corresponding control (CTR) treatments. Data points were presented as average ± standard deviation of duplicates.

Figure 5

Mass balance of AVFA decomposition (including percentages of decreased peptide due to hydrolysis to fragments, remineralization to ammonium, incorporation into bacterial biomass and other unaccounted transformation) in the Pseudoalteromonas and Alteromonas treatments.