Proteomic profiling of Bacillus licheniformis reveals a stress response mechanism in the synthesis of extracellular polymeric flocculants

Abstract

Some bioflocculants composed of extracellular polymeric substances are produced under peculiar conditions. Bacillus licheniformis CGMCC2876 is a microorganism that secretes both extracellular polysaccharides (EPS) and poly-gamma-glutamic acid (γ-PGA) under stress conditions. In this work, SWATH acquisition LC-MS/MS method was adopted for differential proteomic analysis of B. licheniformis, aiming at determining the bacterial stress mechanism. Compared with LB culture, 190 differentially expressed proteins were identified in B. licheniformis CGMCC2876 cultivated in EPS culture, including 117 up-regulated and 73 down-regulated proteins. In γ-PGA culture, 151 differentially expressed proteins, 89 up-regulated and 62 down-regulated, were found in the cells. Up-regulated proteins involved in amino acid biosynthesis were found to account for 43% and 41% of the proteomes in EPS and γ-PGA cultivated cells, respectively. Additionally, a series of proteins associated with amino acid degradation were found to be repressed under EPS and γ-PGA culture conditions. Transcriptional profiling via the qPCR detection of selected genes verified the proteomic analysis. Analysis of free amino acids in the bacterial cells further suggested the presence of amino acid starvation conditions. EPS or γ-PGA was synthesized to alleviate the effect of amino acid limitation in B. licheniformis. This study identified a stress response mechanism in the synthesis of macromolecules in B. licheniformis, providing potential culture strategies to improve the production of two promising bioflocculants.

Effect of glucose on poly-γ-glutamic acid metabolism in Bacillus licheniformis

“…In the medium containing glucose at 5 g/L, the levels of SucA and SdhC decreased by 3.59- and 2.01-fold, respectively (Additional file 3 ) after the glucose was exhausted. The same results revealed that the decrease in SucA and SdhC was beneficial for both the accumulation of α-ketoglutaric acid and the increase in glutamate for producing γ-PGA [ 31 ]. Thus, glycerol metabolism was changed to glycolysis when glucose was added to the medium as a co-carbon source.…”

“…SWATH acquisition LC–MS/MS was performed using an Eksigent nanoLC-ultra system coupled with a Triple-TOF5600 Mass Spectrometer (ABSCIEX, Canada). Details of the parameters and data analysis for SWATH were reported by Yu et al [ 31 ].…”

Glutamic Acid Independent Production of Bioflocculants by Bacillus subtilis UPMB13

“…Production of biopolymeric compounds by bacterial strains could be unpredictable even under rigorously maintained culture conditions (Bajaj and Singhal 2011a). Stressful culture conditions may induce and improve extracellular polymeric substances production by microorganisms (Yu et al 2015).…”

Enhanced Synthesis of Poly Gamma Glutamic Acid by Increasing the Intracellular Reactive Oxygen Species in the Bacillus licheniformis Δ1-pyrroline-5-carboxylate Dehydrogenase Gene ycgN Deficient Strain

“…2 ), which was in line with the previous studies. Since the plasmid was supposed to exhibit metabolic burden on the host and affected host gene expression and phenotype, it was suspicious that the enhancement of γ -PGA synthesis in WX-pHY300 could be an element of response or adaptation response against stress caused by pHY300 (50-53). According to this study, oxidative stress increased γ -PGA production in WX-02 by ycgN deletion or H 2 O 2 addition.…”