Proteome Profile Changes During Poly-hydroxybutyrate Intracellular Mobilization in Gram Positive Bacillus cereus tsu1

Abstract

Background Bacillus cereus is a bacterial species which grows efficiently on a wide range of carbon sources and accumulates biopolymer poly-hydroxybutyrate (PHB) up to 80% cell dry weight. PHB is an aliphatic polymer produced and stored intracellularly as a reservoir of carbon and energy, its mobilization is a key biological process for sporulation in Bacillus spp. Previously, a B. cereus tsu1 was isolated and cultured on rapeseed cake substrate (RCS), with maximum of PHB accumulation reached within 12 h, and depleted after 48 h. Fore-spore and spore structure were observed after 24 h culture. Results Quantitative proteomic analysis of B. cereus tsu1 identified 2,952 quantifiable proteins, and 244 significantly changed proteins (SCPs) in the 24h-12h pair of samples, and 325 SCPs in the 48h-12h pair of samples. Based on gene ontology classification analysis, biological processes enriched only in the 24h:12h SCPs include purine nucleotide metabolism, protein folding, metal ion homeostasis, response to stress, carboxylic acid catabolism, and cellular amino acid catabolism. The 48h:12h SCPs were enriched into processes including carbohydrate metabolism, protein metabolism, oxidative phosphorylation, and formation of translation ternary structure. A key enzyme for PHB metabolism, poly(R)-hydroxyalkanoic acid synthase (PhaC, KGT44865) accumulated significantly higher in 12h-culture. Sporulation related proteins SigF and SpoEII were significantly higher in 24h-samples. Enzymes for nitrate respiration and fermentation had more accumulation in 48h-culture. Conclusions Changes in proteome of B. cereus tsu1 during PHB intracellular mobilization were characterized in this study. The key enzyme PhaC for PHB synthesis increased significantly after 12h-culture which supports the highest PHB accumulation at this time point. The protein abundance level of SpoIIE and SigF also increased, correlating with sporulation in 24h-culture. Enzymes for nitrate respiration and fermentation were significantly induced in 48h-culture which indicates the depletion of oxygen at this stage and carbon flow towards fermentative growth. Results from this study provide insights into proteome profile changes during PHB accumulation and reuse, which can be applied to achieve a higher PHB yield and to improve bacterial growth performance and stress resistance.