Abstract
Bacillus utilize preferred sugars such as glucose over other carbon sources due to carbon catabolite repression (CCR). Surfactin is a small signal molecule to regulate the quorum-sensing (QS) response such as biofilm formation and sporulation in B. subtilis. Here, the srfA operon for synthesis of surfactin was mutated for disrupting the production of surfactin in B. amyloliquefaciens. The srfA-mutant strain showed a defective biofilm and sporulation but could be restored by addition with surfactin, indicating that surfactin is a QS signal molecule in B. amyloliquefaciens. Unexpectedly, mutation of srfA also led to the cells’ death although nutrients were still enough to support the bacterial growth during this period. Analysis of transcriptomes found that the srfA-mutant strain could not relieve CCR to use non-preferred carbon sources after glucose exhaustion due to deficiency of surfactin. This was further verified by the fact that addition with glucose could dramatically restore the growth, and addition with surfactin could improve the enzymes’ activity (e.g., glucanase and α-amylase) to use non-preferred carbon sources in the srfA-mutant strain. After glucose exhaustion, the cells produce surfactin to relieve CCR for utilizing non-preferred sugars. As a signal molecule to regulate QS, surfactin also directly or indirectly relieves the CcpA-mediated CCR to utilize non-preferred carbon sources countering nutrient limitation (e.g., glucose deprivation) in the environment. In conclusion, our findings provide the first evidence that the QS signal molecule of surfactin is also involved in relieving the CcpA-mediated CCR in B. amyloliquefaciens.
Highlights
Bacillus are generally soil-dwelling Gram-positive bacteria ubiquitously distributed in the natural environment
In the presence of preferable carbon sources such as glucose, the histidinecontaining phosphotransfer protein (HPr) is phosphorylated by HPr kinase (HPrK) at Ser46 by the bifunctional HPr kinase/phosphorylase HPrK/P at high fructose-1,6-bisphosphate and ATP or pyrophosphate concentrations and forms a complex with CcpA that can bind to a conserved cisacting sequence called catabolite responsive elements to repress the gene transcription involved in catabolism of non-preferred carbon sources (Schumacher et al, 2011; Ishii et al, 2013; Charbonnier et al, 2017; Kim and Burne, 2017)
We isolated a strain of B. amyloliquefaciens WH1 with production of several lipopeptides such as surfactin, iturin, and fengycin (Qi et al, 2010)
Summary
Bacillus are generally soil-dwelling Gram-positive bacteria ubiquitously distributed in the natural environment. In the presence of preferable carbon sources such as glucose, the histidinecontaining phosphotransfer protein (HPr) is phosphorylated by HPr kinase (HPrK) at Ser by the bifunctional HPr kinase/phosphorylase HPrK/P at high fructose-1,6-bisphosphate and ATP or pyrophosphate concentrations and forms a complex with CcpA that can bind to a conserved cisacting sequence called catabolite responsive elements (cre) to repress the gene transcription involved in catabolism of non-preferred carbon sources (Schumacher et al, 2011; Ishii et al, 2013; Charbonnier et al, 2017; Kim and Burne, 2017). We hypothesized that after glucose exhaustion, CCR will be relieved to utilize non-preferred sugars supporting the initiated QS response such as biofilm formation and sporulation in Bacillus. Further analysis found that surfactin, a signal peptide to regulate QS, is involved in relieving CCR in B. amyloliquefaciens, by which QS is tightly linked with CCR to counter carbon sources limitation in the natural environment
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