Data_Sheet_1_Surfactin: A Quorum-Sensing Signal Molecule to Relieve CCR in Bacillus amyloliquefaciens.docx

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.

由于碳分解代谢物阻遏（carbon catabolite repression, CCR），芽孢杆菌属细菌会优先利用葡萄糖等优势糖类而非其他碳源。表面活性素（surfactin）是一类小型信号分子，可调控枯草芽孢杆菌（B. subtilis）的群体感应（quorum-sensing, QS）响应，例如生物膜形成与芽孢形成。本研究对解淀粉芽孢杆菌（B. amyloliquefaciens）中负责合成表面活性素的srfA操纵子进行突变，以阻断其表面活性素的产生。srfA突变菌株表现出生物膜与芽孢形成缺陷，但该缺陷可通过添加表面活性素得以恢复，这表明表面活性素是解淀粉芽孢杆菌的群体感应信号分子。出乎意料的是，尽管此阶段营养物质仍足以支持细菌生长，srfA突变仍引发了细胞死亡。转录组分析发现，由于缺乏表面活性素，srfA突变菌株在葡萄糖耗尽后无法解除碳分解代谢物阻遏，从而无法利用非优势碳源。该结论进一步得到验证：添加葡萄糖可显著恢复突变菌株的生长，而向srfA突变菌株中添加表面活性素，可提升其利用非优势碳源的酶活性（如葡聚糖酶（glucanase）与α-淀粉酶（α-amylase））。当葡萄糖耗尽后，细菌会产生表面活性素以解除碳分解代谢物阻遏，进而利用非优势糖类。作为调控群体感应的信号分子，表面活性素还可直接或间接解除CcpA介导的碳分解代谢物阻遏，以应对环境中的营养限制（如葡萄糖匮乏），从而利用非优势碳源。综上，本研究首次证实，表面活性素这一群体感应信号分子也参与了解淀粉芽孢杆菌中CcpA介导的碳分解代谢物阻遏的解除过程。