Table_2_GlnR Activation Induces Peroxide Resistance in Mycobacterial Biofilms.pdf

Mycobacteria spontaneously form surface-associated multicellular communities, called biofilms, which display resistance to a wide range of exogenous stresses. A causal relationship between biofilm formation and emergence of stress resistance is not known. Here, we report that activation of a nitrogen starvation response regulator, GlnR, during the development of Mycobacterium smegmatis biofilms leads to peroxide resistance. The resistance arises from induction of a GlnR-dependent peroxide resistance (gpr) gene cluster comprising of 8 ORFs (MSMEG_0565-0572). Expression of gpr increases the NADPH to NADP ratio, suggesting that a reduced cytosolic environment of nitrogen-starved cells in biofilms contributes to peroxide resistance. Increased NADPH levels from gpr activity likely support the activity of enzymes involved in nitrogen assimilation, as suggested by a higher threshold of nitrogen supplement required by a gpr mutant to form biofilms. Together, our study uniquely interlinks a nutrient sensing mechanism with emergence of stress resistance during mycobacterial biofilm development. The gpr gene cluster is conserved in several mycobacteria that can cause nosocomial infections, offering a possible explanation for their resistance to peroxide-based sterilization of medical equipment.分枝杆菌可自发形成依附于表面的多细胞群落，即生物膜（biofilm），该群落对多种外源胁迫具备抗性。目前学界尚未明确生物膜形成与胁迫抗性产生之间的因果关系。本研究发现，在耻垢分枝杆菌（Mycobacterium smegmatis）生物膜发育过程中，氮饥饿应答调控因子GlnR的激活可赋予菌株过氧化物抗性。该抗性源于一个由8个开放阅读框（Open Reading Frames，ORFs）组成的GlnR依赖性过氧化物抗性（gpr）基因簇（MSMEG_0565-0572）的诱导表达。gpr的表达可提升还原型烟酰胺腺嘌呤二核苷酸磷酸（NADPH）与氧化型烟酰胺腺嘌呤二核苷酸磷酸（NADP）的比值，提示生物膜内氮饥饿细胞的胞质还原环境有助于过氧化物抗性的形成。gpr活性所带来的NADPH水平升高，可能为氮同化相关酶的功能提供支持，这一点可由gpr突变株形成生物膜时所需的氮补充阈值更高得到印证。综上，本研究首次将营养感知机制与分枝杆菌生物膜发育过程中的胁迫抗性产生建立联系。gpr基因簇在多种可引发院内感染的分枝杆菌中均具有保守性，这或许可以解释此类菌株对基于过氧化物的医疗设备灭菌手段产生抗性的原因。