Hufnagel David A, DePas William H, Chapman Matthew R
Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, Michigan, USA.
Department of Microbiology and Immunology, University of Michigan, Ann Arbor, Michigan, USA.
J Bacteriol. 2014 Nov;196(21):3690-9. doi: 10.1128/JB.02019-14. Epub 2014 Aug 11.
The bacterial extracellular matrix encases cells and protects them from host-related and environmental insults. The Escherichia coli master biofilm regulator CsgD is required for the production of the matrix components curli and cellulose. CsgD activates the diguanylate cyclase AdrA, which in turn stimulates cellulose production through cyclic di-GMP (c-di-GMP). Here, we identified and characterized a CsgD- and AdrA-independent cellulose production pathway that was maximally active when cultures were grown under reducing conditions or when the disulfide bonding system (DSB) was compromised. The CsgD-independent cellulose activation pathway was dependent on a second diguanylate cyclase, called YfiN. c-di-GMP production by YfiN was repressed by the periplasmic protein YfiR, and deletion of yfiR promoted CsgD-independent cellulose production. Conversely, when YfiR was overexpressed, cellulose production was decreased. Finally, we found that YfiR was oxidized by DsbA and that intraprotein YfiR disulfide bonds stabilized YfiR in the periplasm. Altogether, we showed that reducing conditions and mutations in the DSB system caused hyperactivation of YfiN and subsequent CsgD-independent cellulose production.
细菌细胞外基质包裹着细胞，并保护它们免受与宿主相关的和环境的损害。大肠杆菌主要生物膜调节因子CsgD是产生细胞外基质成分卷曲纤维和纤维素所必需的。CsgD激活双鸟苷酸环化酶AdrA，AdrA进而通过环二鸟苷酸（c-di-GMP）刺激纤维素的产生。在这里，我们鉴定并表征了一条不依赖CsgD和AdrA的纤维素产生途径，当培养物在还原条件下生长或二硫键结合系统（DSB）受损时，该途径的活性最高。不依赖CsgD的纤维素激活途径依赖于另一种双鸟苷酸环化酶YfiN。YfiR这种周质蛋白会抑制YfiN产生c-di-GMP，缺失yfiR会促进不依赖CsgD的纤维素产生。相反，当YfiR过表达时，纤维素产生减少。最后，我们发现YfiR被DsbA氧化，并且YfiR蛋白内的二硫键使YfiR在周质中稳定。总之，我们表明还原条件和DSB系统中的突变会导致YfiN过度激活以及随后不依赖CsgD的纤维素产生。
