Kwak Gi-Young, Choi Okhee, Goo Eunhye, Kang Yongsung, Kim Jinwoo, Hwang Ingyu
Department of Agricultural Biotechnology, Seoul National University, Seoul, South Korea.
Division of Applied Life Science, Institute of Agriculture and Life Sciences, Gyeongsang National University, Jinju, South Korea.
Front Microbiol. 2020 Jan 17;10:3090. doi: 10.3389/fmicb.2019.03090. eCollection 2019.
Bacteria form biofilms as a means to adapt to environmental changes for survival. Pellicle is a floating biofilm formed at the air-liquid interface in static culture conditions; however, its functional roles have received relatively little attention compared to solid surface-associated biofilms in gram-negative bacteria. Here we show that the rice pathogen BGR1 forms cellulase-sensitive pellicles in a bis-(3'-5')-cyclic dimeric guanosine monophosphate (c-di-GMP)- and flagellum-dependent, but quorum sensing (QS)-independent, manner. Pellicle formation was more favorable at 28°C than at the optimum growth temperature (37°C), and was facilitated by constitutive expression of , a diguanylate cyclase gene from , or , the GGDEF response regulator from . Constitutive expression of or raised the levels of c-di-GMP, facilitated pellicle formation, and suppressed swarming motility in . QS-defective mutants of formed pellicles, while flagellum-defective mutants did not. Pellicles of were sensitive to cellulase but not to proteinase K or DNase I. A gene cluster containing seven genes involved in bacterial cellulose biosynthesis, , , , , , , and , homologous to known genes involved in cellulose biosynthesis in other bacteria, was identified in . Mutations in each gene abolished pellicle formation. These results revealed a positive correlation between cellulase-sensitive pellicles and putative cellulose biosynthetic genes. Pellicle-defective mutants did not colonize as successfully as the wild-type strain BGR1 in rice plants, which resulted in a significant reduction in virulence. Our findings show that cellulase-sensitive pellicles produced in a QS-independent manner play important roles in the interactions between rice plants and .
细菌形成生物膜作为一种适应环境变化以生存的手段。菌膜是在静态培养条件下于气液界面形成的漂浮生物膜；然而，与革兰氏阴性菌中与固体表面相关的生物膜相比，其功能作用受到的关注相对较少。在此我们表明，水稻病原菌BGR1以双（3'-5'）-环二鸟苷单磷酸（c-di-GMP）和鞭毛依赖性但群体感应（QS）非依赖性的方式形成对纤维素酶敏感的菌膜。菌膜形成在28°C比在最适生长温度（37°C）时更有利，并且通过来自[具体菌名1]的双鸟苷酸环化酶基因[具体基因1]或来自[具体菌名2]的GGDEF应答调节因子[具体基因2]的组成型表达而得到促进。[具体基因1]或[具体基因2]的组成型表达提高了c-di-GMP水平，促进了菌膜形成，并抑制了[具体菌名]中的群体游动。[具体菌名]的QS缺陷型突变体形成菌膜，而鞭毛缺陷型突变体则不形成。[具体菌名]的菌膜对纤维素酶敏感，但对蛋白酶K或DNase I不敏感。在[具体菌名]中鉴定出一个包含七个参与细菌纤维素生物合成的基因的基因簇，即[具体基因3]、[具体基因4]、[具体基因5]、[具体基因6]、[具体基因7]、[具体基因8]和[具体基因9]，它们与其他细菌中参与纤维素生物合成的已知基因同源。每个基因的突变都消除了菌膜形成。这些结果揭示了对纤维素酶敏感的菌膜与假定的纤维素生物合成基因之间的正相关关系。菌膜缺陷型突变体在水稻植株中不像野生型菌株BGR1那样成功定殖这导致了毒力的显著降低。我们的研究结果表明，以QS非依赖性方式产生的对纤维素酶敏感的菌膜在水稻植株与[具体菌名]之间的相互作用中起重要作用。
