Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, Mexico.
Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan, USA.
J Bacteriol. 2020 Nov 19;202(24). doi: 10.1128/JB.00134-20.
produces the linear exopolysaccharide alginate, a compound of significant biotechnological importance. The biosynthesis of alginate in and has several similarities but is regulated somewhat differently in the two microbes. Here, we show that the second messenger cyclic dimeric GMP (c-di-GMP) regulates the production and the molecular mass of alginate in The hybrid protein MucG, containing conserved GGDEF and EAL domains and N-terminal HAMP and PAS domains, behaved as a c-di-GMP phosphodiesterase (PDE). This activity was found to negatively affect the amount and molecular mass of the polysaccharide formed. On the other hand, among the diguanylate cyclases (DGCs) present in , GReg, a globin-coupled sensor (GCS) DGC that directly binds to oxygen, was identified as the main c-di-GMP-synthesizing contributor to alginate production. Overproduction of GReg in the parental strain phenocopied a Δ strain with regard to alginate production and the molecular mass of the polymer. MucG was previously shown to prevent the synthesis of high-molecular-mass alginates in response to reduced oxygen transfer rates (OTRs). In this work, we show that cultures exposed to reduced OTRs accumulated higher levels of c-di-GMP; this finding strongly suggests that at least one of the molecular mechanisms involved in modulation of alginate production and molecular mass by oxygen depends on a c-di-GMP signaling module that includes the PAS domain-containing PDE MucG and the GCS DGC GReg. c-di-GMP has been widely recognized for its essential role in the production of exopolysaccharides in bacteria, such as alginate produced by and spp. This study reveals that the levels of c-di-GMP also affect the physical properties of alginate, favoring the production of high-molecular-mass alginates in response to lower OTRs. This finding opens up new alternatives for the design of tailor-made alginates for biotechnological applications.
产生线性胞外多糖藻酸盐，这是一种具有重要生物技术意义的化合物。 和 中藻酸盐的生物合成有几个相似之处，但在这两种微生物中的调控方式略有不同。在这里，我们表明第二信使环二鸟苷酸（c-di-GMP）调节 中藻酸盐的产生和分子量。 含有保守 GGDEF 和 EAL 结构域以及 N 端 HAMP 和 PAS 结构域的杂合蛋白 MucG 表现为 c-di-GMP 磷酸二酯酶（PDE）。 发现这种活性会负影响形成的多糖的数量和分子量。 另一方面，在 中存在的二鸟苷酸环化酶（DGCs）中，GReg，一种直接与氧结合的球蛋白偶联传感器（GCS）DGC，被鉴定为产生藻酸盐的主要 c-di-GMP 合成贡献者。 在亲本菌株中过量表达 GReg 会导致与 alginate 生产和聚合物分子量相关的 alginate 生产表型类似于 Δ 突变体。MucG 先前被证明可防止在氧传递速率（OTR）降低时合成高分子质量的藻酸盐。 在这项工作中，我们表明，暴露于低 OTR 的培养物积累了更高水平的 c-di-GMP； 这一发现强烈表明，参与调节藻酸盐产生和分子量的分子机制至少有一个依赖于包括含有 PAS 结构域的 PDE MucG 和 GCS DGC GReg 的 c-di-GMP 信号模块。 c-di-GMP 已被广泛认为在细菌中产生胞外多糖（如 和 spp 产生的藻酸盐）中起关键作用。 这项研究表明，c-di-GMP 的水平也会影响藻酸盐的物理性质，有利于在较低 OTR 下产生高分子质量的藻酸盐。 这一发现为生物技术应用中定制藻酸盐的设计开辟了新的选择。
