Azotobacter vinelandii produces the linear exopolysaccharide alginate, a compound of significant biotechnological importance. The biosynthesis of alginate in A. vinelandii and Pseudomonas aeruginosa 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 A. vinelandii. 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 A. vinelandii, AvGReg, 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 AvGReg in the parental strain phenocopied a ΔmucG 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 AvGReg.

中文翻译：

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增加的 c-di-GMP 水平导致在 Azotobacter vinelandii 中产生高分子量藻酸盐

Azotobacter vinelandii产生线性胞外多糖藻酸盐，这是一种具有重要生物技术重要性的化合物。A. vinelandii和Pseudomonas aeruginosa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节有所不同。在这里，我们表明第二信使环状二聚体 GMP (c-di-GMP) 调节A. vinelandii中藻酸盐的产生和分子量。杂合蛋白 MucG 包含保守的 GGDEF 和 EAL 结构域以及 N 端 HAMP 和 PAS 结构域，表现为 c-di-GMP 磷酸二酯酶 (PDE)。发现这种活性对形成的多糖的量和分子量有负面影响。另一方面，在存在于A. vinelandii，Av GReg，一种直接与氧结合的珠蛋白耦合传感器 (GCS) DGC，被确定为藻酸盐生产的主要 c-di-GMP 合成贡献者。亲本菌株中Av GReg 的过度生产表现出Δ mucG关于藻酸盐生产和聚合物分子量的应变。MucG 先前被证明可以防止高分子量藻酸盐的合成，以响应降低的氧转移率 (OTR)。在这项工作中，我们表明暴露于减少的 OTR 的培养物积累了更高水平的 c-di-GMP。这一发现有力地表明，至少有一种参与通过氧气调节藻酸盐产生和分子质量的分子机制依赖于一个 c-di-GMP 信号模块，该模块包括含有 PAS 结构域的 PDE MucG 和 GCS DGC Av GReg。