Mongiardini Elías J, Quelas J Ignacio, Dardis Carolina, Althabegoiti M Julia, Lodeiro Aníbal R
Instituto de Biotecnología y Biología Molecular, Facultad de Ciencias Exactas, Universidad Nacional de La Plata y CCT-La Plata, CONICET, La Plata, Argentina.
Instituto de Biotecnología y Biología Molecular, Facultad de Ciencias Exactas, Universidad Nacional de La Plata y CCT-La Plata, CONICET, La Plata, Argentina
J Bacteriol. 2017 Jul 11;199(15). doi: 10.1128/JB.00253-17. Print 2017 Aug 1.
, a soybean N-fixing symbiont, possesses a dual flagellar system comprising a constitutive subpolar flagellum and inducible lateral flagella. Here, we analyzed the genomic organization and biosynthetic regulation of the lateral-flagellar genes. We found that these genes are located in a single genomic cluster, organized in two monocistronic transcriptional units and three operons, one possibly containing an internal transcription start site. Among the monocistronic units is blr6846, homologous to the class IB master regulators of flagellum synthesis in and and required for the expression of all the lateral-flagellar genes except , whose locus encodes a single lateral flagellin. We therefore named blr6846 (teral-lagellar egulator). Despite its similarity to two-component response regulators and its possession of a phosphorylatable Asp residue, behaved as an orphan response regulator by not requiring phosphorylation at this site. Among the genes induced by is , a class III regulator. We observed different requirements for FlbT in the synthesis of each flagellin subunit. Although the accumulation of , but not , transcripts required FlbT, the production of both flagellin polypeptides required FlbT Moreover, the regulation cascade of this lateral-flagellar regulon appeared to be not as strictly ordered as those found in other bacterial species. Bacterial motility seems essential for the free-living style in the environment, and therefore these microorganisms allocate a great deal of their energetic resources to the biosynthesis and functioning of flagella. Despite energetic costs, some bacterial species possess dual flagellar systems, one of which is a primary system normally polar or subpolar, and the other is a secondary, lateral system that is produced only under special circumstances. , an N-fixing symbiont of soybean plants, possesses dual flagellar systems, including the lateral system that contributes to swimming in wet soil and competition for nodulation and is expressed under high energy availability, as well as under requirement for high torque by the flagella. The structural organization and transcriptional regulation of the 41 genes that comprise this secondary flagellar system seem adapted to adjust bacterial energy expenditures for motility to the soil's environmental dynamics.
大豆固氮共生菌拥有一个双鞭毛系统，由一个组成型亚极鞭毛和可诱导的侧鞭毛组成。在此，我们分析了侧鞭毛基因的基因组组织和生物合成调控。我们发现这些基因位于一个单一的基因组簇中，组织成两个单顺反子转录单元和三个操纵子，其中一个可能含有一个内部转录起始位点。在单顺反子单元中有blr6846，它与[其他细菌]鞭毛合成的IB类主调节因子同源，并且是除blr6847（其基因座编码单一的侧鞭毛蛋白）之外所有侧鞭毛基因表达所必需的。因此，我们将blr6846命名为FlbT（侧鞭毛调节因子）。尽管它与双组分应答调节因子相似且拥有一个可磷酸化的天冬氨酸残基，但FlbT表现为一个孤儿应答调节因子，因为它在此位点不需要磷酸化。在由FlbT诱导的基因中有FlbB，一个III类调节因子。我们观察到在每个鞭毛蛋白亚基的合成中对FlbT有不同的需求。尽管blr6848转录本的积累需要FlbT，但blr6847转录本的积累不需要FlbT，但两种鞭毛蛋白多肽的产生都需要FlbT。此外，这个侧鞭毛调控子的调控级联似乎不像在其他细菌物种中那样严格有序。细菌的运动性似乎对其在环境中的自由生活方式至关重要，因此这些微生物将大量的能量资源分配到鞭毛的生物合成和功能上。尽管存在能量成本，但一些细菌物种拥有双鞭毛系统，其中一个是通常为极鞭或亚极鞭的主要系统，另一个是仅在特殊情况下产生的次要的侧鞭毛系统。大豆植物的固氮共生菌拥有双鞭毛系统，包括有助于在潮湿土壤中游动以及竞争结瘤的侧鞭毛系统，该系统在高能量可用性以及鞭毛对高扭矩的需求下表达。构成这个次要鞭毛系统的41个基因的结构组织和转录调控似乎适应于根据土壤环境动态调整细菌用于运动的能量消耗。
