Quiroz-Rocha Elva, Bonilla-Badía Fernando, García-Aguilar Valentina, López-Pliego Liliana, Serrano-Román Jade, Cocotl-Yañez Miguel, Guzmán Josefina, Ahumada-Manuel Carlos L, Muriel-Millán Luis Felipe, Castañeda Miguel, Espín Guadalupe, Nuñez Cinthia
Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Av. Universidad 2001, Col Chamilpa, Cuernavaca, Morelos, CP 62210, México.
Present address: Departamento de Medicina, Centro Interdisciplinario de Ciencias de la Salud-Unidad Milpa Alta, Instituto Politécnico Nacional, CICITEC, Ex-Hacienda del Mayorazgo, Km. 39.5 Carretera Xochimilco - Oaxtepec, Ciudad de México, CP 12000, México.
Microbiology (Reading). 2017 Jul;163(7):1105-1115. doi: 10.1099/mic.0.000457. Epub 2017 Jul 21.
Azotobacter vinelandii, belonging to the Pseudomonadaceae family, is a free-living bacterium that has been considered to be a good source for the production of bacterial polymers such as alginate. In A. vinelandii the synthesis of this polymer is regulated by the Gac/Rsm post-transcriptional regulatory system, in which the RsmA protein binds to the mRNA of the biosynthetic algD gene, inhibiting translation. In several Pseudomonas spp. the two-component system CbrA/CbrB has been described to control a variety of metabolic and behavioural traits needed for adaptation to changing environmental conditions. In this work, we show that the A. vinelandii CbrA/CbrB two-component system negatively affects alginate synthesis, a function that has not been described in Pseudomonas aeruginosa or any other Pseudomonas species. CbrA/CbrB was found to control the expression of some alginate biosynthetic genes, mainly algD translation. In agreement with this result, the CbrA/CbrB system was necessary for optimal rsmA expression levels. CbrA/CbrB was also required for maximum accumulation of the sigma factor RpoS. This last effect could explain the positive effect of CbrA/CbrB on rsmA expression, as we also showed that one of the promoters driving rsmA transcription was RpoS-dependent. However, although inactivation of rpoS increased alginate production by almost 100 %, a cbrA mutation increased the synthesis of this polymer by up to 500 %, implying the existence of additional CbrA/CbrB regulatory pathways for the control of alginate production. The control exerted by CbrA/CbrB on the expression of the RsmA protein indicates the central role of this system in regulating carbon metabolism in A. vinelandii.
棕色固氮菌属于假单胞菌科，是一种自由生活的细菌，被认为是生产藻酸盐等细菌聚合物的良好来源。在棕色固氮菌中，这种聚合物的合成受Gac/Rsm转录后调控系统的调节，其中RsmA蛋白与生物合成藻酸D基因的mRNA结合，抑制翻译。在几种假单胞菌属中，双组分系统CbrA/CbrB已被描述为控制适应不断变化的环境条件所需的各种代谢和行为特征。在这项研究中，我们表明棕色固氮菌的CbrA/CbrB双组分系统对藻酸盐合成有负面影响，这一功能在铜绿假单胞菌或任何其他假单胞菌属中尚未被描述。发现CbrA/CbrB控制一些藻酸盐生物合成基因的表达，主要是藻酸D的翻译。与这一结果一致，CbrA/CbrB系统对于最佳的rsmA表达水平是必需的。CbrA/CbrB对于σ因子RpoS的最大积累也是必需的。这一最后的效应可以解释CbrA/CbrB对rsmA表达的积极作用，因为我们还表明驱动rsmA转录的启动子之一是RpoS依赖性的。然而，尽管rpoS的失活使藻酸盐产量增加了近100%，但cbrA突变使这种聚合物的合成增加了高达500%，这意味着存在额外的CbrA/CbrB调控途径来控制藻酸盐的产生。CbrA/CbrB对RsmA蛋白表达的控制表明该系统在调节棕色固氮菌碳代谢中起核心作用。
