Silva-Rocha Rafael, de Lorenzo Victor
Systems Biology Program, Centro Nacional de Biotecnologia CSIC, Cantoblanco-Madrid, Spain
FEMS Microbiol Lett. 2014 Jul;356(2):176-83. doi: 10.1111/1574-6968.12400.
Environmental plasmids often expand the metabolic repertoire of bacteria that carry them, but they also interfere with the biochemical and genetic network of the host. The pWW0 plasmid born by Pseudomonas putida mt-2 encodes the TOL pathway for degradation of toluene/m-xylene through production of intermediate compounds benzoate/3-methylbenzoate. These can be also recognized as substrates by the chromosomally encoded ben and cat gene products, thereby creating a manifest regulatory and biochemical conflict. In this context, we have investigated how the introduction of the pWW0 plasmid into P. putida affects behaviour of the promoter of the ben pathway (Pb) in single cells. Using a series of standardized transcriptional fusions to green fluorescent protein, we found that acquisition of the TOL pathway switches the activation course of the Pb promoter from unimodal/graded to bimodal/stochastic when cells were exposed to benzoate. This behaviour was propagated downstream into the Pc promoter of the cat gene cluster, which responds to the benzoate-degradation intermediate cis,cis-muconate. The TOL plasmid thus imposes expression of the chromosomal Pb with a stochastic behaviour likely to result in biochemical heterogeneity of the otherwise genetically clonal population when exposed to benzoate as a growth substrate.
环境质粒通常会扩展携带它们的细菌的代谢能力，但它们也会干扰宿主的生化和遗传网络。恶臭假单胞菌mt-2携带的pWW0质粒通过产生中间化合物苯甲酸/3-甲基苯甲酸来编码甲苯/间二甲苯降解的TOL途径。这些中间化合物也可以被染色体编码的ben和cat基因产物识别为底物，从而产生明显的调控和生化冲突。在此背景下，我们研究了将pWW0质粒导入恶臭假单胞菌后，如何影响单细胞中ben途径启动子（Pb）的行为。通过使用一系列与绿色荧光蛋白的标准化转录融合，我们发现当细胞暴露于苯甲酸时，获得TOL途径会使Pb启动子的激活过程从单峰/分级转变为双峰/随机。这种行为向下游传播到cat基因簇的Pc启动子，该启动子对苯甲酸降解中间产物顺，顺-粘康酸有反应。因此，当以苯甲酸作为生长底物时，TOL质粒会使染色体Pb的表达具有随机行为，这可能导致原本基因克隆的群体出现生化异质性。
