Búsqueda y caracterización de nuevos factores implicados en represión catabólica en pseudomonas putida

Zusammenfassung

Pseudomonas putida is a ubiquitous Gram negative bacteria characterized for its metabolic versatility and its ability to thrive in different environments, such as soil, water or the rhizosphere, even when these sites are polluted by different contaminants. Its capacity to utilize many different compounds as carbon source is tightly regulated by complex global regulation networks. Some of these regulatory systems are responsible for the preferential assimilation of one ore more compounds when several potential carbon sources are present in the medium. This implies the repression of the genes coding for the metabolic pathways of less preferred compounds, a process called Carbon Catabolite Repression (CCR). The understanding of the mechanisms underlying CCR is important to learn how this bacterium behaves in its natural environments, and to optimize the applications of this microorganism in biotechnology, for example in bioremediation or agriculture. In this work, we have analysed the possible role of two factors in Carbon Catabolite Repression in P. putida: the RNase R and low growth temperatures. RNase R has been previously proposed to participate, together with Crc (a well known global regulator of CCR in Pseudomonas), in the repression in rich media of the expression of BkdR, a transcriptional regulator of the branched-chain amino acids assimilation pathway. We have studied the global role of this exoribonuclease in catabolite repression as well as the effect of the inactivation of this enzyme in the phenotype and transcriptome of P. putida. We have found that this ribonuclease is not relevant for catabolite repression, but has an important role in the degradation and turnover of mRNAs in this bacterium. In P. fluorescens, the catabolite repression exerted by malate on the glucose assimilation pathway is known to be relieved at low temperature. To investigate whether growth temperature has a general role in catabolite repression, we have compared the transcriptome and proteome profiles of P. putida growing exponentially in a rich media at either 10ºC or 30ºC. We found that low temperature has a deep impact on the gene expression pattern of the cells. Many changes are devoted to cope with the problems generated by low temperature. Interestingly, we found that the catabolite repression that inhibits expression of many genes related with the transport and metabolism and of diverse compounds is relieved when cells grow at 10ºC. We have investigated the mechanisms underlying this effect.