RESUMO
The bacterial strain Pseudomonas putida IsoF, isolated from a tomato rhizosphere, possesses a quorum sensing regulation system, which allows the bacteria to recognise aspects of their environment or to communicate with each other by the so-called autoinducer molecules. In an experimental study, the time series of the autoinducer production did not show the expected behaviour, as it was observed for other bacterial species by indirect measurements. The modelling approach introduced here allows an explanation of the behaviour, supporting the hypothesis of the existence of a further (not yet detected) enzyme, which degrades the autoinducer into an inactive form. Especially the properties of the considered delay differential system allow for the description of the time series. For example the appearance of a first small maximum in the initial phase can be explained by a delay differential equation.
Assuntos
Algoritmos , Modelos Biológicos , Pseudomonas putida/fisiologia , Percepção de Quorum/fisiologia , Acil-Butirolactonas/metabolismo , Proteínas de Bactérias/metabolismo , Solanum lycopersicum/microbiologia , Pseudomonas putida/isolamento & purificação , Pseudomonas putida/metabolismo , Rizosfera , Fatores de TempoRESUMO
By using mini-Tn5 transposon mutagenesis, random transcriptional fusions of promoterless bacterial luciferase, luxAB, to genes of Pseudomonas putida KT2442 were generated. Insertion mutants that responded to ammonium deficiency by induction of bioluminescence were selected. The mutant that responded most strongly was genetically analyzed and is demonstrated to bear the transposon within the assimilatory nitrate reductase gene (nasB) of P. putida KT2442. Genetic evidence as well as sequence analyses of the DNA regions flanking nasB suggest that the genes required for nitrate assimilation are not clustered. We isolated three second-site mutants in which induction of nasB expression was completely abolished under nitrogen-limiting conditions. Nucleotide sequence analysis of the chromosomal junctions revealed that in all three mutants the secondary transposon had inserted at different sites in the gltB gene of P. putida KT2442 encoding the major subunit of the glutamate synthase. A detailed physiological characterization of the gltB mutants revealed that they are unable to utilize a number of potential nitrogen sources, are defective in the ability to express nitrogen starvation proteins, display an aberrant cell morphology under nitrogen-limiting conditions, and are impaired in the capacity to survive prolonged nitrogen starvation periods.