TouR-mediated effector-independent growth phase-dependent activation of the sigma54 Ptou promoter of Pseudomonas stutzeri OX1

Degradation strategies and associated regulatory mechanisms/features for aromatic compound metabolism in bacteria

As a result of anthropogenic activity, large number of recalcitrant aromatic compounds have been released into the environment. Consequently, microbial communities have adapted and evolved to utilize these compounds as sole carbon source, under both aerobic and anaerobic conditions. The constitutive expression of enzymes necessary for metabolism imposes a heavy energy load on the microbe which is overcome by arrangement of degradative genes as operons which are induced by specific inducers. The segmentation of pathways into upper, middle and/or lower operons has allowed microbes to funnel multiple compounds into common key aromatic intermediates which are further metabolized through central carbon pathway. Various proteins belonging to diverse families have evolved to regulate the transcription of individual operons participating in aromatic catabolism. These proteins, complemented with global regulatory mechanisms, carry out the regulation of aromatic compound metabolic pathways in a concerted manner. Additionally, characteristics like chemotaxis, preferential utilization, pathway compartmentalization and biosurfactant production confer an advantage to the microbe, thus making bioremediation of the aromatic pollutants more efficient and effective.

Diversity of the transcriptional regulation of the pch gene cluster in two indigenous p-cresol-degradative strains of Pseudomonas fluorescens

p-Cresol methylhydroxylase (PCMH), a key enzyme responsible for the catabolism of p-cresol via the protocatechuate ortho pathway, was used as a tool to characterize catabolic differences between phenol- and p-cresol-degrading Pseudomonas fluore-scens strains PC18 and PC24. Although both strains catabolize p-cresol using PCMH, different whole-cell kinetic parameters for this compound were revealed. Affinity for the substrate and the specific growth rate were higher in PC18, whereas maximum p-cresol tolerance was higher in PC24. In addition, PCMH of strain PC18 was induced during growth on phenol. In both strains, the pchACXF operon, which encodes p-hydroxybenzaldehyde dehydrogenase and PCMH, was sequenced. Transcriptional regulation of these operons by PchR, a putative sigma(54)-dependent regulator, was shown. Although the promoters of these operons resembled sigma(54)-controlled promoters, they differed from the consensus sequence by having T instead of C at position -12. Complementation assays confirmed that the amino acid sequence differences of the PchR regulators between the two strains studied led to different effector-binding capabilities of these proteins: (1) phenol was a more efficient effector for PchR of PC18 than p-cresol, (2) phenol did not activate the regulator of PC24, and (3) both regulators responded similarly to p-cresol.

Biology of Pseudomonas stutzeri

Pseudomonas stutzeri is a nonfluorescent denitrifying bacterium widely distributed in the environment, and it has also been isolated as an opportunistic pathogen from humans. Over the past 15 years, much progress has been made in elucidating the taxonomy of this diverse taxonomical group, demonstrating the clonality of its populations. The species has received much attention because of its particular metabolic properties: it has been proposed as a model organism for denitrification studies; many strains have natural transformation properties, making it relevant for study of the transfer of genes in the environment; several strains are able to fix dinitrogen; and others participate in the degradation of pollutants or interact with toxic metals. This review considers the history of the discovery, nomenclatural changes, and early studies, together with the relevant biological and ecological properties, of P. stutzeri.

Genotypic Characterization and Phylogenetic Relations of Pseudomonas sp. (Formerly P. stutzeri) OX1

Pseudomonas sp. OX1, an aromatic compound-degrading bacterium that was tentatively identified by conventional biochemical methods as P. stutzeri, has now been investigated at the molecular level to clarify its taxonomic position. Amplified ribosomal DNA restriction analysis and multiple enzyme restriction fragment length polymorphism (MERFLP) analysis suggested that Pseudomonas sp. OX1 could not be classified as P. stutzeri. Phylogenetic analyses based on 16S rRNA and gyrB genes further confirmed that this strain belongs to the Pseudomonas (sensu stricto) genus, but not to the stutzeri species. The data obtained demonstrated that Pseudomonas sp. OX1 belongs to intrageneric cluster II and is related to the P. fluorescens-P. syringae complex.

Product and product-independent induction of butane oxidation in Pseudomonas butanovora

Pseudomonas butanovora grows on butane by means of an inducible soluble alkane monooxygenase (sBMO). The induction of sBMO was studied using the wild type and a sBMO reporter strain. The reporter strain has the lacZ::kan cassette inserted into bmoX, the gene that encodes the alpha-subunit of the hydroxylase of sBMO. The beta-galactosidase activity in the reporter strain was not induced by butane, but was induced by 1-butanol and butyraldehyde. P. butanovora expressed sBMO product-independent activity at 3.0+/-1 nmol ethylene oxide min(-1) mg protein(-1) in stationary phase. The sBMO product-independent activity likely primes the expression of sBMO by butane.