Characteristics of transposon insertion mutants of mandelic acid-utilizing Pseudomonas putida strain A10L

Proline confers acid stress tolerance to Bacillus megaterium G18

Proline plays a multifunctional role in several organisms including bacteria in conferring protection under stress conditions. In this paper we report the role of proline in conferring acid tolerance to Bacillus megaterium G18. An acid susceptible mutant of B. megaterium G18 which required proline for its growth under acid stress condition was generated through Tn5 mutagenesis. Further, targeted inactivation of proC involved in osmo-adaptive proline synthesis in B. megaterium G18 resulted in the loss of ability of the bacterium to grow at low pH (pH 4.5). Exogenous supply of proline (1 mM) to the growth medium restored the ability of the mutant cells to grow at pH 4.5 which was not the same in case of other osmoprotectants tested. Proline was produced and secreted to extracellular medium by B. megaterium G18 when growing in low pH condition as evidenced by the use of Escherichia coli proline auxotrophs and HPLC analysis. Further, pHT01 vector based expression of full length proC gene in the ∆proC mutant cells restored the survival capacity of the mutant cells in acidic pH, suggesting that proline production is an important strategy employed by B. megaterium G18 to survive under acid stress induced osmotic stress.

Phylogeny of the genus Pseudomonas: intrageneric structure reconstructed from the nucleotide sequences of gyrB and rpoD genes

Phylogenetic analysis of the genus Pseudomonas: was conducted by using the combined gyrB and rpoD nucleotide sequences of 31 validly described species of Pseudomonas: (a total of 125 strains). Pseudomonas: strains diverged into two major clusters designated intrageneric cluster I (IGC I) and intrageneric cluster II (IGC II). IGC I was further split into two subclusters, the 'P: aeruginosa complex', which included P: aeruginosa, P: alcaligenes, P: citronellolis, P: mendocina, P: oleovorans and P: pseudoalcaligenes, and the 'P: stutzeri complex', which included P: balearica and P: stutzeri. IGC II was further split into three subclusters that were designated the 'P: putida complex', the 'P: syringae complex' and the 'P: fluorescens complex'. The 'P: putida complex' included P: putida and P: fulva. The 'P: syringae complex' was the cluster of phytopathogens including P: amygdali, P: caricapapayae, P: cichorii, P: ficuserectae, P: viridiflava and the pathovars of P. savastanoi and P. syringae. The 'P. fluorescens complex' was further divided into two subpopulations, the 'P. fluorescens lineage' and the 'P. chlororaphis lineage'. The 'P. fluorescens lineage' contained P. fluorescens biotypes A, B and C, P. azotoformans, P. marginalis pathovars, P. mucidolens, P. synxantha and P. tolaasii, while the 'P. chlororaphis lineage' included P. chlororaphis, P. agarici, P. asplenii, P. corrugata, P. fluorescens biotypes B and G and P. putida biovar B. The strains of P. fluorescens biotypes formed a polyphyletic group within the 'P. fluorescens complex'.

Population dynamics of phenol-degrading bacteria in activated sludge determined by gyrB-targeted quantitative PCR

A method for quantifying bacterial populations introduced into an activated-sludge microbial community is described. The method involves extraction of DNA from activated sludge, appropriate dilution of the extracted DNA with DNA extracted from nonintroduced activated sludge, PCR amplification of a gyrB gene fragment from the introduced strain with a set of strain-specific primers, and quantification of the electrophoresed PCR product by densitometry. The adequacy of the method was examined by analyzing the population dynamics of two phenol-degrading bacteria, Pseudomonas putida BH and Comamonas sp. strain E6, that had been introduced into phenol-digesting activated sludge. The density of each of the two populations determined by the PCR method immediately after the introduction was consistent with the density estimated from a plate count of the inoculum. This quantitative PCR method revealed different population dynamics for the two strains in the activated sludge under different phenol-loading conditions. The behavior of both of these strains in the activated sludge reflected the growth kinetics of the strains determined in laboratory axenic cultures.