Pseudomonas putida

Abstract: The structural organization of four microbial communities was analysed by a novel computer program, COMSTAT, which comprises ten features for quantifying three-dimensional biofilm image stacks. Monospecies biofilms of each of the four bacteria, Pseudomonas putida, P. aureofaciens, P. fluorescens and P. aeruginosa, tagged with the green fluorescent protein (GFP) were grown in flow chambers with a defined minimal medium as substrate. Analysis by the COMSTAT program of four variables describing biofilm structure ‐ mean thickness, roughness, substratum coverage and surface to volume ratio ‐ showed that the four Pseudomonas strains represent different modes of biofilm growth. P. putida had a unique developmental pattern starting with single cells on the substratum growing into micro-colonies, which were eventually succeeded by long filaments and elongated cell clusters. P. aeruginosa colonized the entire substratum, and formed flat, uniform biofilms. P. aureofaciens resembled P. aeruginosa, but had a stronger tendency to form micro-colonies. Finally, the biofilm structures of P. fluorescens had a phenotype intermediate between those of P. putida and P. aureofaciens. Analysis of biofilms of P. aureofaciens growing on 0<03 mM, 0< 1m M or 0< 5m M citrate minimal media showed that mean biofilm thickness increased with increasing citrate concentration. Moreover, biofilm roughness increased with lower citrate concentrations, whereas surface to volume ratio increased with higher citrate concentrations.

Abstract: Many plant-associated bacteria synthesize the phytohormone indoleacetic acid (IAA). While IAA produced by phytopathogenic bacteria, mainly by the indoleacetamide pathway, has been implicated in the induction of plant tumors, it is not clear whether IAA synthesized by beneficial bacteria, usually via the indolepyruvic acid pathway, is involved in plant growth promotion. To determine whether bacterial IAA enhances root development in host plants, the ipdc gene that encodes indolepyruvate decarboxylase, a key enzyme in the indolepyruvic acid pathway, was isolated from the plant growth-promoting bacterium Pseudomonas putida GR12-2 and an IAA-deficient mutant constructed by insertional mutagenesis. The canola seedling primary roots from seeds treated with wild-type P. putida GR12-2 were on average 35 to 50% longer than the roots from seeds treated with the IAA-deficient mutant and the roots from uninoculated seeds. In addition, exposing mung bean cuttings to high levels of IAA by soaking them in a suspension of the wild-type strain stimulated the formation of many, very small, adventitious roots. Formation of fewer roots was stimulated by treatment with the IAA-deficient mutant. These results suggest that bacterial IAA plays a major role in the development of the host plant root system.

Abstract: Pseudomonas putida is a metabolically versatile saprophytic soil bacterium that has been certified as a biosafety host for the cloning of foreign genes. The bacterium also has considerable potential for biotechnological applications. Sequence analysis of the 6.18 Mb genome of strain KT2440 reveals diverse transport and metabolic systems. Although there is a high level of genome conservation with the pathogenic Pseudomonad Pseudomonas aeruginosa (85% of the predicted coding regions are shared), key virulence factors including exotoxin A and type III secretion systems are absent. Analysis of the genome gives insight into the non-pathogenic nature of P. putida and points to potential new applications in agriculture, biocatalysis, bioremediation and bioplastic production.

Abstract: We report the complete genome sequence of the model bacterial pathogen Pseudomonas syringae pathovar tomato DC3000 (DC3000), which is pathogenic on tomato and Arabidopsis thaliana. The DC3000 genome (6.5 megabases) contains a circular chromosome and two plasmids, which collectively encode 5,763 ORFs. We identified 298 established and putative virulence genes, including several clusters of genes encoding 31 confirmed and 19 predicted type III secretion system effector proteins. Many of the virulence genes were members of paralogous families and also were proximal to mobile elements, which collectively comprise 7% of the DC3000 genome. The bacterium possesses a large repertoire of transporters for the acquisition of nutrients, particularly sugars, as well as genes implicated in attachment to plant surfaces. Over 12% of the genes are dedicated to regulation, which may reflect the need for rapid adaptation to the diverse environments encountered during epiphytic growth and pathogenesis. Comparative analyses confirmed a high degree of similarity with two sequenced pseudomonads, Pseudomonas putida and Pseudomonas aeruginosa, yet revealed 1,159 genes unique to DC3000, of which 811 lack a known function.

Abstract: Organic solvents can be toxic to microorganisms, depending on the inherent toxicity of the solvent and the intrinsic tolerance of the bacterial species and strains. The toxicity of a given solvent correlates with the logarithm of its partition coefficient in n-octanol and water (log Pow). Organic solvents with a log Pow between 1.5 and 4.0 are extremely toxic for microorganisms and other living cells because they partition preferentially in the cytoplasmic membrane, disorganizing its structure and impairing vital functions. Several possible mechanisms leading to solvent-tolerance in gram-negative bacteria have been proposed: (a) adaptive alterations of the membrane fatty acids and phospholipid headgroup composition, (b) formation of vesicles loaded with toxic compounds, and (c) energy-dependent active efflux pumps belonging to the resistance-nodulation-cell division (RND) family, which export toxic organic solvents to the external medium. In these mechanisms, changes in the phospholipid profile and extrusion of the solvents seem to be shared by different strains. The most significant changes in phospholipids are an increase in the melting temperature of the membranes by rapid cis-to-trans isomerization of unsaturated fatty acids and modifications in the phospholipid headgroups. Toluene efflux pumps are involved in solvent tolerance in several gram-negative strains, e.g., Escherichia coli, Pseudomonas putida, and Pseudomonas aeruginosa. The AcrAB-TolC and AcrEF-TolC efflux pumps are important for n-hexane tolerance in E. coli. A number of P. putida strains have been isolated that tolerate toxic hydrocarbons such as toluene, styrene, and p-xylene. At least three efflux pumps (TtgABC, TtgDEF, and TtgGHI) are present in the most extensively characterized solvent-tolerant strain, P. putida DOT-T1E, and the number of efflux pumps has been found to correlate with the degree of solvent tolerance in different P. putida strains. The operation of these efflux pumps seems to be coupled to the proton motive force via the TonB system, although the intimate mechanism of energy transfer remains elusive. Specific and global regulators control the expression of the efflux pump operons of E. coli and P. putida at the transcriptional level.