Chitinolytic and cellulolytic Pseudomonas sp. antagonistic to fungal pathogens enhances nodulation by Mesorhizobium sp. Cicer in chickpea.

Pseudomonas strains isolated from the rhizosphere of chickpea (Cicer arietinum L.) and green gram (Vigna radiata L.) were screened for the production of chitinases and cellulases. Five Pseudomonas strains were found to produce appreciable amounts of both enzymes in culture-free supernatants and showed growth inhibition of the two fungi Pythium aphanidermatum (Oomycete) and Rhizoctonia solani (Basidiomycete) in plates on potato dextrose agar medium. The fungal growth inhibition was not correlated with cell wall-degrading enzyme activity, which suggested that other antifungal compounds produced by these rhizobacteria were also involved in antagonism. Coinoculation of the Pseudomonas strains with the Mesorhizobium sp. Cicer strain Ca181 resulted in a significant increase in nodule biomass when grown under sterilized chillum jar conditions. The results suggest that hydrolytic enzymes produced by Pseudomonas sp. contribute to suppression of plant diseases by inhibiting growth of phytopathogenic fungi and also promote nodulation of legumes by rhizobia.     

Oxidation of C1 compounds by Pseudomonas sp. MS

Pseudomonas sp. MS is capable of growth on a number of compounds containing only C₁ groups. They include trimethylsulphonium salts, methylamine, dimethylamine and trimethylamine. Although formaldehyde and formate will not support growth they are rapidly oxidized by intact cells. Methanol neither supports growth nor is oxidized. A particulate fraction of the cell oxidizes methylamine to carbon dioxide in the absence of any external electron acceptor. Formaldehyde and formate are more slowly oxidized to carbon dioxide by the particulate fraction, although they do not appear to be free intermediates in the oxidation of methylamine. Soluble NAD-linked formaldehyde dehydrogenase and formate dehydrogenase are also present. The particulate methylamine oxidase is induced by growth on methylamine, dimethylamine and trimethylamine, whereas the soluble formaldehyde dehydrogenase and formate dehydrogenase are induced by trimethylsulphonium nitrate as well as the aforementioned amines.     

Evidence of aerobic utilization of di-ortho-substituted trichlorobiphenyls as growth substrates by Pseudomonas sp. SA-6 and Ralstonia sp. SA-4

Robust and effective bioremediation strategies have not yet been developed for polychlorinated biphenyl (PCB)-contaminated soils. This is in part a result of the fact that ortho - or ortho - and para -substituted congeners, frequent dead-end products of reductive dechlorination of PCB mixtures, have greatly reduced aerobic biodegradability. In this study, we report substantial evidence of utilization of diortho -substituted trichlorobiphenyls (triCBs) as growth substrates by Ralstonia sp. SA-4 and Pseudomonas sp. SA-6 in which ortho -substitution resulted in no obvious patterns of recalcitrance. These stains exhibited unusual preferences for growth on congeners chlorinated on both rings. Substrate uptake studies with benzoate-grown cells revealed that the isolates attacked the 2-chlorophenyl rings of 2,2',4- and 2,2',5-triCB. Between 71% and 93% of the initial 0.23–0.34 mM dose of congeners were transformed in less than 261 h concomitant with non-stoichiometric production of respective dichlorobenzoates and chloride ion. In enzyme assays, activity of 2,3-dihydroxybiphenyl-1,2-dioxygenase was constitutive. Additionally, these strains harboured no detectable plasmids which, coupled with exponential growth on the two triCB congeners, suggested chromosomal location of PCB degradative genes. In addition to the fact that there is a paucity of information on degradation of PCBs by tropical isolates, growth on triCBs as a sole carbon and energy source has never been demonstrated for any natural or engineered microorganisms. Such isolates may help prevent accumulation of ortho -substituted congeners in natural systems and offer the hope for development of effective bioaugmentation or sequential anaerobic–aerobic bioremediation strategies.     

Induction of carbofuran oxidation to 4-hydroxycarbofuran by Pseudomonas sp. 50432

Pseudomonas sp. 50432 biotransformed a highly toxic pesticide, carbofuran (2,3-dihydro-2,2-dimethylbenzofuran-7-yl methylcarbamate) to 7-phenol (2,3-dihydro-2,2-dimethyl-7-hydroxy benzofuran) and several unknown metabolites. One of the unknown metabolites identified by gas chromatography/mass spectroscopy was 4-hydroxycarbofuran (2,3-dihydro-2,2-dimethyl-4-hydroxybenzofuran-7-yl methylcarbamate). It had a mass (237) similar to 3-hydroxycarbofuran and 5-hydroxycarbofuran but different fragmentation patterns. This is the first report in which an inducible oxidative enzyme, hydroxylase, mediated the conversion of carbofuran to 4-hydroxycarbofuran. A second constitutively synthesized enzyme hyrolase transformed carbofuran to 7-phenol.     

Biodegradation of 4-nitrotoluene by Pseudomonas sp. strain 4NT.

A strain of Pseudomonas spp. was isolated from nitrobenzene-contaminated soil on 4-nitrotoluene as the sole source of carbon, nitrogen, and energy. The organism also grew on 4-nitrobenzaldehyde, and 4-nitrobenzoate. 4-Nitrobenzoate and ammonia were detected in the culture fluid of glucose-grown cells after induction with 4-nitrotoluene. Washed suspensions of 4-nitrotoluene- or 4-nitrobenzoate-grown cells oxidized 4-nitrotoluene, 4-nitrobenzaldehyde, 4-nitrobenzyl alcohol, and protocatechuate. Extracts from induced cells contained 4-nitrobenzaldehyde dehydrogenase, 4-nitrobenzyl alcohol dehydrogenase, and protocatechuate 4,5-dioxygenase activities. Under anaerobic conditions, cell extracts converted 4-nitrobenzoate or 4-hydroxylaminobenzoate to protocatechuate. Conversion of 4-nitrobenzoate to protocatechuate required NADPH. These results indicate that 4-nitrotoluene was degraded by an initial oxidation of the methyl group to form 4-nitrobenzyl alcohol, which was converted to 4-nitrobenzoate via 4-nitrobenzaldehyde. The 4-nitrobenzoate was reduced to 4-hydroxylaminobenzoate, which was converted to protocatechuate. A protocatechuate 4,5-dioxygenase catalyzed meta-ring fission of the protocatechuate. The detection of 4-nitrobenzaldehyde and 4-nitrobenzyl alcohol dehydrogenase and 4-nitrotoluene oxygenase activities in 4-nitrobenzoate-grown cells suggests that 4-nitrobenzoate is an inducer of the 4-nitrotoluene degradative pathway.     

The mating projections of Saccharomyces cerevisiae and Candida albicans show key characteristics of hyphal growth

Fungi can grow in a variety of growth forms: yeast, pseudohyphae and hyphae. The human fungal pathogen Candida albicans can grow in all three of these forms. In this fungus, hyphal growth is distinguished by the presence of a Spitzenk?rper-like structure at the hyphal tip and a band of septin bars around the base of newly evaginated germ tubes. The budding yeast Saccharomyces cerevisiae grows as yeast and pseudohyphae, but is not normally considered to show hyphal growth. We show here that in mating projections of both C. albicans and S. cerevisiae a Spitzenk?rper-like structure is present at the growing tip and a band of septin bars is present at the base. Furthermore, in S. cerevisiae mating projections, Spa2 and Bni1 form a cap to the 3-dimensional ball of FM4-64 staining, exactly as previously observed in C. albicans hyphae, suggesting that the putative Spitzenk?rper may be a distinct structure from the polarisome. Taken together this work shows that mating projections of both S. cerevisiae and C. albicans show the key characteristics of hyphal growth.     

Cells of Pseudomonas putida and Enterobacter sp. adapt to toxic organic compounds by increasing their size

The phenol-degrading solvent-tolerant bacterium Pseudomonas putida P8 changed its cell shape when grown in the presence of aromatic compounds such as phenol and 4-chlorophenol. The sizes of cells that had been growing after addition of different concentrations of the toxic compounds were measured using a coulter counter that calculates the sizes of the rod-shaped bacteria to diameters of virtual spheres. The cells showed an increase in the diameter depending on the toxic effects of the applied concentrations of both solvents. The same effect was measured for an alkanol degrading bacterium, Enterobacter sp. VKGH12, in the presence of n-butanol. The reaction of the cells to different concentrations of n-butanol was examined by scanning electron microscopy. With this technique it could be shown that the size of the bacteria increased with increasing concentrations of n-butanol. These changes in cell size were dependent on the cellular activity and occurred only after addition of non-lethal concentrations. In the presence of lethal concentrations that completely inhibited cell growth, the cell sizes were similar to those of cells without intoxication. Taking into account the mathematical formula for spherical and cylindrical diameter and surface, respectively, the cells reacted to the presence of organic solvents by decreasing the ratio between surface and volume of the cells and therefore reducing their relative surfaces. As the cell surface and especially the cytoplasmic membrane are the major targets for the toxic effects of membrane-active compounds, this reduction of the relative surface represents an adaptive response to the presence of such compounds.     

Novel biotransformations of 4-chlorobiphenyl by a Pseudomonas sp.

A bacterium, tentatively identified as a representative of the genus Pseudomonas (strain MB86), was isolated from soil contaminated by wood-preservation chemicals by using 4-chlorobenzoate as an enrichment substrate. The pseudomonad was able to grow on 4-chlorobenzoic acid and 4-chlorobiphenyl as sole carbon and energy sources. Spent culture medium from 4-chlorobiphenyl-grown cells contained 4-chlorobenzoic acid, 4'-chloroacetophenone, 2-hydroxy,2-[4'-chlorophenyl] ethane, and 2-oxo,2-[4'-chlorophenyl] ethanol as metabolites. 4'-Chloroacetophenone was produced in large amounts, possibly as a dead-end metabolite.     

Influence of calcium on fungal growth, hyphal morphology and citric acid production inaspergillus niger

Addition of 0.5 g/L CaCl₂ to the fermentation medium lowered the final biomass dry mass by 35% and increased the uptake of phosphate and sucrose, and the production of citric acid by 15, 35 and 50%, respectively. In a medium deprived of Ca²⁺ the microorganism displayed both a pelleted and a filamentous form of growth, the hyphae being scarcely branched, without bulbous cells. An addition of Ca²⁺ induced a pelleted form of growth, highly branched hyphae and numerous bulbous cells. Bulbous cells growing in the presence of Ca²⁺ exhibited cell walls composed of laminated layers, and featured vesicles associated with the wall and/or the cell membrane, containing numerous inclusions. The cytotoxic effect of high concentrations of citric acid in the medium as well as an increase of the activity of N-acetyl-β-d-glucosaminidase, a lytic enzyme, might be involved in these morphological changes.     

Plasmid determined degradation of sulfo-aromatic compounds by Pseudomonas sp. BS1304]

Utilized sulfo-aromatic compounds of Pseudomonas sp. BS1304 were isolated. It was shown that the first step of conversion is desulfonation with following meta-cleavage of the substituted aromatic ring. At least two steps are controlled by the plasmid pBS1004 (120 kb), belonging to the IncP-9 incompatibility group. The degradative plasmid marked by Tn5-lac may be mobilized to P. putida, P. aeruginosa, P. mendocina, where a degradative phenotype is expressed.     

Biodegradation of Phthalate Isomers by Pseudomonas aeruginosa PP4, Pseudomonas sp. PPD and Acinetobacter lwoffii ISP4

Pseudomonas aeruginosa PP4, Pseudomonas sp. PPD and Acinetobacter lwoffii ISP4 capable of utilizing phthalate isomers were isolated from the soil using enrichment culture technique. The strain ISP4 metabolizes isophthalate, while PPD and PP4 utilizes all three phthalate isomers (ortho-, iso- and tere-) as the sole carbon source. ISP4 utilizes isophthalate (0.1%) more rapidly (doubling time, 0.9 h) compared to PPD (4.64 h), PP4 (7.91 h) and other reported strains so far. The metabolic pathways in these isolates were initiated by dihydroxylation of phthalate isomers. Phthalate is hydroxylated to 3,4-dihydro-3,4-dihydroxyphthalate and 4,5-dihydro-4,5-dihydroxyphthalate in strains PP4 and PPD, respectively; while terephthalate is hydroxylated to 2-hydro-1,2-dihydroxyterephthalate. All three strains hydroxylate isophthalate to 4-hydro-3,4-dihydroxyisophthalate. The generated dihydroxyphthalates were subsequently metabolized to 3,4-dihydroxybenzoate (3,4-DHB) which was further metabolized by ortho ring-cleavage pathway. PP4 and PPD cells grown on phthalate, isophthalate or terephthalate showed respiration on respective phthalate isomer and the activity of corresponding ring-hydroxylating dioxygenase, suggesting the carbon source specific induction of three different ring-hydroxylating dioxygenases. We report, for the first time, the activity of isophthalate dioxygenase and its reductase component in the cell-free extracts. The enzyme showed maximum activity with reduced nicotinamide adenine dinucleotide (NADH) in the pH range 8–8.5. Cells grown on glucose failed to respire on phthalate isomers and 3,4-DHB and showed significantly low activities of the enzymes suggesting that the enzymes are inducible.     

Degradation of 4-aminophenol by newly isolated Pseudomonas sp. strain ST-4

Aromatic compounds and their substituted forms are hazardous to the environment. Biodegradation by microorganisms can be used to remove these pollutants from soil and water. During the present investigations, Pseudomonas sp. strain ST-4 was used for the degradation of 4-aminophenol. The strain was able to use 4-aminophenol as growth substrate showing growth up to 400 ppm on mineral salt media plates. In broth, degradation up to 84% was observed. Induction with 4-aminophenol proved to be effective as it increased the degradation rate more than by the uninduced cell. Biodegradation was found to be more effective than autoxidation of 4-aminophenol, indicating bioremediation as main process to eliminate aromatic amines. In order to locate the responsible genes for degradation, curing and then isolation of plasmid showed the involvement of plasmid encoded genes in this mechanism since the cured strains do not grow with 4-aminophenol.     

Control of glyphosate uptake and metabolism in Pseudomonas sp. 4ASW

Abstract The tandem mini-exon gene repeat is an ideal diagnostic target for trypanosomatids because it includes sequences that are conserved absolutely coupled with regions of extreme variability. We have exploited these features and the polymerase chain reaction to differentiate Phytomonas strains isolated from phloem, fruit or latex of various host plants. While the transcribed regions are nearly identical, the intergenic sequences are variable in size and content (130–332 base pairs). The mini-exon genes of these phytomonads can therefore be distinguished from each other and from the corresponding genes in insect trypanosomes, with which they are oft confused.     

Denitrifying Pseudomonas aeruginosa: some parameters of growth and active transport.

Optimal cell yield of Pseudomonas aeruginosa grown under denitrifying conditions was obtained with 100 mM nitrate as the terminal electron acceptor, irrespective of the medium used. Nitrite as the terminal electron acceptor supported poor denitrifying growth when concentrations of less than 15 mM, but not higher, were used, apparently owing to toxicity exerted by nitrite. Nitrite accumulated in the medium during early exponential phase when nitrate was the terminal electron acceptor and then decreased to extinction before midexponential phase. The maximal rate of glucose and gluconate transport was supported by 1 mM nitrate or nitrite as the terminal electron acceptor under anaerobic conditions. The transport rate was greater with nitrate than with nitrite as the terminal electron acceptor, but the greatest transport rate was observed under aerobic conditions with oxygen as the terminal electron acceptor. When P. aeruginosa was inoculated into a denitrifying environment, nitrate reductase was detected after 3 h of incubation, nitrite reductase was detected after another 4 h of incubation, and maximal nitrate and nitrite reductase activities peaked together during midexponential phase. The latter coincided with maximal glucose transport activity.     

Denitrifying Pseudomonas aeruginosa: some parameters of growth and active transport.

Optimal cell yield of Pseudomonas aeruginosa grown under denitrifying conditions was obtained with 100 mM nitrate as the terminal electron acceptor, irrespective of the medium used. Nitrite as the terminal electron acceptor supported poor denitrifying growth when concentrations of less than 15 mM, but not higher, were used, apparently owing to toxicity exerted by nitrite. Nitrite accumulated in the medium during early exponential phase when nitrate was the terminal electron acceptor and then decreased to extinction before midexponential phase. The maximal rate of glucose and gluconate transport was supported by 1 mM nitrate or nitrite as the terminal electron acceptor under anaerobic conditions. The transport rate was greater with nitrate than with nitrite as the terminal electron acceptor, but the greatest transport rate was observed under aerobic conditions with oxygen as the terminal electron acceptor. When P. aeruginosa was inoculated into a denitrifying environment, nitrate reductase was detected after 3 h of incubation, nitrite reductase was detected after another 4 h of incubation, and maximal nitrate and nitrite reductase activities peaked together during midexponential phase. The latter coincided with maximal glucose transport activity.     

Kinetics of growth and caffeine demethylase production of Pseudomonas sp. in bioreactor

The effect of various initial caffeine concentrations on growth and caffeine demethylase production by Pseudomonas sp. was studied in bioreactor. At initial concentration of 6.5 g l^?1 caffeine, Pseudomonas sp. showed a maximum specific growth rate of 0.2 h^?1, maximum degradation rate of 1.1 g h^?1, and caffeine demethylase activity of 18,762 U g CDW^?1 (CDW: cell dry weight). Caffeine degradation rate was 25 times higher in bioreactor than in shake flask. For the first time, we show highest degradation of 75 g caffeine (initial concentration 20 g l^?1) in 120 h, suggesting that the tested strain has potential for successful bioprocess for caffeine degradation. Growth kinetics showed substrate inhibition phenomenon. Various substrate inhibition models were fitted to the kinetic data, amongst which the double-exponential (R ² = 0.94), Luong (R ² = 0.92), and Yano and Koga 2 (R ² = 0.94) models were found to be the best. The Luedeking–Piret model showed that caffeine demethylase production kinetics was growth related. This is the first report on production of high levels of caffeine demethylase in batch bioreactor with faster degradation rate and high tolerance to caffeine, hence clearly suggesting that Pseudomonas sp. used in this study is a potential biocatalyst for industrial decaffeination.