Production, purification and kinetics of chitinase of Stenotrophomonas maltophilia isolated from rhizospheric soil

Chitinases, through decomposition of chitin, have wide applications, and hence are in demand. Researchers over the period, are looking for potential microbial sources and for optimal production of chitnases. Here, we report isolation of three chitinolytic bacterial species belonging to three genera from different agricultural soil sample collected from Shahada, Maharashtra, India, on minimal agar plates containing colloidal chitin as source of chitin. Stenotrophomonas was found to be the most dominant species, followed by Pseudomonas and Alcaligenes. Stenotrophomonas maltophilia identified using 16s rRNA sequencing, Biolog and GC-FAME analysis showed optimum (1.5 U/mL) chitinase activity on chitin agar plates and in submerged culture broth with pH 6-7, incubation of 2 days at 37°C. Presence of CaCl2 stimulated the enzyme production but EDTA was suppressive. The enzyme upon purification by using sephadex G-100 gel filtration showed improved chitinolytic activity, enzyme kinetics and 2.4 fold increase in purification yield. The molecular weight of purified chitinase as determined by SDS-PAGE was 50-55 kDa.

Induced systemic resistance by 2,4-diacetylphloroglucinol positive fluorescent Pseudomonas strains against rice sheath blight

Rice sheath blight arising due to lack of systemic resistance against causative agent Rhizoctonia solani has been a major economic threat to rice growers across the globe. This warrants induced systemic resistance (ISR) in plant to make them disease resistant. Application of antibiotic producing Pseudomonads that also secrete defense inducing enzymes is known to impart resistance to plants. Here, we report induction of the induced systemic resistance (ISR) by six strains of rhizosphere fluorescent Pseudomonas possessing 2,4-diacetyl phloroglucinol (2,4-DAPG) antibiotic genes against rice sheath blight pathogen Rhizoctonia solani. In the preliminary screening, isolate EP5 (endophytic Pseudomonas fluorescens) showed 76.5% inhibition against R. solani. EP5 treated rice grains showed the highest germination of 96.6%, mean root length of 15.3 cm, shoot length of 12.6 cm and vigour index of 2104.9. Paddy grains treated with EP5 (through seed treatment followed by root dipping) upon challenge inoculation with R. solani (Rs1) gave higher activity of peroxidase (PO) 2.50 change in absorbance at 470 nm/min/mg protein), polyphenol oxidases (PPO), 2.25 change absorbance at 420 nm/ min/mg protein, phenyl alanine ammonia lyase (PAL) and 28.5 nmol transcinnamic acid/hr/mg protein. 2,4-DAPG positive fluorescent Pseudomonas strains produced PO, PPO, PAL and 28.5 nmol transcinnamic that resulted in ISR against rice sheath blight pathogen R. Solani.

Dynamism of PGPR in bioremediation and plant growth promotion in heavy metal contaminated soil.

Heavy metal contamination, particularly of cultivable lands, is a matter of concern. Bioremediation helps in reversing such contamination to certain extent. Here, we report isolation, polyphasic identification and the role of siderophore producing rhizobacteria Alcaligenes feacalis RZS2 and Pseudomonas aeruginosa RZS3 in bioremediation of heavy metal contaminated soil and plant growth promotion activity in such contaminated soil. Siderophore produced by A. feacalis RZS2 and P. aeruginosa RZS3 strains chelated various heavy metal ions like MnCl2.4H2O, NiCl2.6H2O, ZnCl2, CuCl2 and CoCl2 other than FeCl3.6H2O at batch scale. Their bioremediation potential was superior over the chemical ion chelators like EDTA and citric acid. These isolates also promoted growth of wheat and peanut seeds sown in heavy metal contaminated soil. Effective root colonizing ability of these isolates was observed in wheat and peanut plants.