Pankaj Trivedi

Pseudomonas corrugata (NRRL B-30409) Mutants Increased Phosphate Solubilization, Organic Acid Production, and Plant Growth at Lower Temperatures

A study for screening and selection of mutants of Pseudomonas corrugata (NRRL B-30409) based on their phosphate solubilization ability, production of organic acids, and subsequent effect on plant growth at lower temperatures under in vitro and in situ conditions was conducted. Of a total 115 mutants tested, two (PCM-56 and PCM-82) were selected based on their greater phosphate solubilization ability at 21°C in Pikovskaya’s broth. The two mutants were found more efficient than wild-type strain for phosphate solubilization activity across a range of temperature from psychotropic (4°C) to mesophilic (28°C) in aerated GPS medium containing insoluble rock phosphate. High-performance liquid chromatography analysis showed that phosphate solubilization potential of wild-type and mutant strains were mediated by production of organic acids in the culture medium. The two efficient mutants and the wild strain oxidized glucose to gluconic acid and sequentially to 2-ketogluconic acid. Under in vitro conditions at 10°C, the mutants exhibited increased plant growth as compared to wild type, indicating their functionality at lower temperatures. In greenhouse trials using sterilized soil amended with either soluble or rock phosphate, inoculation with mutants showed greater positive effect on all of the growth parameters and soil enzymatic activities. To the best of our knowledge, this is the first report on the development of phosphate solubilizing mutants of psychotropic wild strain of P. corrugata, native to the Indian Himalayan region.

Synergistic effects of inoculating arbuscular mycorrhizal fungi and Methylobacterium oryzae strains on growth and nutrient uptake of red pepper (Capsicum annuum L.)

A greenhouse experiment was conducted to examine the effects of inoculation with two Methylobacterium oryzae strains (CBMB20 and CBMB110) and a consortium of three arbuscular mycorrhizal (AM) fungi on the growth of red pepper (Capsicum annum L.). Inoculation of red pepper plants with the M. oryzae strains resulted in a significant increase in root length and root fresh weight compared to untreated control plants. The combined inoculation of M. oryzae strains and AM fungi significantly increased various plant growth parameters and chlorophyll content compared to uninoculated controls. Mycorrhizal colonisation and the number of AM fungal spores were higher in co-inoculation treatments. In addition, the combined inoculation of M. oryzae strains and AM fungi resulted in significantly higher nitrogen (N) accumulation in the roots and shoots of red pepper plants compared to uninoculated controls. The combined inoculation of M. oryzae strain CBMB110 and AM fungi increased the phosphorus (P) content by 23.3% compared to untreated controls. The micronutrient content of the red pepper plants also increased in most of the inoculation treatments. A perfect mutualism among CBMB100-AMF was found which was attributed to the improved macro- and micronutrient uptake along with higher chlorophyll content in red pepper. Further research on in-depth understanding of the co-operative microbial interactions will facilitate the successful application of Methylobacterium-AM fungi products in biotechnology.

Isolation, enumeration, and characterization of diazotrophic bacteria from paddy soil sample under long-term fertilizer management experiment

A study was undertaken to determine the free-living culturable diazotrophic bacteria of paddy soils from a long-term fertilizer management experiment. Long-term application of different fertilizers significantly affected the population of free-living diazotrophs. Out of 165 distinct bacterial morphotypes observed during the isolation process, only 32 were positive for both acetylene reduction assay (ARA), and nifH gene screening. The ARA activity of the isolates ranged from 1.8 to 2,844.7xa0nmol ethylene h−1xa0mg protein−1. The 16S rRNA analysis identified the isolates to be members of 13 different genera viz. Bacillus, Pseudomonas, Paenibacillus, Serratia, Ochrobactrum, Lysinibacillus, Burkholderia, Brevundimonas, Herbaspirillum, Novosphingobium, Sphingomonas, Xanthomonas, and Azorhizobium. Though partial nifH gene sequencing of diazotrophic isolates showed good consistency with that of 16S rRNA-based identification, some nifH sequences were similar to a variety of uncultured nitrogen-fixing bacteria. The diversity of free-living diazotrophic bacteria and the wide distribution of nifH sequences indicate the potential contribution of these microorganisms to nitrogen input to paddy fields.

Chitinase and Glucanase Activities of Antagonistic Streptomyces Spp Isolated From Fired Plots under Shifting Cultivation In Northeast India

Antagonistic Streptomyces spp (Streptomyces sp NEA55 and Streptomyces cavourensis NEA5), isolated from fired plots under shifting cultivation in northeast India, are studied for their chitinase and glucanase activities. The species showed strong antagonism against test fungi (Rhizoctonia solani and Cladosporium sp.) in plate assays. Maximum % inhibition was observed due to the effect of diffusible compounds produced by these species. Streptomyces sp. NEA55 showed 54.83 % inhibition against R. solani while S. cavourensis NEA5 showed up to 50.00 % inhibition against Cladosporium sp. The inhibitory effect of volatile compounds by Streptomyces sp NEA55 was recorded up to 50.7 % against R. solani and 37.50 % against Cladosporium sp. While S. cavourensis NEA5 showed 49.23 % inhibition against R. solani and 34.37 % inhibition against Cladosporium sp. S. cavourensis NEA5 and Streptomyces sp. NEA55 produced 0.138±0.006 μg/ml and 0.15±0.004 μg/ml chitinase, 0.22±0.001 μg/ml and 0.25±0.002 μg/ml β 1,3 glucanase, respectively. Both the species showed maximum chitinase activity at pH 6 and temperature 50 oC, while minimum enzyme activity was observed at pH 10 and temperature 20 oC. Both the species showed glucanase activity maximum at pH 7 and temperature 40 oC and minimum activity at pH 10 and temperature 20 oC. Both the species hydrolyzed glycol–chitin as a substrate in denaturing conditions showing variable amount of different isoforms. This study demonstrates that the antagonistic species of Streptomyces survive the fire operations under shifting cultivation.