Characterization of plant growth-promoting traits of bacteria isolated from larval guts of diamondback moth Plutella xylostella (lepidoptera: plutellidae).
ABSTRACT Eight bacterial isolates from the larval guts of Diamondback moths (Plutella xylostella) were tested for their plant growth-promoting (PGP) traits and effects on early plant growth. All of the strains tested positive for nitrogen fixation and indole 3-acetic acid (IAA) and salicylic acid production but negative for hydrogen cyanide and pectinase production. In addition, five of the isolates exhibited significant levels of tricalcium phosphate and zinc oxide solubilization; six isolates were able to oxidize sulfur in growth media; and four isolates tested positive for chitinase and beta-1,3-glucanase activities. Based on their IAA production, six strains including four that were 1-aminocyclopropane-1-carboxylate (ACC) deaminase positive and two that were ACC deaminase negative were tested for PGP activity on the early growth of canola and tomato seeds under gnotobiotic conditions. Acinetobacter sp. PSGB04 significantly increased root length (41%), seedling vigor, and dry biomass (30%) of the canola test plants, whereas Pseudomonas sp. PRGB06 inhibited the mycelial growth of Botrytis cinerea, Colletotrichum coccodes, C. gleospoiroides, Rhizoctonia solani, and Sclerotia sclerotiorum under in vitro conditions. A significant increase, greater than that of the control, was also noted for growth parameters of the tomato test plants when the seeds were treated with PRGB06. Therefore, the results of the present study suggest that bacteria associated with insect larval guts possess PGP traits and positively influence plant growth. Therefore, insect gut bacteria as effective PGP agents represent an unexplored niche and may broaden the spectrum of beneficial bacteria available for crop production.
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ABSTRACT: Plant growth promoting rhizobacteria (PGPR) are known to increase growth and vigor of legumes in conventional cropping systems. Considering this as a basis, this study was aimed at identifying phosphate-solubilizing (PS) rhizobacterial strains expressing higher tolerance to insecticides, fipronil and pyriproxyfen, and synthesizing plant growth regulators even amid insecticide stress. The impact of selected rhizobacteria endowed with multitude of activities was investigated on greengram, grown in soils treated with different concentrations of insecticides. The fipronil and pyriproxyfen tolerant Pseudomonas aeruginosa strain PS1 produced plant growth promoting substances, both in the presence and absence of the insecticides. Both insecticides at recommended and higher rates, in general, had phytotoxic effects and decreased phytomass, symbiotic properties, nutrients uptake, and seed yield of greengram plants. Interestingly, P. aeruginosa PS1 even when used with all concentrations of the two insecticides significantly increased the measured parameters at 50 and 80days after sowing, compared to the plants grown in soils treated with the same concentration of each insecticide but without inoculants. P. aeruginosa PS1 can be used as biofertilizer to augment the growth of greengram exposed to insecticide-stressed soils. Keywords Pseudomonas –Greengram–Plant growth promoting rhizobacteria–Insecticides–Phosphate solubilization– Vigna radiata –Legume–NodulationJournal of Pest Science 01/2011; 84(1):123-131. · 2.17 Impact Factor
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ABSTRACT: The aim of this study was to investigate the side-effects of fungicides on the physiological activities of plant growth promoting rhizobacteria with intrinsic phosphate-solubilizing potential. The fungicide-tolerant and phosphate-solubilizing bacterial strain PS19 was isolated from the mustard rhizosphere and identified as Klebsiella sp. following 16S rDNA sequencing. The Klebsiella sp. strain PS19 normally, produced plant growth promoting (PGP) substances in substantial amount. In this study, four fungicides of different chemical families (tebuconazole, hexaconazole, metalaxyl, and kitazin) at the recommended, two and three times of the recommended rates decreased the PGP attributes of the strain PS19 in fungicide-concentration dependent manner. Moreover, fungicides at the recommended dose had slight inhibitory effect while the dose higher than the recommended ones reduced the PGP traits (phosphate solubilization, salicylic acid, 2,3-dihydroxy benzoic acid, and indole-3-acetic acid production except exo-polysaccharides, hydrogen cyanate and ammonia production) significantly. Of the four fungicides, tebuconazole generally showed the maximum toxicity to the PGP activities of the strain PS19. The results of this study inferred that fungicides, which are used to control various fungal pests detrimental for the crop productivity, must be examined in vitro for their possible adverse impacts on plant-beneficial rhizobacteria before the field application. This study also revealed an additional aspect of the toxicological mechanisms of the fungicides through which they may suppress the plant growth.Journal of Pest Science 01/2012; 100:51-56. · 2.17 Impact Factor
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ABSTRACT: The development of proteinase inhibitors as potential insect control agents has been constrained by insect adaptation to these compounds. The velvet bean caterpillar (Anticarsia gemmatalis) is a key soybean pest species that is well-adapted to proteinase inhibitors, particularly serine-proteinase inhibitors, which are abundant in the caterpillar host. The expression of diverse proteolytic enzymes by gut symbionts may allow the velvet bean caterpillar to circumvent proteinase inhibitors produced by the host plant. In this study, we characterized the proteolytic activity of the four nonpathogenic species of gut bacteria isolated from the velvet bean caterpillar-Bacillus cereus, Enterococcus gallinarum, Enterococcus mundtii and Staphylococcus xylosus. Two proteinase substrates, N-α-benzoyl-L-Arg-p-nitroanilide (L-BApNA) and N-α-p-tosyl-L-Arg methyl ester (L-TAME) and five proteinase inhibitors [aprotinin, E-64, ethylenediamine tetraacetic acid (EDTA), pepstatin and N-α-tosyl-L-lysine chloromethyl ketone (TLCK)] as well as CaCl(2), pH and temperature profiles were used to characterize the expressed proteolytic activity of these bacterial strains in vitro. Kinetic parameters for proteolytic activity were also estimated. The results of these experiments indicated that serine- and cysteine-proteinase activities were expressed by all four gut bacteria symbionts of the velvet bean caterpillar. The cysteine- and serine-proteinase activities of these gut symbionts were distinct and different from that of gut proteinases of the caterpillar itself. This finding provides support for the potential involvement of gut symbionts in the mitigation of the negative effects of serine-proteinase inhibitors in the velvet bean caterpillar.Journal of Comparative Physiology B 02/2013; · 2.02 Impact Factor