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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Penicillium oxalicum was isolated from acidic paddy rhizosphere soil, Milyang, Korea using modified media with AlPO 4 and bromo cresol green (BCG). Ability of fungus to solubilize mineral phosphates and its cause for solubilization were studied in vitro. The fungus was grown in liquid medium cultures containing AlPO 4 / FePO 4 /Ca 3 (PO 4 ) 2 (1000 mg P L )1 ). Concentration of organic acids, soluble phosphate and pH were determined periodically during 7 to 78 h incubation. Penicillium oxalicum demonstrated higher levels of Ca 3 (PO 4 ) 2 (129.10 mg L )1 ) and AlPO 4 (119.80 mg L )1 ) solubilization than that of FePO 4 (54.70 mg L )1 ) solubilization. Soluble phosphate concentrations in the culture medium were directly proportional to the organic acids and inversely related to pH. Malic acid production may have contributed the higher Al-P solubilization in culture media. Evidence from abiotic solubilization using sodium malate and HCl to solubilize P also indicated that malic acid may have been a main organic acid involved in the solubilization of AlPO 4 and Ca 3 (PO 4 ) 2 .