Studies Of Nitrogen Fixing Bacteria Associated With Aerial Roots Of Rhynchostylis Retusa L Blume

Abstract

newline ABSTRACT newlineIn this study, the diversity of diazotrophic bacteria of the orchid Rhynchostylis retusa newline(L.) Blume and its potential application in plant growth promotion were evaluated. newlineAbout 183 nitrogen-fixing bacteria were isolated to screen various plant growthpromoting newlinetraits viz. phosphate solubilization, IAA, siderophore, HCN, biofilm, and newlineammonia production. A bacterial isolate, Microbacterium testaceum Y411 was found newlineto be the most active producer of indole-3-acetic acid (IAA). The maximum IAA newlineproduction (170and#956;g/ml) was recorded with the bacterium at optimum process parameters newlinesuch as pH 7, temperature 30 °C and tryptophan 1000 and#956;g/ml in a culture medium for 48 newlineh. The extracted auxin was purified and analyzed by FT-IR, HPLC, and HR-MS newlineindicating bacterial auxin has a similar mass value to 4-chloroindole-3-acetic acid auxin. newlineFurthermore, the bacterial auxin was tested on in vitro propagation of orchid, newlineCymbidium aloifolium, and 90% seed germination was recorded in Murashige and newlineSkoog s medium supplemented with bacterial auxin. The novel results obtained in this newlinestudy are used for agricultural applications and the Microbacterium testaceum Y411 is newlinea valuable biotechnological resource for a natural auxin. Based on 16S rRNA gene newlinesequencing analysis Achromobacter, Arthrobacter, Acinetobacter, Bacillus, newlineBrevibacterium, Curtobacterium, Erwinia, Kosakonia, Lysinibacillus, Kleibseilla, newlineMicrobacterium, Mixta, Pantoea, Pseudomonas and Stenotrophomonas isolates were newlineselected and showed positive results for PGP traits. Overall, genus Pantoea, newlineBrevibacterium, Achromobacter, Arthrobacter, Klebsiella, Mixta, Bacillus, and newlinePseudomonas had the most pronounced PGP characteristics and acetylene reduction newlineamong the screened isolates. BOX PCR fingerprinting analysis showed variation in newlinepolymorphic banding patterns among diazotrophic strains. PCR amplification of nifH newlinegene and the presence of 37 kDa nitrogenase reductase enzyme band in the western blot newlineindicated the presence of nitrogenase activity. Our study showed that orchid R. retusa newlinediazotrophs interaction helps orchid plants fix nitrogen and essential nutrients and newlinecontrol pathogen entry. To the best of our knowledge, this is the first report on the newlinecharacterization of the diazotrophic bacterial community from aerial roots of R. retusa.