Diversity of root associated microorganisms of selected medicinal plants and influence of rhizomicroorganisms on the antimicrobial property of Coriandrum sativum.

The total heterotrophic bacteria, actinomycetes and fungus were enumerated from the rhizosphere and non-rhizosphere soil of 50 selected locally available medicinal plants in and around Bharathiar University. In all the plants, population of microorganism were higher in the rhizosphere soil than in the non rhizosphere soil. Among the microorganisms, bacterial population was higher in number followed by fungus and actinomycetes. Of the medicinal plants, the maximum rhizosphere effect was observed in Annona squamosa and the minimum effect was seen in Eclipta alba and Cassia auriculata. Among the bacteria the dominant species was Bacillus followed by Pseudomonas, Enterobacter, Corynebacterium, Micrococcus and Serratia. The Streptomyces species was found to be dominant followed by Deuteromycetes and Frankia among the actinomycetes. Among the fungal isolates Rhizopus was found to be higher in number followed by Aspergillus, Penicillium, Mucor and Fusarium. About 70.96% of the bacterial isolates were found to be nitrate reducers and 90.60% of the bacteria solubilised phosphate. The rhizosphere bacterial isolates were also capable of hydrolyzing starch, cellulose, casein, urea and gelatin. The isolates of bacteria, actinomycetes and fungus were also able to produce phytohormone Indole-3-acetic acid (IAA). The maximum IAA production was recorded by Fusarium sp (5.8 mg/l). The rhizosphere bacterial isolates showed resistance to 14 commercially used antibiotics. In an attempt to check the influence of these plant growth promoting microorganisms on the antimicrobial property of Coriandrum sativum against Escherichia coli MTCC-443 and Aeromonas hydrophila MTCC-646, the results observed was not encouraging since the inoculants did not influence the antibacterial property. However extensive and in depth study is required to find out the influence of rhizomicroorganisms on the antibacterial property of medicinal plants. The other results clearly indicated that the rhizosphere microorganisms could be exploited for its innumerable properties and active metabolites.