Indole acetic acid production by the actinomycetes of coffee plantation soils of western ghats

Background: The isolation of actinomycetes from coffee plantation soil increases the chance for the production of high auxins—IAA producers, helping in maximum increase in growth of the plants. Objectives: In the present study, actinomycetes were isolated from the less explored coffee plantation soils and the strains were screened for IAA producing activity which can be exploited for the production of agroactive compounds like auxins. Methods: The actinomycete strains were isolated from coffee plantation soils of Chikkamagalur district Karnataka, India. They were identified by molecular characterization and used for studying the IAA-producing ability. The identification of IAA was confirmed by spectrophotometric and chromatographic analyses. Results: A total of thirty two distinct actinomycete strains were isolated from coffee plantation soils of Chikkamagalur district Karnataka, India. Morphological and molecular studies (16S rRNA) revealed that 50% of the isolates belonged to the genus Streptomyces, and 50% were non-streptomycetes comprising Actinomadura, Arthrobacter, Spirillospora, Sachharopolyspora, Nonomuraea, Gordonia, Micromonospora, Nocardia, Rhodococcus, and Pseudonocardia. Of the thirty two actinomycete strains, twenty seven strains showed the IAA-producing ability which was confirmed by spectrophotometric analysis. The strain Streptomyces violaceolatus CMCS 016 produced maximum amount of IAA (109.24±0.2 µg/ml) in the ISP2 medium supplemented with 0.5% L-tryptophan. The chromatographic studies (TLC and HPLC) revealed that the extracted IAA had similarity to standard IAA with the same Rf value and retention time respectively. This study indicates the potential of S. violaceolatus CMCS 016 as a significant IAA producer. Conclusion: The present study is the first report on the IAA-producing potential of actinomycetes from coffee plantation soil enhancing the significance of non-rhizospheric soil which are equal proficient auxin producers compared to rhizospheric soil. The nutrient-rich soils of coffee plantations containing litter from both the tree species and the coffee plants are indeed rich sources of soil actinomycetes with biotechnological applications.