Species Composition and Diversity Dynamics of Actinomycetes in Arid and Semi-arid Salt Basins of Rajasthan.

Species composition and diversity dynamics of the actinomycetes was studied in five salt basins of arid and semi-arid areas of Rajasthan, India. A novel approach integrating molecular (16S rRNA gene) and diversity indices was applied to reveal species composition and diversity dynamics. Fifty-three actinomycetes isolates were isolated from five arid and semi-arid salt basins. Molecular characterization resulted in the identification of actinomycetes species belonging to three genera namely, Streptomyces, Nocardiopsis, and Actinoalloteichus. The diversity study among actinomycetes species validates their universal occurrence in arid and semi-arid regions of Rajasthan. The species N. dassonvillei subsp. albirubida was omnipresent in all the five salt basins but its relative manifestation was not static across habitats. The study revealed that three species N. chromatogenes, S. durbertensis, and S. mangrovicola are being reported for the first time from India. The maximum species of actinomycetes were recorded from Pachpadra (14) and the minimum from Didwana area (6). This study not only documents the hitherto wealth of actinomycetes species in arid and semi-arid salt basins of Rajasthan but also reveals the composition and diversity dynamics of actinomycetes.

Actinomycetes isolates of arid zone of Indian Thar Desert and efficacy of their bioactive compounds against human pathogenic bacteria.

Twenty-six morphotypes of actinomycetes bacteria were isolated from the soils of arid zone of Indian Thar desert, Rajasthan. A significant and positive correlation was found between density of actinomycetes isolates and availability of nitrogen in sandy soil of arid zone suggesting the influence of soil nitrogen on occurrence and propagation of actinomycetes in this region. Molecular identification based on 16S rRNA gene sequencing revealed that the bacterial isolates belong to four actinomycetes genera, viz. Streptomyces (22 species), Nocardiopsis (two species), Saccharomonospora (one species) and Actinoalloteichus (one species). The preliminary screening of 26 isolates against five human pathogenic bacteria, viz. Escherichia coli, Vibrio cholera, Salmonella enterica typhimurium, Staphylococcus aureus and Enterococcus faecalis, showed that only four isolates, viz. Streptomyces sp. (ITD-27), S. enissocaesilis (ITD-29), S. Malachitospinus (ITD-35) and Streptomyces sp. (ITD-47), had antibacterial activity. The secondary screening of these four isolates revealed that the isolate S. malachitospinus (ITD-35) showed the maximum growth inhibition zone and inhibited the growth of all tested gram-positive and gram-negative pathogenic bacteria. Gas chromatography-mass spectrometry analysis of S. malachitospinus (ITD-35) cultural filtrate in n-butanol solvent identified three antibacterial compounds of medicinal significance, viz. 3-octanone, neopentyl isothiocyanate and 2-methyl butyl isothiocyanate.

An invasive Mimosa in India does not adopt the symbionts of its native relatives.

BACKGROUND AND AIMS: The large monophyletic genus Mimosa comprises approx. 500 species, most of which are native to the New World, with Central Brazil being the main centre of radiation. All Brazilian Mimosa spp. so far examined are nodulated by rhizobia in the betaproteobacterial genus Burkholderia. Approximately 10 Mya, transoceanic dispersal resulted in the Indian subcontinent hosting up to six endemic Mimosa spp. The nodulation ability and rhizobial symbionts of two of these, M. hamata and M. himalayana, both from north-west India, are here examined, and compared with those of M. pudica, an invasive species. METHODS: Nodules were collected from several locations, and examined by light and electron microscopy. Rhizobia isolated from them were characterized in terms of their abilities to nodulate the three Mimosa hosts. The molecular phylogenetic relationships of the rhizobia were determined by analysis of 16S rRNA, nifH and nodA gene sequences. KEY RESULTS: Both native Indian Mimosa spp. nodulated effectively in their respective rhizosphere soils. Based on 16S rRNA, nifH and nodA sequences, their symbionts were identified as belonging to the alphaproteobacterial genus Ensifer, and were closest to the 'Old World' Ensifer saheli, E. kostiensis and E. arboris. In contrast, the invasive M. pudica was predominantly nodulated by Betaproteobacteria in the genera Cupriavidus and Burkholderia. All rhizobial strains tested effectively nodulated their original hosts, but the symbionts of the native species could not nodulate M. pudica. CONCLUSIONS: The native Mimosa spp. in India are not nodulated by the Burkholderia symbionts of their South American relatives, but by a unique group of alpha-rhizobial microsymbionts that are closely related to the 'local' Old World Ensifer symbionts of other mimosoid legumes in north-west India. They appear not to share symbionts with the invasive M. pudica, symbionts of which are mostly beta-rhizobial.