Abstract
The Thar Desert harsher environment harbors a limited diversity of life forms due to extreme conditions like low moisture of sandy soils and high soil temperature. In the present study, osmotolerant bacteria from the Thar soils were isolated and characterized. Bacteria were isolated from 20 soil samples (100 g), collected from sand dunes, suspended in water and absolute alcohol. A total of 11 biochemical and morphological tests were carried out for generic identification of bacteria. Osmotic tolerance capacity of isolates was examined on glycerol, NaCI and alcohol; and sequencing of 16S rRNA gene was also performed for bacterial identification. 16S to 23S rRNA internal transcribed spacer analysis (RISA) was done for phylogenetic analysis of isolates. The soil suspended in water contained 2.5 x 10(6) bacteria/g of soil while alcohol suspended soil had 4.4 x 10(4) bacteria/g. The 24 bacterial isolates were found tolerant to 26% glycerol, 14% NaCI and 10% of alcohol, and 22 out of 24 isolates were found Gram positive. The results showed that 45.83% and 41.67% bacteria belong to Bacillus spp. and Corynebacterium spp., respectively, while Acinetobacter spp., Aeromonas spp. and Staphylococcus spp. were in equal proportion (4.16% each). Six isolates were selected for 16S rRNA gene sequencing and five were found 95% similar with Bacillus licheniformis whereas one isolate was identified as B. subtilis. All the isolates showed good growth up to 50 degrees C with gradual reduction on subsequent increment of temperature. Out of 24 isolates, six could survive at 65 degrees C while one isolate could grow at 63 degrees C. Growth kinetic studies revealed that the reduction in generation time in solute(s) and temperature stress was more as compared to generation time in plain medium. This study suggests that virgin sand dunes may be a rich source of bacteria, tolerant to osmotrophic solutes, and can be examined for plant growth promotion activity in agriculture. Moreover, study might help to resolve the tactic adopted by microbes to defeat desiccation induced by various types of solutes.
Highlights
The Thar Desert of North Western India is distributed over 2.34 million km2 with about 91% area endemic to the Rajasthan
Bacterial population decreased with the increasing concentration of chemicals in nutrient medium at various temperatures; both stresses simultaneously caused a detrimental effect on population growth
Sporulating bacteria were avoided from WS3 by picking colonies that could survive at maximum temperature and chemical concentration
Summary
The Thar Desert of North Western India is distributed over 2.34 million km with about 91% area endemic to the Rajasthan. Soil microbial communities are among the most complex, diverse, and important assemblages in the biosphere (Zhou et al, 2003) and soil moisture is a key factor for microbial activity, its biomass and diversity in soils especially in desert (Kieft, 2002), and soil moisture stress leads to severe impact on vital metabolic processes and growth To mitigate such stresses in desert, the bacteria must maintain osmotic equilibrium across the membrane by forming desiccationresistant spores or cysts (Gould & Measures, 1977) or tolerating low water potential as vegetative cells (Busse & Bottomley, 1989). We used RISA and 16S rRNA gene sequencing of extremophilic bacteria from the Thar Desert, screened on water stress causing medium. The selected strains were characterized for morphological and biochemical parameters
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