RESUMO
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 (100g), 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, NaCl 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 2.5×10(6) bacteria/g of soil while alcohol suspended soil had 4.4×10(4) bacteria/g. The 24 bacterial isolates were found tolerant to 26% glycerol, 14% NaCl 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°C with gradual reduction on subsequent increment of temperature. Out of 24 isolates, six could survive at 65°C while one isolate could grow at 63°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.
El duro ambiente del desierto de Thar alberga una diversidad de formas de vida limitado debido a sus condiciones extremas, como el bajo contenido de humedad de los suelos arenosos y la alta temperatura del suelo. En el presente estudio, las bacterias osmotolerantes de los suelos de Thar, fueron aislados y caracterizados. Las bacterias fueron aisladas a partir de 20 muestras de suelo (100g), obtenidas de dunas de arena, suspendidas en agua y alcohol absoluto. Un total de 11 pruebas bioquímicas y morfológicas se llevaron a cabo para identificar géneros de bacterias: la capacidad de tolerancia osmótica de los aislados se examinó con glicerol, NaCl y alcohol, y la secuenciación de los genes 16S rRNA se realizó también para la identificación bacteriana. El análisis de espaciadores internos transcritos de 16S a 23S rRNA (RISA) se realizó para los aislamientos de análisis filogenéticos. El suelo suspendido en el agua contuvo 2.5×10(6) bacteria/g de suelo mientras que el suelo con alcohol suspendido presentó 4.4×104 bacteria/g. Los 24 aislados bacterianos se encontraron tolerantes a 26% glicerol, 14% NaCl y 10% de alcohol y 22 de los 24 aislados fueron grampositivas. Los resultados mostraron que 45.83% y 41.67% de las bacterias son Bacillus spp. y Corynebacterium spp., respectivamente, mientras que Acinetobacter spp., Aeromonas spp. y Staphylococcus spp. se presentaron en la misma proporción (4.16% cada uno). Seis aislamientos fueron seleccionados para secuenciación de genes 16S rRNA y 95% fueron similares a Bacillus licheniformis mientras que un aislamiento fue identificado como B. subtilis. Todos los aislamientos mostraron un buen crecimiento a 50º C con reducción gradual en el incremento subsiguiente de la temperatura. Fuera de 24 aislados, 6 podrían sobrevivir a 65ºC mientras que un aislado podría crecer a 63ºC. Estudios de crecimiento cinéticos revelaron que la reducción en el tiempo de generación en soluto (s) y estrés de temperatura fue mayor en comparación con el tiempo de generación en un medio simple. Este estudio sugiere que las dunas de arena virgen pueden ser una fuente rica de bacterias, tolerantes a los solutos osmotróficos y se pueden examinar para la promoción de crecimiento de plantas en la agricultura. Por otra parte, el estudio podría ayudar a resolver la táctica adoptada por los microorganismos para rechazar la desecación inducida por diversos tipos de solutos.
Assuntos
Bactérias/genética , DNA Bacteriano/genética , /genética , /genética , Microbiologia do Solo , Bactérias/classificação , Bactérias/crescimento & desenvolvimento , Clima Desértico , Índia , Concentração Osmolar , Filogenia , Reação em Cadeia da PolimeraseRESUMO
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.