印度西部卡奇沼泽地沉积物中微生物活性和人工培养细菌多样性的研究

The Great Rann of Kachchh, a vast expanse of salt desert in Western India is a unique hostile ecosystem posing an extreme environment to life forms due to high salt content, hyper-axid climate, seasonal water logging and extremes of temperature. In the virtual absence of natural vegetation, soils and sediments of Rann of Kachchh axe microbially dominated ecosystems. In the present study microbial activity and the diversity of cultivated heterotrophic bacteria were investigated in the sediments collected along a 5-m exposed section at Khadir Island in the Great Rann of Kachchh. Microbial activity （as an index of sediment enzymes） was found to be high in the middle of the section （200-280 cm）. Dehydrogenase （DHA）, substrate-induced DHA and alkaline phosphatase activities revealed the oligotrophic nature of the basal portion （320-480 cm）. Abundant bacterial isolates obtained from different depths were found to be clustered in 12 different phylogenetic groups by amplified ribosomal DNA restriction analysis. 16S rRNA gene sequencing revealed the dominant bacterial ribotypes to be affiliated to Firmicutes （Families Bacillaceae and Staphyloeoccaeeae） and Aetinobaeteria （Family Brevibaeteriaceae） with minor contribution of Proteobacteria （Families Phyllobacteriaeeae and Bartonellaceae）, pointing their endurance and adaptability to environmental stresses. Statistical analysis indicated that sediment organic carbon, salinity, total available nitrogen and total available phosphorous are most likely critical determinants of microbial activity in the Khadir Island sediments.     

Vigna radiata var. GM4 Plant Growth Enhancement and Root Colonization by a Multi-Metal-Resistant Plant GrowthPromoting Bacterium Enterobacter sp. C1D in Cr(VI)-Amended Soils

Contamination of agricultural soils by heavy metals has become a major concern due to their toxic effects on plant growth, symbiosis and consequently the yields of crops. In the present study, to enhance plant growth in Cr(VI)-amended soils, novel metalresistant plant growth-promoting bacteria (PGPB) were isolated from a soil contaminated with industrial waste effluent. One of the bacterial isolates, identified as Enterobacter sp. C1D by 16S rRNA gene sequencing, was found to be multi-metal resistant in nature with excellent plant growth-promoting (PGP) traits. Mung bean (Vigna radiata var. GM4) inoculation with Enterobacter sp. C1D significantly (P < 0.01) increased root and shoot length, shoot and root weight, and chlorophyll content in a range of Cr(VI) treatments. Plant tolerance towards Cr(VI) measured as effective concentration showed higher values with Enterobacter sp. C1Dtreated plants compared to un-inoculated plants. Root colonization study was also carried out using green fluorescence protein-labeled Enterobacter sp. C1D under a hydroponic system. Confocal laser scanning microscopy of the plant roots showed heavy bacterial loads on the surface of the plant root specifically at the root tip and the point of root hair/lateral root formation. The results of PGP traits showed that elevated indole acetic acid levels and 1-aminocyclopropane-1-carboxylate deaminase activity enabled Enterobacter sp. C1D to enhance V. radiata growth in Cr(VI)-amended soils, whereby it significantly increased plant tolerance towards elevated Cr(VI) concentrations.