Bioaugmentation of soil with Enterobacter cloacae AKS7 enhances soil nitrogen content and boosts soil microbial functional-diversity
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Biofertilizer happens to be a promising alternative of chemical fertilizer in the establishment of sustainable agricultural practices. Following this observation, several nitrogen-fixing bacteria were isolated from the soil in which an isolate (AKS7) was selected for further studies as AKS7 showed considerable competence in growth on nitrogen-free growth medium. Acetylene reduction assay confirmed that AKS7 can fix atmospheric nitrogen efficiently. The result of Kjeldahl assay revealed that the organism (AKS7) could fix nitrogen up to 12 mg in 8 days. A strong positive correlation (r = 0.987) was observed between microbial cell biomass and the amount of nitrogen fixed by AKS7 over a period of 8 days. The organism was identified as Enterobacter cloacae through molecular and biochemical tests. To investigate the in situ nitrogen fixation by E. cloacae AKS7, naturally attenuated (AKS7 not-inoculated) and bioaugmented (AKS7-inoculated) soil microcosms were prepared. The bioaugmented microcosm showed higher level of soil nitrogen content than naturally attenuated microcosm. A large number of heterotrophic as well as nitrogen-fixing microorganisms were counted in bioaugmented microcosm than naturally attenuated microcosm. Results of the carbon source utilization patterns of BiOLOG ECO plate revealed that bioaugmented microcosm exhibited higher level of functional richness and evenness that lead to the exhibition of higher level of microbial functional-diversity in bioaugmented microcosm than the naturally attenuated microcosm. Taken together, the results indicated that augmentation of E. cloacae AKS7 into soil enhanced the nitrogen content and soil microbial functional-diversity considerably.
KeywordsSoil fertility Microbial nitrogen fixation Soil microbial activity Microbial functional-diversity
The authors’ would like to express sincere gratitude to the learned experts for their immense guidance and cooperation in improving the manuscript. We sincerely thank Ms. Rakshita Dave and Ms. Sutirtha Dutta for their help in correcting the language of the manuscript. This current work was supported by a grant in aid from the Department of Science and Engineering research board (SERB), DST, Govt. of India (Sanction number: YSS/2015/000387). Reagents like fluorescein diacetate (FDA) and 2,3,5-triphenyl tetrazolium chloride (TTC) were received as a kind gift from Dr. Alok Kumar Sil (Department of Microbiology, University of Calcutta) and Mr. Tapan Saha (Institute of Environmental Studies and Wetland Management, Kolkata), respectively.
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Conflict of interest
Authors’ declare that they do not have any conflict of interest.
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