title: Nitrogen fixing bacterial diversity in a tropical estuarine sediments.
abstract: Microorganisms play a significant role in biogeochemical cycles, especially in the benthic and pelagic ecosystems. Role of environmental parameters in regulating the diversity, distribution and physiology of these microorganisms in tropical marine environment is not well understood. In this study, we have identified dinitrogen (N2) fixing bacterial communities in the sediments by constructing clone libraries of nitrogenase (nifH) gene from four different stations in the Cochin estuary, along the southeastern Arabian Sea. N2fixing bacterial clones revealed that over 20 putative diazotrophs belong to alpha-, beta-, gamma-, delta- and epsilon- proteobacteria and firmicutes. Predominant genera among these were Bradyrhizobium sp. (α-proteobacteria), Dechloromonas sp. (β-proteobacteria); Azotobactor sp., Teredinibacter sp., Methylobacter sp., Rheinheimera sp. and Marinobacterium sp. (γ-proteobacteria); Desulfobacter sp., Desulfobulbus sp. and Desulfovibrio sp. (δ -proteobacteria); Arcobacter sp. and Sulfurospirillum sp. (ε-proteobacteria). Nostoc sp. was solely identified among the cyanobacterial phylotype. Nitrogen fixing Sulfate reducing bacteria (SRBs) such as Desulfobulbus sp., Desulfovibrio sp., Desulfuromonas sp., Desulfosporosinus sp., Desulfobacter sp., were also observed in the study. Most of the bacterial nifH sequences revealed that the identities of N2fixing bacteria were less than 95% similar to that available in the GenBank database, which suggested that the sequences were of novel N2fixing microorganisms. Shannon-Weiner diversity index of nifH gene ranged from 2.95 to 3.61, indicating an inflated diversity of N2fixing bacteria. Canonical correspondence analysis (CCA) implied positive correlation among nifH diversity, N2fixation rate and other environmental variables.
authors.affiliation: Department of Marine Biology, Microbiology and Biochemistry, School of Marine Sciences, Cochin University of Science and Technology, Fine Arts Avenue, Kochi, Kerala, 682016, India.
authors.forename: Jabir
authors.initials: J
authors.lastname: Thajudeen
authors.affiliation: Department of Marine Biology, Microbiology and Biochemistry, School of Marine Sciences, Cochin University of Science and Technology, Fine Arts Avenue, Kochi, Kerala, 682016, India.|School of Environmental Sciences, Mahatma Gandhi University, Kottayam, Kerala, 686560, India.
authors.forename: Jesmi
authors.initials: J
authors.lastname: Yousuf
authors.affiliation: Department of Marine Biology, Microbiology and Biochemistry, School of Marine Sciences, Cochin University of Science and Technology, Fine Arts Avenue, Kochi, Kerala, 682016, India.
authors.forename: Vipindas Puthiya
authors.initials: VP
authors.lastname: Veetil
authors.affiliation: Department of Marine Biology, Microbiology and Biochemistry, School of Marine Sciences, Cochin University of Science and Technology, Fine Arts Avenue, Kochi, Kerala, 682016, India.
authors.forename: Sherin
authors.initials: S
authors.lastname: Varghese
authors.affiliation: Physical Research Laboratory, Ahmedabad, 380009, India.
authors.forename: Arvind
authors.initials: A
authors.lastname: Singh
authors.affiliation: Department of Marine Biology, Microbiology and Biochemistry, School of Marine Sciences, Cochin University of Science and Technology, Fine Arts Avenue, Kochi, Kerala, 682016, India. mohamedhatha@gmail.com.
authors.forename: Mohamed Hatha
authors.initials: MH
authors.lastname: Abdulla
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics; D044822:Biodiversity; D015723:Gene Library; D019015:Geologic Sediments / Q000382:microbiology*; D009586:Nitrogen Fixation; D000072738:Nitrogen-Fixing Bacteria / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification*; D010088:Oxidoreductases / Q000235:genetics*; D010802:Phylogeny; D014329:Tropical Climate; D014871:Water Microbiology
chemical_list: D001426:Bacterial Proteins; D010088:Oxidoreductases; C029130:nitrogenase reductase
keywords: Clone library; N2 fixing bacteria; NifH; PCR-RFLP analysis; Tropical estuary