Molecular Characterization of Arsenic Oxidizing Bacteria from Hot Spots of Assam

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dc.contributor.advisorNath, Dhruba Jyoti
dc.contributor.authorNilakhi Dutta
dc.date.accessioned2024-09-23T10:43:53Z
dc.date.available2024-09-23T10:43:53Z
dc.date.issued2023
dc.description.abstractIn view of wide scale toxicity of Arsenic (As), development of a sustainable low cost As `detoxification technology is an urgent need of time. Bioremediation of As by microorganisms has been widely hailed because of their potential advantage in As transformation through oxidation, reduction, methylation and volatilization. As (III) oxidizing bacteria plays a key role in the biological conversion of highly toxic and mobile As(III) to less toxic As(V) in the environment and hence can be a potent candidate for bioremediation of As contamination. 44 georeferenced soil samples and 22 georeferenced water samples were collected from As contaminated hot spots of Jorhat, Darrang and Nagaon districts of Assam for isolation of As(III) oxidizing bacteria. A total of 52 As tolerant isolates (39 from soil and 13 from water samples) were obtained initially in nutrient agar(NA) media supplemented with 1mM As(III). Highest percentage recovery of As tolerant bacteria was observed in sample DS6 (56.02%) of Darrang district. Significant correlation (p ≤0.01) was established between percent recovery of As tolerant bacteria with total As content in soil and water samples. Following primary screening based on minimum inhibitory concentration (MIC) of As, 15 isolates that could tolerate upto 17.5 mM As(III) or above were selected for further studies. Morphological and biochemical characteristics of the selected As tolerant bacteria were studied. All the 15 isolates showed positive response to citrate utilization tests and negative for Indole, H2S production and Voges Proskauer test. The isolates also showed significant variation in carbon source utilization indicating diversity of organism to utilize different carbon sources. Antibitotic resistance profile of the isolates revealed that all the isolates showed resistance to penicillin. DS1al and DS13a showed resistance against 8 tested antibiotics. The growth of all isolates was found to be optimum at pH 7.2 and at temperature 300C ranging from 20 to 177 cfu mL-1 and 20 to 185 cfu mL-1 respectively. Study of growth pattern in terms of colony forming units (CFU) and optical density(OD) of the isolates at 0h, 24h, 48h and 72h interval showed higher reduction in growth in presence of As(III) compared to the presence of As(V). Heavy metal tolerance limit of the isolates ranged from NiCl2 (1-6 mM), CuSO4(1-7 mM), CoCl2 (0.1-1 mM), ZnSO4 (0.5-3 mM), HgCl2 (0.1-0.5 mM), Pb(NO3)2 (4-10 mM) and AgNo3 (0.5 mM). Ten isolates viz., DS1al, DS2a, DS5a, DS7am, DS8bm, DS11ama, DS13a, DS15a, DS17b and NS12c showed positive oxidation reaction in both AgNO3 and Microplate screening assay done to detect the As oxidizing isolates. Quantitative assessment of As oxidation using high performance liquid chromatography (HPLC) revealed that these isolates can transform As(III) to As(V) in the range of 46.53 -73.29 % in presence of 15.5 mM As(III). Highest oxidation efficiency is shown by isolate DS2a (73.29%) followed by NS12c (62.84%) and the lowest being in DS15a (46.53%). Overall, all these 10 selected isolates showed potential detoxification response against As. Scanning electron microscopy done for observation of invitro As bioaccumulation of the isolates revealed distinct changes in cellular morphology including decrease in cell length, increase in cell volume and typical dents in septal area. Taxonomic identity of the entire ten As oxidizing isolates revealed their close identity to Pseudomonas laurentiana, Glutamicibacter creatinolyticus, Providencia huaxiensis, Myroides profundi, Citrobacter tructae, Citrobacter murliniae, Bacillus pseudomycoides and three isolates identical to Lysinibacillus boronitolerans.
dc.identifier.urihttps://krishikosh.egranth.ac.in/handle/1/5810214823
dc.language.isoEnglish
dc.subSoil Sciences
dc.themeMolecular Characterization of Arsenic Oxidizing Bacteria from Hot Spots of Assam
dc.these.typePh.D
dc.titleMolecular Characterization of Arsenic Oxidizing Bacteria from Hot Spots of Assam
dc.typeThesis
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