Madhusmita Mishra

Microbial community in packed bed bioreactor involved in nitrate remediation from low level radioactive waste

Nitrate is the second largest contaminant of agriculture soil after pesticides. It also is a major pollutant from nuclear and metallurgical operations. Conventional methods for nitrate removal suffers from high cost and complexity leaving bioremediation as a viable alternative strategy. A pilot plant of 2.5 m3/day capacity has been functioning since 2005 based on microbial consortia treating actual effluent from nuclear power plant having pH of 7–8.5 (optimum) with N:C ratio of 1:1.7. The maximum biodegradable nitrate concentration of 3000 ppm could be reduced to below permissible limit (44.2 ppm) within 24 h in presence of sodium acetate as carbon source. Culture independent analysis (16S rDNA based) revealed clones having closest identity with uncultured bacterium, Pseudomonas stutzeri and Azoarcus sp. The existence of dissimilatory pathway of nitrate reduction in the community DNA is indicated by presence of nirS and nirK gene. Though the microbial mass was developed using municipal sewage, absence of Mycobacterium sp was confirmed using PCR. The understanding of the molecular identification of the consortium would help in developing the preservation strategy of the microbial mass for replication and perpetuation of the system.

Microbe-Based Strategy for Plant Nutrient Management

The rapid industrialization and urbanization of developing countries such as India have encroached on cultivable lands to meet the demands of an ever-increasing population. The altered land use patterns with increased fertilizer use has increased crop yields with leaching of major portion of the applied nutrients from the soil. Nitrates and phosphates are the agricultural pollutants that are discharged into aquifers due to anthropogenic reasons causing severe environmental and health problems. Production of these nutrients requires energy and finite resources (rock phosphate, which has gradually depleting reserves). An alternative management strategy would be to sequester excess nutrients within a biomass that is reused for agriculture. Two discrete enriched microbial consortia with the potential of simultaneous nitrate and phosphate sequestration upon application as biofertilizer restricted them within the plant root zone, ensuring prevention of eutrophication through leaching while making it available for uptake by plants. The nutrient accumulated biomass enhanced the crop yield by 21.88% during mung bean cultivation with maintained elemental content and other nutritional qualities. The major drawback of conventional biofertilizer application (slow release and action) could be overcome using this formulation leading to environmental protection, crop yield enhancement and soil fertility maintenance post-cultivation.

Novel Microbial System Developed from Low-Level Radioactive Waste Treatment Plant for Environmental Sustenance

packed bed bioreactor efficiently treated low-level radioactive waste for years with a retention time of 24 h using acetate as the sole carbon source. However, there was generation of dead biomass. This bioreactor biomass was used to develop a bacterial consortium, which could perform the function within 4 h while simultaneously accumulating nitrate and phosphate. The dead mass was negligible. Serial dilution technique was used to isolate the world’s first pure culture of a nitrate accumulating strain from this consortium. This isolate could simultaneously accumulate nitrate and phosphate from solution. Its ability to form biofilm helped develop a packed bed bioreactor system for waste water treatment, which could optimally remove 94.46% nitrate within 11 h in batch mode while 8 h in continuous mode from waste water starting from 275 ppm of nitrate. The conventional approach revealed the strain to be a member of genus Bacillus but showed distinct differences with the type strains. Further insilico analysis of the draft genome and the putative protein sequences using the bioinformatics tools revealed the strain to be a novel variant of genus Bacillus. The sequestered nitrate and phosphate within the cell were visualized through electron microscopy and explained the reason behind the ability of the isolate to accumulate 1.12 mg of phosphate and 1.3 gm of nitrate per gram of wet weight. Transcriptome analysis proposed the mechanism behind the accumulation of nitrate and phosphate in case of this novel bacterial isolate (MCC 0008). The strain with the sequestered nutrients work as biofertilizer for yield enhancement in case of mung bean while maintaining soil fertility post-cultivation.