Characterization of bacteria isolated from palaeoproterozoic metasediments for sequestration of carbon dioxide and formation of calcium carbonate

Bacterial community of palaeoproterozoic metasediments was enriched in the chemostat in the presence of different concentrations of NaHCO₃. Six bacterial isolates were isolated from the chemostat on nutrient agar plates on the basis of distinct morphology. Denaturing gradient gel electrophoresis (DGGE) proved the presence of six operational taxonomic units (OTUs) at 50 and 100 mM NaHCO₃. The OTU was reduced to three and one at enrichment concentration of 150 and 200 mM NaHCO₃respectively. These six isolates were tested for sequestration of carbon dioxide by¹⁴C metabolic labeling of NaH¹⁴CO₃. Among the six isolates, one of the bacterium showed better potency to fix radiolabeled NaH¹⁴CO₃. The isolate (ISTD04) was identified as Serratia sp. by 16S ribosomal RNA (16S rRNA) sequence analysis and was found to be same as the DGGE OTU sequence at 200-mM NaHCO₃concentration. The bacterium was tested for product formation in form of calcite crystals in presence of 5 % CO₂. Scanning electron microscopy (SEM) of product formed by the bacterium revealed defined faceted rhombohedral structure which resembled calcite and vaterite phases of the crystal. Formation of calcium carbonate crystals was further confirmed by Fourier transform infrared (FTIR) spectroscopy as carbonate group showing strong vibration at 1,456 cm⁻¹. Major calcite phase diffraction peaks were determined by X-ray diffraction (XRD) analysis, and energy-dispersive X-ray (EDX) analysis showed the presence of CaO (72 %) and carbon (18 %). Bacterium use bicarbonate as carbon source for their growth as well as by-product formation in form of calcite shows carbon circulation and storage.