Two Cr+6 reducing bacterial strains previously isolated from tannery effluents were used in the present study and identified as Pseudomonas aeruginosa Rb-I and Ochrobacterum intermedium (Rb-2) by 16S rRNA sequencing. Different biowaste materials (waste tea leaves, carrot juice pulp, dry leaves of eucalyptus and rice husk) were assessed for sorption / removal of Cr+6 from aqueous solution of K2Cr2O4. Feasibility of mono and mixed cultures of indigenous bacterial strains was evaluated for Cr+6 removal in conjunction with different biowaste materials. Among all tested biowastes materials, waste tea leaves showed optimum removal of Cr+6 from metal solution alone (77.1%) as well as in combination with bacterial strains (99.4%) after 720 minutes of contact time. Mixed culture of bacterial strains was found to be more efficient in Cr+6 removal than monoculture. The contact time of 720 minutes, pH 7, biomass concentration of 2.5 gram 100 mL-1 , 37°C and shaking speed of 100 rpm were found to be most optimum for optimum Cr+6 sorption alone as well as in combination with bacterial strains. Fourier transform infrared spectroscopy revealed that carboxyl, amino and OH groups present on the waste tea leaves played a significant role in the binding of Cr+6 ions with the biomass. The present study is unique in this respect that this approach involve both living and non-living materials and we could not find any report documenting such findings up to our knowledge.

Chromium pollution is produced in connection with industrial processes like in tanneries. It has been suggested that bioremediation could be a good option for clean up. The stress effect of variable chromate levels, pHs and growth temperatures on biochemical parameters of two Cr(VI) reducing bacterial strains Pseudomonas aeruginosa Rb-1 and Ochrobactrum intermedium Rb-2 was investigated. Transmission electrone microscopy (TEM) was performed to study the intracellular distribution of Cr(VI). It was observed that initial stress of 1000 µgmL-1 caused significant enhancement of all studied biochemical parameters at pH 7.0 and growth temperature of 37 °C showing great bioremediation potential of the strains. Transmission electron microscopy revealed that the distribution of chromium precipitates was not uniform as they were distributed in the cytoplasm as well as found associated with the periplasm and outer membrane. Fourier transform infrared spectroscopy showed the possible involvement of carboxyl, amino, sulpohonate and hydroxyl groups present on the bacterial cell surface for the binding of Cr(VI) ions. Cr(VI) stress brought about changes in the distridution of these functional groups. It can be concluded that the investigated bacterial strains adjust well to Cr(VI) stress in terms of biochemical parameters and along that exhibited alteration in morphology.