Bio-reduction of hexavalent chromium by an indigenous green alga and its impact on the germination of rice seed in chromium enriched environment

Abstract

Rapid mining activities in Sukinda mining area have generated a huge amount of toxic Cr(VI) which accumulated and persisted in the soil for decades and reduced rice plant productivity in adjoining agricultural fields. Hence, for the bioremediation of rice field soil, a Cr(VI) resistant, thermotolerant and fast-growing native green algal strain SM1 was selected, which rendered resistance to 60 ppm of Cr(VI). DPC assay, ICP-OES and Raman-Spectroscopic analysis confirmed 92.765% of Cr(VI) reduction within 48 h by SM1 under optimized condition. Moreover, Cr(VI) adsorption by the green alga was also established by FTIR and SEM-EDX analysis. The alga (SM1) was identified as Chlorella thermophila by 18S rDNA sequencing (MN855377). Its application significantly improved rice (Oryza sativa var. Lalata) seed germination, seedling growth, seed vigor index, pigment and protein content. CHNS(O) and ICP-OES analysis of the algal biomass depicted the presence of several organic and inorganic compounds, which can be utilized as bio-fertilizer for the rice seedlings. Field experiments on rice plant growth characteristics should be conducted to utilize this potent algal strain in chromium contaminated rice fields for the bio-reduction of Cr(VI) and improvement of rice crop productivity.