Evaluating the effect of various environmental factors on the growth of the marine microalgae, Chlorella vulgaris

Heavy metal contamination from anthropogenic activities has an adverse effect on the environment due to its cytotoxicity, carcinogenicity and mutagenicity. Environment harbours microorganisms, some of which have been found to modify physico-chemical conditions of their surrounding environment through certain processes such as detoxification, metal homeostasis, precipitation, redox transformations etc. Investigations in the past have shown that short term contact with metals of certain bacteria causes the selection of resistant bacteria within weeks, while a prolonged exposure showed selected strains able to thrive better. Hence biotic methods could assist removal of heavy metals based on biosorption or bioaccumulation by microorganisms, which are cost-effective and environmental friendly in the long run. Microbial remediation is influenced by biotic and environmental factors as also the contamination site characteristics. The aim of this paper is to highlight and review some of the mechanisms of microbial remediation through techniques such as biostimulation, bioaugmentation etc.

Bacterial strain M1 isolated from soil contaminated with dye was found to be a potential dye decolorizer in the screening studies. The strain was identified as Lysinibacillus fusiformis by 16S rDNA sequencing method. While, the bacteria required 72 h to achieve maximum decolorization of dye in yeast extract broth, it needed 48 h of incubation for achieving 97.1% decolorization in Luria Bertani broth. Plackett–Burman design (PBD) was used to study the effect of most important variables that influence the dye decolorization process under static conditions. In PBD model, 12 experiments were made with seven process variables and the remazol golden yellow decolorization was within the range from 1.01 to 69.29%. From statistically analyzed data, lactose, yeast extract, and pH were found as most important variables that influence the dye decolorization process. These three variables and their combined effect of levels was studied by response surface methodology for an optimization of dye decolorization through central composite design and the outcome varied from 2.05 to 83.80%. The optimized level of lactose, yeast extract, and pH was found to be 0.40% (w/v), 1.30% (w/v), and 7.5, respectively, to achieve maximum dye decolorization of remazol golden yellow (89.66%) in validation of model. This study specifically explored factors influencing the dye decolorization through statistical tools and suggests their appropriate level with interactions playing a key role for an effective dye decolorization process.