Detoxification of Heavy Metals Using Marine Metal Resistant Bacteria: A New Method for the Bioremediation of Contaminated Alkaline Environments

Metal toxicity is of massive environmental concern because of their bioaccumulation and non-biodegradability in nature and they were endlessly released into the aquatic systems from natural and anthropic sources like domestic and industrial sewage discharges, farming, mining, navigation traffic, electronic waste, and climate change events such as floods. Heavy metals contamination is one of the major issues in the aquatic environments. The heavy metal toxicity is higher as a result of enormous release of waste from industrial, agricultural, chemical, domestic, and technological sources, thereby contaminating the water, soil, and air. Any metal which has a relatively high density as well as toxicity at lower dose is known as “heavy metal.” The important heavy metals are Pb, Hg, Cd, Cr, Cu, Zn, Mn, Ni, Ag, etc. The heavy metals are included in the group of inorganic compounds, therefore, they are not biodegradable and persistent and move into aquatic food chains. Expulsion of metals by microorganisms is a troublesome mechanism that depends on the chemistry of the metal ions, cell wall composition of microorganisms, cell physiology, and physicochemical factors such as pH, temperature, ionic strength, and metal concentration. Microbial response to a specific heavy metal is very important in exploiting them in the remediation of metal-contaminated sites. The biosorption process by microorganisms is one of the important methods in the bioremediation of heavy metals. The bacterial cell walls are effectual metal chelating agents and the bacteria consist of polysaccharide slime layers which readily offer amino, carboxyl, phosphate, and sulfate groups for the binding of metals. Over the past several decades, numerous physical and chemical methods were employed to remove metals from environment as they are high-priced, inefficient, and labor intensive. The research on bioremediation or biosorption-based remediation techniques in the past several years found that bioremediation is a natural process and economical. Several conventional technologies such as precipitation, oxidation, reduction, adsorption, filtration, flocculation, sedimentation, osmosis, ion exchange, and biosorption were employed in treating the wastewater contaminated with heavy metals. Among the accessible techniques, biosorption plays a key role in the elimination of heavy metals due to excellent adsorbability, eco-friendliness, cost-effectiveness, and easy availability of biosorbents. Different biosorbents such as bacteria, fungi, yeasts as well as agricultural products have been applied for the biosorption purposes. The bacteria are extensively used as biosorbents due to their small size, ubiquity, and capability to grow in controlled conditions.