Damage of microbial communities caused by metal toxicity in different domains of the environment is a growing challenge worldwide. The present chapter attempted to elucidate how microorganisms tackle and response against the metals toxicity. In response to metal toxicity, microorganisms exhibit a vast array of acclimatization, adaptation and resistant strategies at genetic, cellular and community levels to detoxify metals toxicity and survival. Microorganisms detoxify metals by various mechanisms (sequestration, inhibition of influx, efflux, accumulation, precipitation and chemical modification, repair, and metabolic by-pass) and showed resistance properties (by protein/enzyme synthesis) encoded by genes located in chromosome, plasmid or transposon. Thus, metal toxicity hampers the microbial metabolism, growth, activity and species diversity resulting in severe damage in environmental microbial community. Apart from detrimental consequences of metal toxicity, the novel metal- and antibiotic- resistant microorganisms could be used in environmental and human health benefits.
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Metals* are ubiquitous in nature, since they are an integral part of earth planet. It constitutes about 75% of the known elements and is vital to our industry, infrastructure and daily life. Though many of them are significantly essential in the biochemical process of organisms, nonetheless, excess concentration of any metals causes hazardous and toxic impacts in all organisms of food chains and food webs (Jillian, Robert, & Rajakaruna, 2015) by bioconcentration, bioaccumulation and biomagnifications phenomena. The anthropogenic and geogenic activities are major causes for generating and releasing pollutants of metal and its derivatives, which are undoubtedly responsible for contamination and deterioration of different domains of global environment. Natural geologic processes continue at a very slow pace to concentrate and disperse metals, forming large zones of elevated metal concentrations and constantly releasing metals into the environment. Besides, awful consequences of rapid and continuous economic development and growth, industrialization, urbanization and population explosion are the prime reasons for generation of massive amount of toxic and hazardous metal wastes in the environment in developed and developing countries around the world. It is generally occurred in high concentration in the mining (extraction sites) as well as industrial zones which is greatly responsible for the contamination of the surrounding local ecosystems. Mining, manufacturing, and the use of synthetic products (e.g. pesticides, paints, batteries, industrial waste, and land application of industrial or domestic sludge) can result the heavy metal contamination in urban and agricultural soils. Worldwide coal burning, municipal solid waste incineration, electronic, paper, paint, pharmaceutical industries (Biester, Muller, & Scholer, 2002; Tack, Vanhaesebroeck, Verloo, Rompaey, & Ranst, 2005) and tailings of gold mines are identified as the major anthropogenic origins of metals contaminating the environment.
Contamination of metals is one of the growing global problems during last few decades due to exerting severe environmental and human health risks. The priority toxic metal (Ag, As, Be, Cd, Cr, Cu, Hg, Ni, Pb, Sb, Se, Tl, Zn) pollutants (Sparks, 2005), their chemical derivatives and organometals significantly pose tremendous detrimental effects in all forms of organisms in environment. Non-biodegradable and persistent natures of metals is responsible to easily accumulate in soil (Nwachukwu, Feng, & Alinnor, 2010), sediment, plant (Ashraf, Maah, & Yusoff, 2011; Rahman, Saha, Molla, & Al-Reza, 2014) and aquatic flora and fauna leading to biomagnifications in the food chain. It is well known that metal contamination can causes various health hazardous, such as mental disorder; skin poisoning; affects kidneys, lung, liver, heart and central nervous system; and even responsible for causing cancer in human.