REVIEW Mercury pollution: an emerging problem and potential bacterial remediation strategies Arif Tasleem Jan Æ Imtiyaz Murtaza Æ Arif Ali Æ Qazi Mohd. Rizwanul Haq Received: 20 January 2009 / Accepted: 19 April 2009 / Published online: 7 May 2009 Ó Springer Science+Business Media B.V. 2009 Abstract Heavy metal toxicity represents an uncommon but clinically significant medical condition, which if unrecognized or inappropriately treated results in signifi- cant morbidity and mortality. Mercury is recognized as a potent and widely distributed toxicant in the global environment having ability to accumulate at various lev- els of food chain besides possessing ability to cross pla- cental and blood–brain barrier. It has been seen that bacteria growing near mercury polluted sites have evolved various means of resistance based on the expression of different genes of mer operon against different forms of mercury. Microbe based remediation/detoxification of mercury is on forefront due to low cost and less health hazardous compared to physicochemical based strategies, which are cost intensive and hazardous to human health. However, strategies based on the modern aspects of bio- logical technologies employing mer operon genes in dif- ferent combination are needed to be designed for exploitation in the remediation of mercury completely from mercury contaminated environments. Keywords Heavy metals Á Mercury Á Remediation Á Bacteria Á mer genes Introduction Mercury, 6th most abundant toxic element is released into the environment as a result of both natural processes as well as due to anthropogenic activities. It is present in the earth’s crust at concentrations ranging from 21 ppm (lower crust) to 56 ppm (upper crust) in the elemental form and as a variety of binary minerals such as cin- nabar, metacinnabar and hypercinnabar (Barkay et al. 2003). In nature, mercury exists in three forms: Metallic or elemental form (Hg 0 ), inorganic (Hg 2? or Hg ? ) and organic form (R-Hg ? or R-Hg-X, where ‘‘R’’ is methyl or phenyl and ‘‘X’’ is acetate). Elemental mercury is volatile and is commonly used to extract gold from its ores. Inorganic mercury commonly exists as mercuric sulfide (H 2 S), which along with mercuric oxide is used as a coloring agent in tattoos and paints. All the forms are hazardous but extent of toxicity varies among dif- ferent forms of mercury; organic being the most and elemental as the least one. Toxicity to organic mercury is accredited due of its lipid solubility, which it employs while crossing the placental and blood–brain barrier (Nishigaki and Harada 1975; Nascimento and Chartone- Souza 2003). Unlike organic mercury, inorganic mercury is less efficient in crossing biological membranes. Their transport across the membrane occurs with the involve- ment of certain protein carriers present in the membrane. Inspite of the fact that both organic as well as inorganic forms of mercury crosses the membrane with different abilities; both have high affinity for thiol groups of enzymes and proteins. Binding of mercury to thiol groups of enzymes and proteins result in their inactiva- tion, inturn associated with halting normal cell func- tioning within an organism (Horn et al. 1994; Hajela et al. 2002; Gupta and Ali 2004). A. T. Jan Á A. Ali Á Q. Mohd. Rizwanul Haq (&) Department of Biosciences, Jamia Millia Islamia, New Delhi 110025, India e-mail: qmrhaq@yahoo.co.in I. Murtaza Biochemistry and Molecular Biology Laboratory, Division of PHT, SKUAST, Srinagar, Kashmir 191121, India 123 World J Microbiol Biotechnol (2009) 25:1529–1537 DOI 10.1007/s11274-009-0050-2