ORIGINAL ARTICLE Multi-metal biosorption and bioaccumulation by Exiguobacterium sp. ZM-2 Mohammad Zubair Alam & Shamim Ahmad Received: 6 June 2012 / Accepted: 6 November 2012 / Published online: 23 November 2012 # Springer-Verlag Berlin Heidelberg and the University of Milan 2012 Abstract The present work deals with the biosorption per- formance of dried and non-growing biomasses of Exiguo- bacterium sp. ZM-2, isolated from soil contaminated with tannery effluents, for the removal of Cd 2+ , Ni 2+ , Cu 2+ , and Zn 2+ from aqueous solution. The metal concentrations studied were 25 mg/l, 50 mg/l, 100 mg/l, 150 mg/l and 200 mg/l. The effect of solution pH and contact time was also studied. The biosorption capacity was significantly altered by pH of the solution. The removal of metal ions was conspicuously rapid; most of the total sorption oc- curred within 30 min. The sorption data have been ana- lyzed and fitted to the Langmuir and Freundlich isotherm models. The highest Q max value was found for the bio- sorption of Cd 2+ at 43.5 mg/g in the presence of the non- growing biomass. Recovery of metals (Cd 2+ , Zn 2+ , Cu 2+ and Ni 2+ ) was found to be better when dried biomass was used in comparison to non-growing biomass. Metal re- moval through bioaccumulation was determined by grow- ing the bacterial strain in nutrient broth amended with different concentrations of metal ions. This multi-metal resistant isolate could be employed for the removal of heavy metals from spent industrial effluents before dis- charging them into the environment. Keywords Biosorption . Bioaccumulation . Metal . Bioremediation . Adsorption isotherms Introduction Heavy metal pollution is one of the most important environ- mental problems today. Various industries, such as mining, metallurgy, electroplating, leather working, photography, electric appliance manufacturing, metal surface treating etc., produce and discharge waste containing various heavy metals into the environment. The metals are not biodegradable and tend to accumulate in living organisms, leading to various diseases and disorders (Kobya et al. 2005; Liao et al. 2008). Thus metals, a valuable resource, can also cause serious environmental pollution, threatening ecosystem and human health through their extreme toxic- ity. Low concentrations of certain transition metals such as cobalt, copper, nickel and zinc are essential for many cellular processes of bacteria, since they provide vital cofactors for metalloproteins and enzymes. (Nies 1999; Li et al. 2004) However, higher concentrations of these metals are often toxic (Nies 1999). On the other hand, cadmium is extremely toxic, and to date no biological function has been ascribed to it (Gadd 2004). The removal of heavy metal ions from industrial wastewater is a prob- lem of increasing concern that has been addressed primar- ily by chemical and physical treatments. However, these procedures have significant disadvantages, such as incom- plete metal removal, high reagent or energy requirements, or generation of toxic sludge or other waste products, and are generally very expensive (Volesky and Naja 2005). Therefore, there is a need for the development of low cost and easily available materials able to adsorb toxic heavy metals from wastewater. Microorganisms are potent bioremediators, removing heavy metals via active or passive uptake mechanisms. Metal accumulative bioprocesses generally fall into one of two categories, biosorptive uptake by non-living and/or non-growing biomass and bioaccumulation by living cells. M. Z. Alam (*) King Fahd Medical Research Center, King Abdulaziz University, P. O. Box 80216, Jeddah 21589, Saudi Arabia e-mail: mohdzubairalam@yahoo.com S. Ahmad Microbiology Division, Institute of Ophthalmology, Faculty of Medicine, J.N. Medical College, Aligarh Muslim University, Aligarh 202 002, India Ann Microbiol (2013) 63:1137–1146 DOI 10.1007/s13213-012-0571-z