ISSN 0367-6315 Korean J. Soil Sci. Fert. 45(4), 593-601 (2012) http://dx.doi.org/10.7745/KJSSF.2012.45.4.593 Actinobacteria Isolation from Metal Contaminated Soils for Assessment of their Metal Resistance and Plant Growth Promoting (PGP) Characteristics Seifeddine BEN TEKAYA, Sherlyn Tipayno, Murugesan Chandrasekaran, Woojong Yim, and Tongmin Sa* Department of Agricultural and biological Chemistry, Chungbuk National University, Cheongju, Chungbuk 361-763, Republic of Korea. Heavy metals and metalloids removal can be considered as one of the most important world challenges because of their toxicity and direct impact on human health. Many processes have been introduced but biological processes of remediation seem to offer the most suitable solution in terms of efficiency and low cost. Actinobacteria constitute one of the major microbial populations in soil, and this can be attributed to their adaptive morphological structure as well as their exceptional metabolic power. Among microbes, actinobacteria are morphologic intermediate between fungi and bacteria. Studies on microbial diversities in metal contaminated lands have shown that actinobacteria may constitute a dominantly active microbiota in addition to α Proteobacteria. Furthermore, isolation studies have shown metal removal mechanisms which are reminiscent of notable multiresistant strains, such as Cupriavidus metallidurans. Apart from members of genus Streptomyces, which produce more than 90% of commercialized antibiotics, and the nitrogen fixing Frankia, little attention has been given to other members of this phylum. This is because of difficult culture condition requirements and maintenance. In this review, we focused on specific isolation of actinobacteria and their potential applications in metal bioremediation and plant growth promotion. Key words: Actinobacteria, Metal resistance, Bioremediation, PGP. Received : 2012. 7. 18 Accepted : 2012. 8. 16 *Corresponding author : Phone: +82432612561 E-mail: tomsa@chungbuk.ac.kr Article Introduction The earth’s surface is affected by around 240,000 square kilometers of mining operations, with widespread consequences that directly alters the biotopes (Furrer et al., 2002). Transmission of heavy metals and metalloids in nature is noxious for micro and macroorganisms, including humans (De Boer et al., 1999). Among those affected, soil microorganisms play key roles in the global biogeochemical cycle of elements. Disruption of such ecological niches from metal contamination can have an injurious impact on the biosphere stability. As much as metal contamination shows deleterious effects on microbes, it also leads to rise of resistance in order to survive in such hostile environments. Micro- organisms can survive at certain metal concentrations through biosorption activities, bioprecipitation, extra- cellular sequestration, transport mechanisms and chelation. Microorganisms that exhibit such traits hold great potential applications in bioremediation programs (Haferburg and Kothe, 2007). Results of previous works dealing with microbial diversity in metal contaminated soils in Korea showed abundance of different taxonomic groups predominated by α proteobacteria (Tipayno et al., 2012; Karelova et al., 2011). Members of phylum proteobacteria are relatively well documented, however, other less studied phyla have also been found in these metal contaminated soils, including members of actinobacteria. This group holds a very interesting population from which 90% of practical antibiotics, two third of all biologically active substances from microbial origin come from (Hamaki et al., 2005). Actinobacteria includes many extremophilic, and stress- resistant genera like Geodermatophilus, Blastococcus and Modestobacter as well as the well known Strep- tomyces known as with many other actinobacteria for biosynthesis of pigments in response to stress conditions. Interest in the study of plant growth promoting (PGP)