HGT is an important force modulating bacterial evolution and depends on the number of transferred genes and their maintenance in the host cells by means of positive selection. In this way, genes coding for new proteins with novel properties are preserved while nonbeneficial genes tend to be removed. Also, it depends on the extent of the phenomenon, in both evolutionary

time and phylogenetic distance between the organisms involved (Boto, 2010). Although HGT is a widespread phenomenon among bacteria, there are few reports on gene transfer in extreme cold environments probably due to our lack of knowledge and understanding of polar microbial diversity. There are a few reports concerning gene transfer from bacteria to arthropods (Song Adriamycin manufacturer et al., 2010), crustacea (Kiko, 2010), or prokaryotes. Table 1 summarizes PS-341 chemical structure examples of HGT in Antarctic prokaryotes. The transfer of genes associated with antibacterial metabolites such as the biosynthesis

of violacein (Hakvåg et al., 2009), hydrocarbon biodegradation (Ma et al., 2006; Pini et al., 2007), signal transduction (López-García et al., 2004; Allen et al., 2009), vitamin metabolism (López-García et al., 2004; Moreira et al., 2006), central metabolism (López-García et al., 2004; Allen et al., 2009), and hydrolytic enzyme production (Xiao et al., 2005) illustrates the crucial role of HGT in the evolution and the adaptation of bacterial communities in a changing environment. In the oligotrophic Antarctic environment, the production of the hydrolytic enzyme chitinase, which breaks

down glycosidic bonds, might confer a fitness improvement to a microbe that can now use the chitin found in the outer skeleton of invertebrates as a C- and N-source. Another recalcitrant substrate available for microorganisms in Antarctica is fossil fuels. It is used for human activities and has led to hydrocarbon contamination, a serious environmental problem because of their persistence and high toxicity SPTLC1 in biological systems. Studies carried out by Flocco et al. (2009) showed a relative abundance of ndo genes in polluted soils from anthropogenic sources compared to noncontaminated sites. In those sites, the transfer of genes related to hydrocarbon degradation clearly has an impact on the bacterial fitness. It is very likely that the acquisition of genes related to antibiotics, biodegradation of carbon and nitrogen supplies, or contaminants, plays a key role in such environmental conditions. Usually, among prokaryotes, HGT is facilitated by a number of genetic elements, including plasmids, transposons, and integrons, and most attention has been focused on the first two. However, considering that nonindigenous microorganisms are not likely to be metabolically active, natural transformation might be the predominant form of HGT in Antarctic soils (Cowan et al., 2011).