Since then several different FGAs have been developed, although most of these cover only a limited number of genes and focus on specific functional groups or locations. For example, FGAs have been designed to examine methanotrophs (Bodrossy et al., 2003 (Bodrossy et al., , 2006 Stralis-Pavese et al., 2004) , N-cycling genes (Taroncher-Oldenburg et al., 2003; Jenkins et al., 2004; Steward et al., 2004; Zhang et al., 2007a) , pathogens and virulence factors (Call et al., 2003; Kostić et al., 2005; Cleven et al., 2006; Miller et al., 2008; Palka-Santini et al., 2009) , rhizobial isolates (Bontemps et al., 2005) , and acid mine drainage (AMD) and bioleaching systems (Yin et al., 2007) .