 Another early metagenomics study consisted of the analysis of an acidophilic biofilm with low microbial diversity from an acid mine drain in California (Tyson et al. 2004). The analysed biofilm survives in one of the most extreme environments including a very low pH (i.e., high acidity), relatively high temperature and high concentration of metals. Importantly, this specific biofilm truly displays low complexity as it is composed of only three bacterial and two archaeal species. This simplicity greatly aided the analysis effort and allowed the researchers an almost complete recovery of two of the genomes and a partial recovery of the other three.