Microorganisms are omnipresent in every ecosystem on earth and the majority of identified species belong to the domains Bacteria and Archaea of which bacteria are considered to represent the greatest diversity (Staley et al., 2007). Microbes are organised in complex and diverse communities depending on the environmental conditions, and they commonly live closely associated with eukaryotic hosts. The body surfaces of nearly all higher organisms are populated by diverse microbial communities and this microbiota is understood to have large impacts on the hosts’ biology (Ley et al., 2008). The greater part of the microbiota consists of microorganisms that are beneficial to the host and interactions between the host and its microbiota are often of symbiotic nature. For instance, the presence of bacteria can enhance the immune response of the host and protect it from other pathogenic microorganisms, and in return the host offers a habitat to the bacteria and provides them with nutrients (Fraune and Bosch, 2010)...

Tietjen, M. (2014) '"You are what you eat": How diet can influence the gut microbiota of marine invertebrates', The Plymouth Student Scientist, 7(2), p. 2013-211.