ABSTRACT
Hypothesis: DHA/EPA-producing bacteria have evolved to thrive in the gastrointestinal tracts of marine animals and to supply these oils to their hosts.
Mutualism denes a symbiotic relationship in which organisms belonging to different species provide benet to each other. The importance of mutualism between animals and the microbial communities living in their digestive systems has long been established (i.e., for ruminants) but is now being recognized more broadly, including for human health. In the marine realm, genomic sequencing of marine bacteria has revealed many genes contributed by these bacteria that might benet their hosts. For example, many marine animals eat organisms having exoskeletons composed of chitin, whose degradation can benet from chitinoclastic bacteria. Chitin is the second most abundant polymer formed in nature, with annual production in the aquatic biosphere estimated to be several billion metric tons. Chitin degrading genes have been identied in many marine bacteria, a fact that is consistent with a mutualistic role. In another example, pioneering research using germ-free zebrash (Figure 14.1) shows that gut bacteria favored by the host animal quickly reestablish themselves when sterile conditions are removed. This nding is consistent with the view that at least some of these bacteria-host relationships have evolved to be mutually benecial.
