Meeting Abstract
All animals evolved and live today in a countless and immensely diverse ’sea’ of microbes. Despite this, hundreds of marine animal species have evolved intimate associations with one or a few specific types of chemosynthetic bacteria, which provide them with nutrition. The chemosynthetic symbionts are at least as diverse as their hosts, and have evolved from numerous bacterial lineages multiple times in convergent evolution. ‘Omics’ technologies have helped to usher in a new age of discovery on these so-far uncultivated organisms. Previously, only sulfide and methane were known to power chemosynthetic symbioses, but we recently showed that they can also be fuelled by hydrogen. Carbon fixation by sulfur-oxidizing symbionts is well established, but we have also discovered the genes for nitrogen fixation in the chemosynthetic symbionts of a number of animal hosts. Until now, no nitrogen-fixing chemosynthetic symbiont was known from the marine environment. This discovery raises the intriguing possibility that some chemosynthetic symbionts provide a source of newly fixed nitrogen in the ecosystems their hosts inhabit. ‘Omics’ also promises new insights into the genetic mechanisms of host-symbiont communication. We recently discovered a unique ‘arsenal’ of toxin-like genes, resembling those from pathogens such as Yersinia and Vibrio, in the genomes of deep-sea mussel symbionts. We hypothesise that some of these toxin-like genes are involved in molecular communication with their hosts, and others protect their hosts against parasites. Symbioses are usually classified as either ’nutritional’ or ‘defensive’, therefore, a defensive role for these iconic nutritional symbionts would be surprising.
