Symbioses between Worms and Bacteria in Shallow Marine Sediments

Shallow marine sediments are of great importance for the cycling of carbon, nitrogen, sulfur and other elements of organic matter. The degradation processes by which these elements are re-circulated are performed mainly by bacteria. Some of these bacteria are involved in symbioses with tiny marine roundworms, i.e. nematodes, living inside their hosts as endosymbionts or attached to the worm cuticle, as ectosymbionts. In some cases the symbiosis goes so far as the entire gut of the host is completely replaced by bacteria and consequently the worms live exclusively at the expense of their symbionts. Moreover, considering that each nematode host carries more than one million bacteria, and that these nematodes are abundant in sediments, their bacterial symbionts play also a significant role in the cycling of carbon and sulfur. This book offers an insight into the structure, diversity and dynamics of microbial communities of marine sandy sediments and presents new and exciting findings about specificity and identity of the endosymbionts of mouthless nematode Astomonema, and of the ectosymbionts of gut-bearing nematodes, Leptonemella.