Characteristics
Corals have been found to form characteristic associations with symbiotic nitrogen-fixing bacteria. Corals have evolved in oligotrophic waters which are typically poor in nitrogen. Corals must therefore form a mutualistic relationship with nitrogen fixing organism, in this case the subject of this study, namely Symbiodinium. In addition to this dinoflagellate, coral also form relationship with bacteria, archae and fungi. The problem is that these dinoflagellates are also nitrogen limited and must form a symbiotic relationship with another organism, here it is suggested to be diazotrophs. In addition, cyanobacteria have been found to possess genes that enable them to undergo nitrogen fixation. (Lema et al. article) This particular study goes further to investigate the possibility that in addition to the named dinoflagellate and certain cyanobacteria, that endosymbiotic algae and the coral contain enzymes enabling them to both undergo ammonium assimilation.
Due to the small size of the genome of most endosymbionts, they are unable to exist for any length of time outside of the host cell, thereby preventing a long-term symbiotic relationship. However in the case of the endonuclear symbiotic bacterium Holospora, it has been discovered that Holospora species can maintain their infectivity for a limited time and form a symbiotic relationship with Paramecium species.
It is well accepted and understood that there is a mutualistic relationship between plants and rhizobial bacteria and mycorrhizal fungi enabling the plants to survive in an otherwise nitrogen poor soil environment. Co-evolution is described as a situation where two organisms evolve in response to one another. In a study reported in these scientists investigated whether such a mutualistic relationship conferred an evolutionary advantage to either plant or symbiont. In the end, they did not find that the rhizobial bacteria studied had any evolutionary advantage with their host but did find great genetic variation among the populations of rhizobial bacteria studied.
Organisms typically establish a symbiotic relationship due to their limited availability of resources in their habitat or due to a limitation of their food source. Triatomine vectors have only one host and therefore must establish a relationship with bacteria to enable them to obtain the nutrients required to maintain themselves.
A use for symbiotic bacteria has recently been in paratransgenesis for controlling important vectors for disease, such as the transmission of Chagas disease by Triatome kissing bugs. Symbiotic bacteria in legume roots provide the plants with ammonia in exchange for the plants carbon and a protected home.
Symbiotic, chemosynthetic bacteria have recently been discovered associated with mussels (Bathymodiolus) located near hydrothermal vents have a gene that enables them to utilize hydrogen as an source of energy. This in preference to sulphur or methane as their energy source for production of energy.
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