As long as 400 years ago, man has recorded luminescent species of nematode and associated diseases. But it was Poinar in the 1970’s that first documented the relationship of bacteria in the lifecycle of the nematode. This bacteria actually forms a symbiotic relationship with its host, in that it produces light and pigments to help attract food and enables the nematode to complete its life cycle by supplying nutrients and antibiotics during a vulnerable period in that life cycle.
Xenorhabdus luminescens is classified as a large, gram negative, rod shaped bacteria. It is placed in the genera Enterobacteriaceae, but it differs from the genera standard in size, metabolic properties, symbiotic association, and ability to produce antibiotics. The major characteristic of X. luminescens is its ability to be luminescent, or to glow. This is achieved through the enzyme luciferase. This enzyme is found to be of many uses to the bacteria and its host; not only does it produce light to attract prey for the nematode, it can serve as a terminal electron acceptor when oxygen is not available. Like most luminescent bacteria, the regulation of luciferase is controlled by quorum sensing and autoinducer. It has been theorized that the luxI gene is the gene in its operon mainly responsible for the control of autoinduction. X. luminescens is a facultative anaerobe and it can not reduce nitrates to nitrites like other members of its genera. It also is unique for its catalase activity.
It seems counter-intuitive for bacteria to produce antibiotics, but in this case, it turns out to be useful for the bacteria and its host. X. luminescens can produce a wide range of antibiotics that affects almost all other species, including other xenorhabdus species. This gives the bacteria a competitive advantage over other bacteria and helps keep the host free of harmful species.This relationship is so effective, nematodes inhabited with Xenorhabdus were used a biological pest control for insects. It has been used to control populations of Japanese beetles, root and vine weevils, fire ants, mole crickets, cutworms and potato beetles. The species is so effective because of its motility and chemoreceptors which enable the nematode to find hosts quickly and kill quickly. The use of nematodes as pesticides is much favorable over chemical insecticides due to its lack of pollution, researchers hope to refine studies to replace chemical constituents completely.
References
http://www.inclinehs.org/smb/xenorhabdus.htm
http://kbn.ifas.ufl.edu/biology/xenophot.htm
*Disclaimer - This report was written by a student participaring in a microbiology course at the Missouri University of Science and Technology. The accuracy of the contents of this report is not guaranteed and it is recommended that you seek additional sources of information to verify the contents.
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