Bioluminescent bacteria
[1] These bacteria[clarification needed] may be free living (such as Vibrio harveyi) or in symbiosis with animals such as the Hawaiian Bobtail squid (Aliivibrio fischeri) or terrestrial nematodes (Photorhabdus luminescens).
[2] Bacteria also use luminescence reaction for quorum sensing, an ability to regulate gene expression in response to bacterial cell density.
The wide-ranged biological purposes of bio-luminescence include but are not limited to attraction of mates,[7] defense against predators, and warning signals.
It is important that bio-luminescent bacteria decrease production rates of luciferase when the population is sparse in number in order to conserve energy.
[10] Essentially, certain signaling molecules named autoinducers[11] with specific bacterial receptors become activated when the population density of bacteria is high enough.
[13] Though bio-luminescence across a diverse range of organisms such as bacteria, insects, and dinoflagellates function in this general manner (utilizing luciferase and luciferin), there are different types of luciferin-luciferase systems.
For bacterial bio-luminescence specifically, the biochemical reaction involves the oxidation of an aliphatic aldehyde by a reduced flavin mononucleotide.
[16] Nevertheless, all bio-luminescent bacteria share a common gene sequence: the enzymatic oxidation of Aldehyde and reduced Flavin mononucleotide by luciferase which are contained in the lux operon.
After the discovery of the lux operon, the use of bioluminescent bacteria as a laboratory tool is claimed to have revolutionized the area of environmental microbiology.
[20][21][22] Biosensors, created by placing a lux gene construct under the control of an inducible promoter, can be used to determine the concentration of specific pollutants.
[16] Consequently, the lux operon may have been lost in bacteria that evolved more efficient DNA repair systems but retained in those where visible light became a selective advantage.
Quorum sensing allows bacteria to conserve energy by ensuring that they do not synthesize light-producing chemicals unless a sufficient concentration are present to be visible.
[16] All bacterial species that have been reported to possess bioluminescence belong within the families Vibrionaceae, Shewanellaceae, or Enterobacteriaceae, all of which are assigned to the class Gammaproteobacteria.
[24] Factors that affect the distribution of bioluminescent bacteria include temperature, salinity, nutrient concentration, pH level and solar radiation.
[4] Bacteria are able to estimate their density by sensing the level of autoinducer in the environment and regulate their bioluminescence such that it is expressed only when there is a sufficiently high cell population.
[4] When LuxR binds AI, LuxR-AI complex activates transcription of the lux operon and induces the expression of luciferase.
Unlike Aliivibrio fischeri, V. harveyi do not possess the luxI/luxR regulatory genes and therefore have a different mechanism of quorum sensing regulation.
The uses of bioluminescence and its biological and ecological significance for animals, including host organisms for bacteria symbiosis, have been widely studied.
In laboratory culture, luxA and luxB mutants of Vibrio harveyi, which lacked luciferase activity, showed impairment of growth under high oxidative stress compared to wild type.
[36] Bacterial bioluminescence has also been proposed to be a source of internal light in photoreactivation, a DNA repair process carried out by photolyase.
[37] Experiments have shown that non-luminescent V. harveyi mutants are more sensitive to UV irradiation, suggesting the existence of a bioluminescent-mediated DNA repair system.
[37] The symbiotic relationship between the Hawaiian bobtail squid Euprymna scolopes and the marine gram-negative bacterium Aliivibrio fischeri has been well studied.
The two organisms exhibit a mutualistic relationship in which bioluminescence produced by A. fischeri helps to attract prey to the squid host, which provides nutrient-rich tissues and a protected environment forA.
A single expulsion by one bobtail squid produces enough bacterial symbionts to fill 10,000m3 of seawater at a concentration that is comparable to what is found in coastal waters.
[40] Dense populations of P. kishitanii, P. leiogathi, and P. mandapamensis can live in the light organs of marine fish and squid, and are provided with nutrients and oxygen for reproduction[40] in return for providing bioluminescence to their hosts, which can aid in sex-specific signaling, predator avoidance, locating or attracting prey, and schooling.
