Micrococcus luteus possesses unusual abilities to tolerate and to use very toxic organic molecules as carbon sources, and combines these activities with tolerance to metals.
The sequencing of Micrococcus luteus was supported because of its potential role in bioremediation and in its importance in biotechnology. In the former sphere it combines two properties essential to dealing with toxic wastes; the ability to degrade toxic organic pollutants and tolerance to metals [Sandrin and Maier, 2003]. Often found in contaminated soils, oil spills and sludge, M. luteus can degrade hydrocarbons and olefinic compounds [Zhuang, 2003], use biphenyl as a carbon source, and degrade phthalates [Eaton, 1982]. It harbors a plasmid capable of degrading malathione and chlorpyriphos [Guha et al., 1997]. A whole repertoire of functions which deal with metals have been found in M. luteus. It carries out biosorption of strontium [Faison et al., 1990] and to a lesser degree lead, nickel, and zinc [Lo et al., 2001]. The organism was utilized in a filtration system bound to gelatin beads for the biosorption of strontium. Since strontium is an end product of uranium decay, this could be a major component of atomic energy waste management. There is special interest in its ability to bind gold [Levchenko et al., 2001]. Interesting variants of M. luteus have been isolated from gold deposits in Russia, which are able to precipitate gold by concentrating and crystallizing it on their surface. It has been suggested that these properties could be used for gold adsorption and concentration from low abundance ores and depleted deposits [Marakushev, 1991].
Actively growing cell
In the chemical and pharmaceutical industries, M. luteus may be exploited for its capability in isoprene synthetic reactions. This is the cornerstone of sterol, carotenoid, rubber, and fatty acid synthesis and M. luteus has been the platform for isolation of important enzymes in this most basic of processes, including the cis-prenyltransferase gene, whose gene product carries out the condensation of isopentyl phosphate with allelic diphosphate [Oh et al., 2000]. This is an essential step in the biosynthesis of terpenes, major components of a number of commercial products. The membranes of M. luteus are rich in enzymes that catalyze the synthesis of prenyl pyrophosphates at chain lengths between 15 to 45 carbon atoms [Saito and Ogura, 1981].
A number of interesting biological issues are also inherent in the study of M. luteus, including dormancy without spore formation, resuscitation from dormancy, and the significance of tetrad formation. Although capable of survival under stress conditions, such as low temperature and starvation, M. luteus does not form spores as survival structures, usually thought of as a prerequisite for long term survival in some other bacteria like Bacilli and Actinomycetes. This capability to survive for long periods in extreme environments, may well explain their repeated isolation from within fossilized amber [Greenblatt et. al., 2004]. Of special recent interest is the elucidation of the resuscitation promoting factor (Rpf) described in Micrococcus luteus [Mukamolova et al., 2002; Mukamolova et al., 1998; Mukamolova et al., 1999]. This was the founder member of a family of secreted transglycosylase-like proteins that can resuscitate bacteria from a dormant state (Kell & Young, 2000; Cohen-Gonsaud et al., 2005; Mukamolova et al., 2006). M. luteus Rpf can improve the cultivability of other high G+C organisms with a low plating efficiency many fold. Rpf has many important implications for the detection and culturing of these organisms, a number of which are important human pathogens (e.g. Mycobacterium tuberculosis).Genes similar to rpf have a widespread distribution throughout the actinobacteria and most organisms, including M. tuberculosis, contain multiple gene homologues. M. luteus is very unusual in containing only a single, apparently essential rpf-like gene [Mukamolova, 2002], which makes M. luteus the organism of choice for further work on the mechanism of restoration of cultivability. The tetrad of Micrococcus luteus may share with that of Deincoccus radiodurans a special function in DNA repair [Englander et al., 2004]. Comparative genomics should, therefore, also provide clues to understanding developmental physiology and morphology in actinobacteria. The ability to adapt to oligotrophic environments, tolerate toxic metals and organic compounds may also relate to these morphological alterations. Finally, M. luteus (formerly Micrococcus lysodeikticus) is of historical interest in microbiology and medicine, since it played a prominent part in Fleming’s discovery of lysozyme, to which it shows exquisite sensitivity (Fleming, 1922a,b).
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