Abstract
Metagenomic based strategies have previously been successfully employed as powerful tools to isolate and identify enzymes with novel biocatalytic activities from the unculturable component of microbial communities from various terrestrial environmental niches. Both sequence based and function based screening approaches have been employed to identify genes encoding novel biocatalytic activities and metabolic pathways from metagenomic libraries. While much of the focus to date has centred on terrestrial based microbial ecosystems, it is clear that the marine environment has enormous microbial biodiversity that remains largely unstudied. Marine microbes are both extremely abundant and diverse; the environments they occupy likewise consist of very diverse niches. As culture-dependent methods have thus far resulted in the isolation of only a tiny percentage of the marine microbiota the application of metagenomic strategies holds great potential to study and exploit the enormous microbial biodiversity which is present within these marine environments.
Highlights
It has been estimated that pelagic bacteria are extremely abundant, achieving densities of up to 106 per ml of seawater, and account for most oceanic biomass and metabolism [1]; while numbers of bacteria which are thought to colonize marine snow can reach levels of up to 109 per ml [2]
Marine environments, including the subsurface are believed to contain a total of approximately 3.67 × 1030 microorganisms [3] and with approximately 71% of the earth's surface of 361 million square kilometers covered by the ocean, this environment represents an enormous pool of potential microbial biodiversity and exploitable biotechnology or "blue biotechnology"
As with terrestrial environments, where more than 99% of bacteria cannot be cultured by conventional means, the same is true for marine environments where the vast majority of these marine microbes have to date not yet been identified, classified or cultured
Summary
It has been estimated that pelagic bacteria are extremely abundant, achieving densities of up to 106 per ml of seawater, and account for most oceanic biomass and metabolism [1]; while numbers of bacteria which are thought to colonize marine snow can reach levels of up to 109 per ml [2]. A number of novel hydrolytic enzymes have recently been cloned from Antarctic sea water bacterial metagenomic DNA [54], while a novel low-temperature-active lipase has recently been isolated from a metagenomic library of Baltic Sea marine sediment bacteria This low-temperature-active lipase gene which displayed 54% amino acid similarity to a Pseudomonas putida esterase was successfully heterologously expressed in E. coli and subsequently biochemically characterised [55]. While this is the first report of the genetic characterisation of an alkane hydroxylase from a deep-sea environment, it is interesting to note that these two alkane hydroxylase genes were functionally expressed in a Pseudomonas fluorescens strain [17]. Using such an approach in tandem perhaps with the more established metagenomic based approaches would greatly enhance the probability of obtaining novel biocatalysts
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