Hydrocarbon-Degrading Microbes as Sources of New Biocatalysts

Abstract

Petroleum hydrocarbons, including those discharged to the marine environment, are metabolized through different catabolic pathways by a number ofmicroorgan- isms. Each hydrocarbon-degrading microorganism produces interesting enzymes for degrading alkanes and/or aromatic compounds that allow them to be used as sources of carbon and energy, and thus, these microbes occupy hydrocarbon-rich ecological niches. Their diversity and hydrocarbon-degrading metabolic abilities have been extensively examined in multiple environmental and phylogenetic contexts. Genes encoding enzymes involved in degradation, such as alkane hydrox- ylases and other monooxygenases, P450 cytochromes, rubredoxin reductases, and ferredoxin reductases, have been examined by genome analysis, and a number of them have been successfully cloned, expressed, purified, and their activities con- firmed. However, in these microorganisms, the accumulated information regarding other types of enzymes, particularly those most used at industrial level, is limited. Here, we compile information about the accumulated enzymatic knowledge of obligate marine hydrocarbonoclastic bacteria (OMHCB), key players in bioreme- diation of hydrocarbons in contaminated marine ecosystems. We focused on bacteria of the genera Cycloclasticus, Alcanivorax, Oleispira, Thalassolituus,and Oleiphilus. Enzymatic data ofthese representative OMHCB members are restricted to enzymes of the class hydroxylases, cytochrome P450, dioxygenases, synthases, dehalogenases, ligases, and mostly for hydrolases with a typical α/β hydrolase fold. Despite the limited information reported, the available data suggest that these organisms may be important sources of industrial biocatalysts, the analysis of which may deserve deeper investigation. Comparative information is provided regarding the occurrence of key biotechnologically relevant ester-hydrolases in the genomes of OMHCB and suggesting which of the OMHCB may potentially have higher promise as a source ofbiocatalysts. We also discuss how the properties of these enzymes could be biologicallly important for these bacteria, as some of them can convert a broad range of compound