3 Marine, Hydrocarbon- Degradingria

Abstract: Several marine hydrocarbon-degrading strains in the class Alphaproteobacteria arereported. Among them, Kordiimonas gwangyangensis, Tranquillimonas alkanivorans, Thalas-sospira tepidiphila, Novosphingobium pentaromativorans, and Sphingomonas sp. KH3–2 aremarine hydrocarbon degraders belonging to Kordiimonadales (family Kordiimonadaceae),Rhodobacterales, Rhodospirillales (family Rhodospirillaceae), and Sphingomonadales (familySphingomonadaceae), respectively. A recent comparative genomic study of three genera fromthe marine Roseobacter clade revealed numerous pathways for the catabolism of structurallydiverse aromatic substrates. 1 Introduction The Alphaproteobacteria is a physiologically and phylogenetically diverse class of bacteria,consisting of nine orders: Caulobacterales, Kordiimonadales, ‘‘Parvularculales,’’ Rhizobiales,Rhodobacterales, Rhodospirillales, Rickettsiales, Sneathiellales, and Sphingomonadales. Thereare contrasting reports on the effect of hydrocarbon addition to seawater on populations ofAlphaproteobacteria. On the one hand they have often been shown to decrease in relativeabundance, especially when compared with Gammaproteobacteria (e.g., Teira et al., 2007). Onthe other hand, there are several examples where numbers of specific groups of Alphaproteo-bacteria have increased in abundance, for example Roseobacter-like species increased afteraddition of n-alkanes (McKew et al., 2007). Although several reports have described thetaxonomy of Alphaproteobacteria isolated from hydrocarbon-polluted marine environments,it is difficult to confirm whether these microorganisms are able to degrade or utilize hydro-carbons. So far, only a few species of hydrocarbonoclastic Alphaproteobacteria have beenisolated. A recent study of hydrocarbon-degrading bacteria in Indonesian seawater revealedthat diverse marine Alphaproteobacteria belonging to the Sphingomonadales and Rhodobac-terales were involved in the degradation of aliphatic and low-molecular-weight aromatichydrocarbons (Harwati et al., 2007). One of them, an alkane-degrading bacterium, wasidentified and described in detail by Harwati et al. (2008). The phylogenetic relationshipbetween the strains of hydrocarbon-degrading Alphaproteobacteria discussed in this chapter isshown in