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NEWS & ANALYSIS

GENOME WATCH Ocean’s elevenses Helena Seth-Smith

The recent publication of the genome Hahella chejuensis is a bacterium that pro- the degradation of many hydrocarbons. To sequences of two marine γ-proteobacteria duces a red pigment that kills a red-tide algal enhance the bioavailability of oil and speed from the order Oceanospirillales might species. At 7.2 Mb, the genome is the largest up alkane degradation, A. borkumensis pro- lead to the development of new methods marine prokaryotic genome sequenced so duces a surfactant and the CDSs potentially to detoxify oceanic contamination. far, and comprises 6,783 coding sequences involved in the synthesis of this surfactant (CDSs), with an average GC content of 54.8% were identified3. Oil pollution and algal blooms are two of the (REF. 1). Alcanivorax borkumensis is prevalent main environmental threats to the marine bio- in oil-polluted waters and uses oil hydro- A. borkumensis lacks components sphere. An overgrowth of dinoflagellate spe- carbons as carbon and energy sources. The cies produces algal blooms, which deplete local genome of this bacterium, first reported in of several pathways and cannot derive oxygen levels and cause harm to many marine 2003 (REF. 2), is just 3.1 Mb and comprises energy from most sugars. Instead, it species. Up to three million tonnes of oil, origi- 2,755 CDSs, with an average GC content of feasts on the alkanes found in oil. nating from natural sources, the oil industry 54.7% (REF. 3). and tanker accidents, pollute the sea annually. Despite the difference in genome size these Oil pollution has deleterious effects on the bacteria share several common features. Both The mechanism by which H. chejuensis marine ecosystem, both short- and long-term, species require salt for growth and encode kills Cochlodinium polykrikoides, an important as polyaromatic hydrocarbons persist in the several Na+/H+ antiporters, including a multi- red-tide alga, was elucidated1. A gene cluster environment as toxins and carcinogens, and subunit pump used to maintain the sodium was identified that codes for the synthesis of become incorporated into the food chain. motive force. This is used to power nutri- prodigiosin, a red pigment that rapidly lyses ent transport in both species, and flagellar the alga. Extracellular hydrolytic enzymes rotation in H. chejuensis. Both genomes also might digest the nutrients released by lysis for encode uptake systems to scavenge nutrients uptake by H. chejuensis. from the environment. Extracellular polysac- The information deduced from these charide (EPS) gene clusters are present in both genomes should lay the foundations for tack- species, with H. chejuensis harbouring five ling the dual blights of algal blooms and oil such gene clusters. pollution.

The difference in genome size reflects both Helena Seth-Smith is at the Sanger Institute, the number of regulatory proteins in the two Wellcome Trust Genome Campus, Hinxton, species (considerably more in H. chejuensis), Cambridge CB10 1SA, UK. and the propensity of each bacterium for the e-mail: [email protected] acquisition of foreign DNA. Up to 23% of doi:10.1038/nrmicro1589 the H. chejuensis genome might have been 1. Jeong, H. et al. Genomic blueprint of Hahella chejuensis, a marine microbe producing an algicidal horizontally acquired, whereas A. borkumensis agent. Nucleic Acids Res. 33, 7066–7073 (2005). 2. Gloyshin, P. N. et al. Genome sequence completed of contains little mobile DNA. Alcanivorax borkumensis, a hydrocarbon-degrading Whereas H. chejuensis has complete bacterium that plays a global role in oil removal from marine systems. J. Biotechnol. 106, 215–220 (2003). pathways for central carbon metabolism, 3. Schneiker, S. et al. Genome sequence of the ubiquitous A. borkumensis lacks components of several hydrocarbon-degrading marine bacterium Alcanivorax borkumensis. Nature Biotechnol. 24, 997–1004 pathways and cannot derive energy from (2006). most sugars. Instead, it feasts on the alkanes found in oil. The CDSs encoding the alkane DATABASES hydroxylases AlkB and AlkB are found The following terms in this article are linked online to: 1 2 Entrez Genome Project: http://www.ncbi.nlm.nih.gov/ near the origin of replication, giving a higher entrez/query.fcgi?db=genomeprj gene dosage. In addition, P450s, rubredoxin Alcanivorax borkumensis | Hahella chejuensis Access to this links box is available online. and other oxidoreductases are implicated in