Environmental Microbiology (2003) 5(10), 1002–1008 doi:10.1046/j.1462-2920.2003.00507.x © 2003 Society for Applied Microbiology and Blackwell Publishing Ltd Blackwell Science, LtdOxford, UKEMIEnvironmental Microbiology 1462-2920Society for Applied Microbiology and Blackwell Publishing Ltd, 20035 1010021008Original ArticleChemotaxis to hexadecaneM. P. Lanfranconi, H. M. Alvarez and C. A. Studdert Received 27 February, 2003; accepted 1 July, 2003. *For correspon- dence. E-mail studdert@biology.utah.edu; Tel. (+1) 801 5816307; Fax (+1) 801 5812174. †Present address. Biology Department, University of Utah, 257 South 1400 East, Salt Lake City, 84112, UT, USA. A strain isolated from gas oil-contaminated soil displays chemotaxis towards gas oil and hexadecane Mariana P. Lanfranconi, 1 Héctor M. Alvarez 2 and Claudia A. Studdert 1 * † 1 Instituto de Investigaciones Biológicas, Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Mar del Plata, CC 1245, 7600 Mar del Plata, Argentina. 2 Departamento de Bioquímica, Facultad de Ciencias Naturales, Universidad Nacional de la Patagonia San Juan Bosco, km 4, 9000 Comodoro Rivadavia, Argentina. Summary In this report we describe the isolation of a strain from soil contaminated with gas oil by taking bacteria from a chemotactic ring on gas oil-containing soft agar plates. Partial 16 S rDNA sequencing of the isolated strain showed 99.1% identity with Flavimonas oryzi- habitans. It was not only able to degrade different aliphatic hydrocarbons but it was also chemotactic towards gas oil and hexadecane, as demonstrated by the use of three different chemotaxis methods, such as agarose plug and capillary assays and swarm plate analysis. In addition, the strain was chemotactic to a variety of carbon sources that serve as growth sub- strates, including glucose, arabinose, mannitol, glyc- erol, gluconate, acetate, succinate, citrate, malate, lactate and casaminoacids. This is the first report on chemotaxis of a hydrocarbon-degrading bacterium towards a pure alkane, such as hexadecane. The fact that environmental isolates show chemot- axis towards contaminant/s present in the site of iso- lation suggests that chemotaxis might enhance biodegradation by favouring contact between the degrading microorganism and its substrate. Introduction Many bacteria exhibit directed movement towards nutri- ents and away from toxic substances. This behaviour, called chemotaxis, has been extensively studied in the enteric bacteria Escherichia coli and Salmonella typhimu- rium, and it perhaps represents the best known signal transduction system mediated by histidine kinase coupled receptors (reviewed in Stock and Surette, 1996). This signal transduction system has shown to be highly con- served between distantly related bacteria, like flagellated, light and chemicals-responding archaea and also in non- flagellated bacteria that move by gliding on surfaces. Even though the ability of bacteria to detect gradients of chemicals and to respond to them by positioning them- selves in optimal conditions for growth may have obvious advantages for survival, the ecological significance of such ability, with respect to the efficiency of degradation of environmental pollutants in nature, has not been stud- ied in detail. Environmental pollutants can be degraded by different kinds of bacteria. The enzymes and genes involved in such degradation have been largely studied during the past two decades in order to develop strategies for biore- mediation, but the chemotactic behaviour of the identified strains towards pollutants has not been taken into consid- eration until more recently. Three Pseudomonas strains have been shown to respond chemotactically to naphtha- lene, depending on the presence of the well characterized naphthalene catabolic plasmid (Grimm and Harwood, 1997; Samanta and Jain, 2000). Moreover, it has been demonstrated for the strain P. putida G7 that the lack of specific chemotaxis towards naphthalene influences neg- atively on the velocity of degradation of that pollutant (Marx and Aitken, 2000). In the last few years, there have been many other reports of bacterial strains responding chemotactically to environmental pollutants (Pandey and Jain, 2002; Parales and Harwood, 2002; and references therein), suggesting that this ability may be widespread and have substantial significance on the potential of these microorganisms as biodegraders. By using a chemotactic enrichment technique, we were able to isolate, from gas oil-contaminated soil, a strain which displays chemotaxis towards both gas oil and hexa- decane. To our knowledge, this is the first report demon- strating a chemotactic response towards an alkane. Results Isolation of the chemotactic strain To enrich for hydrocarbon degraders, a soil sample obtained from a site contaminated with hydrocarbons was inoculated into minimal medium supplemented with gas