Bacteria can use n-hexadecane as a carbon source, but it remains incompletely understood whether n-hexadecane is transformed into metabolic intermediates prior to cellular uptake or not. We newly isolated a strain identified as Pseudomonas synxantha LSH-7′ and conducted chemotaxis experiment of this bacterial strain towards n-hexadecane, hexadecanol and hexadecanoic acid with qualitative assays respectively. Furthermore, we described the identification of extracellular alkane hydroxylase and alcohol dehydrogenase activity; acidification of the culture medium; identification of hexadecanoic acid in the culture medium by the GC-MS analysis; and variation concentration of intracellular n-hexadecane and hexadecanoic acid. A detailed analysis of the experimental data revealed the chemotaxis of this bacterial strain towards n-hexadecane instead of its metabolic intermediates. Our results further suggested that only a fraction of total n-hexadecane followed this path, and alkane hydrolase and hexadecanol dehydrogenase were constitutively expressed when grown in the medium of n-hexadecane. Most strikingly, we quantitatively investigated the concentration of n-hexadecane adsorbed by bacterial chemotaxis. Our findings provided an original insight n-hexadecane might be converted to hexadecanoic acid extracellularly before it was taken up across the cell membrane.Alkanes are found highly abundant constituents of petroleum hydrocarbons are major environmental pollutants as a result of terrestrial and freshwater runoff, refuse from coastal oil refineries, off shore oil production, shipping activities and accidental spills 1,2 . Among the alkanes, n-hexadecane is a major component. The solubility of n-hexadecane in water is 5.21 × 10 −5 mg L −1 at 15 °C and has high partitioning co-efficient 9.1 logKow 3 . Biodegradation of n-hexadecane is believed to be a friendly way to environment as well as human beings. For this, it is necessary to know the metabolic mechanisms of n-hexadecane.Singer and Finnerty 4 observed terminal n-hexadecane degradation by Acinetobacter HO1-N and Pseudomonas putida, and identified five intermediates as n-hexadecylhydroperoxide, n-hexadecanol, n-hexadecyldehyde, n-hexadecanoic acid and n-hexadecylhexadecanoate in degradation process. However, Whyte et al. 5 reported both terminal and sub-terminal oxidation of n-C16 by Rhodococcus strain Q15 producing 1-hexadecanol and 2-hexadecanol. Recently, a new insights into alkane metabolism pathways from alkane sensing, chemotaxis, signal transduction, uptake to degradation was put forward by Wang and shao 6 from the aspect of genes. The underlying mechanisms that control the early responses of bacterial cells to n-hexadecane, such as chemotaxis and uptake, remain largely unexplored.Chemotaxis is defined as the capacity of certain organisms to sense substance concentration gradients and in turn moved towards or away from this gradient 7-9 . Most importantly, alkane chemotaxis had been observed in bacterial isolates of Flavimonas oryzihabitans genus 10 , and even ...

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