472 Marine Microbiology 



Linden (12) from experimental evidence obtained by the simul- 

 taneous adaptation method. These investigators noticed, how- 

 ever, that the cells grown on a given alkane had a small but not 

 negligible activity towards the fatty acids with one more or one 

 less carbon atom, so that the parallel occurrence of an a-oxida- 

 tion process could not be conclusively eliminated. In the case of 

 our strain of P. aeruginosa tested in conditions where any 

 secondary adaptation was supressed by chloramphenicol, the 

 existence of an exclusive /S-oxidation is clearly demonstrated. 



The initial dehydrogenation of n-heptane is of special 

 interest and deserves some comments. Studying the oxidation 

 of cyclo-hexane by several strains of Pseudomonas, Imelick (4) 

 has obtained some experimental evidence that the first oxidation 

 step in the case of this substrate consists in a direct oxygenation 

 with the production of a hydro-peroxide. More recently, Stewart 

 et al. (11) have made similar observations with an unidentified 

 Gram-negative coccus which grows on n-hexadecane with the 

 accumulation of cetyl-palmitate. From the incorporation and re- 

 partition of 0^^ into the products, these investigators have con- 

 cluded that the first intermediate is 1-hexadecyl-hydroperoxide. 



Thus, it appears that there are two different mechanisms 

 for the initial attack of the paraffin molecule, one of them involv- 

 ing a direct participation of atmospheric oxygen, and the other 

 starting with an anaerobic dehydrogenation. It may be that the 

 second mechanism is restricted to the lower alkanes of less than 

 10 carbon atoms. This interpretation is supported by the fact that 

 the cells of our P. aeruginosa strain grown on hexadecane and the 

 cell free extracts prepared from these bacteria do not reduce 

 anaerobically pyocyanin in the presence of hexadecane and are 

 apparently devoid of the corresponding dehydrogenase. 



It must be stressed that the alkanes lower than Cio are 

 slightly soluble in water. At 16 C, the water solubility per liter 

 is still 130. 8mg for 7?-hexane and 15 mg for n-octane. Moreover, 

 previous experiments ( 1 ) have demonstrated that P. aeruginosa 

 is able to grow from n-heptane dissolved into the water phase of 

 the media. In the case of cyclo-hexane and n-hexadecane, which 

 are quite insoluble, the bacterial attack must obviously take 

 place at the surface of the hydrocarbon particles dispersed into 



