468 Marine Microbiology 



place on a single terminal carbon with successive formation of 

 the mono-alcohol, aldehyde and fatty acid, then proceeding 

 further through a /3-oxidation mechanism. 



The demonstration of a /3-oxidation for the higher (Cs to 

 Cio) fatty acids is quite conclusive. However, it must be noticed 

 that the cells grown on hexane and on heptane are respectively 

 adapted to propionate (Cs) and to butyrate (C4). This is corre- 

 lated with the observed accumulation of butyrate with bacteria 

 cultivated on heptane (Fig.l). As suggested by Thijsse and van 

 der Linden (12) propionic and butyric acids most likely do not 

 enter into the specific pathway of alkane oxidation and are 

 formed through some independent "side" metabolism. 



Initial Step of Alkane Oxidation 



Cell free extracts have been prepared from heptane grown 

 cells by grinding in the cold with alumina as already described 

 (7). The dehydrogenase activities of these preparations were 

 measured in Thunberg tubes under vacuum with purified pyo- 

 cyanin as the final electron acceptor, the quantities of pyocyanin 

 reduced to its leuco-form being determined colorimetrically from 

 the absorbance of this pigment at 380 m/x (As = 17.2). 



The results recorded in Table 3 show that the cell free ex- 

 tracts actively reduce pyocyanin in the presence of n-heptane or 

 1 n-heptanol. The reduced form of the pigment is strongly fluores- 

 cent in U.V. and recolorizes immediately to blue upon the intro- 

 duction of air into the systems. A sharp optimum of activity has 

 been observed at pH 7.3. 



The crude extracts have a high DPNH oxidase activity, 

 which is 75 per cent inhibited by mercapto-ethanol, 0.03 M. In 

 the presence of this compound, the extracts reduce DPN, but not 

 TPN, at the expense of n-heptane, 1 n-heptanol and heptanal 

 (Table 3). No activity is observed when the extract has been 

 previously boiled or when heptane is omitted. Furthermore it is 

 interesting that in the absence of mercapto-ethanol (Fig. 2, 

 curve 2), DPN is not appreciably reduced by heptane. This 

 seems to indicate that mercapto-ethanol not only inhibits the 

 interfering activity of DPNH-oxidase, but even more activates 



