?() BACTERIOLOGICAL CHEMISTRY 



claimed that Meth. aliphatica liquefaciens can behave as a 

 true autotroph and live by the oxidation of hydrogen in 

 presence of carbon dioxide as well as on paraffins. 



Sarcina inetluinica decomposes methanol, CH3OH, 

 in the presence of carbon dioxide with formation of 

 methane. If carbon dioxide containing radioactive 

 carbon is used, the methane is also found to contain 

 radioactive carbon ; that is the methane is produced by 

 reduction of the carbon dioxide. Meiliaiiohacterium 

 omelianski similarly oxidises primary and secondary 

 alcohols to the corresponding fatty acids with simul- 

 taneous reduction of carbon dioxide to methane. Neither 

 formate, methanol, nitrate, sulphate nor atmospheric 

 oxygen can replace carbon dioxide as the oxidising 

 agent. It is, therefore, considered that formate and 

 methanol are not intermediate products. It has been 

 shown by the use of radioactive carbon dioxide and car- 

 bon balance sheets that most of the carbon of the cell 

 constituents is derived from sources other than the 

 carbon dioxide. 



Another group of intermediate organisms comprises 

 the strictly anaerobic purple " sulphur-free " bacteria, 

 Athiorhodacece. They are peculiar in that they are 

 photosynthetic, but differ from the autotrophs in requiring 

 simple fatty acids for their growth as well as carbon 

 dioxide. In the absence of the fatty acids, carbon 

 dioxide is not taken up. It is claimed that when sub- 

 jected to infra-red radiation they can use hydrogen, 

 that is, they are true autotrophs. The pigment of these 

 organisms consists of two components, one carotenoid 

 and the other chlorophyll-like, photocatalytic, and similar 

 to that in the purple sulphur bacteria. 



We know virtually nothing of the way in which the 

 reduction of carbon dioxide, which seems to be an 

 essential factor in the metabolism of the autotrophs, 

 occurs. It has been suggested that it may be by one 

 of three routes : — 



