NUTRITION OF THE AUTOTROPHIC BACTERIA 75 



I'eactions accompanying growth and pait is oxidised to 

 carbonic acid : — 



HCHO + O2 > H/'Og 



The mechanism 



2H2 + CO2 > HCHO + H2O 



has also been suggested. 



Some strains will only grow in symbiosis with one 

 another, for example when one of the pair needs the 

 pyrimidine moiety of anenrin and the other the thiazole 

 moiety. (See Chapter IX). Pure cultures of each may 

 be gro^yn if small amounts of the gro^\i:h factors are 

 provided. 



The Carbon Monoxide and Methane Bacteria.^Strictly 

 speaking these are not autotrophic bacteria since they 

 can utilise the carbon of their substrates for their gro^\i;h. 

 They are best regarded as intermediate t^^es between 

 the autotrophs and the heterotrophic bacteria. An 

 organism, Carhoxydomonas oligocarbopkila, which oxidises 

 carbon monoxide to carbon dioxide was isolated by 

 Beijerinck from soil. It is a facultative autotroph which 

 exists as a filamentous actinomyces-like organism when 

 grown in carbon monoxide, but exhibiting a coccal form 

 when growTi in the presence of organic compounds. 



The methane -oxidising organism, Methanoynonas 

 methanica, was isolated from the mud of canals and 

 marshes by Sohngen. It oxidises methane, but not 

 other hydrocarbons, to carbon dioxide and water : — 



CH4 + 2O2 > CO., -r 2H2O. 



Other hydrocarbon-utilising organisms are loiown 

 which, although not autotrophs, may be mentioned liere 

 as forming part of the transition group between them 

 and the heterotrophs . They are Metha n omonas a lipJmtica , 

 Meth. aliphatica liquefaciens and " Paraffin Bakterien," 

 which utilise paraffins, including methane in the case of 

 the two former, a;S their source of carbon and energy. 

 They can also grow on ordinary media. It has been 



