352 UNITY AND DIVERSITY IN BIOCHEMISTRY 



The autotrophic bacteria are chimiosynthetic, that is, they synthesize 

 sugars using the energy of oxidation of a constituent of the surrounding 

 medium. 



(a) Nitrous Bacteria 



These bacteria accomplish a nitrosation (ammonium sahs -> nitrites). 

 These bacteria are numerous and belong to the genera Nitrosomonas 

 (aerobic, widely distributed in the soil of Europe and Asia, ovoid or 

 spherical in shape, able to move in a liquid habitat by means of their 

 flagellae they group themselves in mucilaginous zoogloeae) and Nitro- 

 sococcus, (in American soil, always non-mobile). The chimiosynthesis of 

 carbohydrates in the nitrous bacteria consists of a transfer of hydrogen 

 from ammonia to COg: 



2NH3 + 2O2 -> 2NO2H + 2H2 



2H2 + CO2 -> CH2O + H2O 



{b) Nitric Bacteria 



These oxidize nitrites to nitrates thus performing a nitration. Among 

 the nitric bacteria are the Nitrobacter which are bacilliform, non-mobile, 

 and aerobic (Fig. 93). 







^^ 0. ^N 



/ ^.s. ^^ n 



Fig. 93 (Winogradsky) — Nitrobacter 



{c) Colourless Sulphur Bacteria 



Certain of these are aerobic, others anaerobic. Among the aerobes are 

 Thiobacillus thioparus and Thiobacillus thiooxydans. The former is present 

 in soil in the form of small rods. It multiplies when the medium is neutral. 

 It oxidizes thiosulphates (hyposulphites) or sulphides to sulphate and 

 sometimes sulphur is deposited inside the cell. 



2Na2S203 + O2 -> 2Na2S04 + 2S 



Thiobacillus thiooxydans is found in the soil in the vicinity of sulphur 

 deposits. It produces large amounts of H2SO4 and only grows under acid 

 conditions (pH 8 = 2-0-3 -0). It oxidizes sulphur or thiosulphate to 

 sulphuric acid: 



2S + 3O2 + 2H2O -> 2H2SO4 



Na2S203 + H2O + 2O2 -> Na2S04 + H2SO4 



