NUTRIENT FUNCTION OF INORGANIC SALTS 83 



knowledge of the synthetic abilities of the nutritionally non- 

 exacting. 



NUTRITIONAL REQUIREMENTS 

 Inorganic salts 



All bacteria require the presence of certain inorganic ions 

 for growth. Salts are required for the regulation of osmotic 

 pressures, for the maintenance of membrane equilibria, and 

 for the action of enzymes. Enzymes such as catalase, cyto- 

 chrome oxidase, and polyphenol oxidase, possess a metal as 

 part of their structure, phosphatases require the presence of 

 magnesium as coenzyme, while pyrophosphatase is optimally 

 active only in the presence of a definite ratio of magnesium 

 and calcium ions. Traces of metals such as zinc, cobalt, 

 molybdenum, vanadium, etc., are found to be essential for 

 certain activities in some organisms. The presence of phos- 

 phate plays an essential role in energy transfer and many 

 fermentation reactions. A nutrient salt mixture which will 

 support growth must contain Na+, K+, Fe++, Mg++, Cu++, 

 NH4+, Cr, SO/', PO4'", CaCOg, and traces of other metals 

 which are usually present in sufficient quantities as impurities 

 in the commercial salt preparations. Recent investigations on 

 the properties of Esch. coli and Aerohact. indologenes grown in 

 iron -deficient media have showm that the organisms grown 

 under such conditions are deficient in certain enzymes such 

 as formic dehydrogenase, hydrogenase, and formic hydro- 

 genlyase (see p. 132), with the result that they carry out an 

 acid fermentation of glucose without the usual formation of 

 gas (see Chap. VII). If the iron deficiency is severe, the 

 organisms may show a decreased content of catalase and 

 cytochrome. 



Autotrophic bacteria 



The least exacting group of organisms is the autotrophic 

 group, members of which are able to multiply in a purely 

 inorganic environment, synthesising their carbon substances 

 from CO2 or HCO3', their nitrogenous material from ammonia 

 or nitrate, and obtaining their energy in one of two ways. 



