THE GASEOUS REQUIREMENTS OF BACTERIA 69 



as a growth factor, however, has become a little clearer with the identification of biotin 

 (du Vigneaud, Hofmann and Melville 1942). Wildiers (1901) described a growth-promoting 

 fraction in yeast extract, to which he gave the name " bios." Many of the individual 

 growth-promoting substances in bios have been identified, and include t-inositol, ^-leucine, 

 /?-alanine, thiamin and pantothenic acid (see Koser and Saunders 1938) and pyridoxin 

 (Schultz et al. 1939, Eakin and Wilhams 1939). There remained biotin (Kogl and Tonnis 

 1936), a remarkable growth factor active in concentrations of 10"-^*' or less. Biotin 

 proves to be a keto-imidazolido-thiophane-valeric acid, and it is possible that pimelic 

 acid may contribute the fatty-acid chain in the bacterial synthesis of biotin by C. diph- 

 therice. In support of this, du Vigneaud, Dittmer, Hague and Long (1942) found that 

 pimelic acid and biotin behaved aUke in the growth stimulation of C. diphtherice. Working 

 with the mould Aspergillus niger, Eakin and Eakin (1942) showed that not only was 

 pimelic acid a growth stimulant, but its addition to the medium incJreased the biotin 

 content of the culture about twenty-fold. 



Biotin itself has been found essential for a number of bacteria, including Str. piyogenes 

 (Hottle, Lampen and Pappenheimer 1941), Staph, aureus (Porter and Pelczar 1941), 

 and Br. abortus (Koser, Breslove and Dorfman 1941). 



Biotin preparations are apparently essential for CI. acetohutylicum (Oxford, Lampen 

 and Peterson 1940), Brucella (Koser, Breslove and Dorfman 1941), Sir. pyogenes (Hottle, 

 Lampen and Pappenheimer 1941), and Staph, aureus (Porter and Pelczar 1941). There 

 are also many factors as yet not fully identified, such as an apparently lipoid stimulating 

 factor for the tubercle bacillus (Boissevain and Schultz 1938). Another vitamin-like 

 substance as yet unidentified that appears to have a wide distribution in bacteria, first 

 isolated by Knight and Fildes (1933) from a yeast gum, was necessary for CI. sporogenes 

 and CI. hotulinum (Fildes 1935). It is probably synthesized by a number of organisms, 

 including Salm. typhi •murium and the tubercle bacillus. 



The identity of many bacterial and animal vitamins, and the discovery of 

 large numbers of bacterial species for which the various vitamins are essential 

 nutrients, enables us to use bacteria in the assay of these substances for therapeutic 

 and other purposes. The vitamin for assay is added in varying concentrations 

 to cultures of the bacterium for which it is an essential nutrient, in a medium 

 lacking the vitamin, and the growth-promoting effect estimated. Clearly the 

 assay will be accurate only with bacteria whose growth requirements are defined 

 in every respect. Even so, errors will arise, for minute traces of contaminating 

 vitamins may be present in the materials used for the basal medium, and the 

 preparation of vitamin to be assayed may contain substances which are not essential 

 nutrients, but nevertheless have a stimulating action on growth. 



(For a discussion of the B-vitamin content of media in common bacteriological 

 use, see Stokes, Gunness and Foster 1944). 



The Gaseous Requirements of Bacteria. 



Examples of autotrophic bacteria utilizing hydrogen and COj have been given 

 in previous sections, but COj has been considered only as a main source of carbon. 

 COg may also act as a subsidiary source of carbon, or as an accessory growth 

 factor. Reference to Chapter 34 will afford a striking example of a heterotroph, 

 which on first isolation from the tissues fails to grow in air unless 5 to 10 per cent. 

 of CO2 is added to the atmosphere. Other species flourish only in a similar excess, 

 while others still require CO2, but in smaller concentrations. 



Numerous observations of the COj effect suggest that this gas is necessary for the growth 

 of many bacterial species, including anaerobes (see, for instance, Chapin 1918, Cohen 

 and Fleming 1918, Rockwell and McKhann 1921, Rockwell 1921, 1923, 1924, Rockwell 

 and Highbergher 1926, 1927, Valley and Rettger 1927, Valley 1928, McLeod, Coates, 



