480 X. BILE PIGMENT FORMATION, ETC. 



dinitrate, and sodium chlorate; but, as in the instance of the green 

 hemoglobin formed by nitrite and hydrogen peroxide (cf. Section 6.3.), 

 some of these are perhaps of different nature. 



4.4.5. The "Viridans" Effect. If some microorganisms, e.g.. Strep, 

 viridans and Pnewnococcus {D. pneumoniae) are grown on blood agar 

 plates, a zone of green discoloration is found around the colonies. 

 This was previously explained as due to the formation of hemiglobin 

 from oxyhemoglobin, but it is now clear that the green color is due 

 to choleglobin, not to heniiglobin, although the same systems probably 

 produce both pigments from oxyhemoglobin. The effect was dis- 

 covered by Schottmuller in 1903 {21^61) and the literature is reviewed 

 in the textbook of Topley and Wilson, page 433 {2998; cf. also 350). 



Oxyhemoglobin solutions are transformed into green pigment by 

 the same bacteria and, to a lesser degree, also by other bacteria such 

 as /3-streptococci {Streptococcus pyogenes), S. faecalis. Staphylococcus 

 aureus, and Escherichia coli {lll^l). Hart and Anderson {IHl) 

 obtained the system responsible for the formation of this pigment in 

 cell-free autolysates. We have seen above that the green color is due 

 to choleglobin and denatured choleglobin. 



The pigment-producing system in pneumococci and streptococci 

 is apparently identical with the heniiglobin-forming system of bacteria 

 studied in detail by Avery, Morgan, and Neill {101-102,1985-1986, 

 2027-2030). They established the presence in bacterial autolysates 

 of a dehydrogenase system which, under anaerobic conditions, decolor- 

 ized methylene blue and, in the presence of oxygen, oxidized oxy- 

 hemoglobin to hemiglobin. Thermostable diffusible hydrogen donors, 

 probably derived from carbohydrate metabolism, and a thermolabile 

 factor, probably enzymic in nature, were found to play a role. The 

 latter factor is released from the cell only by autolysis and is labile 

 to oxygen and small amounts of hydrogen peroxide, but is protected 

 by the reducing thermostable factor. Hydrogen peroxide is formed 

 by a dehydrogenase system able to react with molecular oxygen; the 

 formation of hydrogen peroxide was demonstrated by distillation 

 and the starch-iodine reaction {cf. also 1^22,1266). 



The formation of green rings by bacteria (pneumococci and streptococci, 

 but also anaerobes, such as Clostridium welchii and C. tetani) in deep-shake 

 cultures in heated blood agar has also been explained by IMcLeod and Gordon 

 {lH2Jf) as due to hydrogen peroxide formation, but here the liydrogen peroxide 

 may be formed by the autoxidation of diffusible hydrogen donors produced 

 by the bacteria. It has been discussed above that, in addition to hydrogen 



