JJl-:SCRli'TION OF A BACTERIUM WHICH OXIDIZES 

 ARSENITE TO ARSENATE, AND OF ONE WHICH 

 REDUCES ARSENATE TO ARSENITE, ISOLATED 

 FROM A CATTLE-DIPPING TANK. 



By Henrv Hamilton Green, D.Sc, F.C.S. 



{Abstract.) 



{Printed in Annwal Report of the Director of Veterinary 

 Research, Pretoria.) 



By means of a combination of enriching and plating methods 

 a number of arsenic-resistant organisms have been isolated from 

 the cattle-dipping tank at Onderstepoort. 



Oxidizing rganism.—T\\\s appears to be a new organism, 

 and has been provisionally named Bacterium arseno.vydans. 

 According to the classification system of the Society of Ameri- 

 can Bacteriologists it woidd have the group number 212.3331033. 

 It is the causal organism in deterioration of arsenical dips, and 

 so far as has been ascertained, it appears to be the only one to 

 which rapid oxidation is to be ascribed. Its dimensions are 

 variable, usually i /x to 3 /a in length and o. 3 /* to 0.6 /x w- breadth, 

 slender forms predominating. Involution forms are larger, and 

 vary considerably in size and shape. It stains well with ordin- 

 ary stains, shows a beaded structtire. and is gram-negative. It 

 is generally non-motile, although motile forms which readily lose 

 their motility ha^'e been observed. 



Apart from its its denitrifying activity and its power to 

 oxidize arsenite to arsenate, its characteristics are rather nega- 

 tive. Apart (from the negative characters indicated by the j^roup 

 number it does not produce alkalinity in milk media, produces 

 neither indol nor sulphuretted hydrogen, nor any characteristic 

 odour in bouillon. It grows either poorly or not at all in 

 synthetic media, such as Uchinsky's. Giltay's or Cohn's. (Growth 

 on agar is slow, but g(H)d : on gelatine, ]:)oor, and ma\- fail : <)n 

 alkalinized potato, slow and uncertain, but may be good; in 

 organic media, such as bouillon, pe])tone. hay infusion, is good, 

 but slow. Plate cultures on agar, and agar slopes, are not unlike 

 those of coli except that growth is slower and more comjjact. It 

 is easily differentiated from most of the commoner organisms, 

 especially those of the coli gr(~)up, by its high tolerance for 

 arsenite and its capacity to oxidize this to arsenate. The limit 

 of tolerance is about i per cent. Xs.X),,. as arsenite and oxidation 

 can proceed slowly in concentrations as high as 0.8 ])er cent. 

 The rate of oxidation, tmder suitable conditions, increases as the 

 concentration of arsenite decreases. At 0.2 per cent. As.,03, 

 oxidation, after light inoculation, may be complete in five or six 

 days. Oxidation proceeds best in a faintly alkaline medium, 

 being inhibited by very slight acidity and rapidly coming to a 



