BEHAVIOUR OF BACTERIA TOWARDS ARSENIC. 



By Henkv Hamilton Green, D.Sc, and Nrolaas Hoemeyr 



Kestell. B.A.* 



{Abbrcvialcd Prcliiiiiiutrx Paper.) 



{Read. July ii, 1918. J 



A cursory orientation of the general distribution of arsenic- 

 resistant bacteria has been commenced, and several highly 

 tolerant organisms are described. A preliminary study of the 

 significance of arsenic-resistance as a g"rou]j characteristic is 

 made, althottgh the data are limited b\- the fact that no bacterial 

 museum was available. 



Two organisms, B. arseiioxydaiis and B. arsciircdiiccns, 

 responsible for oxidation of arsenite and reduction of arsenate 

 in arsenical dipping tanks, have been previously described by one 

 of us, but very little detailed work has yet been published in 

 regard to the general behaviour of bacteria towards arsenic. 



The method adopted was simply to make plate cultures from 

 soil, air, fa?ces, and tank dip. on ordinary agar an<l on agar 

 containing (|uantities of sodium arsenite varying from o. i per 

 cent, to 0.5 per cent. As./), cqiu'valent. Arsenite-resistant 

 organisms were then isolated from one set of )>lates and non- 

 resistant colonies picked off from the others. Isolation of 

 infrequently occurring bacteria by enriching methods has not yet 

 been carried out. 



Aerial Distrihiitioit. — rwo-minute exposures to laboratory 

 air and stable air gave varying results. On the ordinary plates 

 miscellaneous colonies developed, but for the most part these 

 were non-resistant. On o.i per cent, arsenite ])lates B. siibtilis 

 was suppressed, while on ]jlates containing over 0.2 per cent, to 

 0.3 per cent., the only surviving colonies were motilds and yeasts. 

 On one plate containing 0.5 per cent, of arsenite, and exposed to 

 stable air, a few colonies of the putidinn group ap])eared. 



Soil. — Cultiu'es were ])lated from soil taken from a shrub 

 bed. Tlie dominant types appearing on ordinary agar belonged 

 to the mesentericus-mycoides group, although several other 

 forms, including a strei)tothrix, appeared. C,)n arsenified plates 

 no colonies developed, even at concentrations as low as o.i per 

 cent. As^Ov as arsenite, and at dilutions showing as many as 100 

 colonies on ordinary agar. Arsenite-resistant organisms of the 

 type which grow readily on agar are therefore not frequent in 

 soil. It is probable that recently-dunged soil would show more, 

 and it is not unlikely that infrequent forms could be demonstrated 

 by enriching methods. 



Fcsces. — A mixed sample of stable manure was taken for 



* Honorary Researcli Worker. L^nivcrsity Innti vacation, T917-1918. 



