The requirements for X and V factors and for CO, and the biochemical reactions of the Khairat and Hunka strains of were re-examined. The four Khairat strains were found to be dependent on X factor and CO although they produced a relatively high proportion of X-independent variants. Gas was not produced during fermentation of carbohydrates by the Khairat strains in tests made by two methods. The presence or absence of 0·6 per cent. NaCl in Yeastrel agar made no difference to the growth requirements of the four strains in cultures grown in air or in cultures grown in air with added CO, although better growth was obtained on NaCl-containing media.

Toshach's Hunka strain showed no dependence upon either X factor or V factor and in our view does not belong to the genus .

Our findings suggest that retention of the taxon is justified, and we designate the Khairat strain NCTC no. 5906 as the holotype.


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