Screening for Bacillus subtilis group isolates that degrade cyanogens at pH 4.5–5.0

Cyanogenic food crops abound in nature with important crops like cassava forming the staple food for over half a billion people. Detoxification by hydrolysis of cassava cyanogenic glycosides often involves acid fermentation, and in some of these processes Bacillus species are encountered. Forty Bacillus spp. (20 Bacillus subtilis, 11 Bacillus licheniformis, 7 Bacillus sonorensis, 2 Bacillus cereus) isolated from acid fermented primary starters to produce Gergoush, a Sudanese fermented snack, were screened for their ability to grow and to hydrolyze linamarin, the major cyanogen found in cassava at pH levels below 5.0; also the cyanogen amygdalin was assessed. The B. subtilis isolates grew in both HCl and lactic acid environments from pH 4.5–6.0 while being able to break down the cyanogenic glycosides. The B. licheniformis and B. sonorensis isolates grew and degraded cyanogens at pH 5.0 in a HCl environment, while two B. cereus isolates used in the study showed no breakdown reaction under all conditions tested. One B. subtilis isolate was observed to have substrate specificity between the breakdown of linamarin and amygdalin. We conclude that some Bacillus spp. isolates are important in the microbiological breakdown of cyanogens in cassava fermentations even at pH 4.5–5.0 though further investigations are required.

► We looked at the contribution of Bacillus isolates in the breakdown of cyanogens at pH 4.5–5.0.
► We assayed 40 isolates from low pH fermentations for their ability to break down linamarin and amygdalin.
► The isolates were of 4 different Bacillus species; 20 were B. subtilis.
► We report distinction in acid tolerance of different Bacillus spp. during fermentation; B. subtilis being most tolerant.
► B. subtilis isolate C45 was observed to have substrate specificity in degrading cyanogens.