The physiological and genetic diversity of bovine Streptococcus bovis strains

Abstract

Laboratory Streptococcus bovis strains and isolates obtained from a steer fed increasing amounts of grain had similar growth characteristics, but they differed in their sensitivity to 2-deoxyglucose (2DG), a non-metabolizable glucose analog. The addition of 2DG decreased both growth rate (0.92±0.34 h −1) and growth yield (ranging from 25 to 63%), but these differences could not be correlated with diet. However, isolates from a steer fed a 90% grain diet were more prone to 2DG-dependent lysis than those from a hay diet ( P<0.001). All S. bovis laboratory strains and isolates had an identical restriction fragment length polymorphism pattern, when their 16S rDNA was digested with HaeIII and HhaI. However, when genomic BOX elements were amplified, 5–12 bands were observed, and the S. bovis isolates and laboratory strains could be grouped into 13 different BOX types. Strains 26 and 581AXY2 had the same BOX type, but the remaining laboratory strains did not form closely related clusters. Strains JB1 and K27FF4 were most closely related to each other. Most of the fresh isolates (24 out of 30) could be grouped into a single cluster (>90% Dice similarity). This cluster contained isolates from all three diets, but it did not have any of the laboratory strains. The majority (90%) of the isolates obtained from the hay-fed steer exhibited the same BOX type. Because more BOX types were observed if grain was added to the diet, it appears that ruminal S. bovis diversity may be a diet-dependent phenomenon.