When deprived of biotin, Arthrobacter globiformis 425 exhibits abnormal morphology (large, branched forms of variable size) and a retardation of its normal growth rate. In chemostat cultures, when cells were grown under glucose limitation, the morphology was normal (coccoids or rods) at specific growth rates between 0.05 and 0.125 h-1 (doubling times between 14 and 5.5 h, respectively) at 25 degrees C. The coccoid-to-rod morphogenesis occurs at a specific growth rate of 0.11 h-1. At the same specific growth rates and temperature, but under biotin limitation, abnormal morphology was observed.