Pigment production in chemostat cultures of Streptococcus bovis

Summary Streptococcus bovis 2B altered its morphology and metabolism in response to changes in the rate of glucose addition. Specific pigment (measured by a simple spectrophotometric method) and lactic acid production increased with dilution rate (D) in a glucose-limited chemically defined medium. Lactic acid production increased immediately after a D stepup or a glucose pulse; increase of pigment production was slower and occurred with a lag of one generation. No increase in specific pigment production was seen after a starch pulse. Electron micrographs of thin sections showed that slow growing cells had thick cell walls. Faster growing cells had thinner cell walls but more bound pigment, suggesting a tradeoff between cell wall thickening and pigment production. Ammonia-limited cells continued to use all the glucose available and lactate and pigment production increased only slightly with D. Thin sections again showed thick cell walls for slow growing cells. Division irregularities characteristic of unbalanced growth were seen, which may explain the early washout of the ammonia-limited culture. Cystine in the medium was not used as a nitrogen source.