Metabolic and morphologic differentiation in Escherichia coli and Clostridium beijerinckii

The focus of the studies is the relationship of the growth rate and differentiation in bacterial genera. The first system is a division mutant of Escherichia coli which produces chromosome-less cells only after a mass doubling time of 20 h is reached. I determined that this unique growth-rate dependent division phenotype is caused by a mutation mapping within 1 min of the minB operon. This mutation is proposed to be in the topologic regulator of MinE activity. We also conclude that guanosine tetraphosphate interacts with this regulator to inhibit MinE activity at the cell poles. The second system was Clostridium beijerinckii. Differentiation from acidogenesis to solventogenesis and its link to sporulation were investigated using a recycling fermentor. This unique growth system with its 100% cell recycle allows of the study of bacteria as their growth-rate slows. We determined that the shift from acidogenesis to solventogenesis did not occur at a single mass doubling time, but as a series of events. The rate of acetic acid production decreased immediately after the fermentor was switched from chemostat to recycle mode, whereas the rate of butyric acid production did not change. Propanol was detected 4.5 h after the switch, followed 44.5 h later by an increase in the rates of ethanol and propanol production and the detection of propionic acid. An increase in the rate of butanol production occurred 9 h later, as also did the appearance of phase-dark forespores. This sequence of events did not require elevated levels of guanosine tetraphosphate to occur. An acidogenic recycling fermentor culture stimulated to sporulate and monitored using both phase contrast and electron microscopy produced only butanol as phase-dark forespores were formed. This would suggest a link between sporulation stage III and butanol production in C. beijerinckii