GROWTH AND DIVISION OF ESCHERICHIA-COLI UNDER MICROGRAVITY CONDITIONS

The growth rate in glucose minimal medium and time of entry into the s tationary phase in pepton cultures were determined during the STS 42 m ission of the space shuttle Discovery. Cells were cultured in plastic bags and growth was stopped at six different time points by lowering t he temperature to 5 degrees C, and at a single time point, by formalde hyde fixation. Based on cell number determination, the doubling time c alculated for the flight samples of glucose cells was shorter (46 min) than for the ground samples (59 min). However, a larger cell size exp ected for more rapidly growing cells was not observed by volume measur ements with the electronic particle counter, nor by electron microscop ic measurement of cell dimensions. Only for cells fixed in flight was a larger cell length and percentage of constricted cells found. An opt ical density increase in the peptone cultures showed an earlier entry into the stationary phase in flight samples, but this could not be con firmed by viability counts. The single sample with cells fixed in flig ht showed properties indicative of growth stimulation. However, taking all observations together, we conclude that microgravity has no effec t on the growth rate of exponentially growing Escherichia coli cells.