THE EARLIER PHASES OF THE BACTERIAL CULTURE CYCLE

Acoustic Emission Signal of Lactococcus lactis before and after Inhibition with NaN 3 and Infection with Bacteriophage c2

The detection of acoustic emission (AE) from Lactococcus lactis, ssp lactis is reported in which emission intensities are used to follow and define metabolic activity during growth in nutrient broths. Optical density (OD) data were also acquired during L. lactis growth at 32°C and provided insight into the timing of the AE signals relative to the lag, logarithmic, and stationary growth phases of the bacteria. The inclusion of a metabolic inhibitor, NaN₃, into the nutrient broth eliminated bacteria metabolic activity according to the OD data, the absence of which was confirmed using AE data acquisition. The OD and AE data were also acquired before and after the addition of Bacteriophage c2 in L. lactis containing nutrient broths during the early or middle logarithmic phase; c2 phage m.o.i. (Multiplicity of infection) was varied to help differentiate whether the detected AE was from bacteria cells during lysis or from the c2 phage during genome injection into the cells. It is proposed that AE measurements using piezoelectric sensors are sensitive enough to detect bacteria at the amount near 10⁴ cfu/mL, to provide real time data on bacteria metabolic activity and to dynamically monitor phage infection of cells.

In situ and laboratory studies of bacterial survival using a microporous membrane sandwich

A new device and procedure for the study of bacterial survival in an aquatic environment are described. The device uses two appressed presterilized microporous membranes to expose a bacterial cell suspension to the environment at a cell concentration that closely resembles those levels found in natural aquatic ecosystems. The device has been used under laboratory controlled conditions and in situ to study and compare bacterial survival times. In laboratory studies, Escherichia coli and Streptococcus faecalis survived the longest at 12 degrees C, pH 5, and in the presence of iron or calcium ions and cysteine. Cells in mid-stationary growth phase survived longer than those in mid- or late-logarithmic phase, whereas those maintained for a year or more as stock cultures survived for shorter period of time than did recent environmental isolates. In situ studies indicate that 5% of the starting number of E. coli and S. faecalis cells may survive longer than 96 h at 16 degrees C in potable lake water, whereas survival times in polluted lake water were approximately 12 h.

Changes in the ultraviolet sensitivity of Escherichia coli during growth in batch cultures

The ultraviolet (UV) sensitivity of Escherichia coli B/r harvested at various times during growth in batch cultures was measured. The results showed a period of increased UV sensitivity in late log phase, just before the cultures entered stationary phase. This increase in sensitivity was associated with a decreased shoulder in the UV survival curves. The postirradiation division delay of survivors was shortest for cells harvested during the period of maximal sensitivity. This period of increased UV sensitivity during late log phase was not found in the radiation-sensitive, repair-deficient mutant B(s-1) (a strain which is unable to excise pyrimidine dimers from UV-damaged deoxyribonucleic acid). These results suggest that the variation in UV sensitivity of E. coli B/r as a function of time of harvesting of the cells from batch cultures is related to the varying capacities of these populations to repair UV-damaged deoxyribonucleic acid. Further experiments designed to elucidate the mechanism underlying this variation in UV sensitivity indicated that it arises from the partial depletion of nutrients in the medium during late log phase. We suggest that growth in such depleted media leads to a depression in the intercellular concentration or activity of one or more of the repair enzymes concerned with the repair of damaged deoxyribonucleic acid.

Synchronization of bacteria by a stationary-phase method

Cutler, Richard G. (University of Houston, Houston, Tex.), and John E. Evans. Synchronization of bacteria by a stationary-phase method. J. Bacteriol. 91:469-476. 1966.-Cultures of Escherichia coli and Proteus vulgaris have been synchronized, with a high percentage phasing, in large volumes and at high cell densities by a method which takes advantage of a tendency of cells to synchronize themselves when entering the stationary phase of growth. The method consists of growing the bacteria to an early stationary phase, harvesting them quickly under minimal conditions of stress, and inoculating them into fresh medium at a dilution of about sevenfold. Cellular division is then partially synchronized. Four-generation cycles of a high percentage of phasing are obtained by repeating this procedure on the partially synchronized culture. Deoxyribonucleic acid (DNA), ribonucleic acid (RNA), and protein analyses were made throughout all phases of the growth curve. Advantage has been taken of this method of synchrony to isolate selected segments of the bacterial genome in significant amounts. A working hypothesis to explain the synchrony suggests that the unfavorable conditions of growth as the bacteria near the stationary phase are detected by a decrease in the amino acid pool size, and that this results in a gradual decrease of DNA transcription activity through the inhibition of RNA polymerase by transfer RNA. The synchronizing method may be unique in producing cultures that grow both in cellular division and in genomic synchrony.