Effects of Thermal Stress on Viability and Ribonucleic Acid of Aerobacter aerogenes in Aqueous Suspension

SUMMARYZymomonas anaerobia and 2. mobilis, grown on glucose + peptone + yeastextract medium, degraded no endocellular carbohydrate, DNA and protein even in prolonged starvation. No significant qualitative changes in protein content during starvation were detected by disc gel electrophoresis of crude extracts. Both organisms had a high content of RNA (22 % w/w) which was degraded on starvation. In 2. anaerobia RNA decreased linearly to 5 % of the dry weight in 125 hr. With 2. mobilis, half the RNA was degraded in the first 24 hr of starvation after which time the decline was much slower. MgC12 (33 mM) prevented RNA breakdown. During growth, the intracellular ATP concentration increased from 0.5 to 1.0 ,ug./mg. dry wt, but began to decrease exponentially in the last generation before growth ceased because of glucose exhaustion. Intracellular ATP content correlated with viability determined by slide culture. The addition of 33 mM-MgC1, to the starvation medium did not affect ATP content, but increased viability. On prolonged starvation (up to 7 days), populations whose viability had fallen to 3 % possessed unimpaired ability to produce ATP from glucose; only after even longer starvation periods was this ability impaired. I N T R O D U C T I O NDuring recent years considerable attention has been focused on the nature of the endogenous metabolism of micro-organisms (for reviews, see Dawes & Ribbons, 1962, 1964 although this work has been confined mainly to aerobic and facultatively anaerobic organisms. By investigating the changes in chemical composition which occur during starvation an insight can be afforded into the substrates utilized in endogenous metabolism and their relation to the viability of the organisms. Anaerobic bacteria, which obtain their energy by substrate-level phosphorylation reactions which are well charted, ought to be particularly amenable to investigation, especially in relation to the problem of 'maintenance energy' (Dawes & Ribbons, 1964 (NCIB 8938) was maintained in a similar manner. This organism grew with a doubling time of about 2 hr, compared with 3.5 hr for 2. anaerobia.Growth of larger quantities of either organism was achieved by transfer of an inoculum from the stock culture to 20 ml. sterile liquid medium. When this culture was gassing vigorously (after about 12 hr) it was used to inoculate one or more litres of medium in round flat-bottomed flasks or aspirators filled to the neck. Zymomonas anaerobia attained stationary phase in 20 hr at 30°, while 2. mobilis took 12 to 15 hr.For starvation experiments organisms were harvested aseptically in closed, sterile centrifuge bottles and the cultures were examined for contamination by phasecontrast microscopic examination of a wet smear.Measurement of bacterial concentration. This was performed turbidimetrically with a Unicam SP 600 spectrophotometer at 570 nm. Extinctions were related to population density by a dry wt calibration curve.Preparation of washed suspensions for starvation experiments. After the appropriate period of growth ...

Section: Discussionmentioning

confidence: 99%

Effect of Starvation on the Viability and Cellular Constituents of Zymomonas anaerobia and Zymomonas mobilis

Dawes

Large

1970

“…Conditions which accelerated RNA breakdown in other bacteria were generally more lethal (e.g. see Strange & Shon, 1964;Strange & Dark, 1965) and Postgate (1967) has concluded that RNA degrada- tion is a critical process in the survival of Aerobacter aerogenes. However, no absolute correlation between the rates of death and RNA breakdown could be demonstrated.…”

Section: Discussionmentioning

confidence: 99%

Degradation of Cell Constituents by Starved Streptococcus lactis in Relation to Survival

Thomas

Batt

1969

SUMMARYStreptococcus lactis organisms were grown in lactose-limited batch culture and transferred, after washing, to phosphate buffer at the growth temperature. Soluble protein was released from viable organisms into the suspending buffer and the intracellular free amino acid pool declined steadily with the components appearing in the suspending buffer; a net increase in the total amount of free amino acid indicated some protein hydrolysis. RNA was hydrolysed, resulting in the release of u.v.-absorbing bases and ribose from the organisms, Conditions which promoted rapid RNA breakdown also produced rapid death rates and long cell division lags in surviving organisms. After 28 hr starvation in buffer containing Mg2+, the bacterial dry wt decreased by 26 %; loss of RNA, protein and free amino acids accounted for 10.3 %, 7-3 % and 2.7 % of the total bacterial mass loss. The products of polymer hydrolysis appeared to be released in an undegraded form into the external buffer and there was no appreciable formation of lactate, ammonia or volatile fatty acids, possibly indicating the absence of any important endogenous energy sources. There was no appreciable degradation of DNA or carbohydrate but phospholipid was broken down on prolonged starvation. No polyglucose or poly-@-hydroxybutyrate was detected in the organisms.

“…less than 80% of the available magnesium was taken up by the organisms. Sodium can displace magnesium that is adsorbed on the surface of bacteria (Strange & Shon, 1964;Tempest & Strange, 1966) and the adsorption process may be a necessary stage in the assimilation of magnesium by bacteria (Tempest, Dicks & Meers, 1967). Hence, NaCl toxicity in general may be due, at least in part, to interference in the uptake of magnesium by the growing organisms.…”

Section: Glycerol-limited Organismsmentioning

confidence: 99%

The Influence of NaCl Concentration of the Medium on the Potassium Content of Aerobacter aerogenes and on the Inter-relationships between Potassium, Magnesium and Ribonucleic Acid in the Growing Bacteria

Tempest

Meers

1968

SUMMARYIrrespective of the nature of the growth-limiting substance, the potassium content of Aerobacter aerogenes (growing in a chemostat at a fixed dilution rate) increased progressively from about 1.3 % to 4-2 yo of the bacterial dry weight with changes in culture NaCl concentration from o to 40 g./l. Similarly, the potassium content of glycerol-limited A. aerogenes organisms, growing in a low ionic strength medium, varied with growth rate (from 0.9 % to 1.6 yo of the bacterial dry weight with changes in dilution rate from 0.05 to 0.7 hr-l); but this was not related to the small changes in culture NaCl content that occurred simultaneously. These observations are discussed with reference to conflicting views on the particular role of potassium in growing bacteria that accounts for its presence intracellularly in high concentration.