J. gen. Microbiol. (I970), 60, 31-42 Printed in Great Britain Effect of Starvation on the Viability and Cellular Constituents of Zymomonas anaerobia and Zymomonas mobilis By E. A. DAWES AND P. J. LARGE Department of Biochemistry, The University, Hull, HU6 7RX (Accepted for publication 29 September 1969) SUMMARY Zymomonas anaerobia and 2. mobilis, grown on glucose + peptone + yeast- extract 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 intra- cellular 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. INTRODUCTION During 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). Forrest & Walker (1965) studied the endogenous metabolism of the homofermentative organism Streptococcus faecalis which degrades glucose to lactate via the Embden- Meyerhof pathway, and Thomas (I968) has investigated Streptococcus lactis. Accordingly, for the present work, Zyrnomonas anaerobia (McGill, Dawes & Ribbons, I 965 ; McGill, I 966) and 2. mobilis (Stern, Wang & Gilmour, I 960 ; Dawes, Ribbons & Large, 1966) were chosen; they ferment glucose to ethanol and carbon dioxide by the Entner-Doudoroff (I 952) pathway. Characteristic of this pathway is an energy yield of I mole ATP/mole glucose fermented, i.e. half that obtained by the Embden- Meyerhof pathway (Elsden & Peel, 1958). 3 MIC 60