Non-conditional morphological mutant envC derived from Escherichia coli K-I 2 strain ~6 7 8 , isolated after treatment with I-methyl-3-nitro-I -nitrosoguanidine, produced chains of bacteria on synthetic or rich media at 30 "C and 40 "C. It was sensitive to deoxycholate and less resistant to penicillin and rifampicin than the parent strain. In section under the electron microscope, the mutant showed greatly disorganized septum formation. Preliminary mapping of envC by conjugation located it near xyl. The morphological and physiological characteristics of eniC+ recombinants and the envC+ parent were identical.
Heat or ethanol shock of Zymomonas mobiis enhanced the labeling by [35S]methionine of several polypeptides and induced the synthesis of a new polypeptide (molecular weight, 18,500) associated with the envelope fraction. These results indicate the existence of a typical heat-shock response in Z. mobilis. This response could be involved in the induction of increased ethanol tolerance in Z. mobilis cells.Zymomonas mobilis converts glucose or fructose to ethanol and CO2 in equimolar amounts. Hence it may be assumed that this organism should be particularly well adapted to withstand elevated alcohol concentrations accumulating in the growth medium. Indeed, its growth yield is unaffected by ethanol up to 7% (2). Ethanol tolerance is correlated with a characteristic membrane lipid composition (1,3,15,16), but its mechanism appears to be more complex (2). In some organisms, ethanol has been shown to have an effect similar to that of heat in stimulating the synthesis of specific heat-shock proteins controlled by the htpR gene (6,10,17) and in the accumulation of alarmones (5). Of particular interest is the simultaneous enhancement of ethanol tolerance and thermotolerance of Escherichia coli induced by a short incubation at a supraoptimal temperature (10). Cross-resistance between ethanol and heat was also observed in Saccharomyces cerevisiae (13) and other eucaryotic organisms (7).We have reported specific changes in the membrane protein composition of Z. mobilis induced by high ethanol concentrations (9), but it was not clear whether they were correlated with the heat-shock response. A basic question remained: does ethanol induce heat-shock proteins in an obligately fermentative organism? In this communication we present evidence for the existence of a typical heat-shock response induced by heat or ethanol and conferring increased heat and ethanol cross-resistance on Z. mobilis.Induction of heat or ethanol resistance in Z. mobilis ZM4(1) was investigated by shifting bacteria grown at 30°C in a complex MYPG medium (9) to higher temperatures or by adding increasing concentrations of alcohol. After plating on solid MYPG medium, cell viability was estimated by counting colonies after 72 h of incubation at 30°C. Incubation at 45°C for 10 min or addition of up to 7% (vol/vol) ethanol followed by incubation at 30°C for 30 min in the presence of ethanol had no effect on colony-forming ability. Higher temperatures or ethanol concentrations caused a rapid decline of the cell viability. As expected, sublethal ethanol or heat shock enhanced cell resistance to subsequent heat and ethanol treatment. Indeed, when bacteria were shifted from 30 to 450C for 10 min and then transferred to 50°C for 10 min before plating, 96% of cells remained viable, whereas a control heated at 50°C without pretreatment had only 42% survival. Similarly, 95% of cells shifted to 500C for 10 min retained viability when they were preincubated at 30°C for 30 min in medium with 5% ethanol. Finally, 5% ethanol pretreatment for 20 min followed by 30 min of incubat...
Low doses of penicillin which inhibited division but permitted filament formation in Escherichia coli did not influence the total rate of phospholipid formation but altered the ratio of individual phospholipids to that characteristic of resting organisms: the filaments contained more cardiolipin and less phosphatidyl glycerol than normal exponentially dividing organisms. Addition of penicillinase to growing filaments restored both normal division and the normal phospholipid ratio. Filaments induced by u.v.-irradiation showed similar changes in phospholipid ratio. These findings suggest that phospholipids or their derivatives are directly involved in division.
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