Lon Protease Promotes Survival of Escherichia coli During Anaerobic Glucose Starvation

In Escherichia coli, Lon is an ATP-dependent protease which degrades misfolded proteins and certain rapidly-degraded regulatory proteins. Given that oxidatively damaged proteins are generally degraded rather than repaired, we anticipated that Lon deficient cells would exhibit decreased viability during aerobic, but not anaerobic, carbon starvation. We found that the opposite actually occurs. Wild-type and Lon deficient cells survived equally well under aerobic conditions, but Lon deficient cells died more rapidly than the wild-type under anaerobiosis. Microarray analysis revealed that genes of the Clp family of ATP-dependent proteases were induced during aerobic growth but not during anaerobic growth. Thus, Clp may compensate for loss of Lon when cells are in an oxygen containing atmosphere. Under anaerobic carbon starvation conditions, Lon must be active to support survival. Keywords: Other Three aliquots of isolated total RNA, drawn from one of four cultures containing 3E+9 cells, were each divided in half. The first half was labeled with Cy5 and the second half was added to a reference pool of RNA. The reference pool, containing an equal amount of RNA from each pooled culture sample, was labeled with Cy3. Triplicate samples yielded three expression measurements per gene for each experimental condition. Five arrays of lower quality, as determined by within-group correlation of log(base 2) ratio (cy5/cy3) measurements of all array features, were excluded from further analysis. Data from the remaining nineteen arrays were grouped as follows: Group A: day 1, anaerobic, lon(+) (wild-type) Group B: day 1, anaerobic, lon(-) Group C: day 1, aerobic, lon(+) Group D: day 1, aerobic, lon(-) Group E: day 3, anaerobic, lon(+) Group F: day 3, anaerobic, lon(-) Group G: day 3, aerobic, lon(+) Group H: day 3, aerobic, lon(-).