Regulation of carbon metabolism in Chlamydia trachomatis

The biological significance of glycogen accumulation and how the process is regulated in Chlamydia trachomatis remains poorly defined. C. trachomatis- infected HeLa cells were cultured in medium containing various glucose conc entrations (0, 0.1, 1 or 10 mg ml(-1)) or in the presence of gluconeogenic carbon sources (20 mM glutamate, 20 mM malate, 20 mM or-ketoglutarate or 20 mM oxaloacetate), and the effects of these different culture conditions on the production of infectious chlamydial elementary bodies and glycogen acc umulation were monitored. When chlamydiae were cultured in glucose concentr ations greater than 1 mg ml(-1), optimal growth and maximal glycogen accumu lation occurred. In contrast to uninfected HeLa cells, which increased thei r glycogen stores when grown in the presence of high glucose concentrations , chlamydial glycogen accumulation remained essentially constant. When cult ured in medium supplemented with either reduced glucose concentrations or a ny of the gluconeogenic carbon sources, chlamydiae still grew; however, the yield of elementary bodies was substantially decreased, and there was no s ignificant amount of glycogen accumulated by host HeLa cells or C. trachoma tis. This suggests that glycogen accumulation may not be essential for chla mydial survival. Reverse transcriptase-polymerase chain reaction (RT-PCR) r esults indicated that, despite the fact that the source and amount of carbo n available in the medium affected chlamydial glycogen accumulation, the ex pression of genes required for glycogen metabolism was not significantly ch anged. Similarly, the expression of several genes encoding key enzymes of c entral metabolism was not affected by alterations in carbon source or avail ability. Taken together, the data suggest that, unlike most free-living bac teria, chlamydia are unable to alter the expression of genes involved in ca rbon metabolism in response to changes in environmental conditions.