The gcpE gene product controls one of the terminal steps of isoprenoid biosynthesis via the mevalonate independent 2-C-methyl-D-erythritol-4-phosphate (MEP) pathway. This pathway is utilized by a variety of eubacteria, the plastids of algae and higher plants, and the plastid-like organelle of malaria parasites. Recombinant GcpE protein from the hyperthermophilic bacterium Thermus thermophilus was produced in Escherichia coli and puri¢ed under dioxygen-free conditions. The protein was enzymatically active in converting 2-C-methyl-Derythritol-2,4-cyclodiphosphate (MEcPP) into (E)-4-hydroxy-3-methyl-but-2-enyl diphosphate (HMBPP) in the presence of dithionite as reductant. The maximal speci¢c activity was 0.6 W Wmol min 31 mg 31 at pH 7.5 and 55 ‡C. The k cat value was 0.4 s 31 and the K m value for HMBPP 0.42 mM.

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In this study, the gram-negative bacteria Xanthomonas campestris, Xanthomonas maltophilia, and Pseudomonas putida, facultative parasites of plants and animals, were shown to accumulate 2-C-methyl-d-erythritol-2,4-cyclopyrophosphate (MEC) in response to benzyl-viologen-induced oxidative stress. Corynebacterium ammoniagenes mutants capable of accumulating MEC in the absence of an exogenous oxidative stress inducer were obtained. Isoprenoid synthesis and MEC synthesis in these and other bacteria were shown to be alternative processes, while biosynthesis of brominated polyene xanthomonadin (an antioxidant pigment of X. campestris) increased concomitantly with the accumulation of MEC.

In a number of bacteria an unusual glycosyl pyrophosphate (31P NMR signal chemical shift at about −15 ppm) was detected when the cells were subjected to oxidative stress. This substance from Brevibacterium ammoniagenes has now been identified as 2‐methyl‐butan‐1,2,3,4‐tetraol‐2,4‐cyclopyrophosphate, which is accumulated in the cell under certain conditions in concentrations of about 50 mM. It is now suggested that this compound is the long sought after bacterial antistressor.

Upon transition of Mycobacterium smegmatis into the dormant state, accumulation of a dark brown fluorescent pigment was observed. This pigment gave bright red fluorescence in both cells and the culture medium. Based on H-NMR, MALDI and UV spectra, the fluorescent compounds, extracted from the culture medium as well as from the dormant cells, were concluded to be a mixture of free coproporphyrin III and uroporphyrin III and their corresponding methyl esters. A possible significance of porphyrin pigment accumulation in the dormant cells is discussed.