Comparative studies of putrescine degradation by microorganisms

Putrescine production by engineered Corynebacterium glutamicum

Here, we report the engineering of the industrially relevant Corynebacterium glutamicum for putrescine production. C. glutamicum grew well in the presence of up to 500 mM of putrescine. A reduction of the growth rate by 34% and of biomass formation by 39% was observed at 750 mM of putrescine. C. glutamicum was enabled to produce putrescine by heterologous expression of genes encoding enzymes of the arginine- and ornithine decarboxylase pathways from Escherichia coli. The results showed that the putrescine yield by recombinant C. glutamicum strains provided with the arginine-decarboxylase pathway was 40 times lower than the yield by strains provided with the ornithine decarboxylase pathway. The highest production efficiency was reached by overexpression of speC, encoding the ornithine decarboxylase from E. coli, in combination with chromosomal deletion of genes encoding the arginine repressor ArgR and the ornithine carbamoyltransferase ArgF. In shake-flask batch cultures this strain produced putrescine up to 6 g/L with a space time yield of 0.1 g/L/h. The overall product yield was about 24 mol% (0.12 g/g of glucose).

Ornithine delta-aminotransferase: An enzyme implicated in salt tolerance in higher plants

This review deals with biochemical and physiological aspects of plant ornithine d-aminotransferase (OAT, EC 2.6.1.13). OAT is a mitochondrial enzyme containing pyridoxal-5'-phosphate as a cofactor, which catalyzes the conversion of L-ornithine to L-glutamate gamma-semialdehyde using 2-oxoglutarate as a terminal amino group acceptor. It has been described in humans, animals, insects, plants and microorganisms. Based on the crystal structure of human OAT, both substrate binding and reaction mechanism of the enzyme are well understood. OAT shows a large structural and mechanistic similarity to other enzymes from the subgroup III of aminotransferases, which transfer an amino group from a carbon atom that does not carry a carboxyl function. In plants, the enzyme has been implicated in proline biosynthesis and accumulation (via pyrroline-5-carboxylate), which represents a way to regulate cellular osmolarity in response to osmotic stress. However, the exact metabolic pathway involving OAT remains a subject of controversy.

Enzymes and pathways of polyamine breakdown in microorganisms

The information currently available on the breakdown of spermidine and putrescine by microorganisms is reviewed. Two major metabolic routes have been described, one for the free bases via delta 1-pyrroline (4-aminobutyraldehyde), the other via N-acetyl derivatives. In both pathways oxidases or aminotransferases are the key enzymes in removing the nitrogen atoms. The two routes converge at 4-aminobutyrate, which is then metabolized via succinate. The degradation of putrescine in Escherichia coli has been well characterized at both genetic and biochemical levels, but for other bacteria much less information is available. The C3 moiety of spermidine is broken down via beta-alanine, but the metabolism of this compound and its precursors is poorly understood. In yeasts, a catabolic route for spermidine and putrescine via N-acetyl derivatives has been described in Candida boidinii, and the evidence for its occurrence in other species is reviewed. Except for the terminal step of this pathway, the same group of enzymes can metabolize both the C3 and C4 moieties of spermidine. It is likely that other routes of polyamine catabolism also exist in both bacteria and yeasts.

Spermidine biosynthesis during germination and subsequent vegetative growth of Bacillus megaterium spores

Spermidine biosynthesis was extremely low early in germination of Bacillus megaterium spores and the spermidine level remained constant. Rapid synthesis began after 130 min and thereafter accounted for the increase in spermidine level which began at this time. Biosynthesis was greatly (>84%) diminished by exogenous spermine or spermidine. Arginine and ornithine were both converted efficiently into spermidine, but arginine was the more immediate precursor as shown by isotope competition studies and by the absence of ornithine decarboxylase and the presence of arginine decarboxylase. Exogenous putrescine was not incorporated into spermidine, although it was taken up rapidly and degraded.