Sulfur (S), nitrogen (N) and oxygen (O) heterocycles areamong the most potent environmental pollutants.Microbial degradation of these pollutants is attractingmore and more attention because such bioprocesses areenvironmentally friendly. The biotechnological potentialof these processes is being investigated, for example, toachieve better sulfur removal by immobilized biocatalystswith magnetite nanoparticles or by solvent-tolerantbacteria, and to obtain valuable intermediates fromthese heterocycles. Other recent advances have demonstratedthe mechanisms of angular dioxygenation ofnitrogen heterocycles by microbes. However, these technologiesare not yet available for large-scale applicationsso future research must investigate proper modificationsfor industrial applications of these processes. Thisreview focuses on recent progress in understanding howmicrobes degrade S, N and O heterocycles.

The microbial production of 1,3-propanediol (1,3-PD) by Klebsiella pneumoniae under micro-aerobic conditions was investigated in this study. The experimental results of batch fermentation showed that the final concentration and yield of 1,3-PD on glycerol under micro-aerobic conditions approached values achieved under anaerobic conditions. However, less ethanol was produced under microaerobic than anaerobic conditions at the end of fermentation. The batch micro-aerobic fermentation time was markedly shorter than that of anaerobic fermentation. This led to an increment of productivity of 1,3-PD. For instance, the concentration, molar yield, and productivity of 1,3-PD of batch microaerobic fermentation by K. pneumoniae DSM 2026 were 17.65g/l, 56.13%, and 2.94g l-1 h-1, respectively, with a fermentation time of 6 h and an initial glycerol concentration of 40g/l. Compared with DSM 2026, the microbial growth of K. pneumoniae AS 1.1736 was slow and the concentration of 1,3-PD was low under the same conditions. Furthermore, the microbial growth in fed-batch fermentation by K. pneumoniae DSM 2026 was faster under micro-aerobic than anaerobic conditions. The concentration, molar yield, and productivity of 1,3-PD in fed-batch fermentation under micro-aerobic conditions were 59.50g/l, 51.75%, and 1.57g l-1 h-1, respectively. The volumetric productivity of 1,3-PD under microaerobic conditions was almost twice that of anaerobic fedbatch fermentation, at 1.57 and 0.80g l-1 h-1, respectively.