Improved Candida methylica formate dehydrogenase fermentation through statistical optimization of low-cost culture media.

NAD⁺-dependent formate dehydrogenase (FDH, EC 1.2.1.2) is of use in the regeneration of NAD(P)H coenzymes, and therefore has strong potential for practical application in chemical and medical industries. A low-cost production of recombinant Escherichia coli (E. coli) containing FDH from Candida methylica (cmFDH) was optimized in molasses-based medium by using response surface methodology (RSM) based on central composite design (CCD). The beet molasses as a sole carbon source, (NH4)2HPO4 as a nitrogen and phosphorus source, KH2PO4 as a buffer agent, and Mg2SO4 · 7H2O as a magnesium and sulfur source were used as variables in the medium. The optimum medium composition was found to be 34.694 g L⁻¹ of reducing sugar (equivalent to molasses solution), 8.536 g L⁻¹ of (NH4)2HPO4, 3.073 g L⁻¹ of KH2PO4, and 1.707 g L⁻¹ of Mg2SO4 · 7H2O. Molasses-based culture medium increased the yield of cmFDH about three times compared to LB medium. The currently developed media has the potential to be used in industrial bioprocesses with low-cost production.

Conventional morphological and functional evaluation of the microbial populations in a sequencing batch reactor performing EBPR.

To help confirm and interpret the Enhanced Biological Phosphorus Removal (EBPR) performance of the microbial populations in a laboratory-scale activated sludge (AS) system, conventional microscopic examinations were carried out. A lab-scale sequencing batch reactor (SBR), named ARC, was fed with acetate, as the sole carbon source, and operated for EBPR. Daily monitoring and cyclic behavior evaluation studies indicated that the system always worked for EBPR in the long run, with efficiencies depending on the influent characteristics and operational stability. Poly-P and PHB-staining experiments revealed that the enriched biomass of the reactor was quite diverse in terms of morphology, hosting populations of traditional rod-shaped PAOs, tetrad/sarcina-like cells (referred here as TFOs, rather than GAOs), diplococci-shaped cells, and staphylococci-like clustered populations, in addition to few filaments. Although the microscopic observations were qualitative, rather than quantitative, they seemed likely to correlate well to the biochemical performance of the reactor.