Browsing by Author "Basnet, Subash"

The literature review of this thesis was focused on the pathway of folate biosynthesis with enzymes involved in it and factors effecting the synthesis of folate by bacteria. The literature was also partly focused on the introduction to propionic acid bacteria (PAB) and the folate production by these bacteria. The aim of the experimental part of the thesis was to screen the folate productivity of selected PAB strains isolated from various dairy and cereal sources after 96-hours anaerobic fermentation and also to see the effect of precursor (para-aminobenzoic acid) of folate biosynthesis on folate production by the strains. Then to further investigate the folate production of some promising PAB strains from screening part either with glucose or lactate as carbon source at four growth phases in aerobic fermentation. The propionic agar medium was used with either glucose or lactate as carbon source in the medium. Optical densities, pH, cell masses were measured after fermentation and folate produced by the strains was determined from biomass and supernatant of the samples using microbiological assay. Carbon consumption and metabolic end-products were analysed with HPLC after fermentation. Some of the screened PAB strains were promising folate producers. Strain 257 produced folate up to 124 µg/l which is even higher than production by some good Lactic acid bacteria (LAB). PAB strains produced intracellular folate upto 28954 ng/g cell biomass and excreted folate into medium upto 107 ng/ml. Strains grew faster with lactate than glucose but cell masses were higher with glucose than lactate even in the low pH. PAB strains showed the highest folate productivity in anaerobic fermentation with lactate as carbon source and aerobic fermentation with lactate as source was observed to be the best for high organic acid production. However, further studies are needed to optimise the cultivation condition of selected PAB strains for their best folate production in different matrices.