Improved production of docosahexaenoic acid in batch fermentation by newly-isolated strains of Schizochytrium sp.and Thraustochytriidae sp.through bioprocess optimization

Thraustochytrids,rich in docosahexaenoic acid(DHA,C22:6u3),represent a potential source of dietary fatty acids.Yet,the effect of culture conditions on growth and fatty acid composition vary widely among different thraustochytrid strains.Two different thraustochytrid strains,Schizochytrium sp.PKU#Mn4 and Thraustochytriidae sp.PKU#Mn16 were studied for their growth and DHA production characteristics under various culture conditions.Although they exhibited similar fatty acid profiles,PKU#Mn4 seemed a good candidate for industrial DHA fermentation while PKU#Mn16 displayed growth tolerance to a wide range of process conditions.Relative DHA content of 48.5%and 49.2%(relative to total fatty acids),respectively,were achieved on glycerol under their optimal flask culture conditions.Maximum DHA yield(Yp/x)of 21.0%and 18.9%and productivity of 27.6 mg/L-h and 31.9 mg/L-h were obtained,respectively,in 5-L bioreactor fermentation operated with optimal conditions and dual oxygen control strategy.A 3.4-and 2.8-fold improvement of DHA production(g/L),respectively,was achieved in this study.Overall,our study provides the potential of two thraustochytrid strains and their culture conditions for efficient production of DHA-rich oil.

Statistical modeling and optimization for enhanced hyaluronic acid production by batch culture of Sreptococcus zooepidemicus via the supplement of uracil

This work is aimed to achieve the optimal hyaluronic acid(HA)production by batch culture of Streptococcus zooepidemicus via the supplement of nucleotide bases using response surface methodology(RSM).First,the influence of nucleotide bases(adenine,guanine,cytosine,thymine,and uracil)on microbial HA production was investigated using fractional factorial design(FFD).By a 2^(5-2)FFD,uracil was found to be the most significant factor for cell growth and HA production,while the other nucleotide bases were shown to have no significant effects on cell growth and HA production.Also,the impact of uracil on cell growth and HA production was further investigated by RSM,where two variables were considered:uracil concentration and supplement time.The optimal uracil concentration and supplement time were found to be 0.051 g/L and 7 h,respectively,and the predicted maximal HA production reached 6.42 g/L.The maximal HA production increased from 5.0 g/L of the control without uracil supplement to 6.31 g/L at the optimal conditions in validation experiments.

Acid resistance of methanogenic bacteria in a two-stage anaerobic process treating high concentration methanol wastewater

In this study,the two-stage upflow anaerobic sludge blanket(UASB)system and batch experiments were employed to evaluate the performance of anaerobic digestion for the treatment of high concentration methanol wastewater.The acid resistance of granular sludge and methanogenic bacteria and their metabolizing activity were investigated.The results show that the pH of the first UASB changed from 4.9 to 5.8 and 5.5 to 6.2 for the second reactor.Apparently,these were not the advisable pH levels that common metha-nogenic bacteria could accept.The methanogenic bacteria of the system,viz.Methanosarcina barkeri,had some acid resis-tance and could still degrade methanol at pH 5.0.If the meth-anogenic bacteria were trained further,their acid resistance would be improved somewhat.Granular sludge of the system could protect the methanogenic bacteria within its body against the impact of the acidic environment and make them degrade methanol at pH 4.5.The performance of granular sludge was attributed to its structure,bacteria species,and the distribution of bacterium inside the granule.