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.

A novel D(−)-lactic acid-inducible promoter regulated by the GntR-family protein D-LldR of Pseudomonas fluorescens

Lactic acid has two stereoisomers of D(−)-and L(+)-forms,both of which are important monomers of biodegradable plastic,poly-lactic acid.In this study,a novel D-lactate inducible system was identified in Pseudomonas fluorescens A506,partially characterized and tested as biosensor.The D-lactate catabolic operon(lldP-dld-II)was negatively regulated through the inversely transcribed D-lldR(encoding a GntR-type regulator),where the repression is relieved by addition of D-lactate.The derepression was specific to D-lactate and marginally affected by L-lactate.The D-LldR-responsive operator,showing dyad symmetry and separated by one base,was located between+11 and+27 from the transcription start site of the lldP-dld-II operon.By site-directed mutagenesis,a motif with a dyad symmetry(AATTGGTAtTACCAATT),present in the upstream region of lldP,was identified as essential for the binding of LldR.D-lactate biosensors were developed by connecting the upregulation by D-lactate to a green fluorescent readout.About^6.0-fold induction by 100mM D-lactate was observed compared to Llactate.