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, C22:6??3), 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

Culturable Diversity and Lipid Production Profile of Labyrinthulomycete Protists Isolated from Coastal Mangrove Habitats of China

Labyrinthulomycete protists have gained significant attention in the recent past for their biotechnological importance. Yet, their lipid profiles are poorly described because only a few large-scale isolation attempts have been made so far. Here, we isolated more than 200 strains from mangrove habitats of China and characterized the molecular phylogeny and lipid accumulation potential of 71 strains. These strains were the closest relatives of six genera namely Aurantiochytrium, Botryochytrium, Parietichytrium, Schizochytrium, Thraustochytrium, and Labyrinthula. Docosahexaenoic acid (DHA) production of the top 15 strains ranged from 0.23 g/L to 1.14 g/L. Two labyrinthulid strains, GXBH-107 and GXBH-215, exhibited unprecedented high DHA production potential with content >10% of biomass. Among all strains, ZJWZ-7, identified as an Aurantiochytrium strain, exhibited the highest DHA production. Further optimization of culture conditions for strain ZJWZ-7 showed improved lipid production (1.66 g/L DHA and 1.68 g/L saturated fatty acids (SFAs)) with glycerol-malic-acid, peptone-yeast-extract, initial pH 7, 28 °C, and rotation rate 150 rpm. Besides, nitrogen source, initial pH, temperature, and rotation rate had significant effects on the cell biomass, DHA, and SFAs production. This study provides the identification and characterization of nearly six dozen thraustochytrids and labyrinthulids with high potential for lipid accumulation

Responses of soil microbial communities to concentration gradients of antibiotic residues in typical greenhouse vegetable soils

To explore the responses of soil microbial communities to concentration gradients of antibiotic residues in soil, 32 soil samples were collected from a typical greenhouse vegetable production base in Northern China in 2019. The total concentrations of 26 antibiotic residues in these soil samples was 83.24–4237.93 μg·kg−1, of which metabolites of tetracyclines were 23.34–1798.80 μg·kg−1. The total concentrations in 32 samples were clustered into three levels (L: 300 μg·kg−1) to elucidate the impacts of antibiotic residues on the diversity, structure, composition, function and antibiotic resistome of soil microbial community. Results showed that higher concentration of antibiotic residues in soil was prone to decrease the diversity and shift the structure and composition of soil microbial community. Antibiotic resistome occurred in soils with antibiotic residues exceeding 300 μg·kg−1. Interactions among soil bacteria followed the order of H > L > M, consistent with the relative abundances of mobile genetic elements. Bacteroidetes and Firmicutes were the top attributors impacting the profile of antibiotics in soil. According to weighted comprehensive pollution index of risk quotient, in 28.1 % of soil samples the residual antibiotics presented high ecological risk, whereas in the rest of soil samples the ecological risk is medium. The results will enrich the database and provide references for antibiotic contamination control in soils of the region and alike

Establishment of a three-step method to evaluate effects of chemicals on development of zebrafish embryo/larvae

Core endpoints in zebrafish embryos are crucial indicators in screening harmful effects of chemicals. In this study, we established a three-step process to more quantitatively and less-subjective determine effects of chemicals on phenotypes of developing zebrafish embryos. Embryos were exposed to each of two concentrations of the representative chemicals cadmium chloride (CdCl2), tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) or 1H, 1H, 2H, 2H-nonafluoro-1-hexanol (4:2 FTOH) from 0.75 h post-fertilization (hpf) to 96 hpf. After exposure, larvae were imaged by use of a three-step method to describe morphology. Seven points were selected, which resulted in acquisition of 21 lines and 105 angles from images of larvae. Exposure to TDCIPP (0.1 or 0.2 mg/L), CdCl2 (1 or 4 mg/L) or 4:2 FTOH (0.3 or 1 mg/L) significantly changed lengths of some lines and magnitudes of some angles, that resulted in differential scoring of points. Points were then prioritized and directions, distances and trajectories of movement were further described and standard reference values were developed. Movement of the point describing the mouth during embryonic development was found to be a sensitive parameter for assessment of adverse effects of chemicals. The present study provides a new strategy to characterize phenotypes of development of zebrafish embryo/larva following exposure to environmental toxins. (C) 2017 Elsevier Ltd. All rights reserved