Cultivation and diversity analysis of novel marine thraustochytrids

Thraustochytrids are a group of unicellular marine heterotrophic protists,and have long been known for their biotechnological potentials in producing squalene,polyunsaturated fatty acids(PUFAs)and other bioactive products.There are less than a hundred known strains from diverse marine habitats.Therefore,the discovery of new strains from natural environments is still one of the major limitations for fully exploring this interesting group of marine protists.At present,numerous attempts have been made to study thraustochytrids,mainly focusing on isolating new strains,analyzing the diversity in specific marine habitats,and increasing the yield of bioactive substances.There is a lack of a systematic study of the culturable diversity,and cultivation strategies.This paper reviews the distribution and diversity of culturable thraustochytrids from a range of marine environments,and describes in detail the most commonly used isolation methods and the control of culture parameters.Furthermore,the perspective approaches of isolation and cultivation for the discovery of new strains are discussed.Finally,the future directions of novel marine thraustochytrid research are proposed.The ultimate goal is to promote the awareness of biotechnological potentials of culturable thraustochytrid strains in industrial and biomedical applications.

Polyunsaturated fatty acid-producing marine thraustochytrids:A potential source for antimicrobials

Objective:To evaluate the antimicrobial activity of marine thraustochytrids extracted from different solvents.Methods:Crude extracts were derived from marine thraustochytrids,isolated from decaying mangrove leaf litter.The extracts were tested for antibacterial activity by using agar disc diffusion method against 10 clinical bacterial strains.The extracts were also analysed for presence of functional chemical groups by using Fourier transform infrared spectroscopy.Results:Thraustochytrid extracts exhibited potent antibacterial activity against both Gramnegative and-positive bacteria.The antibacterial activity was observed prominently in butanol extract,followed by petroleum ether,methanol and chloroform extracts.The antibacterial activity was maximum[(21.33±1.52)mm]against Staphylococcus aureus and minimum[(7.00±2.00)]mm against Klebsiella pneumonia and Salmonella typhi.Conclusions:Thraustochytrids isolated from decaying mangrove leaf litter are potential sources of antibacterial compounds against clinical pathogens,which are called for further investigation of thraustochytrids as natural antibiotics.

Identity and Safety of a Novel <i>Aurantiochytrium sp.</i>for Terrestrial Heterotrophic Docosahexaenoic Acid Production

The objective of the studies in this paper was to expand on the published toxicological assessment of Aurantiochytrium limacinum (AURA) with further strain characterization and to investigate the potential for the biomass or extracted oil to have antimicrobial properties or undesirable substances. AURA is being investigated as a novel source of the omega-3 long-chain polyunsaturated fatty acid docosahexaenoic acid (DHA) for enriching foods of animal origin by means of feed supplementation. In the first studies, we provided the 18S rRNA identification of the novel marine isolated thraustochytrid, established the nutritional composition of AURA biomass for application as a food or feed ingredient including proximate analysis and fatty acid profiling, and confirmed the DHA production potential of the strain. We determined through minimum inhibitory concentration (MIC) analysis that the unextracted AURA biomass was safe, showing no antimicrobial influence and no evidence of any deleterious effects of this product or its extracts at concentrations up to 1% w/w on the reference human intestinal bacteria tested. This would indicate that AURA should not stimulate selective pressure on the commensal microbiota and is therefore unlikely to aid development of antimicrobial resistance and the concomitant harm to humans and animals. Further analysis revealed that the AURA biomass produced through industrial heterotrophic fermentation was free from undesirables;toxic marine microalgal metabolites, heavy metals, pesticides, microbial contaminants, and mycotoxins. Including heterotrophically-grown AURA in food or feed, up to 1% w/w, is a safe and environmentally beneficial strategy for DHA supplementation.

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.