Polyunsaturated fatty acids-enriched lipid from reduced sugar alcohol mannitol by marine yeast Rhodosporidiobolus fluvialis Y2

Exogenous Regulators Enhance the Yield and Stress Resistance of Chlamydospores of the Biocontrol Agent Trichoderma harzianum T4

Trichoderma strains have been successfully used in plant disease control. However, the poor stress resistance of mycelia and conidia makes processing and storage difficult. Furthermore, they cannot produce chlamydospores in large quantities during fermentation, which limits the industrialization process of chlamydospore preparation. It is important to explore an efficient liquid fermentation strategy for ensuring chlamydospore production in Trichoderma harzianum. We found that the addition of mannitol, glycine betaine, and N-acetylglucosamine (N-A-G) during liquid fermentation effectively increases the yield of chlamydospores. Furthermore, we provided evidence that chlamydospores have stronger tolerance to high temperature, ultraviolet, and hypertonic stress after the addition of mannitol and trehalose. Lipids are an important component of microbial cells and impact the stress resistance of microorganisms. We studied the internal relationship between lipid metabolism and the stress resistance of chlamydospores by detecting changes in the lipid content and gene expression. Our results showed that mannitol and trehalose cause lipid accumulation in chlamydospores and increase the unsaturated fatty acid content. In conclusion, we verified that these exogenous regulators increase the production of chlamydospores and enhance their stress resistance by regulating lipid metabolism. In addition, we believe that lipid metabolism is an important part of the chlamydospore production process and impacts the stress resistance of chlamydospores. Our findings provide clues for studying the differentiation pathway of chlamydospores in filamentous fungi and a basis for the industrial production of chlamydospores.

Oleaginous yeasts- substrate preference and lipid productivity: a view on the performance of microbial lipid producers

Background

Oleaginous yeasts are promising microbial platforms for sustainable, bio-based production of biofuels and oleochemical building blocks. Bio-based residues provide sustainable and cost-effective carbon sources for fermentative yeast oil production without land-use change. Considering the regional abundancy of different waste streams, we chose complex biomass residue streams of marine origin; macroalgae hydrolysate, and terrestrial origin; wheat straw hydrolysate in the presence, and absence of corn steep liquor as a complex nitrogen source. We investigated the biomass and lipid yields of an array of well-described oleaginous yeasts; R. glutinis, T. asahii, R. mucilaginosa, R. toruloides, C. oleaginosus growing on these hydrolysates. Furthermore, their sugar utilization, fatty acid profile, and inhibitory effect of the hydrolysates on yeast growth were compared. For correlative reference, we initially performed comparative growth experiments for the strains on individual monomeric sugars separately. Each of these monomeric sugars was a dominant carbon source in the complex biomass hydrolysates evaluated in this study. In addition, we evaluated N-acetylglucosamine, the monomeric building block of chitin, as a low-cost nitrogen and carbon source in yeast fermentation.

Results

C. oleaginosus provided the highest biomass and lipid yields. In the wheat straw and brown algae hydrolysates, this yeast strain gained 7.5 g/L and 3.8 g/L lipids, respectively. Cultivation in algae hydrolysate resulted in a higher level of unsaturated fatty acids in the lipids accumulated by all yeast strains. R. toruloides and C. oleaginosus were able to effectively co-utilize mannitol, glucose, and xylose. Growth rates on wheat straw hydrolysate were enhanced in presence of corn steep liquor.

Conclusions

Among the yeast strains investigated in this study, C. oleaginosus proved to be the most versatile strain in terms of substrate utilization, productivity, and tolerance in the complex media. Various fatty acid profiles obtained on each substrate encourage the manipulation of culture conditions to achieve the desired fatty acid composition for each application. This could be accomplished by combining the element of carbon source with other formerly studied factors such as temperature and oxygen. Moreover, corn steep liquor showed promise for enhancement of growth in the oleaginous strains provided that carbon substrate is available.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-021-01710-3.