Enhanced co-production of extracellular biopolymers and intracellular lipids by Rhodotorula using lignocellulose hydrolysate and fish oil by-product urea

Background

A key objective in microbial biorefinery technologies is to identify resilient microorganisms capable of simultaneously synthesizing diverse bioactive metabolites. Among these, Rhodotorula yeasts emerge as promising candidates for converting various waste streams and by-products into high-value chemicals. Their industrial potential stems from their ability to accumulate significant amounts of lipids and carotenoids while also secreting extracellular polymers such as exopolysaccharides, polyol esters of fatty acids, glycolipids, and enzymes—many of which remain to be fully characterized.

Results

Among the five Rhodotorula strains tested, three exhibited substantial exopolysaccharide production. Notably, Rhodotorula graminis CCY 20-2-47 strain was identified, for the first time, to produce two distinct extracellular biopolymers—exopolysaccharides or polyol esters of fatty acids—depending on the growth conditions. It was observed enhanced production of exopolysaccharides up to 7.2 g L⁻¹ and 14.7 g L⁻¹ lipid-rich biomass by Rhodotorula graminis CCY 20-2-47 using lignocellulose hydrolysate and urea by-product. This study, for the first time, reports triggering effect of Mn²⁺ on exopolysaccharide production in Rhodotorula. Glucose-based medium resulted in co-production of polyol esters of fatty acids (3.9 g L⁻¹) and lipid-rich biomass (15 g L⁻¹) for Rhodotorula graminis CCY 20-2-47. Batch bioreactor fermentation for Rhodotorula graminis CCY 20-2-47 resulted in production of 13.1 g L⁻¹ of exopolysaccharides and 50% w/w intracellular lipids when using lignocellulose hydrolysate and urea by-product. In contrast, 7.4 g L⁻¹ of polyol esters of fatty acids and 35% w/w intracellular lipids were produced by the same strain on medium with pure glucose.

Conclusions

In conclusion, Rhodotorula yeasts demonstrate significant potential for microbial biorefineries due to their ability to efficiently convert diverse waste substrates into valuable biomaterials, including lipids and extracellular biopolymers. This study provides new insights into a potential metabolic switch in extracellular polymer biosynthesis, driven by Mn²⁺ availability in the culture medium.

Graphical abstract