# Native oleaginous yeasts Rhodotorula mucilaginosa and Solicoccozyma gelidoterrea: a sustainable biotechnological alternative for lipid production with potential application in diets for farmed fish

## TL;DR

This study explores two native yeast strains from Chile that can produce lipids efficiently, offering a sustainable alternative for fish feed in aquaculture.

## Contribution

The study provides the first evidence of lipid accumulation in Solicoccozyma gelidoterrea and reveals contrasting lipid metabolic strategies in native oleaginous yeasts.

## Key findings

- Rhodotorula mucilaginosa achieved 30% lipid content under optimal conditions (25°C and C/N 20).
- Solicoccozyma gelidoterrea accumulated 26.6% lipid at 7°C and C/N 20, showing cold adaptation.
- Both yeasts displayed distinct fatty acid profiles, with R. mucilaginosa enriched in unsaturated fatty acids.

## Abstract

The rapid global expansion of aquaculture has intensified the demand for sustainable and alternative lipid sources for fish feed formulations, driving interest in microbial platforms with specialized metabolic capabilities. Among these, oleaginous yeasts have emerged as promising candidates due to their ability to accumulate substantial intracellular lipid reserves and to modulate fatty acid composition in response to environmental and nutritional cues.

In this study, the lipid production potential and physiological responses of two native yeast strains isolated from volcanic soils of southern Chile were investigated. The strains were identified by ITS sequencing as Solicoccozyma gelidoterrea (7C) and Rhodotorula mucilaginosa (Rho 6S). Growth kinetics, substrate utilization, and lipid accumulation were systematically evaluated under different carbon sources, carbon-to-nitrogen (C/N) ratios, and temperature regimes (7–25 °C). Response surface methodology was applied to determine the combined effects of nutritional and thermal factors on biomass production and lipid yield, while fatty acid composition was analyzed to elucidate lipid remodeling strategies.

R. mucilaginosa exhibited pronounced metabolic versatility, characterized by higher maximum specific growth rates on alternative carbon sources such as xylose, sucrose, and raffinose. Under optimal conditions (25 °C and C/N 20), this strain achieved a lipid content of 30% and a biomass concentration of 2.54 g/L. In contrast, S. gelidoterrea displayed a distinct physiological profile associated with cold adaptation, reaching optimal lipid accumulation at 7 °C and C/N 20, with 26.6% lipid content and 2.11 g/L biomass. Increasing the C/N ratio to 90 significantly constrained lipid accumulation in both strains, highlighting the central role of nitrogen availability in regulating yeast lipid metabolism. Fatty acid profiling revealed clear species-specific lipid remodeling patterns: R. mucilaginosa produced a nutritionally favorable lipid profile enriched in mono and polyunsaturated fatty acids, reflected by high MUFA/SAFA and PUFA/SAFA ratios. In contrast, S. gelidoterrea exhibited a distinctive lipid profile dominated by monounsaturated fatty acids, particularly oleic acid, under nitrogen limited and low temperature conditions, and demonstrated the capacity to synthesize long chain polyunsaturated fatty acids under stress conditions, suggesting the activation of adaptive and stress responsive lipid metabolic pathways.

This study provides the first evidence of lipid accumulation and fatty acid composition in S. gelidoterrea and puts into evidence contrasting lipid metabolic strategies among native oleaginous yeasts. Collectively, these findings contribute to a deeper understanding of fungal lipid physiology and environmental adaptation and support the potential of native yeast strains as sustainable lipid sources for functional foods and aquaculture nutrition.