Lactose-assimilating yeasts with high fatty acid accumulation uncovered by untargeted bioprospecting.

Bioprospecting can uncover new yeast strains and species with interesting ecological characteristics and valuable biotechnological traits, such as the capacity to convert different carbon sources from industrial side and waste streams into bioproducts. In this study, we conducted untargeted yeast bioprospecting in tropical West Africa, collecting 1,996 isolates and determining their growth in 70 different environments. While the collection contains numerous isolates with the potential to assimilate several cost-effective and sustainable carbon and nitrogen sources, we focused on characterizing the 203 strains capable of growing on lactose, the main carbon source in the abundant side stream cheese whey from dairy industries. Through internal transcribed spacer sequencing of the lactose-assimilating strains, we identified 30 different yeast species from both the Ascomycota and Basidiomycota phyla, of which several have not previously been shown to grow on lactose, and some are candidates for new species. Observed differences in growth and ratios of intra- and extracellular lactase activities suggest that the yeasts use a range of different strategies to metabolize lactose. Notably, several basidiomycetous yeasts, including Apiotrichum mycotoxinivorans, Papiliotrema laurentii, and Moesziomyces antarcticus, accumulated lipids up to 40% of their cell dry weight, proving that they can convert lactose into a bioproduct of significant biotechnology interest.

Importance: This study paves the way to a better understanding of the natural yeast biodiversity in the largely under-sampled biodiversity hotspot area of tropical West Africa. Our discovery of several yeasts capable of efficiently converting lactose into lipids underscores the value of bioprospecting to identify yeast strains with significant biotechnological potential, which can aid the transition to a circular bioeconomy. Furthermore, the extensive strain collection gathered will facilitate future screening and the development of new cell factories.