Cross-feeding and stress response are the basis of increased fruitiness and leavening capacity of a new consortium of the sourdough microorganisms Companilactobacillus crustorum and Wickerhamomyces anomalus

The use of mixed-strain starter cultures in sourdough production can result in distinct flavour profiles, leading to new sourdough-containing baked products. Recently, a newly discovered mixed-strain starter culture composed of the lactic acid bacterium (LAB) Companilactobacillus crustorum LMG 23699 T and the yeast Wickerhamomyces anomalus IMDO 010110 has been successfully used for sourdough productions. Knowledge about the interactions among the strains involved will allow for the further optimization of sourdough production. In the present study, a differential gene expression analysis was performed to reveal transcriptional responses of the strains as a result of cocultivation, including those related to their metabolism, cross-feeding interactions, and production of esters, the latter imparting fruity notes. The same approach was used to characterize the transcriptional response of the LAB strain to the presence of ester precursor molecules. The main changes for the LAB strain included the upregulation of genes related to the D-alanylation of lipoteichoic acids, the upregulation of nucleotide biosynthesis, and the downregulation of fatty acid biosynthesis, indicating a stress response and possible cross-feeding or scavenging interactions with the yeast. The yeast strain upregulated genes related to ammonium formation, respiration, gluconeogenesis, fatty acid biosynthesis, and ethyl acetate biosynthesis. Further, this analysis defined the estC gene of the Coml. crustorum strain as an ester biosynthesis gene involved in ethyl lactate production. In conclusion, the present study showed the added value of RNAseq-based transcriptomics in investigating interactions in a mixed-strain starter culture and the potential effects of using this starter culture for sourdough production.