Comparative analysis of five Mucor species transcriptomes.

Mucor species belong to the Mucorales order within the Mucoromycota phylum, an early diverging fungal lineage. Although Mucor species are often ubiquitous some species have been reported to specifically occur in certain ecological niches. In this study, similarities and differences of a representative set of Mucor species with contrasted lifestyles were investigated at the transcriptome level. Five strains pertaining to five different species were studied, namely M. fuscus and M. lanceolatus, two species used in cheese production (during ripening), M. racemosus, a recurrent cheese spoiler sometimes described as an opportunistic pathogen, M. circinelloides, often described as an opportunistic pathogen and M. endophyticus, a plant endophyte. A core transcriptome was delimited and a phylogenetic analysis led to an altered phylogenetic placement of M. endophyticus compared to previously published topologies. Interestingly, the core transcriptome comprising 5566 orthogroups included genes potentially involved in secondary metabolism. As expected, given the wide taxonomic range investigated, the five transcriptomes also displayed specificities that can be, for some of them, linked to the different lifestyles such as differences in the composition of transcripts identified as virulence factors or carbohydrate transporters.

Effect of temperature, pH, and water activity on Mucor spp. growth on synthetic medium, cheese analog and cheese.

The Mucor genus includes a large number of ubiquitous fungal species. In the dairy environment, some of them play a technological role providing typical organoleptic qualities to some cheeses while others can cause spoilage. In this study, we compared the effect of relevant abiotic factors for cheese production on the growth of six strains representative of dairy technological and contaminant species as well as of a non cheese related strain (plant endophyte). Growth kinetics were determined for each strain in function of temperature, water activity and pH on synthetic Potato Dextrose Agar (PDA), and secondary models were fitted to calculate the corresponding specific cardinal values. Using these values and growth kinetics acquired at 15 °C on cheese agar medium (CA) along with three different cheese types, optimal growth rates (µopt) were estimated and consequently used to establish a predictive model. Contrarily to contaminant strains, technological strains showed higher µopt on cheese matrices than on PDA. Interestingly, lag times of the endophyte strain were strongly extended on cheese related matrices. This study offers a relevant predictive model of growth that may be used for better cheese production control but also raises the question of adaptation of some Mucor strains to the cheese.

Dataset of differentially accumulated proteins in Mucor strains representative of four species grown on synthetic potato dextrose agar medium and a cheese mimicking medium.

The data presented are associated with the "Proteomic analysis of the adaptative response of Mucor spp. to cheese environment" (Morin-Sardin et al., 2016) article [1]. Mucor metabolism is poorly documented in the literature and while morphology and growth behavior suggest potential adaptation to cheese for some strains, no adaptation markers to cheese environment have been identified for this genus. To establish the possible existence of metabolic functions related to cheese adaptation, we used a gel based 2-DE proteomic approach coupled to LC-MS/MS to analyze three strains from species known or proposed to have a positive or negative role in cheese production as well as a strain from a non-related cheese-species.

Proteomic analysis of the adaptative response of Mucor spp. to cheese environment.

In the cheese industry context, Mucor species exhibit an ambivalent behavior as some species are essential "technological" organisms of some cheeses while others can be spoiling agents. Previously, we observed that cheese "technological" species exhibited higher optimal growth rates on cheese related matrices than on synthetic media. This growth pattern combined with morphological differences raise the question of their adaptation to cheese. In this study, using a comparative proteomic approach, we described the metabolic pathways of three Mucor strains considered as "technological" or "contaminant" in the cheese environment (M. lanceolatus UBOCC-A-109153, M. racemosus UBOCC-A-109155, M. circinelloides CBS 277-49) as well as a non-cheese related strain (M. endophyticus CBS 385-95). Overall, 15.8 to 19.0% of the proteomes showed a fold change ≥1.6 in Potato Dextrose Agar (PDA) versus Cheese Agar (CA), a cheese mimicking-medium. The 289 differentially expressed proteins identified by LC MS-MS analysis were mostly assigned to energy and amino-acid metabolisms in PDA whereas a higher diversity of biological processes was observed for cheese related strains in CA. Surprisingly, the vast majority (72.9%) of the over-accumulated proteins were different according to the considered medium and strain. These results strongly suggest that the observed better adaptative response of "technological" strains to cheese environment is mediated by species-specific proteins. BIOLOGICAL SIGNIFICANCE: The Mucor genus consists of a multitude of poorly known species. In the food context, few species are known for their positive role in the production of various food products, including cheese, while others are spoiling agents. The present study focused on the analysis of morphological and proteome differences of various Mucor spp. representative strains known as either positively (hereafter referred as "technological") or negatively (hereafter referred as "contaminant") associated with cheese or non-related to cheese (endophyte) on two different media, a synthetic medium and a cheese-mimicking medium. The main goal was to assess if adaptative traits of "technological" strains to the cheese environment could be identified. This work was based on observations we did in a recently published physiological study (Morin-Sardin et al., 2016). One of the important innovative aspects lies in the use for the first time of an extensive 2-DE approach to compare proteome variations for 4 strains on two different media. Results obtained offered an insight in the metabolic mechanisms associated with growth on a given medium and showed that adaptation to cheese environment is probably supported by species-specific proteins. The obtained data represent an essential step point for more targeted studies at the genomic and transcriptomic levels.