No abstract

In this study, the M13 primer was used to distinguish Geotrichum candidum from the anamorphic and teleomorphic forms of other arthrospore-forming species (discriminatory power = 0.99). For intraspecific characterization, the GATA4 primer showed the highest level of discrimination for G. candidum among the 20 microsatellite primers tested. A molecular typing protocol (DNA concentration, hybridization temperature and type of PCR machine) was optimized through a series of intra- and interlaboratory trials. This protocol was validated using 75 strains of G. candidum, one strain of G. capitatum and one strain of G. fragrans, and exhibited a discrimination score of 0.87. This method could therefore be used in the agro-food industries to identify and to evaluate biodiversity and trace strains of G. candidum. The results show that the GATA4 primer might be used to differentiate strains according to their ecological niche.

Aims: Assessment of genetic diversity within the species Geotrichum candidum and development of tools to trace the strains that play an important role in the agro food industry. Methods and Results: RAM‐PCR and RAPD‐PCR techniques were assessed for their ability to discriminate 57 strains of various morphotypes, substrates and geographical origin. The techniques were complementary and, when combined, allowed us to discriminate isolates. Moreover, we established a link between a taxon and its occupation of an ecological niche, which should not be confused with the substrate of isolation. Conclusions: We observed a high degree of diversity, which could be linked to the variety of the ecological niches chosen and to the high degree of morphological polymorphism encountered within the species. Significance and Impact of the Study: Used in combination, RAM‐PCR and RAPD‐PCR permit traceability and monitoring systems for G. candidum strains during food processing.

The gene (aspA) encoding the extracellular aspartyl protease from Penicillium roqueforti was cloned and characterized. Northern hybridization analyses and beta-casein degradation assays revealed that aspA was strongly induced by casein in the medium and efficiently repressed by ammonia. External alkaline pH overrides casein induction, resulting in aspA repression. Cis-acting motifs known to mediate nitrogen and pH regulation of fungal gene expression are present in the aspA promoter and protein-DNA binding experiments showed that mycelial proteins interact with various regions of the promoter. Due to the efficient environmental controls on aspA expression, the promoter of aspA is an attractive candidate for the development of a controllable gene expression system in P. roqueforti.