Microbial species are inherently variable, which is reflected in intraspecies genotypic and phenotypic differences. Strain-to-strain variation gives rise to variability in stress resistance and... Show moreMicrobial species are inherently variable, which is reflected in intraspecies genotypic and phenotypic differences. Strain-to-strain variation gives rise to variability in stress resistance and plays a crucial role in food safety and food quality. Here, strain variability in heat resistance of asexual spores (conidia) of the fungal species Aspergillus niger, Penicillium roqueforti and Paecilomyces variotii was quantified and compared to bacterial variability found in the literature. After heat treatment, a 5.4- to 8.6-fold difference in inactivation rate was found between individual strains within each species, while the strain variability of the three fungal species was not statistically different. We evaluated whether the degree of intraspecies variability is uniform, not only within the fungal kingdom, but also amongst different bacterial species. Comparison with three spore-forming bacteria and two non-spore-forming bacteria revealed that the variability of the different species was indeed in the same order of magnitude, which hints to a microbial signature of variation that exceeds kingdom boundaries. Show less
Seekles, S.J.; Teunisse, P. P. P.; Punt M.; Brule, T. van den; Dijksterhuis, J.; Houbraken, J.; ... ; Ram, A.F.J. 2021
BackgroundThe filamentous fungi Paecilomyces variotii and Penicillium roqueforti are prevalent food spoilers and are of interest as potential future cell factories. A functional CRISPR/Cas9 genome... Show moreBackgroundThe filamentous fungi Paecilomyces variotii and Penicillium roqueforti are prevalent food spoilers and are of interest as potential future cell factories. A functional CRISPR/Cas9 genome editing system would be beneficial for biotechnological advances as well as future (genetic) research in P. variotii and P. roqueforti.ResultsHere we describe the successful implementation of an efficient AMA1-based CRISPR/Cas9 genome editing system developed for Aspergillus niger in P. variotii and P. roqueforti in order to create melanin deficient strains. Additionally, kusA− mutant strains with a disrupted non-homologous end-joining repair mechanism were created to further optimize and facilitate efficient genome editing in these species. The effect of melanin on the resistance of conidia against the food preservation stressors heat and UV-C radiation was assessed by comparing wild-type and melanin deficient mutant conidia.ConclusionsOur findings show the successful use of CRISPR/Cas9 genome editing and its high efficiency in P. variotii and P. roqueforti in both wild-type strains as well as kusA− mutant background strains. Additionally, we observed that melanin deficient conidia of three food spoiling fungi were not altered in their heat resistance. However, melanin deficient conidia had increased sensitivity towards UV-C radiation. Show less
