The impact of inter- and intra-species spore density on germination of the food spoilage fungus Aspergillus niger
The impact of inter- and intra-species spore density on germination of the food spoilage fungus Aspergillus niger (https://doi.org/10.1016/j.ijfoodmicro.2023.110495)
A subset of approximately 1000 random spores of each Aspergillus species was selected from the monoculture datasets. The Euclidean distance in a two-dimensional space was calculated between each spore in the co-culture and the monoculture dataset based on "area" and "contrast". Each spore was assigned to the species with the shortest Euclidean distance and scored 100 to 0. To assess spore overlap between A. niger and other Aspergillus species in co-culture, we defined a range of spore scores < 50 for each species in co-culture. Then the overlap percentage was calculated by dividing the number of spores falling within this range by the total number of spores in the co-culture. Only spores of A. niger were selected for swelling and germ tube formation analysis with a score > 90 to ensure a lack of misclassification with the other species.
We compared the germination dynamic at low (5,000 spores) and high (40,000 spores) density of Aspergillus niger. In the next step, we assessed whether replacing the 35,000 extra A. niger spores with those of other aspergilli (A. clavatus, A. nidulans, A. terreus, and A. oryzae) has the same effect on the incidence and rate of swelling and germ tube formation of A. niger spores. Differences in circularity, surface area, and contrast of the different conidia were determined at t = 1. There was no detectable difference between the circularity of the spores of the different Aspergillus species (all ranging between 1.0 and 1.1). In contrast, surface area and contrast did differ between the spores of the aspergilli. Yet, they partly overlapped with a spore percentage of 0.5%, 3.8%, 33.9%, and 34.7% when A. niger was mixed with A. terreus, A. nidulans, A. oryzae, and A. clavatus, respectively. To overcome the overlap problem, especially in the case of co–cultures with A. clavatus and A. oryzae, the Euclidean distance was calculated for each spore in the co-culture with those of the monoculture datasets. We only selected the A. niger spores with scores > 90 for germination analysis in co-culture. The selected spores of A. niger depended on the contrast and surface area of the other Aspergillus species in co-culture, and therefore they were different for each co-culture.
Microbiology and Theoretical Biology and Bioinformatics, Department of Biology, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands. Email me ; Email me