Know your enemy by Webmaster News 2019-09-11 11:47:24

Know your enemy

Heat resistance in conidia of Paecilomyces variotii

Paecilomyces variotii. A-F Conidiospores and conidia.
Source: ‘Fungal Biodiversity’ P.W.Crous et al.

It’s the first article Tom van den Brule writes as Westerdijk Institute PhD Student for the project 'Heterogeneity in spores of food spoilage fungi' and it is published in Environmental Microbiology. A nice start.
In his article he studies conidia, the asexual spores, of Paecilomyces variotii, known for spoiling foods like margarine, fruit juices, canned fruit and non-carbonized sodas. Van den Brule looks into the amount of temperature stress that spores of different strains can survive. In order to do that he studies conidia of an unprecedented 108 strains of Paecilomyces variotii at two temperatures: 58°C and 59°C. At first sight a bit low, these temperatures, but at this level the first big differences between different strains arise. And in a time in which the trends are toward milder processing methods it is interesting to know at what temperature, spores start to die and others still survive, and why this is the case. It’s always good to know the enemy, especially in the food processing industry.

Strain variation in heat resistance of dormant P. variotii conidia. The screening results of the strains used for the in-depth analysis.

Champion of heat resistance

In his study Tom chooses three different strains because of the heat-resisting qualities of their spores: a heat-sensitive strain, a heat-resistant strain and one in between. These three strains are studied in greater detail and characterized on morphology, heat resistance, spore size distribution, their content of protective sugars and growth under salt stress conditions.
Paecilomyces variotii DTO-217-A2 is the absolute champion of heat resistance in this cell type at 60°C. This coincides with some more remarkable differences; DTO-217-A2 produces less aerial structures when cultured and containes larger average conidia in size, having a higher trehalose (a kind of sugar) concentration. On the other hand, this strain is slightly more susceptible for salt stress.

Colony morphology of DTO 217-A2 (A, D), DTO 032-I3 (B, E) and DTO 212-C5 (C, F). The stereo microscopy pictures show a detailed top view of a three-day-old colony (A-C).

‘Fundamental research with a goal’

‘If we know the strongest spores, industry can use them to improve their models and challenge tests’.
Van den Brule’s main interest however is to truly understand the processes behind heat resistance and diversity, this research being the first step. ‘I want to know the genetic mechanisms behind heat resistance. It’s nice for industry if we find that out, it is fundamental research with a goal. That’s what I like about this subject.’

 Title of the article: ‘The most heat-resistant conidia observed to date are formed by distinct strains of Paecilomyces variotii’