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Published on: April 19, 2017
Serum stimulates growth of and proteinase secretion by Aspergillus fumigatus
Anna H T Gifford1, Jodine R Klippenstein, Margo M Moore
1Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia, Canada.
Abstract:
Serum contains iron-binding proteins, which inhibit the growth of most pathogenic microorganisms, including fungi. The purpose of this research was to investigate the effect of serum on growth of the opportunistic fungal pathogen Aspergillus fumigatus. Supplementing minimal essential medium (MEM) with up to 80% human serum or up to 80% fetal bovine serum (FBS) stimulated growth and increased the amount of A. fumigatus dry biomass approximately fourfold. In addition, a 100-fold increase in proteinase secretion, as measured by azocasein hydrolysis, was observed when 10% human serum or 10% FBS was added to MEM. The fungal proteinases secreted in serum-containing media were shown to degrade (3)H-labeled basal lamina proteins. The factor in serum that stimulated proteinase secretion was larger than 10 kDa and was 85% inactivated when the serum was heated for 30 min at 66 degrees C. The proportions of proteinases of each catalytic class secreted by A. fumigatus in the presence of serum were different from the proportions secreted in media containing single proteins. Proteinase secretion did not result from increased protein concentration in the medium per se because bovine serum albumin (BSA) at a concentration equivalent to the concentration of serum produced only 20% of the proteinase activity per milligram (dry weight) that was produced by FBS. Addition of BSA plus 100 microM FeCl(3) to MEM resulted in the same level of growth as addition of serum, indicating that a combination of nutritional factors in serum may stimulate growth. However, the level of proteinase secretion was still only 30% of the level observed with FBS. These data indicate that serum does not inhibit the growth of A. fumigatus and that the nutrients in serum result in high levels of proteinase secretion, potentially increasing the invasiveness of this species.
Insights
Serum enhances the growth and proteinase secretion of Aspergillus fumigatus, an opportunistic fungal pathogen. This suggests serum may increase fungal invasiveness, contrary to expectations.
Area of Science:
- Medical Mycology
- Microbial Pathogenesis
- Biochemistry
Background:
- Serum contains iron-binding proteins that typically inhibit microbial growth.
- Aspergillus fumigatus is an opportunistic fungal pathogen with significant clinical implications.
- The effect of serum on A. fumigatus growth and virulence factor production requires clarification.
Purpose of the Study:
- To investigate the impact of human and fetal bovine serum on the growth of Aspergillus fumigatus.
- To determine the effect of serum on the secretion of fungal proteinases by A. fumigatus.
- To elucidate the role of serum components in modulating A. fumigatus virulence.
Main Methods:
- Supplementation of minimal essential medium (MEM) with varying concentrations of human serum or fetal bovine serum (FBS).
- Measurement of A. fumigatus dry biomass to assess growth.
- Quantification of proteinase secretion using azocasein hydrolysis assay.
- Degradation assays using (3)H-labeled basal lamina proteins.
- Heat inactivation and size exclusion chromatography to characterize serum factors.
- Comparison with bovine serum albumin (BSA) and iron supplementation.
Main Results:
- Serum (up to 80%) significantly stimulated A. fumigatus growth, increasing dry biomass approximately fourfold.
- Serum (10%) induced a 100-fold increase in proteinase secretion.
- Secreted fungal proteinases degraded basal lamina proteins.
- The proteinase-inducing factor in serum is heat-labile (>10 kDa).
- Serum-stimulated growth is attributed to nutritional factors, while high proteinase secretion is serum-specific.
- BSA plus iron mimicked growth but not proteinase secretion.
Conclusions:
- Serum does not inhibit, but rather promotes, the growth of Aspergillus fumigatus.
- Serum significantly enhances the secretion of virulence-associated proteinases by A. fumigatus.
- These findings suggest that serum components may increase the invasiveness of A. fumigatus, potentially impacting host-pathogen interactions.
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