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Serial passage of the opportunistic pathogen Aspergillus flavus through an insect host yields decreased saprobic
Lisa R Scully1, Michael J Bidochka
1Department of Biological Sciences, Brock University, St. Catharines, ON L2S 3A1, Canada.
Abstract:
To study the early stages of the effect of host restriction on pathogen evolution, we subjected the opportunistic fungus Aspergillus flavus to a serial propagation scheme, whereby insect-virulent conidia were selected for repeated passage through an insect host (Galleria mellonella larvae) for 5 generations. Of the 35 lineages promulgated through this scheme, there were no consistent changes in virulence, which was measured by percent mortality of the larvae. There were, however, increases in the number of conidia on the insect cadavers (9 of 35 lineages) and decreases in the number of days between death and the appearance of fungal growth on the cadavers (4 of 35 lineages). Notably, most of the lineages (28 of 35 lineages) demonstrated a statistically significant decrease in the diameter of the colonies subcultured onto artificial media, indicating a decreased ability to grow saprobically. Conversely, most of the A. flavus cultures successively grown on agar media (9 of 10 lineages) exhibited no change in colony diameter after 15 rounds of subculturing. Propagation of the opportunist A. flavus through the insect host G. mellonella resulted in a diminished capacity to grow on an alternate substrate, while maintaining or increasing its ability to use the host as a nutrient supply.
Insights
Host restriction in Aspergillus flavus (A. flavus) led to reduced growth on artificial media. This opportunistic fungus adapted to insect hosts by enhancing nutrient acquisition, not virulence.
Area of Science:
- * Evolutionary biology
- * Mycology
- * Pathogen adaptation
Background:
- * Opportunistic fungal pathogens pose significant health and agricultural risks.
- * Understanding pathogen evolution under host-imposed selective pressures is crucial for predicting and controlling infections.
Purpose of the Study:
- * To investigate the early evolutionary responses of Aspergillus flavus to host restriction.
- * To determine how serial propagation through an insect host affects fungal virulence and saprobic growth.
Main Methods:
- * Serial propagation of Aspergillus flavus through Galleria mellonella larvae for 5 generations.
- * Assessment of fungal virulence via larval mortality.
- * Evaluation of saprobic growth on artificial media (colony diameter).
Main Results:
- * No consistent changes in virulence (larval mortality) were observed.
- * Increased conidia on insect cadavers and faster fungal growth post-mortem occurred in some lineages.
- * A significant decrease in saprobic growth (colony diameter) was noted in most A. flavus lineages adapted to the insect host.
Conclusions:
- * Adaptation to the insect host G. mellonella resulted in a trade-off, diminishing the fungus's ability to grow on artificial substrates.
- * Aspergillus flavus evolved enhanced nutrient utilization from the host rather than increased virulence.
- * Host-restriction can drive rapid evolutionary changes in fungal pathogens, impacting their ecological niche and potential for infection.
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