Effect of resource availability on evolution of virulence and competition in an environmentally transmitted pathogen
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CitationPulkkinen, Katja. Pekkala, Nina. Ashrafi, Roghaieh. Hämäläinen, Dorrit M. Nkembeng, Aloysius N. Lipponen, Anssi. Hiltunen, Teppo. Valkonen, Janne K. Taskinen, Jouni. (2018). Effect of resource availability on evolution of virulence and competition in an environmentally transmitted pathogen. FEMS MICROBIOLOGY ECOLOGY, 94 (5) , fiy060. 10.1093/femsec/fiy060.
Understanding ecological and epidemiological factors driving pathogen evolution in contemporary time scales is a major challenge in modern health management. Pathogens that replicate outside the hosts are subject to selection imposed by ambient environmental conditions. Increased nutrient levels could increase pathogen virulence by pre-adapting for efficient use of resources upon contact to a nutrient rich host or by favouring transmission of fast-growing virulent strains. We measured changes in virulence and competition in Flavobacterium columnare, a bacterial pathogen of freshwater fish, under high and low nutrient levels. To test competition between strains in genotype mixtures, we developed a quantitative real-time PCR assay. We found that a virulent strain maintained its virulence and outcompeted less virulent strains independent of the nutrient level and resource renewal rate while a less virulent strain further lost virulence in chemostats under low nutrient level and over long-term serial culture under high nutrient level. Our results suggest that increased outside-host nutrient levels might maintain virulence in less virulent strains and increase their contribution to epidemics in aquaculture. The results highlight a need to further explore the role of resource in the outside-host environment in maintaining strain diversity and driving evolution of virulence among environmentally growing pathogens.