Effect of resource availability on evolution of virulence and competition in an environmentally transmitted pathogen

• Published in: FEMS microbiology ecology Vol. 94; no. 5; p. 1
• Main Authors: Pulkkinen, Katja, Pekkala, Nina, Ashrafi, Roghaieh, Hämäläinen, Dorrit M, Nkembeng, Aloysius N, Lipponen, Anssi, Hiltunen, Teppo, Valkonen, Janne K, Taskinen, Jouni
• Format: Journal Article
• Language: English
• Published: England Oxford University Press 01.05.2018
• Subjects: Animals; Aquaculture; Aquaculture industry; Biological Evolution; Competition (Biology); disease outbreaks; disease transmission; Environmental aspects; environmental factors; evolution; fish culture; Fish Diseases - microbiology; Fishes; Flavobacterium - genetics; Flavobacterium - metabolism; Flavobacterium - pathogenicity; Flavobacterium columnare; freshwater fish; Genotype; genotype mixtures; Gram-negative bacteria; Health aspects; hosts; nutrient content; pathogens; quantitative polymerase chain reaction; strain differences; Virulence; Virulence (Microbiology); virulent strains; Finland
• ISSN: 1574-6941; 0168-6496; 1574-6941
• DOI: 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.