REVIEW: Extinction of microbes: evidence and potential consequences

Abstract

Microbes, i.e. viruses, prokaryotes, protists and fungi are main players in biogeochemical cycles in aquatic and soil systems. As predators, pathogens, commensals and symbionts they are associated with multicellular life forms. Microbes show a dazzling array of biodiversity and it has been argued that due to their small size and huge numbers, microbes are distributed worldwide (‘everything is everywhere’). However, we summarize evidence that even free-living microbes have biogeographies and thus might be subject to at least local extinctions. Furthermore, some microbes do seem to be restricted to very particular environments and are endangered in as much as these environments are threatened. Finally, microbes intimately associated with other organisms share (partially) the biogeographies of their hosts. As far as they are species-specific, they could potentially become extinct along with their hosts. Overall, extinction rates typically reported are underestimates, since they do not take into account associated microorganisms which likely become extinct with the host organism, plant or animal. As multicellular species can have specific viral, prokaryotic, protistan and fungal species associated with them, extinction rates could be several times higher than assumed previously.