Microbial experimental evolution as a novel research approach in the Vibrionaceae and squid-Vibrio symbiosis

Abstract

The Vibrionaceae are a genetically and metabolically diverse family living in aquatic habitats with a great propensity toward developing interactions with eukaryotic microbial and multicellular hosts (as either commensals, pathogens, and mutualists). The Vibrionaceae frequently possess a life history cycle where bacteria are attached to a host in one phase and then another where they are free from their host as either part of the bacterioplankton or adhered to solid substrates such as marine sediment, riverbeds, lakebeds, or floating particulate debris. These two stages in their life history exert quite distinct and separate selection pressures. When bound to solid substrates or to host cells, the Vibrionaceae can also exist as complex biofilms. The association between bioluminescent Vibrio spp. and sepiolid squids (Cephalopoda: Sepiolidae) is an experimentally tractable model to study bacteria and animal host interactions, since the symbionts and squid hosts can be maintained in the laboratory independently of one another. The bacteria can be grown in pure culture and the squid hosts raised gnotobiotically with sterile light organs. The partnership between free-living Vibrio symbionts and axenic squid hatchlings emerging from eggs must be renewed every generation of the cephalopod host. Thus, symbiotic bacteria and animal host can each be studied alone and together in union. Despite virtues provided by the Vibrionaceae and sepiolid squid-Vibrio symbiosis, these assets to evolutionary biology have yet to be fully utilized for microbial experimental evolution. Experimental evolution studies already completed are reviewed, along with exploratory topics for future study.

Adaptation to temperature stress by Vibrio fischeri facilitates this microbe's symbiosis with the Hawaiian bobtail squid ( Euprymna scolopes )

“…; Soto and Nishiguchi ). Although attached to animal skin, invertebrate chitin, or as part of the gut microflora, V. fischeri can also persist as a commensal associated with marine animals (Soto and Nishiguchi ). Thus, due to its widespread nature, V. fischeri experiences extensive temperature variation in the various aquatic environments it occupies.…”

“…). Although the Vibrionaceae can freely adopt a planktonic lifestyle, they also are highly proficient at forming biofilms, which permits microbial dispersal via rafting (Theil and Gutow ; Soto and Nishiguchi ). These characteristics greatly facilitate the Vibrionaceae's ability to disseminate throughout the world's oceans, a feature that will be immensely heightened with climate change (Martinez‐Urtaza et al.…”

“…V. fischeri is a cosmopolitan microbe with a ubiquitous distribution (Soto and Nishiguchi ). V. fischeri has been isolated from oceans, estuaries, brackish waters, and marine sediments throughout the world.…”

“…As biofilms, bacterial cells may either be attached to abiotic surfaces (suspended particulate matter) or adhered to the external surfaces of animals (Soto et al. ; Soto and Nishiguchi ). Although attached to animal skin, invertebrate chitin, or as part of the gut microflora, V. fischeri can also persist as a commensal associated with marine animals (Soto and Nishiguchi ).…”

“…Monocentrid fishes are found in the Indo‐West Pacific, Asia‐Pacific, and South Pacific (Soto et al. ; Soto and Nishiguchi ).…”