Vibrio fischeri : a model for host-associated biofilm formation

Abstract

Multicellular communities of adherent bacteria known as biofilms are often detrimental in the context of a human host, making it important to study their formation and dispersal, especially in animal models. One such model is the symbiosis between the squid Euprymna scolopes and the bacterium Vibrio fischeri . Juvenile squid hatch aposymbiotically and selectively acquire their symbiont from natural seawater containing diverse environmental microbes. Successful pairing is facilitated by ciliary movements that direct bacteria to quiet zones on the surface of the squid’s symbiotic light organ where V. fischeri forms a small aggregate or biofilm. Subsequently, the bacteria disperse from that aggregate to enter the organ, ultimately reaching and colonizing deep crypt spaces. Although transient, aggregate formation is critical for optimal colonization and is tightly controlled. In vitro studies have identified a variety of polysaccharides and proteins that comprise the extracellular matrix. Some of the most well-characterized matrix factors include the symbiosis polysaccharide (SYP), cellulose polysaccharide, and LapV adhesin. In this review, we discuss these components, their regulation, and other less understood V. fischeri biofilm contributors. We also highlight what is currently known about dispersal from these aggregates and host cues that may promote it. Finally, we briefly describe discoveries gleaned from the study of other V. fischeri isolates. By unraveling the complexities involved in V. fischeri ’s control over matrix components, we may begin to understand how the host environment triggers transient biofilm formation and dispersal to promote this unique symbiotic relationship.

Lighting the way: how the Vibrio fischeri model microbe reveals the complexity of Earth’s “simplest” life forms

“…Transcriptional regulation of the syp locus and its downstream products have been intensively studied, and a complex regulatory scheme has been uncovered that includes multiple sensor and response regulatory proteins and environmental- and/or squid-relevant signals [for a recent review, see reference ( 148 )]. For example, calcium, which is present in seawater, and nitric oxide, which is found in the context of the light organ, positively and negatively regulate biofilm formation, respectively ( 97 , 149 , 150 ).…”

“…V. fischeri also contains the bacterial cellulose synthesis locus, bcs , and uses cellulose to form biofilms on in vitro surfaces such as glass and plastic ( 148 ). In E. coli and Salmonella , where cellulose production has been most heavily studied, the second messenger c-di-GMP promotes biofilm formation by binding to and activating cellulose synthase ( 156 , 157 ).…”