AUTHOR=Schaudinn Christoph , Rydzewski Kerstin , Meister Beate , Grunow Roland , Heuner Klaus 

TITLE=Francisella tularensis subsp. holarctica wild-type is able to colonize natural aquatic ex vivo biofilms

JOURNAL=Frontiers in Microbiology

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2023.1113412

DOI=10.3389/fmicb.2023.1113412

ISSN=1664-302X

ABSTRACT=<p>Biofilms are a matrix-associated lifestyle of microbial communities, often enabling survivability and persistence of such bacteria. The objective of this study was to investigate the survival of the wild-type strain A-271 of <italic>Francisella tularensis</italic> subsp. <italic>holarctica</italic> (<italic>Fth</italic>) in a natural aquatic <italic>ex vivo</italic> biofilm. To that purpose, we allowed <italic>Fth</italic> A-271 to produce its own biofilm on solid surfaces but also to colonize naturally formed biofilms from aquatic habitats, which were infected with <italic>Francisella</italic> in the laboratory. The survival rates of the bacteria in biofilms were compared to those of planktonic bacteria as a function of the employed culture condition. It could be shown by light- and electron microscopy that <italic>Fth</italic> is able to form a complex, matrix-associated biofilm. The biofilm form of <italic>Francisella</italic> showed longer cultivability on agar plates in natural water when compared to planktonic (free-living) bacteria. Be it as a part of the existing <italic>ex vivo</italic> biofilm or free-floating above as planktonic bacteria, more than 80% of <italic>Francisella</italic> were not only able to survive under these conditions for 28 days, but even managed to establish microcolonies and areas with their own exclusive biofilm architecture within the <italic>ex vivo</italic> biofilm. Here, we can demonstrate for the first time that a <italic>Francisella tularensis</italic> wild-type strain (Type B) <italic>is able</italic> to successfully colonize an aquatic multi-species <italic>ex vivo</italic> biofilm. It is worthwhile to speculate that <italic>Fth</italic> might become more persistent in the environment when it forms its own biofilm or integrates in an existing one. Multi-species biofilms have been shown to be more resistant against stress compared to single-species biofilms. This may have an important impact on the long-term survival of <italic>Francisella</italic> in aquatic habitats and infection cycles in nature.</p>