Horizontal Gene Transfer in Planktonic and Biofilm Modes - Antibiofilm Agents: From Diagnosis to Treatment and Prevention - page 77

Vibrio cholerae , the causative agent of cholera and a natural inhabitant of
aquatic environments, regulates various behaviors by a quorum-sensing system
conserved among many members of the genus Vibrio . The quorum-sensing system
is mediated by two extracellular autoinducers, CAI-1, which is secreted only by
vibrios, and AI-2, which is produced by many bacteria (Antonova and Hammer
2011 ). In marine biofilms on chitinous surfaces, quorum-sensing-proficient
V. cholerae cells become naturally competent to take up eDNA. It could be
hypothesized that V. cholerae can switch to the competent state in a chitinous
environmental biofilm by responding to autoinducers derived from members of the
multispecies bacterial consortium (Antonova and Hammer 2011 ). Antonova and
Hammer ( 2011 ) also showed that comEA transcription and the horizontal uptake of
DNA by V. cholerae are induced in response to purified CAI-1 and AI-2, and also
by autoinducers originating from other vibrios cocultured with V. cholerae within a
mixed-species biofilm.
3.4 Transduction in Biofilms
Roberts and Mullany ( 2010 ) summarized recent data on transduction in the human
oral cavity. One of the main barriers to the activity of phage in oral biofilms is the
access to the cells within the EPS secreted by the biofilm residents themselves
(Sutherland 2001 ). Little is known about the effect of phage and the extent to which
transduction contributes to genetic exchange within oral biofilms. There are some
studies that indicate transduction may be occurring within the oral cavity. Although
these works demonstrated the isolation of distinct phages from human saliva
(Bachrach et al. 2003 ; Hitch et al. 2004 ), DNA transduction mediated by these
phages to bacteria resident in oral biofilms could not be demonstrated so far.
Evidence for the involvement of phage in the HGT of DNA among residents of
oral biofilms only comes from studies carried out in vitro: for instance, tetracycline
resistance encoded on Tn 916 and chloramphenicol resistance present on plasmid
pKT210 have been transferred between Actinobacillus actinomycetemcomitans by
the generalized transducing phageAaØ23 (Willi et al. 1997 ). Additional evidence
that this phage may be transducing DNA between bacteria in the oral cavity was
obtained by isolation of phage particles from subgingival plaque from periodontitis
patients (Sandmeier et al. 1995 ; Willi et al. 1997 ).
Dissemination of Shiga toxin (Stx)-encoding phages is the most likely mecha-
nism for the spread of Stx-encoding genes and the emergence of new Stx-producing
E. coli (STEC) (Solheim et al. 2013 ). Solheim and coworkers observed transfer of
Stx-encoding phages to potentially pathogenic E. coli in biofilm at both 20 C and
37 C, with the infection rates being higher at 37 C than at 20 C. The study of
Solheim and coworkers is the first to show HGT in a laboratory grown biofilm
mediated by a temperate phage.