Bacteria Wars! Antimicrobial Activity of Bacteria in Marine Biofilms

A review of: Wilson, G. S., Raftos, D. A, and Nair, S.V. (2011) Antimicrobial activity of surface attached marine bacteria in biofilms. Microbiological Research 116:437-448

Biofilms exist as complex, interactive communities in which both mutualism and competition exist. Many surface attached marine bacteria in biofilms are likely to seek a competitive advantage over similar bacterial ‘species’ by producing molecules that will inhibit the attachment, growth and/or survival of these competitors. These inhibitory molecules can come with antifouling (inhibiting colonisation) or anti-microbial (inhibiting replication or lysis) properties.

To investigate whether the antimicrobial activity produced in biofilm cultures is targeted toward competing bacteria species, 105 marine isolates were tested for antimicrobial activity, grown as monospecies biofilms. The biofilm culture supernatants were collected about 160h after seeding and the antimicrobial activity was measured using the well diffusion assay.

The study found that 14 of the 105 isolated tested had significant microbial activity in their biofilm culture and that 12 of those 14 had a significantly higher antimicrobial activity in biofilms compared to shaken liquid cultures. This suggests that the surface attached marine bacteria can enhance their antimicrobial activity in biofilms, which previous studies had suggested.

Another experiment, involving the cultivation of biofilms in a media containing metabolites from an ‘inducer’ bacterium resulted in the production of antimicrobial molecules targeted toward that ‘inducer’. This suggests that the induction of antimicrobial activity in biofilms appears to be induced from soluble molecules produced from the competing bacteria and the biofilm itself.

Some of the antimicrobial activity produced in the biofilms may be due to quorum sensing inhibitors that inhibit communication between bacteria, accounting for the higher antimicrobial activity in biofilms as opposed to liquid cultures, due to the much higher cell densities present in biofilms. A proportion of the antimicrobial activity produced in biofilms may also be due to secondary metabolites (organic chemical compounds, not involved in primary metabolism, but that often increase the fitness of the host) which have been shown to possess novel mechanisms to inhibit biofilm growth.

Other research had shown that surface attached marine bacteria induce antimicrobial activity in response to surrounding bacteria, but this study extends this by showing that the antimicrobial activity induced by bacteria in biofilms can be targeted and, is effective against similar competing bacteria surrounding the biofilm and, perhaps, vice versa. This in itself, as the authors indicate, suggests that antimicrobial activities can be tailored to different growth conditions.