Coaggregation amongst aquatic biofilm bacteria

Aquatic autochthonous flora isolated directly from a water biofilm model was tested for its capacity to take part in coaggregation. Two assay methods were compared and a visual semi-quantitative method was found to be the most consistent and easy to use. All isolates demonstrated coaggregation with at least one other isolate to some extent, giving rise to visible flocs. One isolate, identified as Micrococcus luteus, was found to coaggregate with all of the other isolates to different degrees, highlighting a possible role as a bridging organism in the biofilm consortium. The addition of certain simple sugars reversed coaggregation between particular isolates suggesting that lectin-like adhesins were operating between these members of the aquatic autochthonous flora by a mechanism similar to that reported to occur between dental plaque bacteria. The time taken for coaggregation to begin varied considerably between different pairs of isolates (1-16 h), suggesting that this may play a role in determining the successional order of isolates during biofilm development.