The structure of biofilms in drinking water systems is influenced by the interplay between
biological and physical processes. Bacterial aggregates in bulk fluid are important in seeding biofilm
formation on surfaces. In simple pure and co-cultures, certain bacteria, including Methylobacterium,
are implicated in the formation of aggregates. However, it is unclear whether they help to form
aggregates in complex mixed bacterial communities. Furthermore, different flow regimes could affect
the formation and destination of aggregates. In this study, real drinking water mixed microbial
communities were inoculated with the Methylobacterium strain DSM 18358. The propensity of
Methylobacterium to promote aggregation was monitored under both stagnant and flow conditions.
Under stagnant conditions, Methylobacterium enhanced bacterial aggregation even when it was
inoculated in drinking water at 1% relative abundance. Laminar and turbulent flows were developed
in a rotating annular reactor. Methylobacterium was found to promote a higher degree of aggregation
in turbulent than laminar flow. Finally, fluorescence in situ hybridisation images revealed that
Methylobacterium aggregates had distinct spatial structures under the different flow conditions.
Overall, Methylobacterium was found to be a key strain in the formation of aggregates in bulk water
and subsequently in the formation of biofilms on surfaces