Biofilm Formation Protects Escherichia coli against Killing by Caenorhabditis elegans and Myxococcus xanthus

Enteric bacteria, such asEscherichia coli , are exposed to a variety of stresses in the nonhost environment. The development of biofilms providesE. coli with resistance to environmental insults, such as desiccation and bleach. We found that biofilm formation, specifically production of the matrix components curli and cellulose, protectedE. coli against killing by the soil-dwelling nematodeCaenorhabditis elegans and the predatory bacteriumMyxococcus xanthus . Additionally, matrix-encased bacteria at the air-biofilm interface exhibited ∼40-fold-increased survival afterC. elegans andM. xanthus killing compared to the non-matrix-encased cells that populate the interior of the biofilm. To determine if nonhostEnterobacteriaceae reservoirs supported biofilm formation, we grewE. coli on media composed of pig dung or commonly contaminated foods, such as beef, chicken, and spinach. Each of these medium types provided a nutritional environment that supported matrix production and biofilm formation. Altogether, we showed that common, nonhost reservoirs ofE. coli supported the formation of biofilms that subsequently protectedE. coli against predation.