Evidence for Broad-Spectrum Biofilm Inhibition by the Bacterium Bacillus sp. Strain SW9

Abstract

We isolated a Bacillus sp. strain that could display broad-spectrum biofilm inhibition. The broad biofilm prevention could be achieved mainly by direct contact between inhibitor and target cells or was accompanied by an interaction with secreted inhibitory compounds. The repression of cell surface fimbria-like appendages of a biofilm producer was also observed; this was considered to contribute to the reduction in mixed biofilms. Bacterial biofilm can cause enhanced risks of health threats and a multitude of industrial problems (1). The traditional strategy for biofilm prevention is antimicrobial agent application. However, the performance of a biocidal approach is somewhat limited by biofilm hyperresistance phenotypes (1). As a result, the development of nonantimicrobial antibiofilm approaches, which focus on the direct limitation of bacterial surface adhesion and biofilm formation, is increasing (2). Recent studies have suggested that many microbes secrete nonantibiotic compounds within bacterial communities, including signaling antagonists (3, 4), active biosurfactants (5, 6), and enzymes (7-9), which may regulate biofilm architecture or modulate bacterial interaction. In mixed bacterial communities, bacteria communicate with one another in various ways. Besides signaling molecule secretion, cellular communication can also occur through contact during a negative competitive interaction. This phenomenon has been observed in Escherichia coli cells, which touch other bacteria and inhibit bacterial growth, and has been termed contact-dependent growth inhibition (10).In this study, we demonstrated that a bacterium, Bacillus sp. strain SW9, exhibited broad-spectrum biofilm inhibition characteristics in mixed culture biofilms. Interestingly, the biofilm inhibition task was achieved mainly via direct cell-to-cell contact without affecting bacterial growth and was accompanied by interaction with secreted inhibitory molecules. The evidence for this inhibition was subsequently investigated.Bacillus sp. SW9 displays broad-spectrum antibiofilm activity toward biofilm-forming bacteria. More than 70 bacterial strains were isolated from different water treatment environments: source water, tap water, biofilms attached to the granular activated carbon in a full-scale drinking-water biofilter (Pinghu, China), drinking-water biofilms attached to the pipeline in a drinking-water distribution system (Ningbo, China), and granule sludge in a simulated reactor treating artificial wastewater. Thirteen strains, including the inhibitory bacterial strain (Bacillus sp. SW9) that cannot form biofilm and 12 bacterial strains with strong biofilm-forming ability, were used in this study (Table 1). The monospecies and dual-species biofilms of these biofilm formers and their mixed counterparts with Bacillus sp. SW9 were assayed by the use of 96-well polyvinylchloride (PVC) microtiter plates and R2A medium at 28°C as described previously (11). After 24 h of incubation, the biofilms were stained with crystal violet, the dye was dissolved with et...

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