Search for chemical substances regulating the biofilm formation has been carried out. The assay system has been developed by using the marine bacterium possessing the attaching properties (Rhodospirillum salexigens SCRC 113). This bioassay system in laboratory is suitable for screening the crude extracts from marine organisms and the synthetic compounds. First, the adhesion inhibitory of samples was determined by monitoring amounts of polysaccharide produced by the bacteria as evaluation of the biofilm formation. Substances regulating the biofilm formation have been isolated from marine organisms. For example, bisdeacetylsolenolide D, a biofilm formation inhibitor and butenolide derivative (Hateramine), a biofilm formation accelator have been obtained from marine sponges, respectively. Ethyl N-(2-phenethyl) carbamate (1) isolated from the marine bacterium SCRC3P79 (Cytophaga sp.), remarkably inhibited the biofilm formation. The synthetic compound p-nitro derivative (2), exhibited significant inhibition of the biofilm formation. Furthermore, (2) exhibited antibacterial activity. However this assay system was replaced to new method, because procedure described here did not afford enough reproducibility of the data. Secondly, growth inhibition with tested samples against the attaching bacteria was indicated by measurement of absorbance of the culture medium and the biofilm formation was estimated. Aeroplysinin-I isolated from marine sponge Pssamaplysilla purpurea, exhibited inhibition of the biofilm formation. New nitroalkanes, (3) and (4), have been obtained from an unidentified marine sponge. The synthetic compounds (5), (6), (7) and (8) exhibited significant inhibition of the biofilm formation. As expected, the compounds (5), (6), (7) and (8) exhibited remarkable inhibition of the biofilm formation in the field experiment.
