Complexity of cell–cell interactions between Pseudomonas sp. AS1 and Acinetobacter oleivorans DR1: metabolic commensalism, biofilm formation and quorum quenching

Acinetobacter oleivorans DR1 lacks an upper pathway for naphthalene degradation and cannot grow using naphthalene as sole carbon source; however, it is capable of growing under naphthalene-amended conditions in the presence of naphthalene-degrading Pseudomonas sp. AS1. 1H-NMR spectroscopy, high-performance liquid chromatography and gene expression analyses showed that salicylate is a major secreted metabolic intermediate during naphthalene degradation by strain AS1 and that, in turn, it supports the growth of strain DR1. Interspecies biofilm formation, monitored using confocal laser scanning microscopy and microtiter assays, demonstrated that biofilm formation by strain AS1 increased dramatically in the presence of strain DR1 because of the exopolysaccharides generated by the latter. Furthermore, the metabolic commensal interaction of the two strains altered the initial attachment behavior of strain DR1 during biofilm formation. When this strain was cultivated alone under naphthalene-amended conditions, the cells immediately attached to the surface, probably due to the absence of usable substrates, whereas similar behavior was not observed in the mixed culture. This interspecies cell–cell interaction became more complex due to quenching of the quorum-sensing signal of strain DR1 by strain AS1. These complex metabolic and physiological interactions observed in mixed cultures suggest that interspecies interaction is more complicated than previously surmised.