Multispecies Interactions and Biofilm Community Development

Abstract

Most studies of biofilms have focused on single species and on genes that control or are regulated by life on a surface. As more information is uncovered by studies of pure cultures, these data can be applied towards understanding the roles of specific genes in multispecies interactions. This chapter focuses mostly on multi-species interactions among oral bacteria in biofilms: a few single-species biofilms are featured to discuss responses to environmental signals, including signals generated by the occupants within the biofilm. Signals involved in cell-to-cell communication among biofilm cells include acyl homoserine lactones, oligopeptides, and autoinducer-2 (AI-2). Importantly, an optimal concentration of 4,5-dihydroxy-2,3-pentanedione (DPD) was critical for maximal biofilm development. One site where natural multispecies biofilms are unusually accessible is the tooth surface in the human oral cavity. We use a retrievable enamel chip model system that permits us to place three pieces of enamel side by side in a groove cut into an acrylic stent that is placed bilaterally on the buccal surface of the lower dentition. The majority of cells in both sequentially and coaggregateinoculated biofilms were S. gordonii, regardless of the inoculation order. Usually biofilms are formed only on solid or semi-solid substrata, such as steel pipes or agar, respectively. Many environmental cues and signals likely govern multispecies biofilms that form and disperse. One of the most important determinants is the distance between signal generator and signal receiver.