Free-living bacteria (planktonic cells) can bind to the surface and start the formation of a matrix-enclosed microbial community, creating its own microenvironment, which varies depending on the host or other natural niches. A key step is the initial attachment of microbial cells on a surface. Extensive efforts have been devoted to understanding the biofilm initiation and further development ( 5, 6). With few exceptions, biofilms harbor polymicrobial communities displaying complex spatial organization and interspecies interactions. These results suggest an alternative biofilm development process whereby aggregates containing different species or associated with human cells collectively adhere to the surface as “growth nuclei” to build the biofilm and shape polymicrobial communities at various spatial and taxonomic scales.īiofilms are highly organized microbial communities residing on surfaces ( 1, – 4). In contrast, most single cells remain static or are incorporated by actively growing aggregates. When individually tracked during colonization and biofilm initiation, aggregates rapidly proliferate and expand tridimensionally, modulating population growth, spatial organization, and community scaffolding. Phylogenetic analysis reveals a mixture of complex consortia of aerobes and anaerobes in which bacteria traditionally considered early and late colonizers are found mixed together. Using multiscale imaging, cell sorting, and computational approaches combined with sequencing analysis, a diverse mixture of aggregates varying in size, structure, and microbial composition, including bacteria associated with host epithelial cells, can be found in saliva in addition to a few single-cell forms. Here, we conduct a comprehensive analysis of the native structure and composition of aggregated microbial assemblages in human saliva and investigate their spatiotemporal attachment and biofilm community development. However, microorganisms are often found as aggregates in the environment and in biological fluids. Biofilm community development has been established as a sequential process starting from the attachment of single cells on a surface.
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