To survive within complex environmental niches, including the human
host, bacteria have evolved intricate inter-species communities driven
by competition for limited nutrients, cooperation via complementary
metabolic proficiencies, and establishment of homeostatic relationships
with the host immune system. Such complex, interdependent relationships
have hampered attempts to culture many bacterial strains in research
settings, where standard readout of co-culture experiments are usually
limited to the relative abundance of each species. Here, we utilize a
microfluidic-based co-culture system to characterize dynamic
interactions between multiple oral bacterial isolates. Using time-lapse
imaging, we define species-specific effects on spatial community
relationships during co-culture of Streptococcus species and
Staphylococcus aureus with Actinomyces species. Co-culture of
Streptococcus cristatus or S. salivarius in nanoliter compartments with
Actinomyces graevenitzii revealed localized exclusion of Streptococcus
and Staphylococcus from media immediately surrounding A. graevenitzii
micro colonies. This community structure did not occur with S. mitis or
S. oralis strains, or in co-cultures containing other Actinomycetaceae
species such as S. odontolyticus or A. naeslundii. Moreover, fewer
neutrophils were attracted to compartments containing both A.
graevenitzii and Staphylococcus aureus than to equal number of either
species alone, suggesting a possible survival benefit from the
interaction.