Competition amongGardnerellasubgroups from the human vaginal microbiome

Abstract

11Gardnerella spp. are hallmarks of bacterial vaginosis, a clinically significant dysbiosis of the 12 vaginal microbiome. Gardnerella has four subgroups (A, B, C and D) based on cpn60 sequences. 13 Multiple subgroups are often detected in individual women, and interactions between these 14 subgroups are expected to influence their population dynamics and associated signs and 15 symptoms of bacterial vaginosis. In the present study, contact-independent and contact-16 dependent interactions between the four Gardnerella subgroups were investigated in vitro. The 17 cell free supernatants of mono-and co-cultures had no effect on growth rates of the Gardnerella 18 subgroups suggesting that there are no contact-independent interactions (and no contest 19 competition). For contact-dependent interactions, mixed communities of 2, 3 or 4 subgroups 20 were created and the initial (0 h) and final population sizes (48 h) were quantified using 21 subgroup-specific PCR. Compared to the null hypothesis of additive interactions, most (69.3%) 22 of the mixed communities exhibited competition (p < 0.0001). Competition reduced the growth 23 rates of subgroups A, B and C. In contrast, the growth rate of subgroup D increased in the 24 presence of the other subgroups (p < 0.0001). All subgroups were able to form biofilm alone and 25 in mixed communities. Our study suggests that there is scramble competition among 26