title: Interstrain Cooperation in Meningococcal Biofilms: Role of Autotransporters NalP and AutA.
abstract: Neisseria meningitidis(Nm) andNeisseria lactamica(Nl) are commensal bacteria that live in the human nasopharynx, where they form microcolonies. In contrast toNl, Nmoccasionally causes blood and/or meningitis infection with often fatal consequences. Here, we studied interactions between neisserial strains during biofilm formation. Fluorescent strains were engineered and analyzed for growth in single- and dual-strain biofilms with confocal laser-scanning microscopy. Different strains of diverseNeisseriaspecies formed microcolonies of different sizes and morphologies. Pair-wise combinations of two invasiveNmstrains and oneNmcarrier isolate showed that these strains can coexist in spite of the fact that they produce toxins to combat congeners. This lack of competition was even observed when the biofilms were formed under nutrient limitation and can be explained by the observation that the separate microcolonies within mixed biofilms are mostly lineage specific. However, these microcolonies showed different levels of interaction. The coexistence of two strains was also observed in mixed biofilms ofNmandNlstrains. Inactivation of the autotransporter NalP, which prevents the release of the heparin-binding antigen NHBA and the α-peptide of IgA protease from the cell surface, and/or the production of autotransporter AutA increased interactions between microcolonies, as evidenced by close contacts between microcolonies on the substratum. Qualitative and quantitative analysis revealed an altered spatial distribution of each strain in mixed biofilms with consequences for the biomass, biofilm architecture and bacterial viability depending on the synthesis of NalP and AutA, the expression of which is prone to phase variation. Being in a consortium resulted in some cases in commensalism and cooperative behavior, which promoted attachment to the substratum or increased survival, possibly as result of the shared use of the biofilm matrix. We hypothesize thatNmstrains can cooperate during host colonization, but, possibly, the different capacities of the microcolonies of each strain to resist the host's defenses limits the long-term coexistence of strains in the host.
authors.affiliation: Section Molecular Microbiology, Department of Biology, Utrecht University Utrecht, Netherlands.
authors.forename: Jesús
authors.initials: J
authors.lastname: Pérez-Ortega
authors.affiliation: Section Molecular Microbiology, Department of Biology, Utrecht University Utrecht, Netherlands.
authors.forename: Antonio
authors.initials: A
authors.lastname: Rodríguez
authors.affiliation: Section Molecular Microbiology, Department of Biology, Utrecht University Utrecht, Netherlands.
authors.forename: Eduardo
authors.initials: E
authors.lastname: Ribes
authors.affiliation: Section Molecular Microbiology, Department of Biology, Utrecht University Utrecht, Netherlands.
authors.forename: Jan
authors.initials: J
authors.lastname: Tommassen
authors.affiliation: Section Molecular Microbiology, Department of Biology, Utrecht University Utrecht, Netherlands.
authors.forename: Jesús
authors.initials: J
authors.lastname: Arenas
keywords: AutA; IgA protease; NHBA; NalP; Neisseria; bacterial interactions; biofilms