The meningococcal autotransporter AutA is implicated in autoaggregation and biofilm formation

Abstract

Autotransporters (ATs) are proteins secreted by Gram-negative bacteria that often play a role in virulence. Eight different ATs have been identified in Neisseria meningitidis, but only six of them have been characterized. AutA is one of the remaining ATs. Its expression remains controversial. Here, we show that the autA gene is present in many neisserial species, but its expression is often disrupted by various genetic features; however, it is expressed in certain strains of N. meningitidis. By sequencing the autA gene in large panels of disease isolates and Western blot analysis, we demonstrated that AutA expression is prone to phase variation at AAGC nucleotide repeats located within the DNA encoding the signal sequence. AutA is not secreted into the extracellular medium, but remains associated with the bacterial cell surface. We further demonstrate that AutA expression induces autoaggregation in a process that, dependent on the particular strain, may require extracellular DNA (eDNA). This property influences the organization of bacterial communities like lattices and biofilms. In vitro assays evidenced that AutA is a self-associating AT that binds DNA. We suggest that AutA-mediated autoaggregation might be particularly important for colonization and persistence of the pathogen in the nasopharynx of the host.

Expression of the Gene for Autotransporter AutB of Neisseria meningitidis Affects Biofilm Formation and Epithelial Transmigration

“…Thus, NalP regulates biofilm formation. NhhA and NadA are cell-associated trimeric ATs with a role in adhesion to eukaryotic cells (Capecchi et al, 2005; Scarselli et al, 2006), whilst AutA is a monomeric AT involved in bacterial autoaggregation, a function that affects biofilm structure (Arenas et al, 2015). The remaining AT, AutB, has not been characterized yet.…”

“…The expression of the genes for most ATs in N. meningitidis is prone to phase variation by slipped-strand mispairing at short nucleotide repeats (Turner et al, 2002; van Ulsen et al, 2006; Arenas et al, 2015). Besides, expression of several AT genes, e.g., ausI and autA , can be prevented in certain lineages by genetic disruptions, such as deletions or frame-shift mutations, possibly evolved by selection pressure imposed by the immune system (van Ulsen et al, 2006; Arenas et al, 2015).…”

Neisserial Molecular Adaptations to the Nasopharyngeal Niche

“…The autA gene is distributed across the neisseriae, and the in vitro phenotype accompanying its expression, i.e., the formation of small microcolonies consistent with those identified by Sim and colleagues (Sim et al, 2000), led the authors to suggest that AutA expression may be important to establishing the carrier state (Arenas et al, 2015). In their study, conducted on a panel of mostly invasive meningococcal lineages, the authors showed that autA expression was restricted to a narrow range of strains, due to disruption of the open reading frame by premature STOP codons, insertions or deletions.…”

“…AutA is a phase-variable, self-associating, DNA-binding meningococcal autotransporter, which mediates bacterial autoaggregation (Arenas et al, 2015). The autA gene is distributed across the neisseriae, and the in vitro phenotype accompanying its expression, i.e., the formation of small microcolonies consistent with those identified by Sim and colleagues (Sim et al, 2000), led the authors to suggest that AutA expression may be important to establishing the carrier state (Arenas et al, 2015).…”

“…The proportion of commensal bacteria with a complete, phase 'ON' autA gene was much higher than in the meningococcus, but the number of reference genomes of the former was decidedly smaller. These limitations were acknowledged by the authors, who call for a wider screen of carrier isolates to better determine a role for AutA (Arenas et al, 2015). That autA might become mutated in invasive isolates is reasonable, insofar as the AutA protein becomes unnecessary, or perhaps even represents a liability, during meningococcal invasion of the epithelium into underlying tissues, after which capsule expression will necessarily increase and prevent AutA proteins from self-associating.…”