Autotransporters Drive Biofilm Formation and Autoaggregation in the Diderm Firmicute Veillonella parvula

Abstract

The Negativicutes are a clade of Firmicutes that have retained the ancestral diderm character and possess an outer membrane. One of the best studied Negativicute, Veillonella parvula, is an anaerobic commensal and opportunistic pathogen inhabiting complex human microbial communities, including the gut and the dental plaque microbiota. Whereas adhesion and biofilm capacity of V. parvula is expected to be crucial for its maintenance and development in these environments, studies of V. parvula adhesion have been hindered by the lack of efficient genetic tools to perform functional analyses in this bacterium. Here, we took advantage of a recently described naturally transformable V. parvula isolate, SKV38, and adapted tools developed for the closely related Clostridia spp. to perform random transposon and targeted mutagenesis to identify V. parvula genes involved in biofilm formation. We show that type V secreted autotransporters -typically found in diderm bacteria- are the main determinants of V. parvula auto-aggregation and biofilm formation, and compete with each other for binding either to cells or to surfaces, with strong consequences on V. parvula biofilm formation capacity. The identified trimeric autotransporters have an original structure compared to classical autotransporters identified in Proteobacteria with an additional C-terminal domain. We also show that inactivation of the gene coding for a poorly characterized metal-dependent phosphohydrolase HD domain protein conserved in the Firmicutes and their closely related diderm phyla inhibits autotransporter-mediated biofilm formation. This study paves the way for further molecular characterization of V. parvula interactions with other bacteria and the host within complex microbiota environments. IMPORTANCE Veillonella parvula is an anaerobic commensal and opportunistic pathogen whose ability to adhere to surfaces or other bacteria and form biofilms is critical to inhabit complex human microbial communities such as the gut and oral microbiota. Although the adhesive capacity of V. parvula has been previously described, very little is known about the underlying molecular mechanisms due to a lack of genetically amenable Veillonella strains. In this study, we took advantage of a naturally transformable V. parvula isolate and newly adapted genetic tools to identify surface exposed adhesin called autotransporters as the main molecular determinants of adhesion in this bacterium. This work therefore provides new insights on an important aspect of V. parvula lifestyle, opening new possibilities for mechanistic studies of the contribution of biofilm formation to the biology of this major commensal of the oral-digestive tract.

Bacteria autoaggregation: how and why bacteria stick together

“…Prominent among Enterobacteriales adhesins are the type V secreted proteins, otherwise referred to as autotransporters. These include, but are not limited to, the Veillonella monomeric autotransporters A-C [ 19 ]; the Serine Protease Autotransporters of Enterobacteriaceae (SPATEs) such as the tandem autotransporter B and C (TagB and TagC), the serine-protease hemagglutinin autotransporter sha [ 20 ]; the E. coli Antigen 43 (Ag43 or Flu) [ 21 ] and trimeric autotransporter adhesins such as EibC, EibD, Yersinia adhesin A (YadA) of enteropathogenic Yersiniae enterocolitica (YeYadA) and Y. pseudotuberculosis (YpYadA) [ 22 ] and the Veillonella trimeric autotransporters A-I [ 19 ]. Integral β-barrel proteins can also confer autoaggregation [ 23 ].…”

Bacterial protein secretion systems: Game of types

“…In other words, diderm instead of monoderm. That is for example the ironically named clade of Negativicutes, such as Veillonella parvula , for which a class of T5SS autotransporter is now described [202]. This is all taking us back to where we started and the concept of cell envelope organisation to define a type.…”

Comparison of the Oral Microbiota Structure among People from the Same Ethnic Group Living in Different Environments

“…V. parvula is an anaerobic commensal and opportunistic pathogen, and it can adhere to surfaces or other bacteria and form biofilms, which are all essential for its inhabitation in complex human microbial communities, such as the gut and oral microbiota. The genus Veillonella is a major oral microorganism that promotes the conversion of nitrate (NO 3 − ) to nitrite (NO 2 − ) by lactic acid and inhibits the growth and metabolism of oral pathogenic bacteria, such as Streptococcus mutans , and is considered to be beneficial for caries prevention [ 67 , 68 ] However, some studies have found that this genus is associated with dental caries [ 69 ]. Haemophilus parainfluenzae (family Pasteurellaceae ) can maintain a stable oral microbial community that can maintain oral health, suggesting that dental caries is the result of an imbalance in the resident microbial community, similar to that reported in a previous study [ 70 ].…”