Poster Presentation Australian Society for Microbiology Annual Scientific Meeting 2018

Nuc is an extracellular nuclease that mediates competence and biofilm formation in Moraxella catarrhalis (#378)

Aimee Tan 1 , Luke V Blakeway 1 , Wing Li 1 , Kate L Seib 1
  1. Griffith University, Gold Coast, QLD, Australia

Moraxella catarrhalis is a Gram-negative bacterial pathogen, and one of the major bacterial causes of otitis media and exacerbations of chronic obstructive pulmonary disease along with Streptococcus pneumoniae and non-typable Haemophilus influenzae. However, unlike the latter pathogens, no vaccine yet exists for M. catarrhalis, and many aspects of its physiology and pathogenesis remain unexplored. One example of this is that M. catarrhalis exhibits potent extracellular nuclease activity, which can be used to discriminate it from other Gram-negative cocci, but the genetic basis of this activity has not been investigated. In contrast, extracellular nucleases have been studied in both S. pneumoniae (EndA) and H. influenzae (Nuc), where they mediate virulence mechanisms such as biofilm formation and resistance to neutrophil killing, via destruction of extracellular traps.

Our work investigated a putative open reading frame in M. catarrhalis and showed that it encoded an extracellular factor that digests both DNA and RNA, that we have subsequently termed Nuc. Nuc also facilitates the natural competence of M. catarrhalis, with Δnuc mutant strains severely attenuated in transformation efficacy assays. Whilst nuc is not essential to the growth of the cell, Δnuc mutant strains show increased aggregation compared to parental strains. Similarly, Δnuc mutant strains accumulate increased biomass in static biofilm assays, suggesting the nuclease is essential for the correct formation and dispersal of M. catarrhalis biofilms. These phenotypes suggest that Nuc is important for the virulence of M. catarrhalis in infections, as has been seen with nucleases in other otopathogens S. pneumoniae and H. influenzae.