Distribution of nicotinamide phosphoribosyltransferase in genus Aggregatibacter and description of Aggregatibacter animalimorsus sp. nov., Aggregatibacter fructosivorans sp. nov., Aggregatibacter holmi sp. nov., and Aggregatibacter valvarum sp. nov.
Genus Aggregatibacter was created in 2006 to combine species previously affiliated with Actinobacillus and Haemophilus (Nørskov-Lauritsen 2006). From a laboratory perspective, the genus encompasses a group of isolates that are independent of Nicotinamide Adenine Dinucleotide (NAD) (Aggregatibacter actinomycetemcomitans; previously affiliated with Actinobacillus), a group that exhibits satellitism on 5% blood agar plates (NAD-dependence) (Aggregatibacter segnis; previously affiliated with Haemophilus), and a group that encompasses both NAD-dependent and NAD-independent isolates (Aggregatibacter aphrophilus; previously designated Haemophilus aphrophilus for NAD-independent isolates and Haemophilus paraphrophilus for NAD-dependent isolates). Aggregatibacter kilianii was separated from A. aphrophilus in 2018; one of 10 characterised isolates of the new species exhibited NAD-dependence (Murra 2018). Unresolved issues regarding speciation in genus Aggregatibacter are acknowledged. Multilocus enzyme electrophoresis (MLEE) of A. actinomycetemcomitans identified a group of serotype e isolates that were clearly separate from the core of the species (Poulsen 1994). The isolates carry the unusual 16S rRNA type V sequence, as defined by Kaplan et al. (2002). The existence of this outgroup was subsequently documented by genome sequencing (Jorth 2012; Karched 2012; Kittichotirat 2016; Nedergaard 2019), and is sometimes referred to as clade e'. A. segnis is less well studied, but unusual isolates are documented by MLEE (Caugant 1990) and housekeeping gene sequencing (Nørskov-Lauritsen 2006). Strain PN491, isolated from an animal bite, did not belong to any known Aggregatibacter species, as evaluated by Matrix-Assisted Laser Desorption-Ionization Time-Of-Flight (MALDI-TOF) mass spectroscopy or Whole Genome Sequence (WGS) (Murra 2018). Genome sequencing has become a pillar of bacterial taxonomy, and several internet services are available (RefSeq?; Jolley 2012; Meier-Kolthoff 2019; Parks 2020). The Genome Taxonomy Database (Parks 2020) distributes Aggregatibacter WGSs from the public repositories into at least 12 different genomospecies. Personal experience with unidentifiable clinical isolates motivated us to update the taxonomy of genus Aggegatibacter by use of phenotypic data and genome sequencing.