Proposing a subgenus Borreliella

In 2014, it was proposed (validly published in 2015) that the genus Borrelia be divided into two genera, with a new genus Borreliella holding species of the Lyme borreliosis group of spirochetes and the genus Borrelia retaining all other species. As borrelias are medically important bacteria and as concerns about this taxonomic proposal were raised, this genus split was controversial. In particular, the accuracy of the genetic signatures used to support the division of the genus has been questioned, particularly as new taxa have markedly increased the diversity of the genus in recent years. Restoration of the genus Borrelia to its original form was therefore proposed as an emendation in 2018. However, some databases adhere to the policy of using the last validly published name of a genus as the correct name and, hence, fail to recognize a reversion to a previous taxonomy and to previously validly published names (homotypic synonyms). We therefore propose to lower the genus Borreliella in rank to a subgenus. This will create a validly published name newer than the genus name Borreliella that can then be used by databases and provides a means of formally referring to the same group without implying necessary changes of species names. Applying the underused subgenus category instead of splitting an already monophyletic genus into several genera could be a preferable solution for other bacterial groups, too.