Nanosynbacter lyticus gen. nov., sp. nov., an ultrasmall, obligate epibiont bacterium and the proposal of Nanosynbacteraceae fam. nov., Nanosynbacterales ord. nov. and Nanosynbacteria class nov
The recently validly published phylum
Minisyncoccota
(previously
Ca
. Patescibacteriota or candidate phyla radiation) had long been an enigma, with members having remained uncultivated for several decades since the first SSU ribosomal sequence was recovered. We reported on the first isolated strain of
Minisyncoccota
,
Nanosynbacter lyticus
type strain TM7x
T
(ATCC TSD-290
T
), in 2015, using directed cultivation from human oral samples. Strain TM7x
T
had an extremely reduced genome (705 CDS), ultra-small cell size (200–300 nm), and replicated as an obligate epibiont on the surface of another commonly found oral species:
Pauljensenia odontolytica_C
strain XH001 (host bacterium). TM7x
T
also exhibited what has been defined as a parasitic phase, where it disrupts the membrane of the bacterial host cell, resulting in host bacteria lysis. However, free-floating, host-free TM7x
T
cells remain viable and can re-infect fresh host bacterial cells when available. This discovery and coculture marked the first concrete evidence of how these ultrasmall organisms within the
Minisyncoccota
survive and persist despite their reduced genomes missing
de novo
biosynthesis of many essential compounds, including all amino acids and vitamins. This model dual species system has now allowed a deeper understanding of the TM7x–host bacterium interaction and dynamics, with over 15 publications reporting on various aspects of this strain to date. We propose the name
Nanosynbacter lyticus
gen. nov. sp. nov. for strain TM7x
T
. We also propose
Nanosynbacteraceae
fam. nov.,
Nanosynbacterales
ord. nov. and
Nanosynbacteria
class nov. to accommodate the genus
Nanosynbacter
.