The family "Candidatus Midichloriaceae"constitutes the most diverse but least studied lineage within the important order of intracellular bacteria Rickettsiales. "Candidatus Midichloriaceae"endosymbionts are found in many hosts, including terrestrial arthropods, aquatic invertebrates, and protists. Representatives of the family are not documented to be pathogenic, but some are associated with diseased fish or corals. Different genera display a range of unusual features, such as full sets of flagellar genes without visible flagella or the ability to invade host mitochondria. Since studies on "Ca. Midichloriaceae"tend to focus on the host, the family is rarely addressed as a unit, and we therefore lack a coherent picture of its diversity. Here, we provide four new midichloriaceae genomes, and we survey molecular and ecological data from the entire family. Features like genome size, ecological context, and host transitions vary considerably even among closely related midichloriaceae, suggesting a high frequency of such shifts, incomplete sampling, or both. Important functional traits involved in energy metabolism, flagella, and secretion systems were independently reduced multiple times with no obvious correspondence to host or habitat, corroborating the idea that many features of these "professional symbionts"are largely independent of host identity. Finally, despite "Ca. Midichloriaceae"being predominantly studied in ticks, our analyses show that the clade is mainly aquatic, with a few terrestrial offshoots. This highlights the importance of considering aquatic hosts, and protists in particular, when reconstructing the evolution of these endosymbionts and by extension all Rickettsiales.

The "Other" Rickettsiales: an Overview of the Family "Candidatus Midichloriaceae"

Vannini C.;
2022-01-01

Abstract

The family "Candidatus Midichloriaceae"constitutes the most diverse but least studied lineage within the important order of intracellular bacteria Rickettsiales. "Candidatus Midichloriaceae"endosymbionts are found in many hosts, including terrestrial arthropods, aquatic invertebrates, and protists. Representatives of the family are not documented to be pathogenic, but some are associated with diseased fish or corals. Different genera display a range of unusual features, such as full sets of flagellar genes without visible flagella or the ability to invade host mitochondria. Since studies on "Ca. Midichloriaceae"tend to focus on the host, the family is rarely addressed as a unit, and we therefore lack a coherent picture of its diversity. Here, we provide four new midichloriaceae genomes, and we survey molecular and ecological data from the entire family. Features like genome size, ecological context, and host transitions vary considerably even among closely related midichloriaceae, suggesting a high frequency of such shifts, incomplete sampling, or both. Important functional traits involved in energy metabolism, flagella, and secretion systems were independently reduced multiple times with no obvious correspondence to host or habitat, corroborating the idea that many features of these "professional symbionts"are largely independent of host identity. Finally, despite "Ca. Midichloriaceae"being predominantly studied in ticks, our analyses show that the clade is mainly aquatic, with a few terrestrial offshoots. This highlights the importance of considering aquatic hosts, and protists in particular, when reconstructing the evolution of these endosymbionts and by extension all Rickettsiales.
2022
Giannotti, D.; Boscaro, V.; Husnik, F.; Vannini, C.; Keeling, P. J.
File in questo prodotto:
File Dimensione Formato  
2022_Giannotti_Midigenomes.pdf

accesso aperto

Tipologia: Versione finale editoriale
Licenza: Tutti i diritti riservati (All rights reserved)
Dimensione 1.87 MB
Formato Adobe PDF
1.87 MB Adobe PDF Visualizza/Apri

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11568/1141135
Citazioni
  • ???jsp.display-item.citation.pmc??? 4
  • Scopus 7
  • ???jsp.display-item.citation.isi??? 8
social impact