Tick-Bacteria Mutualism Depends on B Vitamin Synthesis Pathways

Curr Biol. 2018 Jun 18;28(12):1896-1902.e5. doi: 10.1016/j.cub.2018.04.038. Epub 2018 May 31.

Abstract

Mutualistic interactions with microbes have facilitated the radiation of major eukaryotic lineages [1, 2]. Microbes can notably provide biochemical abilities, allowing eukaryotes to adapt to novel habitats or to specialize on particular feeding niches [2-4]. To investigate the importance of mutualisms for the exclusive blood feeding habits of ticks, we focused on a bacterial genus of medical interest, Francisella, which is known to include both virulent intracellular pathogens of vertebrates [5, 6] and maternally inherited symbionts of ticks [7-9]. Through a series of physiological experiments, we identified a Francisella type, F-Om, as an obligate nutritional mutualist in the life cycle of the African soft tick Ornithodoros moubata. Francisella F-Om mutualism synthesizes B vitamins that are deficient in the blood meal of ticks. Indeed, experimental elimination of Francisella F-Om resulted in alteration of tick life history traits and physical abnormalities, deficiencies which were fully restored with an oral supplement of B vitamins. We also show that Francisella F-Om is maternally transmitted to all maturing tick oocytes, suggesting that this heritable symbiont is an essential adaptive element in the life cycle of O. moubata. The Francisella F-Om genome further revealed a recent origin from a Francisella pathogenic life style, as observed in other Francisella symbionts [6, 7, 10]. Though half of its protein-coding sequences are now pseudogenized or lost, Francisella F-Om has kept several B vitamin synthesis pathways intact, confirming the importance of these genes in evolution of its nutritional mutualism with ticks.

Keywords: B vitamins; Francisella; hematophagy; symbiosis; ticks.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Biosynthetic Pathways
  • Female
  • Francisella / physiology*
  • Male
  • Ornithodoros / microbiology
  • Ornithodoros / physiology*
  • Rickettsia / physiology*
  • Symbiosis / physiology*
  • Vitamin B Complex / biosynthesis*

Substances

  • Vitamin B Complex