Solving a Bloody Mess: B-Vitamin Independent Metabolic Convergence among Gammaproteobacterial Obligate Endosymbionts from Blood-Feeding Arthropods and the LeechHaementeria officinalis

Abstract

Endosymbiosis is a common phenomenon in nature, especially between bacteria and insects, whose typically unbalanced diets are usually complemented by their obligate endosymbionts. While much interest and focus has been directed toward phloem-feeders like aphids and mealybugs, blood-feeders such as the Lone star tick (Amblyomma americanum), Glossina flies, and the human body louse (Pediculus humanus corporis) depend on obligate endosymbionts which complement their B-vitamin-deficient diets, and thus are required for growth and survival. Glossiphoniid leeches have also been found to harbor distinct endosymbionts housed in specialized organs. Here, we present the genome of the bacterial endosymbiont from Haementeria officinalis, first of a glossiphoniid leech. This as-yet-unnamed endosymbiont belongs to the Gammaproteobacteria, has a pleomorphic shape and is restricted to bacteriocytes. For this bacterial endosymbiont, we propose the name Candidatus Providencia siddallii. This symbiont possesses a highly reduced genome with high A+T content and a reduced set of metabolic capabilities, all of which are common characteristics of ancient obligate endosymbionts of arthropods. Its genome has retained many pathways related to the biosynthesis of B-vitamins, pointing toward a role in supplementing the blood-restricted diet of its host. Through comparative genomics against the endosymbionts of A. americanum, Glossina flies, and P. humanus corporis, we were able to detect a high degree of metabolic convergence among these four very distantly related endosymbiotic bacteria.

Francisella-Like Endosymbionts and Rickettsia Species in Local and Imported Hyalomma Ticks

“…Nevertheless, FLE and other bacterial endosymbionts have been known to colonize salivary glands, and their presence in this organ does not ensure transmission to vertebrate hosts (41). Similar observations have been made for other hard ticks and their obligatory symbionts (36,40), suggesting a potential nutritional role of the symbionts in supplying B vitamins missing in the tick blood meal (11,42).…”

“…carry Francisella-like endosymbionts (FLE) (8)(9)(10) that may be obligatory primary symbionts supporting the restricted blood diet, as with other ticks and hematophagous insects (11). Several endosymbiotic bacteria in arthropod vectors were shown to interact with pathogens and affect their host's susceptibility to infection, including in tick hosts (12)(13)(14).…”

Torix group Rickettsia are widespread in Culicoides biting midges (Diptera: Ceratopogonidae), reach high frequency and carry unique genomic features

“…(Akman et al, 2002;Snyder et al, 2010;Rio et al, 2012). Additional genomic surveys suggest that other proteobacterial symbionts including Coxiella are involved in metabolic homeostasis (Zhong et al, 2007;Manzano-Marin et al, 2015;Smith et al, 2015). As such, these symbioses can have profound effects on the biology, ecology and evolutionary dynamics of vector-pathogen interactions.…”

Comparison of closely related, uncultivated Coxiella tick endosymbiont population genomes reveals clues about the mechanisms of symbiosis

“…Multiple arthropod taxa feed exclusively on vertebrate blood, a highly restricted diet which lacks essential nutrients and metabolites, particularly B vitamin and various cofactor precursors (Duarte et al, 1999). Thus, blood feeding arthropods typically form close associations with nutrient-providing endosymbiotic bacteria that often become essential and even irreplaceable for their hosts fitness and reproduction (i.e., obligate symbionts) (Zientz et al, 2004;Manzano-Marín et al, 2015;Rio et al, 2016). For example, tsetse flies (Diptera: Glossinidae) rely on their obligate endosymbionts Wigglesworthia spp.…”