Comparing the microbiomes of blood-feeding ticks, mites and insects: What bacteria do they have in common; beneficial and/or pathogenic.

Blooding feeding arthropods support a diverse array of symbiotic microbes, much like their non-parasitic relatives. Many bacteria are commensal, whereas others benefit hosts by providing essential nutrients lacking in blood and also aid against oxidative stress. Some symbionts facilitate growth and development of pathogens whereas others prevent pathogen survival. 
We addressed the question of whether all blood-feeding arthropods share certain bacterial genera or families and, if so, do they provide essential nutrients, or other factors enhancing vector fitness? We showed that most share a common core constituency of bacterial orders, or families including Bacillaceae, Rickettsiaceae, Anaplasmataceae, Sphingomonadaceae,Enterobacteriaceae, Pseudomonadaceae, Moraxellaceae and Staphylococcaceae.  We compared 21 genomes of common bacteria found in diverse blood-feeding vectors versus non-blooding insects for contributing essential nutrients absent in host blood.  We found certain enteric bacteria upregulate large numbers of genes coding for these nutrients, especially B vitamins, including biotin, cobalamin, flavin, folate, pimelate, pyridoxal, pyridoxine, pyrimidine, riboflavin, thiamine  and xanthine/uracil. Blood-sucking vectors expressed significantly more genes coding for essential nutrients than non-blooding insects, as well as genes coding for ROS or essential amino acids. Non-blood feeding insects expressed few or none of these gene families coding for these nutrient categories.  We also reviewed specific midgut bacteria essential for  normal development of vector-borne pathogens whereas others were detrimental to the pathogens in their arthropod hosts (e.g., Coxiella-like endosymbionts in tick salivary glands that impair transmission of Ehrlichia chaffiensis. or bacterial toxins that were lethal to Plasmodium sp. in their mosquito hosts).