AUTHOR=Price Daniel R. G. , Bartley Kathryn , Blake Damer P. , Karp-Tatham Eleanor , Nunn Francesca , Burgess Stewart T. G. , Nisbet Alasdair J. 

TITLE=A Rickettsiella Endosymbiont Is a Potential Source of Essential B-Vitamins for the Poultry Red Mite, Dermanyssus gallinae

JOURNAL=Frontiers in Microbiology

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2021.695346

DOI=10.3389/fmicb.2021.695346

ISSN=1664-302X

ABSTRACT=<p>Many obligate blood-sucking arthropods rely on symbiotic bacteria to provision essential B vitamins that are either missing or at sub-optimal levels in their nutritionally challenging blood diet. The poultry red mite <italic>Dermanyssus gallinae</italic>, an obligate blood-feeding ectoparasite, is a serious threat to the hen egg industry. Poultry red mite infestation has a major impact on hen health and welfare and causes a significant reduction in both egg quality and production. Thus far, the identity and biological role of nutrient provisioning bacterial mutualists from <italic>D. gallinae</italic> are little understood. Here, we demonstrate that an obligate intracellular bacterium of the <italic>Rickettsiella</italic> genus is detected in <italic>D. gallinae</italic> mites collected from 63 sites (from 15 countries) across Europe. In addition, we report the genome sequence of <italic>Rickettsiella</italic> from <italic>D. gallinae</italic> (<italic>Rickettsiella – D. gallinae</italic> endosymbiont; <italic>Rickettsiella</italic> DGE). <italic>Rickettsiella</italic> DGE has a circular 1.89Mbp genome that encodes 1,973 proteins. Phylogenetic analysis confirms the placement of <italic>Rickettsiella</italic> DGE within the <italic>Rickettsiella</italic> genus, related to a facultative endosymbiont from the pea aphid and <italic>Coxiella</italic>-like endosymbionts (CLEs) from blood feeding ticks. Analysis of the <italic>Rickettsiella</italic> DGE genome reveals that many protein-coding sequences are either pseudogenized or lost, but <italic>Rickettsiella</italic> DGE has retained several B vitamin biosynthesis pathways, suggesting the importance of these pathways in evolution of a nutritional symbiosis with <italic>D. gallinae</italic>. <italic>In silico</italic> metabolic pathway reconstruction revealed that <italic>Rickettsiella</italic> DGE is unable to synthesize protein amino acids and, therefore, amino acids are potentially provisioned by the host. In contrast, <italic>Rickettsiella</italic> DGE retains biosynthetic pathways for B vitamins: thiamine (vitamin B1) <italic>via</italic> the salvage pathway; riboflavin (vitamin B2) and pyridoxine (vitamin B6) and the cofactors: flavin adenine dinucleotide (FAD) and coenzyme A (CoA) that likely provision these nutrients to the host.</p>