Abstract
Ticks and other arthropods often are hosts to nutrient providing bacterial endosymbionts, which contribute to their host’s fitness by supplying nutrients such as vitamins and amino acids. It has been detected, in our lab, that Ixodes pacificus is host to Rickettsia species phylotype G021. This endosymbiont is predominantly present, and 100% maternally transmitted in I. pacificus. To study roles of phylotype G021 in I. pacificus, bioinformatic and molecular approaches were carried out. MUMmer genome alignments of whole genome sequence of I. scapularis, a close relative to I. pacificus, against completely sequenced genomes of R. bellii OSU85-389, R. conorii, and R. felis, identified 8,190 unique sequences that are homologous to Rickettsia sequences in the NCBI Trace Archive. MetaCyc metabolic reconstructions revealed that all folate gene orthologues (folA, folC, folE, folKP, ptpS) required for de novo folate biosynthesis are present in the genome of Rickettsia buchneri in I. scapularis. To examine the metabolic capability of phylotype G021 in I. pacificus, genes of the folate biosynthesis pathway of the bacterium were PCR amplified using degenerate primers. BLAST searches identified that nucleotide sequences of the folA, folC, folE, folKP, and ptpS genes possess 98.6%, 98.8%, 98.9%, 98.5% and 99.0% identity respectively to the corresponding genes of Rickettsia buchneri. Phylogenetic tree constructions show that the folate genes of phylotype G021 and homologous genes from various Rickettsia species are monophyletic. This study has shown that all folate genes exist in the genome of Rickettsia species phylotype G021 and that this bacterium has the genetic capability for de novo folate synthesis.
Highlights
Symbiotic relationships with microorganisms are widespread across arthropods
Based on MUMmer alignments against complete genomes of R. bellii, R. conorii, and R. felis, 2,903, 7,496, and 7,203 Trace Archive sequences from the I. scapularis genome project with a minimal nucleotide identity of 70% were identified to be homologous to the three reference Rickettsia genome sequences
Two vitamin biosynthetic pathways were manually annotated by MetaCyc metabolic reconstructions in the genome of R. buchneri in I. scapularis, including the vitamin B7 and B9 biosynthetic pathways
Summary
Symbiotic relationships with microorganisms are widespread across arthropods. It has been reported that all insects, and even a majority of arthropods, carry symbiotic microorganismsPLOS ONE | DOI:10.1371/journal.pone.0144552 December 9, 2015A Nutritional Relationship between Rickettsia and Ixodes pacificus [1, 2]. For eukaryotic hosts with limited metabolic capabilities, some of the most discernable benefits of microbial symbionts in a mutualistic relationship involve the provision of essential amino acids [14, 15], vitamins and cofactors [16, 17], and recycling and storage of nitrogenous wastes from hosts [18, 19]. The exchange of these nutritional constituents appears to be a primary driving force for eukaryotic cell evolution [20]
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