The mitochondrial genome of the predatory mite Metaseiulus occidentalis (Arthropoda: Chelicerata: Acari: Phytoseiidae) is unexpectedly large and contains several novel features

The complete mitochondrial genome of the phytoseiid Metaseiulus occidentalis (Arthropoda: Chelicerata: Acari: Phytoseiidae) has been sequenced. It is 24,961 bp in length and contains a 14,695-bp unique region, a 345-bp triplicated region, and a 9921-bp duplicated region, in that order. The A+T content of the unique region is 76.9% and contains 11 protein coding (COI-III, ATP6-8; CytB; ND1, 2, 4, 5 and 4L), two ribosomal RNA (srRNA and lrRNA), 22 transfer RNA (tRNA) genes, and two copies of D-loop control sequence. Two genes (ND3 and 6) appear to be missing, but there is a large intergenic spacer (390 bp) present, which could contain ND3 if a different codon usage is employed. The gene order is completely different from the pattern in all other known chelicerates, including the horseshoe crab Limulus polyphemus [Lavrov et al, Mol. Biol. Evol., 2000; 17:813-824]. All the inferred tRNA genes are missing the T Psi C arm, but this arm has fused with the variable arm to generate a TV replacement loop. The duplicated region (9921 bp) contains 18 genes in the same order as in the unique region from CytB to tRNAHis, plus one copy of D-loop control sequence (311 bp) and a partial tRNA-Leu2 sequence (34 bp). The small triplicated region (345 bp) contains a D-loop control sequence (311 bp) and a partial tRNA-Leu2 sequence (34 bp). Because of these anomalies, amplifying sequences posed technical difficulties, but were accomplished by using a primer-walking strategy and increasing the AT content to 75% in the high-fidelity PCR dNTP mix. This is the first phytoseiid mitochondrial genome to be completely sequenced and the largest (25 kb) detected from the Chelicerata. (c) 2007 Elsevier B.V. All rights reserved.