Characterization of Neoschoengastia gallinarum from subtropical China by rDNA and identification of two genotypes based on mitochondrial cox1

Genetic variations in the 18S ribosomal DNA (18S), 28S ribosomal DNA (28S), second internal transcribed spacer of ribosomal DNA (ITS2), and mitochondrial cytochrome c oxidase subunit 1 (cox1) of Neoschoengastia gallinarum collected from subtropical China were examined. First, a portion of the 18S (p18S), a portion of the 28S (p28S), and the complete ITS2 were separately amplified from individual mites and sequenced. The lengths of the sequences of p18S, p28S, and ITS2 were found to be 1379 bp, 3465~3468 bp, and 200 bp, respectively. The intraspecific sequence variation was 0~0.1% for p28S and 0~1.6% for ITS2, though no variation was observed for p18S, suggesting conservation of rDNA sequences. Second, a portion of the mitochondrial cox1 gene (pcox1) of N. gallinarum was analyzed. The length of the pcox1 sequence is 460 bp, and two distinct groups were observed in N. gallinarum. All pcox1 sequences in group I were identical, and there was only one nucleotide transition observed in group II; however, 7.0~7.2% variations between the two groups were observed, suggesting that two genotypes of N. gallinarum: genotype I and genotype II. Phylogenetic analyses based on pcox1 sequences indicated that N. gallinarum isolates (genotype I or genotype II) clustered into one branch; according to cox1 sequence analysis of Trombiculidae, Walchia hayashii is the closest species. The present study shows that ITS2 rDNA sequence can act as marker for the identification of N. gallinarum samples. Furthermore, analysis of the mitochondrial pcox1 sequence suggests the existence of two genotypes, which has implications for further studies of the ecology and population genetic structures of N. gallinarum.