http://informahealthcare.com/mdn ISSN: 1940-1736 (print), 1940-1744 (electronic) Mitochondrial DNA, Early Online: 1–2 ! 2014 Informa UK Ltd. DOI: 10.3109/19401736.2014.936424 MITOGENOME ANNOUNCEMENT The complete mitochondrial genome of the fire coral-inhabiting barnacle Megabalanus ajax (Sessilia: Balanidae): gene rearrangements and atypical gene content Xin Shen 1,2 , Ka Hou Chu 2 , Benny Kwok Kan Chan 3 , and Ling Ming Tsang 4,5 1 Simon F. S. Li Marine Science Laboratory, School of Life Sciences, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong, China, 2 Jiangsu Key Laboratory of Marine Biotechnology/College of Marine Science, Huaihai Institute of Technology, Lianyungang, China, 3 Biodiversity Research Center, Academia Sinica, Taipei, Taiwan, 4 Institute of Marine Biology, National Taiwan Ocean University, Keelung, Taiwan, and 5 Center of Excellence for the Oceans, National Taiwan Ocean University, Keelung, Taiwan Abstract The complete mitochondrial genome of Megabalanus ajax Darwin, 1854 (Sessilia: Balanidae) is reported. Compared to typical gene content of metazoan mitochondrial genomes, duplication of one tRNA gene (trnL 2 ) and absence of another tRNA gene (trnS 1 ) are identified in M. ajax mitochondrial genome. There is a replacement of one tRNA (trnS 1 ) by another tRNA (trnL 2 ) in M. ajax mitochondrial genome compared to Megabalanus volcano mitochondrial genome. Inversion of a six-gene block (trnP-nd4L-nd4-trnH-nd5-trnF) is found between M. ajax/M. volcano and Tetraclita japonica mitochondrial genomes. With reference to the pancrustacean mitochondrial ground pattern, there is an inversion of a large gene block from the light strand to heavy strand in the two Megabalanus mitochondrial genomes, including three PCGs and two tRNAs (nd4L-nd4-trnH-nd5-trnF). Furthermore, four tRNAs (trnA, trnE, trnQ and trnC) exhibit translocation, while translocation and inversion occur in three tRNAs (trnP, trnY and trnK). Keywords Gene duplication, gene rearrangement, Maxillopoda, mitochondrial genome, Sessilia History Received 14 June 2014 Accepted 15 June 2014 Published online 22 July 2014 Megabalanus ajax (Darwin, 1854) (Crustacea: Maxillopoda: Balanidae) is a symbiotic barnacle on fire corals Millepora (Chan et al., 2009). Here we present the complete mitochondrial genome of M. ajax (collected from Green Island, Taiwan). The mitochondrial genome is 15,511 bp in length and encodes 37 genes (GenBank accession number: KF501046). Compared with typical gene content of metazoan mitochondrial genomes, however, duplication of one tRNA gene (trnL 2 ) and absence of another tRNA gene (trnS 1 ) are identified in M. ajax mitochondrial genome. Both rRNAs are encoded on the light strand, as in the other crustacean and barnacle mitochondrial genomes (Shen et al., 2010, 2011, in press; Tsang et al., in press). Only one protein-coding gene (PCG) is encoded on the light strand (nd1), whereas the other 12 PCGs are located on the heavy strand. There are 3806 codons in the 13 PCGs (excluding the incomplete termination). The most frequently used amino acids were Leu (15.00%), followed by Ser (9.77%), Phe (9.43%), His (8.88%) and Gly (6.54%). A common feature in most metazoan genomes is a bias towards a higher representation of nucleotides A and T, which leads to a subsequent bias in the corresponding encoded amino acids (Shen et al., 2007, 2009). The A + T composition of the first and second codon positions in 13 PCGs is 59.3% and 63.5%, respectively, but that of the third codon positions elevates to 71.4%. PCGs of the two Megabalanus mitochondrial genomes have initiation codons other than ‘‘ATN’’. The nd4L gene exhibits the initiation codon ‘‘GTG’’. Furthermore, variation of initiation codon usage is observed between the two Megabalanus species as well. The cox1 gene of M. ajax and Megabalanus volcano starts with ‘‘CTT’’ and ‘‘TTG’’, respectively. Furthermore, initiation codons of nd3 and atp8 genes in the two Megabalanus mitochondrial genomes are also different (M. ajax have ‘‘ATA’’ in nd3 and ‘‘ATC’’ in atp8, whereas M. volcano uses ‘‘ATT’’ in both of the two correspond- ing genes). Inversion of a six-gene block (trnP-nd4L-nd4-trnH-nd5-trnF) is found between M. ajax/M. volcano and T. japonica mitochon- drial genomes. Compared with M. volcano mitochondrial genome, there is a replacement of one tRNA (trnS 1 ) by another tRNA (trnL 2 ) in the M. ajax mitochondrial genome. With reference to the pancrustacean mitochondrial ground pattern, there is an inversion of a large gene block that includes three PCGs and two tRNAs (nd4L-nd4-trnH-nd5-trnF) from the light strand to heavy strand in the two Megabalanus genomes. In addition, four tRNAs (trnA, trnE, trnQ and trnC) exhibit translocations, while translocations and inversions occur in three tRNAs (trnP, trnY and trnK; Figure 1). In conclusion, large-scale gene rearrangements (including three PCGs and nine tRNAs) are found in the Megabalanus mitochondrial genomes as compared to the pancrustacean ground pattern. Correspondence: Ling Ming Tsang, Institute of Marine Biology, National Taiwan Ocean University, Keelung 20224, Taiwan. Tel: +886 224622192. E-mail: lmtsang@mail.ntou.edu.tw Mitochondrial DNA Downloaded from informahealthcare.com by 36.231.36.61 on 07/22/14 For personal use only.