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Halocynthia aurantium (Stolidobranchia: Pyuridae) is a species of tunicate of commercial value that is commonly found in the northern Pacific Ocean and in the Bering Sea. Here, we determined the complete mitogenome of sea peach H. aurantium using 150 PE high-throughput sequencing. The assembled mitogenome is 14,979 bp in length (overall A þ T contents 56.2%), and contains 13 proteincoding genes, 21 transfer RNAs, two ribosomal RNAs. Phylogenetic analysis of the mitogenome sequence of H. aurantium fully resolved it in a clade with H. roretzi. These data and results will be useful for future studies on the evolution of the Halocynthia and the Pyuridae.

This study aimed to determine the increase in astaxanthin production from Paracoccus haeundaensis by optimizing the medium conditions and co-culturing with lactic acid bacteria. In order to select a suitable strain to co-culture with P. haeundaensis, several strains were co-cultured with P. haeundaensis. Lactobacillus fermentum was selected as the optimal strain. Further to optimize the astaxanthin production in the co-culture, various medium conditions were tested and the PMF medium developed in this study was selected as the optimum medium. For the co-culture under optimal conditions, the dried cell mass and astaxanthin concentration were 1.84 ± 0.09 g/L and 821.09 ± 30.98 μg/g-dried cell weight, respectively, which was 2.5 times higher than that of the P. haeundaensis strain in the Luria-Bertani broth medium. In order to confirm the transcription level of the carotenoid biosynthesis genes such as crtE, crtB, crtI, crtY, crtZ, and crtW of P. haeundaensis in the co-culture, real-time qPCR was performed. Among the six carotenoid biosynthesis genes, crtI, crtY, and crtZ showed a significant difference in relative RNA levels. The mass culture was performed using a 5 L jar fermenter and the astaxanthin concentration was the same as that at the laboratory scale. These results may be used as reference for co-culture and astaxanthin production in carotenoid biosynthesis microorganisms.