Abstract
Dicathais orbita is a marine mollusc recognised for the production of anticancer compounds that are precursors to Tyrian purple. This study aimed to assess the diversity and identity of bacteria associated with the Tyrian purple producing hypobranchial gland, in comparison with foot tissue, using a high-throughput sequencing approach. Taxonomic and phylogenetic analysis of variable region V1-V3 of 16S rRNA bacterial gene amplicons in QIIME and MEGAN were carried out. This analysis revealed a highly diverse bacterial assemblage associated with the hypobranchial gland and foot tissues of D. orbita. The dominant bacterial phylum in the 16S rRNA bacterial profiling data set was Proteobacteria followed by Bacteroidetes, Tenericutes and Spirochaetes. In comparison to the foot, the hypobranchial gland had significantly lower bacterial diversity and a different community composition, based on taxonomic assignment at the genus level. A higher abundance of indole producing Vibrio spp. and the presence of bacteria with brominating capabilities in the hypobranchial gland suggest bacteria have a potential role in biosynthesis of Tyrian purple in D. orbita.
Highlights
Tyrian purple is a dye of historical and religious importance [1, 2] and its indole precursors are reported to have potential anticancer and antimicrobial properties [3,4,5,6,7,8]
The foot samples had a higher number of operational taxonomic units (OTUs) than the hypobranchial gland, across all taxonomic levels (Table 1)
Rarefaction curves indicated the richness of bacterial taxa had not peaked at the maximum number of sequences read, with the exception of female hypobranchial gland 2, which reached an asymptote of < 70 bacterial genera after ~ 10,000 sequences (Table 1)
Summary
Tyrian purple is a dye of historical and religious importance [1, 2] and its indole precursors are reported to have potential anticancer and antimicrobial properties [3,4,5,6,7,8]. Muricid molluscs are the only natural source of Tyrian purple [2], which is formed as a secondary metabolite from indoxyl sulfate precursors stored in the hypobranchial gland [4, 9]. The main pigment in Tyrian purple (6, 6’ dibromoindigo) was the first marine natural product to be structurally elucidated [10], even a century later, little information is available on its biosynthesis or the potential role of endosymbiotic bacteria in its production [4]. Bromoperoxidases are believed to be involved in the bromination of indoxyl sulfate precursors, PLOS ONE | DOI:10.1371/journal.pone.0140725 October 21, 2015
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