The complete genome sequence of Tenacibaculum sp. isolate Pbs-1, the bacterial strain causing black-spot shell disease in pearl oyster, and characterization of its siderophore as a putative pathogenic factor

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Tenacibaculum sp. isolate Pbs-1 causes black-spot shell disease in pearl oyster, resulting in low-quality pearls and high mortality. Here, we report the genome sequence of isolate Pbs-1. We identified the species of isolate Pbs-1 and detected 24 genes involved in iron acquisition that are associated with siderophores, a pathogenic factor in other bacterial genera and potentially this one as well. Sequencing and annotation of isolate Pbs-1's genome predicted 3459 protein-coding sequences, 50 rRNAs (5 rRNA operons), and 55 tRNAs in one circular chromosome with a total length of 3,355,984 bp and a GC content of 31.8 %. Average nucleotide identity and in silico DNA–DNA hybridization analyses indicated that isolate Pbs-1 is conspecific with Tenacibaculum mesophilum (ANI: 98 %, is DDH: 82 %). However, comparison with other T. mesophilum genome sequences revealed a large inversion in Pbs-1's genome sequence, suggesting that isolate Pbs-1 evolved from T. mesophilum and infects pearl oyster as a new host. Although many Tenacibaculum spp., including isolate Pbs-1, have retained siderophore synthesis genes, some Tenacibaculum species have not. Our in silico results indicate that differences in the presence of siderophore-associated genes among Tenacibaculum spp. isolates could impact observed clinical presentations of tenacibaculosis. The siderophore activity of isolate Pbs-1 was affected by seawater concentration (50 %–100 %, F (7, 16) = 23.97, p = 2.40 × 10 −7 ) and temperature (5 °C–37 °C, F (5, 12) = 885, p = 5.72 × 10 −15 ), and was greatly reduced at low temperatures (<15 °C). Low-salinity treatments are currently used to improve pearl quality, but they should be conducted at low temperatures to further improve pearl quality and yield. • The genome of the disease-causing Tenacibaculum sp. isolate Pbs-1 was sequenced. • ANI and isDDH analyses indicated that Pbs-1 is conspecific with T. mesophilum . • Tenacibaculosis may be caused by Tenacibaculum isolates with or without siderophores. • Temperature affected Pbs-1 siderophore activity more than seawater concentration. • Pearl quality can be improved by a low-salinity, low-temperature treatment (≤15 °C).

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