Abstract
A potent marine toxin, tetrodotoxin (TTX), found in a great variety of marine and some terrestrial species, leaves intriguing questions about its origin and distribution in marine ecosystems. TTX-producing bacteria were found in the cultivable microflora of many TTX-bearing hosts, thereby providing strong support for the hypothesis that the toxin is of bacterial origin in these species. However, metagenomic studies of TTX-bearing animals addressing the whole microbial composition and estimating the contribution of TTX-producing bacteria to the overall toxicity of the host were not conducted. The present study is the first to characterize and compare the 16S rRNA gene data obtained from four TTX-bearing and four non-TTX-bearing species of marine ribbon worms. The statistical analysis showed that different nemertean species harbor distinct bacterial communities, while members of the same species mostly share more similar microbiomes. The bacterial species historically associated with TTX production were found in all studied samples but predominated in TTX-bearing nemertean species. This suggests that deeper knowledge of the microbiome of TTX-bearing animals is a key to understanding the origin of TTX in marine ecosystems.
Highlights
Tetrodotoxin (TTX) is a low molecular weight non-proteinaceous neurotoxin found in a variety of marine and some terrestrial species [1]
Six species used in the current research, including Cephalothrix simula, Tubulanus punctatus, Kulikovia alborostrata, Quasitetrastemma stimpsoni, Cerebratulus cf. marginatus and Micrura cf. bella, collected from the Peter the Great Bay (Sea of Japan, Russian Far East) in July and August 2018 were tested for TTX presence or absence using high-performance liquid chromatography in combination with tandem mass spectrometry (HPLC-MS/MS) analysis in the previous study [13]
This number was reduced to 1,867,843 sequences assigned to a total of 457 open-reference operational taxonomic units (OTUs)
Summary
Tetrodotoxin (TTX) is a low molecular weight non-proteinaceous neurotoxin found in a variety of marine and some terrestrial species [1]. TTX is usually detected together with its analogues (TTXs). It causes seafood poisoning in the Indo-Pacific region. Despite numerous data on TTX occurrence in various species including TTX-producing bacterial strains [1] and phytoplankton [3,4], the origin of the toxin and its distribution in marine ecosystems remain unclear. The hypothesis of the bacterial origin of TTX that prevails today has several weaknesses; the most serious one is that the amount of TTX produced by bacteria is small compared to its content in the respective host [2]. All available studies of TTX-producing microflora dealt with its cultivable forms that can be maintained under laboratory conditions, while the microbial communities of TTX-bearing animals were largely ignored. Studying the microbiome of TTX-bearing animals by using metagenomic analysis provides a new approach to detecting potential
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