Occurrence of microplastics in the Haima cold seep area of the South China Sea.

The pollution of deep-sea microplastics has received increasing attention. As a special ecosystem in the deep sea, the cold seep area is of great significance for studying the distribution of microplastics in the deep sea. In this work, the distribution and characteristics of microplastics in seawater, sediments, and shellfish in the Haima cold seep area and the correlation between the characteristics of microplastics in different media and the type of media were studied. Microplastics were found in all three media. The abundance of microplastics in different samples from the Haima cold seep area ranged 1.8-3.8 items/L for the seawater, 11.47-96.8 items/kg (d.w.) for the surface sediments, and 0-5 items/individual (0-0.714 items/g) for the shellfish. The amount of microplastics ingested by shellfish varied among different species. The microplastics in these three media were mainly fibrous, dark-colored, small-sized rayon, polyethylene terephthalate (PET), and polyethylene (PE). In the correlation analysis of microplastic characteristics among the three media, it was found that the characteristics of microplastics in different media in the same area were closely related, and each pair of variables showed a significant positive correlation (P ≤ 0.05). The distinctive geographical conditions would accelerate the interchange of microplastics among various media. Principal component analysis showed that habitat contribute to microplastic feature differences in shellfish. Differences in correlation were observed between the characteristics of shellfish microplastics in different regions and the characteristics of microplastics in surrounding seawater and sediments.

Degradation potential of alkanes by diverse oil-degrading bacteria from deep-sea sediments of Haima cold seep areas, South China Sea.

Marine oil spills are a significant concern worldwide, destroying the ecological environment and threatening the survival of marine life. Various oil-degrading bacteria have been widely reported in marine environments in response to marine oil pollution. However, little information is known about culturable oil-degrading bacteria in cold seep of the deep-sea environments, which are rich in hydrocarbons. This study enriched five oil-degrading consortia from sediments collected from the Haima cold seep areas of the South China Sea. Parvibaculum, Erythrobacter, Acinetobacter, Alcanivorax, Pseudomonas, Marinobacter, Halomonas, and Idiomarina were the dominant genera. Further results of bacterial growth and degradation ability tests indicated seven efficient alkane-degrading bacteria belonging to Acinetobacter, Alcanivorax, Kangiella, Limimaricola, Marinobacter, Flavobacterium, and Paracoccus, whose degradation rates were higher in crude oil (70.3-78.0%) than that in diesel oil (62.7-66.3%). From the view of carbon chain length, alkane degradation rates were medium chains > long chains > short chains. In addition, Kangiella aquimarina F7, Acinetobacter venetianus F1, Limimaricola variabilis F8, Marinobacter nauticus J5, Flavobacterium sediminis N3, and Paracoccus sediminilitoris N6 were first identified as oil-degrading bacteria from deep-sea environments. This study will provide insight into the bacterial community structures and oil-degrading bacterial diversity in the Haima cold seep areas, South China Sea, and offer bacterial resources to oil bioremediation applications.

Corrigendum: Effects of scale worm parasitism on interactions between the symbiotic gill microbiome and gene regulation in deep sea mussel hosts.

[This corrects the article DOI: 10.3389/fmicb.2022.940766.].

Effects of scale worm parasitism on interactions between the symbiotic gill microbiome and gene regulation in deep sea mussel hosts.

Diverse adaptations to the challenging deep sea environment are expected to be found across all deep sea organisms. Scale worms Branchipolynoe pettiboneae are believed to adapt to the deep sea environment by parasitizing deep sea mussels; this biotic interaction is one of most known in the deep sea chemosynthetic ecosystem. However, the mechanisms underlying the effects of scale worm parasitism on hosts are unclear. Previous studies have revealed that the microbiota plays an important role in host adaptability. Here, we compared gill-microbiota, gene expression and host-microorganism interactions in a group of deep sea mussels (Gigantidas haimaensis) parasitized by scale worm (PA group) and a no parasitic control group (NPA group). The symbiotic microorganism diversity of the PA group significantly decreased than NPA group, while the relative abundance of chemoautotrophic symbiotic bacteria that provide the host with organic carbon compounds significantly increased in PA. Interestingly, RNA-seq revealed that G. haimaensis hosts responded to B. pettiboneaei parasitism through significant upregulation of protein and lipid anabolism related genes, and that this parasitism may enhance host mussel nutrient anabolism but inhibit the host's ability to absorb nutrients, thus potentially helping the parasite obtain nutrients from the host. In an integrated analysis of the interactions between changes in the microbiota and host gene dysregulation, we found an agreement between the microbiota and transcriptomic responses to B. pettiboneaei parasitism. Together, our findings provide new insights into the effects of parasite scale worms on changes in symbiotic bacteria and gene expression in deep sea mussel hosts. We explored the potential role of host-microorganism interactions between scale worms and deep sea mussels, and revealed the mechanisms through which scale worm parasitism affects hosts in deep sea chemosynthetic ecosystem.

The Diversity, Composition, and Putative Functions of Gill-Associated Bacteria of Bathymodiolin Mussel and Vesicomyid Clam from Haima Cold Seep, South China Sea.

The Haima cold seep, which is one of the two active cold seeps in the South China Sea, is known for its great ecological importance. The seep bivalves are assumed to depend mainly on their bacterial symbiosis for survival and growth. However, information on the bacterial diversity, composition, and putative function of gill-associated of dominant dwelling animals in Haima cold seep remain elusive. Herein, we adopted a high-throughput sequencing of 16S rRNA gene amplicons, and function prediction methods (Functional Annotation of Prokaryotic Taxa (FAPROTAX) and Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICURUSTs)) to purposely illustrate the taxonomic and phylogenetic diversity, composition, and putative functions of the symbionts in bathymodiolin mussel Gigantidas haimaensis (Bivalvia: Mytilidae: Gigantidas) and vesicomyid clam Archivesica marissinica (Bivalvia: Glossoidea: Vesicomyidae). The predominant microbes of both species were Proteobacteria and Gammaproteobacteria on the phylum and class level, respectively. The taxonomic and phylogenetic diversity of gill microbial communities in G. haimaensis were significantly different from those in A. marissinica (p < 0.05). Nine functional groups, including seven carbon-related biogeochemical groups, were identified through the FAPROTAX analysis. However, the most dominant groups for G. haimaensis and A. marissinica were both chemoheterotrophic. G. haimaensis and A. marissinica shared many pathways, however, 16 obtained Kyoto Encyclopedia of Genes and Genomes (KEGG) orthologous groups (42.11%) significantly differed between the two species (p < 0.05). These findings would provide insight into the functions of microbes in the element cycling and energy flow as well as the host-symbiont relationship of bivalves in the Haima cold seep environment.