Population-level prokaryotic community structures associated with ferromanganese nodules in the Clarion-Clipperton Zone (Pacific Ocean) revealed by 16S rRNA gene amplicon sequencing.

Although deep-sea ferromanganese nodules are a potential resource for exploitation, their formation mechanisms remain unclear. Several nodule-associated prokaryotic species have been identified by amplicon sequencing of 16S rRNA genes and are assumed to contribute to nodule formation. However, the recent development of amplicon sequence variant (ASV)-level monitoring revealed that closely related prokaryotic populations within an operational taxonomic unit often exhibit distinct ecological properties. Thus, conventional species-level monitoring might have overlooked nodule-specific populations when distinct populations of the same species were present in surrounding environments. Herein, we examined the prokaryotic community diversity of nodules and surrounding environments at the Clarion-Clipperton Zone in Japanese licensed areas by 16S rRNA gene amplicon sequencing with ASV-level resolution for three cruises from 2017 to 2019. Prokaryotic community composition and diversity were distinct by habitat type: nodule, nodule-surface mud, sediment, bottom water and water column. Most ASVs (~80%) were habitat-specific. We identified 178 nodule-associated ASVs and 41 ASVs associated with nodule-surface mud via linear discriminant effect size analysis. Moreover, several ASVs, such as members of SAR324 and Woeseia, were highly specific to nodules. These nodule-specific ASVs are promising targets for future investigation of the nodule formation process.

Three new species of free-living marine nematodes (Nematoda: Enoplida) from the Clarion-Clipperton Fracture Zone (CCFZ), North Pacific.

Three new species of free-living marine nematodes, Phanodermopsis dordi sp. nov., Halalaimus shinkai sp. nov., and Oxystomina hakureiae sp. nov. are described from the abyssal sediments of the Clarion-Clipperton Fracture Zone, North Pacific. Phanodermopsis dordi sp. nov. differs from the congeners by having papilliform anterior sensilla and a long conical tail with an acute tip. Halalaimus shinkai sp. nov., belonging to Keppner's group 2 based on the presence of caudal alae and the absence of precloacal sensillum or pore, can be distinguished from all of the members of this group by the presence of lateral pieces of gubernacula. Oxystomina hakureiae sp. nov. differs from the congeners by the short setiform anterior sensilla, the amphid located posterior to cephalic sensilla, the conico-cylindrical tail in both sexes, the spicules with a velum and a capitulum, the presence of the gubernacula and the precloacal setae, and the diorchic and monodelphic reproductive systems. The amended dichotomous keys to the species of Phanodermopsis, Halalaimus group 2, and Oxystomina are provided. A new combination Nemanema arenaria (Bussau, 1990) comb. nov. transferred from Oxystomina is also provided.