Diversity and Vertical Distribution of <i>Planctomycetota</i> in the Water Column of the Remote North Pacific

The extensive microbial diversity found in the oceans is becoming to be uncovered despite limited knowledge and cultured representatives for many taxonomic groups. This study analysed the distribution and diversity of Planctomycetota at four water column profiles of the Eastern North Pacific subtropical front (ENPSF) using 16S rRNA gene sequencing. A dual approach, utilising PacBio long-reads and Illumina short-reads, was employed to enhance the accuracy of taxonomic assignment and compare sequencing methods. The diversity of Planctomycetota increased below the deep chlorophyll maximum level (175-200 m) and in the mesopelagic layer (500 m), with beta-diversity clustering distinctly separating samples according to different depths, resulting in pronounced vertical stratification. This community structure mirrors nutrient availability, as Planctomycetota favour depths between 175 and 200 m, where high nitrate levels are present. More Planctomycetota amplicon sequence variants (ASVs) were identified with PacBio than with Illumina, improving detection of these bacteria. Phylogenetic analyses performed after manual curation of ASVs led to the discovery of several unknown genera of Planctomycetota, indicating that substantial diversity within this group remains to be discovered and studied in remote oligotrophic oceans.