ESTIMATION OF THE SEAMOUNT EFFECT ON PLANKTONIC BACTERIA DIVERSITY AND DISTRIBUTION USING ENVIRONMENTAL RNA

Seamounts are widely distributed across the ocean floor, harboring diverse and unique biological communities due to their distinctive topography and hydrodynamic environment. Previous studies utilizing environmental DNA sequencing identified cyanobacteria, gammaproteobacteria, and alphaproteobacteria as dominant taxa, playing pivotal roles in the high biodiversity observed in seamount area. However, environmental DNA can not differentiate between living or dead cells, providing an incomplete picture of the distribution of active bacteria. Environmental RNA, prone to degradation outside the cell, offers insights into the biodiversity of active taxa. We investigated the diversity of active bacteria in the M4 seamounts of the western Pacific Ocean using environmental RNA sequencing in comparison with the results of studies based on environmental DNA sequencing, comparing the results with studies based on environmental DNA sequencing. While the species composition exhibited similarities between RNA and DNA datasets, the proportion of cyanobacteria in RNA was notably higher in DNA in the euphotic zone, indicating elevated metabolic activity. Conversely, the proportion of alphaproteobacteria was significantly lower in the RNA dataset, suggesting reduced metabolic activity. Gammaproteobacteria proportions increased in the RNA dataset at greater seawater depths. The co-occurrence network showed increasing complexity followed by a decrease with rising water depth. The RNA-based network was simpler than its DNA counterpart, yet variations along the water depth were more pronounced. Removing cyanobacteria caused a drastic change in the network, whereas the removal of alphaproteobacteria had minimal impact. In conclusion, this study enhances our understanding of active bacterioplankton diversity and distribution in seamounts through environmental RNA sequencing. The proportion of alphaproteobacteria in the total bacterial community and their role in the co-occurrence network in seamounts may have been overestimated.