Diversity of Free-Living and Particle-Attached Prokaryotes in a River-Influenced Coastal Area of the Northern Adriatic Sea

Abstract

The Northern Adriatic Sea is a key area of the Mediterranean Sea, strongly affected by freshwater inputs, mainly from the Po River, which bring high amounts of nutrients as well as organic and inorganic particles. Free-living and particle-attached prokaryotes were characterized by 16S rRNA gene amplicon sequencing of size-fractionated samples collected during a diatom bloom in this area. The diversity of free-living and particle-attached prokaryotic assemblages was investigated with the aim to understand how the microbial communities are structured in the two fractions and whether specific microbial groups are associated to one lifestyle or the other. The results highlight a diverse prokaryotic community dominated by Proteobacteria, Bacteroidetes, and, remarkably, Firmicutes. Taxa within Firmicutes and Alphaproteobacteria are identified as the main particle-attached indicators by LEfSe, while members of Bacteroidetes and Gammaproteobacteria were representative of the free-living lifestyle, although they were also usually found as particle-attached. Collectively, the results suggest that both the free-living and the particle-attached lifestyles are a complex combination of specialization and adaptation to local conditions.

Upper-Layer Bacterioplankton Potentially Impact the Annual Variation and Carbon Cycling of the Bathypelagic Communities in the South China Sea

“…Based on the FAPROTAX analysis, we uncovered that epipelagic-BP connective ASVs held significantly higher carbon cycling functions than BP-specific ASVs. It was consistent with previous observations that particle-associated bacterioplankton carry more abundant active genes than free-living bacteria [26,29,30]. For example, in the Northern Adriatic Sea, one study indicated that most of the functional genes related to substance metabolisms, such as amyA (starch degradation), dmdA (DMSP degradation), ureC (organic nitrogen degradation), and arsC (metal resistance), are more abundant in the particle-associated samples than in the free-living samples [26].…”

“…It was consistent with previous observations that particle-associated bacterioplankton carry more abundant active genes than free-living bacteria [26,29,30]. For example, in the Northern Adriatic Sea, one study indicated that most of the functional genes related to substance metabolisms, such as amyA (starch degradation), dmdA (DMSP degradation), ureC (organic nitrogen degradation), and arsC (metal resistance), are more abundant in the particle-associated samples than in the free-living samples [26]. Furthermore, the particle-associated communities often demonstrate a broader range of carbon cycling enzyme (e.g., polysaccharide hydrolase) activities than the bulk water community [29,30].…”

“…Compared with the BP-specific ASVs, epipelagic-BP connective ASVs were likely to make more impact on the yearly changes of deep-sea bacterioplankton, especially some ASVs belonging to Actinobacteriota, Firmicutes, and Cyanobacteria. Notably, these phyla have consistently been detected with a positive relationship with sinking particles [24][25][26][27]. For example, in the Atlantic Subarctic Upper and Puerto Rico Trench water, the members of Actinobacteriota are observed to dominate the particle-associated bacterioplankton populations [24,25].…”

“…For example, in the Atlantic Subarctic Upper and Puerto Rico Trench water, the members of Actinobacteriota are observed to dominate the particle-associated bacterioplankton populations [24,25]. The taxa within Firmicutes are identified as the leading particle-attached indicators in the Northern Adriatic Sea [26]. In the Baltic Sea, Cyanobacteria ASVs are also found with high abundance in the particles rather than free-living in the water [27].…”

Seasonal and interannual variability of the free‐living and particle‐associated bacteria of a coastal microbiome

“…Our data shows that the long‐term pattern of particle‐associated communities is consistent with these observations, with maximal diversity values in the autumn‐winter transition. On the other hand, as a general rule, richness increases with increasing size fraction in several studies, explained by an increased number of ecological niches (Bižić‐Ionescu et al, 2015 ; Mestre, Borrull et al, 2017 ; Mestre, Ferrera et al, 2017 ; Rieck et al, 2015 ; Yeh & Fuhrman, 2022a ; Yung et al, 2016 ), although higher diversity in free‐living populations have been exceptionally reported in surface (Roth Rosenberg et al, 2021 ; Trano et al, 2022 ) and also in deep marine waters (Salazar et al, 2015 ). Alpha diversity values in the PA communities in our study were higher than those from the FL fraction over all seasons.…”