Abstract
Marine Group II (MGII) archaea (Poseidoniales) are the most abundant surface marine planktonic archaea and are widely distributed in both coastal and pelagic waters. The factors affecting their distribution and activity are poorly understood. MGII archaea have the metabolic potential to utilize algae-derived organic matter and are frequently observed in high abundance during or following phytoplankton blooms, suggesting that they are key players of the marine food web. In this study, we studied interactions between MGII archaea and the diverse taxa of phytoplankton in the northern coast of South China Sea. Non-metric multidimensional scaling and cluster analyses demonstrated distinct MGII community patterns in the Pearl River plume (PRP) and the open regions of the northern South China Sea (ONSCS), with MGIIb dominating the former and MGIIa and MGIIb showing remarkable variations in the latter for the same sampling season. Nevertheless, positive correlations (Pearson correlation: R > 0.8 and P < 0.01) in absolute abundances of ribosomal RNA (rRNA)-derived complementary DNA and rRNA genes from network analyses were found between MGII archaea and phytoplankton (cyanobacteria, haptophytes, and stramenopiles in both PRP and ONSCS) among different particle size fractions, indicating their intrinsic relationships under changing environmental conditions. The results of this study may shed light on the multiple interactions between co-existing species in the micro-niches of different oceanic regions.
Highlights
Planktonic archaea are one of the fundamental life forms in the ocean and play essential roles in ecological function and biogeochemical cycles
Both phytoplankton [one-way analysis of variance (ANOVA): P < 0.01] and Marine Group II (MGII) ribosomal RNA (rRNA) genes in PA fractions had significantly higher abundance in the Pearl River plume (PRP) than in the ONSCS, while in FL fractions, similar abundances existed between the two geographical locations
The higher abundances of phytoplankton and MGII in the PRP than in the ONSCS area and the concentrations of nutrients were significantly higher in the PRP than in the ONSCS area, which might result from the high nutrient input from the river and estuary (Supplementary Figures 3, 4; Xie et al, 2018)
Summary
Planktonic archaea are one of the fundamental life forms in the ocean and play essential roles in ecological function and biogeochemical cycles. They amount up to ∼1.3 × 1028 cells, in the same order of magnitude as the bacteria in seawater (Karner et al, 2001). MGII were observed to co-exist with a variety of phytoplankton such as dinophyta, chlorophyta, bacillariophyta, and cyanobacteria in the Pearl River mouth (Xie et al, 2018; Wang et al, 2019) They were found to co-occur with green algae (chlorophyta)-Micromonas pusilla and Bathycoccus, haptophyta-Phaeocystis, and cryptophytaTeleaulax or in a delayed phase with diatom-Chaetoceros and rhaphidophyta-Heterosigma in other coastal waters (Orsi et al, 2015; Needham and Fuhrman, 2016; Needham et al, 2018; Orellana et al, 2019). Glycoside hydrolase, and protease expressed by MGII archaea may have the function of cracking high-molecular-weight organic matters such as oligosaccharide agarose or agaropectin from intact phytoplankton biomass (Martin-Cuadrado et al, 2015; Zhang et al, 2015; Orsi et al, 2016; Rinke et al, 2019; Tully, 2019; Damashek et al, 2021)
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