Ecological diversity of harmful algae-attached bacteria in the Southern coastal ecosystem, South Korea

Abstract

The dynamics of particle-attached and free-living bacterial communities can be observed through changes in common harmful algal species. Therefore, we analyzed phytoplankton, bacterial communities, and inorganic nutrient factors from the Jangmok coastal ecosystem at weekly intervals for 210 d. The changes in the phytoplankton community were classified into six groups according to the predominant phytoplankton species. These were, harmful algal blooms of Akashiwo sanguinea (late autumn), Cryptomonas cf. sp (early winter), Skeletonema marni-dorhnii complex (winter), Pseudonitzschia delicatissima (early spring), Cryptomonas cf. sp. (spring), and diatom complexes such as Chatoceros curvisetus and Leptocylindrus danicus (early summer). The indicator species for particle-attached bacteria (PAB) and free-living bacteria (FLB) during each phytoplankton bloom period was based on the indicator value of 59 and 32 species, respectively. In addition, correlation analysis showed that PAB had a higher correlation with phytoplankton than FLB. The PABs, ASV#002 (Kordiimonas lacus), #050 (Aurantibacter aestuarii), #013 (Polaribacter marinivivus), and #075 (Sedimenticola thiotaurini) were strongly correlated with A. sanguina blooms (r > 0.90). Additionally, PAB showed significant correlations with P. delicatissima. These results suggest that extracellular polymeric substances may be involved in the relationship between bacteria and phytoplankton. PAB showed higher alpha diversity than FLB and contained amplicon sequence variants corresponding to 96% of all bacteria. Moreover, potentially pathogenic bacteria were more prevalent in the PAB community. These results highlight the importance of substrate or habitat specificity in potentially pathogenic prokaryotes in the marine environment. It is unclear whether these findings are the result of selection by phytoplankton or bacteria; however, a strategic relationship is found among them. Further study is needed to determine whether this relationship is essential for survival between two organism communities.