Abstract
Phaeocystis globosa (P. globosa) is one of the dominant algae during harmful algal blooms (HABs) in coastal regions of Southern China. P. globosa exhibits complex heteromorphic life cycles that could switch between solitary cells and colonies. The ecological success of P. globosa has been attributed to its colony formation, although underlying mechanisms remain unknown. Here, we investigated different bacterial communities associated with P. globosa colonies and their influence on colony formation of two P. globosa strains isolated from coastal waters of Guangxi (GX) and Shantou (ST). Eight operational taxonomic units (OTUs) were observed in ST co-cultures and were identified as biomarkers based on Linear discriminant analysis Effect Size (LEfSe) analysis, while seven biomarkers were identified in P. globosa GX co-cultures. Bacterial communities associated with the P. globosa GX were more diverse than those of the ST strain. The most dominant phylum in the two co-cultures was Proteobacteria, within which Marinobacter was the most abundant genus in both GX and ST co-cultures. Bacteroidota were only observed in the GX co-cultures and Planctomycetota were only observed in the ST co-cultures. Co-culture experiments revealed that P. globosa colony formation was not influenced by low and medium cell densities of Marinobacter sp. GS7, but was inhibited by high cell densities of Marinobacter sp. GS7. Overall, these results indicated that the associated bacteria are selected by different P. globosa strains, which may affect the colony formation and development of P. globosa.
Highlights
The Phaeocystis are globally distributed marine algae, which cause frequent coastal harmful algal blooms and play important roles in carbon and sulfur biogeochemical cycling (Schoemann et al, 2005; Verity et al, 2007)
Significant differences were not observed for the Shannon and Simpson indices when comparing the GX and ST communities (Figure 1A), which is consistent with their bacterial operational taxonomic units (OTUs) compositions (ANOSIM, p > 0.05 for Bray–Curtis metrics) through the Non-parametric multidimensional scaling (NMDS) analysis (Figure 1B)
Bacterial communities associated with two P. globosa strains and their influence on colony formation were evaluated
Summary
The Phaeocystis are globally distributed marine algae, which cause frequent coastal harmful algal blooms and play important roles in carbon and sulfur biogeochemical cycling (Schoemann et al, 2005; Verity et al, 2007). Owing to their negative effects on marine ecosystems, fisheries, and local economies, the bloom development of Phaeocystis has gained much attention in recent decades (Schoemann et al, 2005). Several abiotic and biological factors have been proposed to affect the colony formation of Phaeocystis, such as light exposure (Wang et al, 2014), macronutrient levels (Wang et al, 2010), temperatures (Wang et al, 2010), and zooplankton grazing (Jakobsen and Tang, 2002), or combinations of these factors, while the molecular mechanisms underlying colony formation remain enigmatic (Verity et al, 2007)
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