Spatial Variability and Co-acclimation of Phytoplankton and Bacterioplankton Communities in the Pearl River Estuary, China.

Jianming Zhu,Hui Wang,Yiguo Hong,Sahib Zada,Zhong Hu

doi:10.3389/fmicb.2018.02503

Jianming Zhu, Hui Wang + Show 3 more

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https://doi.org/10.3389/fmicb.2018.02503

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Abstract

Phytoplankton and bacterioplankton play significant roles in estuarine systems. It is important to demonstrate the spatial variability of bacterial and microalgal communities and understand the co-acclimation of these organisms to different environmental factors. In this study, MiSeq sequencing and morphological identification were applied to analyze the variations in bacterial and microalgal communities in the Pearl River Estuary, respectively. Molecular ecological network analysis was used to investigate the potential interactions between microalgae and bacteria and illustrate the responses of these interactions to environmental gradients. The results revealed that microalgal/bacterial communities in freshwater samples were distinct from those in mesohaline water samples. Microalgae affiliated to the genus Skeletonema dominated the mesohaline water phytoplankton communities, while Melosira was the more abundant genus in freshwater communities. Actinobacteria, Alphaproteobacteria, Betaproteobacteria, and Acidimicrobiia dominated bacterial communities in freshwater samples, while Gammaproteobacteria, Bacilli, and Synechococcophycideae were more abundant in mesohaline water samples. Tightly correlations were observed between phytoplankton and bacterioplankton. These interactions were regarded to be key factors in shaping the community structures. Further, the KEGG database and PICRUSt were used to predict the functions of bacterioplankton in the process of nitrogen cycling. The results indicated that denitrification could play an important role in nitrogen loss and might alleviate the eutrophication in the Pearl River Estuary. Collectively, the results in this study revealed that substantial changes in phytoplankton and bacterioplankton communities were correlated with the gradients of environmental parameters in the Pearl River Estuary. The results also demonstrated that the interactions between phytoplankton and bacterioplankton were important for these organisms to acclimate to changing environments.

Highlights

Phytoplankton and bacterioplankton are widely acknowledged as the dominant plankton communities in the oceans and in freshwater (Sarmento and Gasol, 2012)
By analyzing the phytoplankton and bacterioplankton communities in water samples collected from seven sites in the PR Estuary (PRE), this study aims to (1) identify the effects of environmental factors on microbial community structures, (2) reveal the potential co-acclimation of different phytoplankton and bacterioplankton groups to changing environments, and (3) investigate the contribution of these organisms to microorganism-driven nitrogen-cycling in estuarine ecosystems
The salinity at site S6, concentrations of NO2− and NH4+ at site S4 were lower, while concentration of NO3− at sites S3 and S4 were higher than the values of the same parameters at the adjacent stations (Table 1). This could be caused by the dynamic variation in biogeochemical and physical processes in the PRE (Dong et al, 2004)

Summary

Introduction

Phytoplankton and bacterioplankton are widely acknowledged as the dominant plankton communities in the oceans and in freshwater (Sarmento and Gasol, 2012). Phytoplankton are the major primary producers in aquatic ecosystems, capturing energy from sunlight and transforming inorganic matter to organic matter, providing approximately half of the global net primary productivity (NPP) (Field et al, 1998). Phytoplankton often engage in symbiosis with other organisms (especially bacterioplankton) in aquatic ecosystems (Falkowski, 1994). Bacterioplankton represent approximately a quarter of all biomass in the euphotic zones of aquatic habitats and play an important role in aquatic ecosystems by driving biogeochemical cycles (Falkowski et al, 2008). Bacterioplankton can reprocess approximately half of the oceanic NPP in the so-called “microbial loop” (Azam, 1998). Some groups of bacteria, including Rhodobacter, Hyphomicrobium, and Pseudomonas, have been found to be capable of mediating nitrogen cycling by either fixing gaseous nitrogen for utilization by phytoplankton or by denitrifying nitrogenous compounds to nitrogen gas (Shapleigh, 2006)

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