Abstract
In this study, Illumina MiSeq sequencing technique was employed to explore the characteristics and dynamics of cyanobacteria–heterotrophic bacteria between two estuarine reservoirs in sub-tropical (reservoir A in Shanghai) and tropical (reservoir B in Singapore) regions. The results indicated that significant differences in bacterial community composition were found between two estuarine reservoirs, which influenced by varied environmental variables. The environmental heterogeneity in reservoir A was much higher, which indicated that the composition of bacterial community in reservoir A was more complex. In contrast, reservoir B provided a suitable and temperate water environment conditions for bacterial growth, which resulted in higher community diversity and less co-exclusion correlations. The molecular ecological network indicated that the presence of dominant bacterial community in each of the reservoir were significant different. These differences mainly reflected the responses of bacterial community to the variations of environmental variables. Although Synechococcus was the dominant cyanobacterial species in both reservoirs, it exhibited co-occurrence patterns with different heterotrophic bacteria between reservoirs. In addition, the cyanobacteria–heterotrophic bacteria interaction exhibited highly dynamic variations, which was affected by nutrition and survive space. Also, the co-occurrence of Microcystis and Pseudanabaena found in reservoir B implied that the non-N-fixing Microcystis accompanied with N-fixing Pseudanabeana occurrence in freshwater lakes, so as to better meet the demand for nitrogen source.
Highlights
In aquatic ecosystems, the balanced relationships of cyanobacteria–heterotrophic bacteria play important roles in maintaining aquatic ecologic stability (Cole, 1982)
The step-wise distance-based linear model (DistLM) indicated that total nitrogen (TN), TN/total phosphorous (TP), temperature, chloride, Ca2+, Mg2+, sulfate, total cyanobacterial 16S gene copies and rainfall (30 d) were the main environmental factors influencing the variations of bacterial community composition in reservoir A (Table 1)
The two-dimensional non-metric multidimensional scaling (nMDS) plot of reservoir A showed that most of samples presented significant seasonal distribution, where samples from May to October were correlated with high temperature, chlorophyll-a, pH, total cyanobacterial 16S gene copies and rainfall (30 d); whereas samples from November to April were more correlated with high concentrations of chloride, sulfate, Ca2+, Mg2+, TN and TN/TP (Figure 4A)
Summary
The balanced relationships of cyanobacteria–heterotrophic bacteria play important roles in maintaining aquatic ecologic stability (Cole, 1982). The estuarine ecosystems have higher complex structure and diversity than other aquatic ecosystems including freshwater lakes and rivers (Vasconcelos et al, 2015) These complex environmental conditions significantly affect the bacterial community composition in these areas (Dang et al, 2008; Dang and Lovell, 2016). Changes of bacterial community composition are expected to cause functional consequences, which can result in substantial alteration of ecosystems, such as decreases in primary productivity or changes of nitrogen (N) cycle (Dang et al, 2010, 2013) More important, these changes may affect the correlations of cyanobacteria– heterotrophic bacteria, which might cause potential harmful cyanobacteria blooms
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