Abstract
Particle-associated bacteria (PAB) and free-living bacteria (FLB) from aquatic environments during phytoplankton blooms differ in their physical distance from algae. Both the interactions within PAB and FLB community fractions and their relationship with the surrounding environmental properties are largely unknown. Here, by using high-throughput sequencing and network-based analyses, we compared the community and network characteristics of PAB and FLB from a plateau lake during a Microcystis aeruginosa bloom. Results showed that PAB and FLB differed significantly in diversity, structure and microbial connecting network. PAB communities were characterized by highly similar bacterial community structure in different sites, tighter network connections, important topological roles for the bloom-causing M. aeruginosa and Alphaproteobacteria, especially for the potentially nitrogen-fixing (Pleomorphomonas) and algicidal bacteria (Brevundimonas sp.). FLB communities were sensitive to the detected environmental factors and were characterized by significantly higher bacterial diversity, less connectivity, larger network size and marginal role of M. aeruginosa. In both networks, covariation among bacterial taxa was extensive (>88% positive connections), and bacteria potentially affiliated with biogeochemical cycling of nitrogen (i.e., denitrification, nitrogen-fixation and nitrite-oxidization) were important in occupying module hubs, such as Meganema, Pleomorphomonas, and Nitrospira. These findings highlight the importance of considering microbial network interactions for the understanding of blooms.
Highlights
Algal blooms could cause severe ecological problems in both marine and fresh water and have both a high frequency and large distribution (Yang C. et al, 2012; Woodhouse et al, 2016)
In this study, we focused on the following questions during a cyanobacterial bloom in a freshwater lake in the Yunnan-Guizhou plateau: (1) the differences in community composition between Particle-associated bacteria (PAB) and free-living bacteria (FLB) during cyanobacterial blooms; (2) how they respond to environmental fluctuation; and most of all, (3) how the microbes interact in PAB and FLB, considering the role of cyanobacteria in the network interactions
A large bloom dominated the northern portion of Dianchi Lake during the sampling period (Figure 1)
Summary
Algal blooms could cause severe ecological problems in both marine and fresh water and have both a high frequency and large distribution (Yang C. et al, 2012; Woodhouse et al, 2016). Bacteria can live either freely or attached to particle (e.g., algae) surfaces (Jasti et al, 2005), with obvious differences in community composition, phylogeny and metabolism (Riemann and Winding, 2001; Grossart et al, 2005; Cao et al, 2015). The importance of FLB and PAB during algal blooms has been widely addressed (Tuomainen et al, 2006; Cai et al, 2013b; Shao et al, 2014; Cao et al, 2015; Yang C. et al, 2015), the bacterial interactions within the two fractions are still unknown
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