Bacteria are the major organic matter consumer in the aquatic ecosystem, they play a key role in the biogeochemical processes. They convert dissolved organic matter into biomass that fuels microbial food webs and transfers energy and carbon to higher trophic levels(Zhao et al., 2017). At the same time bacteria are also critical drivers of particle organic matter mineralization (Bižić-Ionescu et al. 2015). In estuarine systems, which were subject to intensive anthropogenic disturbance, microbes take significant parts in the decomposition of autochthonous and allochthonous organic matter as well as removal of contaminants. The strong natural and anthropogenic gradients in estuaries make them ideal niches for investigating the response of microbes to various environmental forces (Telesh and Khlebovich, 2010).
Bacterioplankton is frequently categorized as either free-living or attached to particles(Mohit et al., 2014). Attached bacteria may have very high local concentrations compared to free-living bacteria and also provide nutrition for macroscopic filter feeders. However, free-living bacteria are often more abundant than particle-attached bacteria in diverse marine (Ghiglione et al., 2007) as well as freshwater ecosystems (Grossart and Simon, 1998). Free-living and attached communities can differ both morphologically and physiologically, for example, attached bacteria are often larger (Acinas et al., 1999) and are reported to have lower growth efficiency than free-living bacteria, with comparatively less bacterial biomass produced per quantity of organic substrate taken up (Grossart et al., 2003). Some studies report higher per-cell metabolic activity for particle-attached communities compared to free-living communities (Becquevort et al., 1998; Grossart et al. 2007), while other studies report the opposite (Martinez et al., 1996). Ghiglione et al. (2007) reported diel changes in bacterial activity, with the free-living fraction, shows higher activity during the day and the attached fraction more active at night. Such observations suggest that the two communities are favored under different conditions, and understanding the dynamics and diversity of bacterial communities is an important step in characterizing an ecosystem as well as developing indicators to study ecosystem health and function(Mohit et al., 2014).
inputs, which are characterized by high nutrients, salinity gradient, and abundant suspended particles. The complex environmental variations along estuaries make it ideal natural laboratories for studying the association between microbial community and different environmental factors. A number of microbial community studies had conducted in PRE region(Huang et al., 2004; Zhou et al., 2011; Liu et al., 2015; Zhang, Xiao, and Jiao, 2016; Li et al., 2017). However, very few study had investigated both the particle-attached and the free-living communities(Zhang, Xiao, and Jiao, 2016). Most of the studies only did sampling and analyzed the free-living fraction microbial communities(Zhou et al., 2011; Liu et al., 2015; Li et al., 2017). However, to fully understand the microbial community structure and dynamically associated with different environmental factors (e.g., light condition, water temperature, nutrient availability and salinity gradient), and prepare knowledge for future environmental management and remediation, both particle-attached and free-living bacterial communities need to be further investigated.
In this study, the bacterial community composition in two size fractions (0.2–3, and>3μm) will be analyzed for Pearl River Estuary and adjacent coastal SCS areas. 16S Metagenomic Sequencing will be performed to investigate the bacterial community composition. The objectives of this study were to compare both particle-attached and free-living bacterial community composition and their relationships with different physical, chemical, and biological parameters. By determining the variations of both particle-attached and free-living bacterioplankton so as to gain insight into the environmental factors and marine physical processes that regulated microbial dynamics, and to better understand the ecological function of these two different bacteria categories.