The significance of salinity in shaping bacterial communities dwelling in estuarine areas has been well documented. However, the influences of other environmental factors such as dissolved oxygen and nutrients in determining distribution patterns of both individual taxa and bacterial communities inhabited local estuarine regions remain elusive. Here, bacterioplankton community structures of surface and bottom waters from eight sites along the Pearl Estuary were characterized with 16S rRNA gene pyrosequencing. The results showed significant differences of bacterioplankton community between freshwater and saltwater sites, and further between surface and bottom waters of saltwater sites. Synechococcus dominated the surface water of saltwater sites while Oceanospirillales, SAR11 and SAR406 were prevalent in the bottom water. Betaproteobacteria was abundant in freshwater sites, with no significant difference between water layers. Occurrence of phylogenetic shifts in taxa affiliated to the same clade was also detected. Dissolved oxygen explained most of the bacterial community variation in the redundancy analysis targeting only freshwater sites, whereas nutrients and salinity explained most of the variation across all samples in the Pearl Estuary. Methylophilales (mainly PE2 clade) was positively correlated to dissolved oxygen, whereas Rhodocyclales (mainly R.12up clade) was negatively correlated. Moreover, high nutrient inputs to the freshwater area of the Pearl Estuary have shifted the bacterial communities toward copiotrophic groups, such as Sphingomonadales. The present study demonstrated that the overall nutrients and freshwater hypoxia play important roles in determining bacterioplankton compositions and provided insights into the potential ecological roles of specific taxa in estuarine environments.

Surface seawater in the South Pacific Gyre (SPG) is one of the cleanest oceanic environments on earth, and the photosynthetic primary production is extremely low. Despite the ecological significance of the largest aquatic desert on our planet, microbial community composition in the ultra-oligotrophic seawater remain largely unknown. In this study, we collected surface seawater along a southern transect of the SPG during the Integrated Ocean Drilling Program (IODP) Expedition 329. Samples from four distinct sites (Sites U1368, U1369, U1370 and U1371) were examined, representing ∼5400 kilometers of transect line from the gyre heart to the edge area. Real-time PCR analysis showed 16S rRNA gene abundance in the gyre seawater, ranging from 5.96×105 to 2.55×106 copies ml−1 for Bacteria and 1.17×103 to 1.90×104 copies ml−1 for Archaea. The results obtained by statistic analyses of 16S rRNA gene clone libraries revealed the community composition in the southern SPG area: diversity richness estimators in the gyre center (Sites U1368 & U1369) are generally lower than those at sites in the gyre edge (Sites U1370 & U1371) and their community structures are clearly distinguishable. Phylogenetic analysis showed the predominance of Proteobacteria (especially Alphaproteobacteria) and Cyanobacteria in bacterial 16S rRNA gene clone libraries, whereas phylotypes of Betaproteobacteria were only detected in the central gyre. Archaeal 16S rRNA genes in the clone libraries were predominated by the sequences of Marine Group II within the Euryarchaeota, and the Crenarchaeota sequences were rarely detected, which is consistent with the real-time PCR data (only 9.9 to 22.1 copies ml−1). We also performed cultivation of heterotrophic microbes onboard, resulting in 18.9% of phylogenetically distinct bacterial isolates at least at the species level. Our results suggest that the distribution and diversity of microbial communities in the SPG surface seawater are closely related to the ultra-oligotrophic oceanographic features in the Pacific Ocean.

Anaerobic ammonium oxidation (anammox) plays an important role in the marine nitrogen cycle. The Pearl Estuary, a typical subtropical estuary characterized by hypoxia upstream and high loads of organic matter and inorganic nutrients caused by anthropogenic activities, has received extensive attention.

Toxic inhibition and wash-out of nitrifying bacteria in traditional single-activated sludge processes frequently cause instability of nitrification in industrial wastewater treatment and limit the total nitrogen (TN) removal efficiency. A novel oxic–hydrolytic–oxic (O/H/O) process based on a three-sludge regime was developed to treat coking wastewater with a high C/N ratio and biological toxicity. The results demonstrated that high COD removal (89.6%, 91.3%, 90.4%, and 87.1% in four different modes) was achieved with the complete elimination of phenol, sulfide, total cyanide, and thiocyanate. TN removal varied from 14.0% to 88.7% at an influent flow of 1.6–2.0 kg of COD m–3 day–1, depending on prenitrification, internal recycling, and the presence of a sufficient carbon source for denitrification. The first oxic (O1) and hydrolytic (H) reactors made predominant contributions to the removal of organic and toxic pollutants. The removal of these pollutants guaranteed a stable and favorable environment for nitrification in the second oxic (O2) reactor, in which high ammonium removal was observed because of the predominance of Nitrosomonas and Nitrospira. The O/H/O process has the potential to become a promising industrial wastewater treatment process because it promotes functions that are independent of microbial and process stability with respect to the removal of pollutants, especially nitrogen.

No abstract