Using ozone nanobubbles, and microalgae to promote the removal of nutrients from aquaculture wastewater: Insights from the changes of microbiomes.

Integrated aquaculture wastewater treatment systems (IAWTSs) are widely used in treating aquaculture wastewater with the aeration-microalgae unit serving as an important component. In this study, we artificially constructed an IAWTS and applied two aeration-microalgae methods: ordinary aeration or ozone nanobubbles (ONBs) with microalgae (Nannochloropsis oculata). The impact of N.oculata and ONBs on the removal performance of nutrients and the underlying micro-ecological mechanisms were investigated using 16S rRNA gene amplicon sequencing. The results demonstrated that the combined use of ONBs and N.oculata exhibited superior purification effects with 78.25%, 76.59% and 86.71% removal of CODMn, TN and TP. N.oculata played a pivotal role as the primary element in wastewater purification, while ONBs influenced nutrient dynamics by affecting both N.oculata and bacterial communities. N.oculata actively shaped bacterial communities, with a specific focus on nitrogen and phosphorus cycling in the micro-environment remodeled by ONBs. Rare bacterial communities displayed heightened activity in response to the changes in N.oculata, ONBs, and nutrient levels. These findings provide a novel approach to improve the technological processes the IAWTS, contributing to the advancement of sustainable aquaculture practices by offering valuable insights into wastewater purification efficiency and micro-ecological mechanisms.

Exogenous compound bacteria enhance the nutrient removal efficiency of integrated bioremediation systems: Functional genes and microorganisms play key roles.

With the continuous development of intensive mariculture, the application of the integrated bioremediation system of aquaculture wastewater (IBSAW) is increasingly promoted. However, the process and nutrients removal performance of the IBSAW need to be further optimized due to its immature technologies. In this study, exogenous compound bacteria (ECB) were added to IBSAW to investigate its pollutants removal efficiency and the relevant mechanisms. High-throughput sequencing and Geochip gene array were used to analyze the correlation between nutrients and bacteria, and the abundance of N and P cycling genes were quantified. Multivariable statistics, dimensionality reduction analysis, and network analysis were applied to explore the mechanisms of IBSAW operation. The results showed that the nutrients decreased significantly after adding ECB, with the brush treatment group significantly outperforming the ceramsite in removing NO3- and PO43-. Ceramsite has an advantage in removing NO2--N. The addition of ECB and different substrates significantly affected the composition of bacterial communities. The contents of nosZ and nirKS related to denitrification in the treatment groups were significantly higher than those in the control group, and the contents in the brush treatment group were significantly higher than that of ceramsite. The biomarkers Psychroserpens and Ruegeria on the biofilm of the brush treatment group were positively correlated with nirKS, while Mycobacterium, Erythrobacter and Paracoccus, Pseudohaliea in the ceramsite group were positively correlated with nirS and nirK, respectively. Therefore, it is speculated that the ECB significantly promoted the increase of denitrification bacteria by affecting the composition of bacterial communities, and the ECB combined with functional genera improved the efficiency of nutrients removal in the system. This study provided a reference for understanding the process and mechanism of nutrients removal, optimizing the wastewater purification technology of the IBSAW and improving the performance of the system.

The effects of Cyclina sinensis bioturbation on alkaline phosphatase and total microbial hydrolytic activities in marine clam-shrimp integrated ponds.

This study investigated the influence of Venus clam Cyclina sinensis bioturbation activities on the total benthic microbial and phosphatase activities and selected sediment properties: total phosphorus (TP), total organic nitrogen (TON), and total organic carbon (TOC) in aquaculture ponds. Sediments samples from clam-shrimp integrated pond and non-clam integrated pond were sampled for the study, in which sediment microbial activity (MBA) and alkaline phosphatase activity (APA), sediment organic contents (TP, TON, TOC, TOM) and water quality parameter (dissolved oxygen, temperature, pH, and moisture content) were analyzed. The p-nitrophenyl phosphate disodium (p-NPP) and fluorescein diacetate (FDA) were adopted to measure APA and MBA, respectively. Results indicated that MBA and alkaline phosphatase activity (APA) in sediments significantly increased in the pond cultured with clam/shrimp compared to a non-clam cultured pond. Phosphorus concentration increased significantly and varied among months (P < 0.05), implying an increased phosphate mineralization in the sediments. The concentrations of TON and TOC did not differ significantly among months and with the treatments (P > 0.05), implying increased TON mineralization. Correlation analyses showed that there was a positive correlation with the total MBA, APA, phosphorus concentration, and organic matter content within the sediments bioturbated by the Venus clam. The results suggest that, the Venus clam sediment reworking mechanisms influenced the sediment-microbial and APA activities and mineralization, thereby affecting the pond alkaline phosphatase enzyme-related activities.

Bacterioplankton community assembly in migratory fish habitat: a case study of the southern East China Sea.

The health conditions of fish habitats, which affect fish health, can be reflected by the structure and ecological function of the bacterioplankton community to some extent. However, studies on bacterioplankton in the whole habitat of migratory fish, which can be divided into different functional types, are still limited. To fill this gap, we investigated the characteristics of bacterioplankton communities in three habitat types in a typical migratory fish habitat, the southern East China Sea, using 16S rRNA gene amplicon sequencing. Our study showed that the structure of the bacterioplankton community was significantly divided according to habitat type. Dispersal limitation and heterogeneous selection both contributed to the bacterioplankton community assembly through estimation of ß nearest taxon index (ßNTI), and redundancy analysis (RDA) further explained that the water temperature, salinity, and nutrients were deterministic factors responsible for differences in the bacterioplankton community. Additionally, different ecological functional modules dominated by functional bacterioplankton in different habitat types were identified by co-occurrence network analysis, including a hydrocarbon-degrading module dominated by Psychrobacter and health-related modules containing Ascidiaceihabitans and Pseudoalteromonas. Based on the composition of environmental bacterioplankton, our findings provide a theoretical basis for understanding the distribution of different habitat types in the southern East China Sea during the breeding period of migratory fish.

Microbial community and interspecies interaction during grazing of ark shell bivalve (Scapharca subcrenata) in a full-scale bioremediation system of mariculture effluents.

A novel biological approach using ark shell bivalves as potential species for remediation of effluents was studied to determine the microbial community interspecies interaction and nutrient cycling in a restoration system of mariculture effluents. A field study showed that Scapharca subcrenata was the main driver of the microbial community's interspecies-interaction (PERMANOVA, R = 0.0572, P = 0.005) in the treatment zone (TZ). Analysis of co-occurrence networks based on random matrix theory (RMT) indicated that the network's complexity parameters were enhanced in the TZ and disrupted in the control zone (CZ) due to eutrophic disturbances. Concurrently, the TZ was correlated with more profound network modifications (i.e., higher modularity, total nodes (n), cohesion, and proportion of positive links), suggesting that S. subcrenata influenced microbial interspecies interactions in the system. Similarly, the co-occurring networks of generalists Proteobacteria (OTU2037) at genus Anaerospora and Actinobacteria (OTU9660) at genus Candidatus aquiluna for anaerobic ammonia-oxidation (ANAMMOX) were highly significant in the TZ. The top-down and bottom-up forces of S. subcrenata influenced the removal efficiency of nitrogenous compounds by reducing 81.51% of nitrite (NO2--N), 84.61% of total ammonium nitrogen (TAN) and 72.78% of nitrate (NO3--N). Generally, the introduction of ark shell bivalve (S. subcrenata) to the system as a biofilter provides a very low-cost bioremediation technology that could be one of the best restorations and remediation tools for mariculture effluents.

Bacterioplankton community in response to biological filters (clam, biofilm, and macrophytes) in an integrated aquaculture wastewater bioremediation system.

Integrated systems with appropriate bio-filters can be used to treat aquaculture effluents. However, the information on bio-filters that alters the ecological functions of the bacterioplankton community (BC) in biodegradation of the aquaculture effluents remains controversial. In this study, we implemented a comprehensive restoration technology combined with bio-filters [biofilm, clam (Tegillarca granosa), and macrophytes (Spartina anglica)] to investigate their influence on the stability of the BC and nutrient removal. We found that the diversity of BC was linked with biogeochemical factors in processing and upcycling nitrogen-rich effluents into high-value biomass. The BC exhibited significant distinct patterns in the bio-filter areas. Potential biomarkers for constrained harmfully algae-bacteria (Nitriliruptoraceae, Bacillales, and Rhodobacteraceae) and nutrient removal were significantly higher in the bio-filters areas. The bio-filters significantly promoted the restoration effects of N and P balance by reducing 82.34% of total nitrogen (TN) and 81.64% of total phosphorus (TP) loads at the water interface. The main mechanisms for TN and TP removal and nutrient transformation were achieved by assimilation and absorption by the emergent macrophytes (Spartina anglica). The bio-filters significantly influenced the biodegradability and resolvability of particulate organic matter through ammonification, nitrification, and denitrification of microbes, which meliorated the nutrient removal. Beside bio-filter effects, the BC was significantly controlled by abiotic factors [nitrate (NO3--N), dissolved oxygen (DO), total nitrogen (TN), and water temperature (WT)], and biotic factors (chlorophyll ɑ and green algae). Our study revealed that the co-existence system with bio-filters may greatly improve our understanding on the ecological functions of the BC in aquaculture systems. Overall, combined bio-filters provide an opportunity for the development of efficient and optimized aquaculture wastewater treatment technology.

Bioturbation by the razor clam (Sinonovacula constricta) on the microbial community and enzymatic activities in the sediment of an ecological aquaculture wastewater treatment system.

Bioturbation by the razor clam, Sinonovacula constricta, influenced the redox conditions and changed the sedimentary environment, providing a suitable micro-environment for microbial growth. However, the mechanism of the integrated razor clam-microbial community in organic matter mineralization remains elusive. To study this mechanism, an in situ experiment was conducted to investigate the bioturbation effects of S. constricta on the microbial community and enzyme activities in the sediment of an ecological aquaculture wastewater treatment system. According to principal coordinate analysis (PCoA) and PERMANOVA, we found that the microbial community was significantly (P < 0.05) influenced by the bioturbation effect of S. constricta. Linear discriminant analysis effect size (LEfSe) showed that species involved in reduced effluent concentrations of TN and TP, such as Prolixibacteraceae, Nitrospira and Actinobacteria, were increased significantly (P < 0.05) by S. constricta. Molecular ecological network (MENs) analysis indicated that the bioturbation effect of S. constricta increased the complexity of interspecies interaction and changed the topological properties of individual OTUs. The results elucidated that S. constricta increased the microbial community network, as substantiated by a higher total number of nodes and a shorter geodesic distance. Zi < 2.5 and Pi <0.62 in MENs showed that the S. constricta treatment significantly increased (P < 0.05) the potential microbial community, with the keystone (OTU747049) Proteobacteria and (OTU74388) Bacteroidetes family Prolixibacteraceae, which connected different co-expressed OTUs. Furthermore, S. constricta significantly increased (P < 0.05) the enzymatic activities (alkaline phosphatase (APA), dehydrogenase and urease) of the substrate at different sampling depths. Overall, this study provides evidence that the bioturbation effect of S. constricta changes the microbial community structure, increases enzymatic activities and accelerates the degradation of organic matter in an aquaculture wastewater environment.