Ammonia removal from prawn aquaculture water using immobilized nitrifying bacteria

The mechanism of reactive oxygen species generation, DNA damage and apoptosis in hemocytes of Litopenaeus vannamei under ammonia nitrogen exposure

Ammonia-N poses a significant threat to aquatic animals. However, the mechanism of ROS production leading to DNA damage in hemocytes of crustaceans is still unclear. Additionally, the mechanism that cells respond to DNA damage by activating complex signaling networks has not been well studied. Therefore, we exposed shrimp to 0, 2, 10, and 20 mg/L NH4Cl for 0, 3, 6, 12, 24, 48, and 72 h, and explored the alterations in endoplasmic reticulum stress and mitochondrial fission, DNA damage, repair, autophagy and apoptosis. The findings revealed that ammonia exposure led to an increase in plasma ammonia content and neurotransmitter content (DA, 5-HT, ACh), and significant changes in gene expression of PLC and Ca2+ levels. The expression of disulfide bond formation-related genes (PDI, ERO1) and mitochondrial fission-related genes (Drp1, FIS1) were significantly increased, and the unfolded protein response was initiated. Simultaneously, ammonia-N exposure leads to an increase in ROS levels in hemocytes, resulting in DNA damage. DNA repair and autophagy were considerably influenced by ammonia-N exposure, as evidenced by changes in DNA repair and autophagy-related genes in hemocytes. Subsequently, apoptosis was induced by ammonia-N exposure, and this activation was associated with a caspase-dependent pathway and caspase-independent pathway, ultimately leading to a decrease in total hemocytes count. Overall, we hypothesized that neurotransmitters in the plasma of shrimp after ammonia-N exposure bind to receptors on hemocytes membrane, causing endoplasmic reticulum stress through the PLC-IP3R-Ca2+ signaling pathway and leading to mitochondrial fission. Consequently, this process resulted in increased ROS levels, hindered DNA repair, suppressed autophagy, and activated apoptosis. These cascading effects ultimately led to a reduction in total hemocytes count. The present study provides a molecular support for the understanding of the detrimental toxicity of ammonia-N exposure to crustaceans.

Acute Ammonia Causes Pathogenic Dysbiosis of Shrimp Gut Biofilms

Acute ammonia exposure has detrimental effects on shrimp, but the underlying mechanisms remain to be fully explored. In the present study, we investigated the impact of acute ammonia exposure on the gut microbiota of the white shrimp Litopenaeus vannamei and its association with shrimp mortality. Exposure to a lethal concentration of ammonia for 48 h resulted in increased mortality in L. vannamei, with severe damage to the hepatopancreas. Ammonia exposure led to a significant decrease in gut microbial diversity, along with the loss of beneficial bacterial taxa and the proliferation of pathogenic Vibrio strains. A phenotypic analysis revealed a transition from the dominance of aerobic to facultative anaerobic strains due to ammonia exposure. A functional analysis revealed that ammonia exposure led to an enrichment of genes related to biofilm formation, host colonization, and virulence pathogenicity. A species-level analysis and experiments suggest the key role of a Vibrio harveyi strain in causing shrimp disease and specificity under distinct environments. These findings provide new information on the mechanism of shrimp disease under environmental changes.

A multi-step nitrifying microbial enrichment to remove ammonia and nitrite in brackish aquaculture systems

One of the most important advancements in harnessing the biological nitrification in the field is enrichment solution of nitrifying microbial consortia. In the current study, we developed an improved multi-step enrichment to amplify a targeted microbial consortium from a sediment sample collected in tropical mangrove, Vietnam. The results showed that it took 122 culturing days with five unique continuous enrichment steps, the microbial consortium consumed total 5665 mgN L^-1. Relative substrate removal rate increased rapidly from 0.114 mgN L^-1 h^-1 at the end of the first-step enrichment up to 3.58 mgN L^-1 h^-1 at the end of the fifth-step enrichment. High-throughput sequencing revealed that Nitrospirae, Proteobacteria and Bacteroidetes were the dominant taxa at the phylum level while Nitrospira, Marinobacter, Denitromonas and Nitrosomonas were the dominant taxa at the genus level in the enriched consortia. A pilot-scale experiment for shrimp cultivation of L. vannamei in 84 day-period proved the efficiency of Total ammonium nitrogen and nitrite removal in the consortium-activated treatment was much higher than the control.

Modification of expanded clay carrier for enhancing the immobilization and nitrogen removal capacity of nitrifying and denitrifying bacteria in the aquaculture system

In aquaculture systems, the treatment of nitrogen pollution has always been a center of attention due to its impact on productiveness. The bioremediation method based on simultaneous nitrification and denitrification was often used to effectively remove ammonium, nitrite, and nitrate compounds. In addition, the attachment and biofilm formation of the nitrogen-converting bacteria on carriers had superior removal efficiency over the suspended bacteria. Thus, this study focused on the fabrication of a porosity floatable expanded clay (EC) carrier that provided the basic structure for the immobilization of the nitrifiers Nitrosomonas sp., Nitrobacter sp., and the denitrifier Bacillus sp. The EC was also coated with alginate and essential nutrient to support the cohesion and growth of bacteria. Especially, the selected Bacillus sp. previously proved was able to reduce nitrite/nitrate in aerobic conditions. The co-immobilization of these three aerobic bacteria on the prepared carrier would simply the treatment process in practical use. Initial results showed that the integration of essential nutrients (N, P, K) on alginate coated EC (EC_Alg_N) increased bacterial density to (57 ± 3) × 10⁷ - (430 ± 30) × 10⁸ CFU/g, which then led to the enhancement of removal efficiency up to 91.62 ± 0.67% in the medium containing initial nitrogen content of 60 mg-N/L. The nitrogen removal efficacy of bacterial immobilized EC_Alg_N remained at 83.95 ± 0.15% after being reused for 6 cycles. In conclusion, the bacterial immobilized EC_Alg_N could be a potential material for nitrogen polluted wastewater treatment in aquaculture systems.

Analysis of rapid culture of high-efficiency nitrifying bacteria and immobilized filler application for the treatment of municipal wastewater

Activated sludge from the A²/O process in a wastewater treatment plant (WWTP) was used as the seed sludge for enrichment to achieve faster growth of nitrifying bacteria and higher nitrification efficiency of the filler made by nitrifying bacteria. The bacterial community was enriched in a self-circulating bacteria culture tank by a continuous ammonia feeding mode. The study found that the nitrifying bacteria community was enriched in 38 days with the ammonia oxidation rate of approximately 275.58 mg (L h)⁻¹. High-throughput sequencing demonstrated that Nitrosomonas belonging to ammonia-oxidizing bacteria (AOB) was predominant in the sludge after 38 days at a ratio extending from 0.43% to 61.91%. The enriched sludge was used as the bacterial source and the immobilization was carried out with polyvinyl alcohol (PVA). After the recovery culture, the ammonia oxidation rate of the filler was up to 44.61 mg (L h)⁻¹ for the treatment of municipal wastewater, and the effluent ammonia was below 1 mg L⁻¹, indicating that the immobilized filler is effective for municipal wastewater nitrification. Scanning electron microscope (SEM) observations showed that immobilized fillers were highly porous and bacteria adhered to the network structure, demonstrating that the filler provided a good growth microenvironment for microorganisms.

This research proposed an improved method to solve the nitrification problem.

Enrichment of nitrifying bacteria and microbial diversity analysis by high-throughput sequencing

The nitrifying bacteria community can be enriched by an alternating operation mode.

The denitrification characteristics of Pseudomonas stutzeri SC221-M and its application to water quality control in grass carp aquaculture

To reduce ammonium and nitrite in aquaculture water, an isolate of the denitrifying bacterium Pseudomonas stutzeri, SC221-M, was obtained. The effects of various nitrogen and carbon sources, the ratio of carbon to nitrogen and temperature on bacterial growth, denitrification rates and the expression levels of nirS and nosZ in SC221-M were studied. The following conditions were determined to be optimal for growth and denitrification in SC221-M: NaNO₂ as the nitrogen source, sodium citrate as the carbon source, a carbon to nitrogen ratio range of 4–8, and a temperature range of 20–35°C. Subsequently, SC221-M and the Bacillus cereus BSC24 strain were selected to generate microbial preparations. The results showed that addition of the microbial preparations decreased various hydrochemical parameters, including total dissolved solids, ammonium, nitrite, total nitrogen and the chemical oxygen demand. Nitrogen removal rates were highest on day 9; the removal rates of BSC24, SC221-M, a mixed preparation and a 3× mixed preparation were 24.5%, 26.6%, 53.9% and 53.4%, respectively. The mixed preparation (SC221-M+BSC24) was more effective at removing nitrogen than either the SC221-M or BSC24 preparation. Roche 454 pyrosequencing and subsequent analysis indicated that the control and other groups formed separate clusters, and the microbial community structure in the water changed significantly after the addition of microbial preparations. These results indicate that the addition of microbial preparations can improve both the water quality and microbial community structure in an experimental aquaculture system. P. stutzeri strain SC221-M and its related microbial preparations are potential candidates for the regulation of water quality in commercial aquaculture systems.

The Quality Control of Eutrophic Culture Sediment by Immobilized Cells and Conditions Manipulation

The sediment in intensive culture pond is overloaded by substantial unused nutrients and is conventionally discharged into adjacent coastal areas, which is detrimental to environment. This paper produced a preliminary quality control experiment to mitigate pollution of culture sediment by immobilized Bacillus sp. HSW cells on the composite carrier of sodium alginate and artificial zeolite. Glucose and calcium peroxide respectively were used to improve the sediment conditions of C/N ratio and oxygen level. The sediment quality was monitored periodically for 30 days. The results showed that biocontrol by immobilized Bacillus sp. HSW cells alone would be infeasible. However, the immobilized cells would better perform under controlled conditions. The significant decreases for total nitrogen (TN), total ammonia nitrogen (TAN), and organic nitrogen (ON) were observed at 71%, 91% and 64%, respectively. The phosphorus precipitated as phosphate raised approximately 120 mg/kg, and 60% of organic phosphorus was removed in 30 days. Moreover, the total bacteria abundance presented an obvious increase for over an order of magnitude, which was positive relationship (p < 0.01) to the removal rates of ON and OP. Therefore, the immobilized cells accompanied by environmental manipulation are promising for biocontrol of culture sediment.

Water quality and bacteriology in an aquaculture facility equipped with a new aeration system

The HOBAS aeration system was tested to compare changes in environmental and bacteriological parameters in ponds growing Penaeus monodon during a single production cycle. The stocking density in the aerated pond was doubled to 12 post-larvae (PL) m(-2) in contrast to the non-aerated pond with 6 (PL) m(-2). Microbial abundance in the ponds ranged between 10(5-6) cells ml(-1). Among the physiological groups of bacteria enumerated, the heterotrophs dominated with an abundance of 10(4) CFU ml(-1). Of the nitrogen and sulfur cycle bacteria, the nitrifiers flourished in the aerated pond and could maintain ammonia-N concentration within permissible levels. Bacterial activity also maintained sulfide concentrations at < 0.03 mg l(-1). Non-aerated conditions promoted denitrification maintaining nitrate concentration between 0.32 and 0.98 microM NO(3)(-)-N l(-1). However, a marked increase in ammonium content was observed in the non-aerated pond at the end of the culture period. Thus in high-density ponds, the aerators served to stimulate bacterial growth and activity which consequently maintained the quality of the water to match that of low-density ponds. Accordingly, these aerators could be effectively used to sustain higher yields. The effluent from the aerated pond is less likely to alter the redox balance of the receiving waters.

Optimization of fermentation media for nitrite oxidizing bacteria using sequential statistical design

The sequential statistical experimental design (Plackett-Burman, factorial, response surface and steepest ascent experiment) was applied to optimize the culture medium of nitrite oxidizing bacteria for improving the nitrite oxidizing rate. Estimated optimum medium composition of the nitrite oxidizing rate was as follows: NaHCO3, 1.86gl(-1); NaNO2, 2.04gl(-1); Na2CO3, 0.2gl(-1); NaCl, 0.2gl(-1); KH2PO4, 0.1gl(-1); MgSO4 x7H2O, 0.1gl(-1); and FeSO4 x 7H2O, 0.01gl(-1). The nitrite oxidizing rate was increased by 48.0% and reached a maximum at 859.5+/-8.4mgNO2-N/gMLSS.d as compared to 580.7+/-25.8mgNO2-N/gMLSS x d. In the field trial, 50L of nitrite oxidizing bacteria concentrate (1.99gVSS/L) with 850mgNO2-N/gMLSS x d were added to 0.6ha of the aquaculture water. Nitrite level in all treated ponds remained very low compared to the steady increase observed in all of the control ponds during 7 days.

Hydrodynamic characteristics of airlift nitrifying reactor using carrier-induced granular sludge

Since nitrification is the rate-limiting step in the biological nitrogen removal from wastewater, many studies have been conducted on the immobilization of nitrifying bacteria. A laboratory-scale investigation was carried out to scrutinize the effectiveness of activated carbon carrier addition for granulation of nitrifying sludge in a continuous-flow airlift bioreactor and to study the hydrodynamics of the reactor with carrier-induced granules. The results showed that the granular sludge began to appear and matured 60 and 108 days, respectively, after addition of carriers, while no granule was observed in the absence of carriers in the control test. The mature granules had a diameter of 0.5-5 mm (1.6 mm in average), settling velocity 22.3-55.8 m h(-1) and specific gravity of 1.086. The relationship between the two important hydrodynamic coefficients, i.e. gas holdup and liquid circulation velocity, and the superficial gas velocity were established by a simple model and were confirmed experimentally. The model also could predict the critical superficial gas velocity for liquid circulation and that for granules circulation, with respective values of 1.017 and 2.662 cm min(-1), accurately.

The development of a DNA microarray-based assay for the characterization of commercially formulated microbial products

Commercially formulated bioproducts containing a complex consortia of bacteria as an active ingredient pose a significant challenge for regulatory agencies and companies seeking to assess the safety and efficacy of these bioproducts. The main challenge stems from how to characterize the bacterial composition of these products, for which there is presently a lack of suitable methods. A prototype DNA microarray composed of oligonucleotide probes for functional genes, virulence factors, and taxonomic genes for a number of bacterial species was developed to examine the utility of microarray technology as a molecular tool for characterizing consortia bioproducts. The genomic DNA from four different products was extracted by two methods and examined with the microarray prototype and by denaturing gradient gel electrophoresis (DGGE). Although the identity of the consortial species remains unknown, the microarray assay provided unique and reproducible hybridization patterns for all four products, and agreed with the fingerprints generated by DGGE. The ability to differentiate between a variety of consortia products demonstrates that DNA microarrays have the potential to be a powerful tool in monitoring complex microbial communities.