Hongsheng Wu

Presence of diverse Candidatus Methylomirabilis oxyfera‐like bacteria of NC10 phylum in agricultural soils

To better explore the distribution and diversity of Candidatus Methylomirabilis oxyfera (M. oxyfera)‐like bacteria of NC10 phylum in soil environments.

Evidence for anaerobic ammonium oxidation process in freshwater sediments of aquaculture ponds

The anaerobic ammonium oxidation (anammox) process, which can simultaneously remove ammonium and nitrite, both toxic to aquatic animals, can be very important to the aquaculture industry. Here, the presence and activity of anammox bacteria in the sediments of four different freshwater aquaculture ponds were investigated by using Illumina-based 16S rRNA gene sequencing, quantitative PCR assays and 15N stable isotope measurements. Different genera of anammox bacteria were detected in the examined pond sediments, including Candidatus Brocadia, Candidatus Kuenenia and Candidatus Anammoxoglobus, with Candidatus Brocadia being the dominant anammox genus. Quantitative PCR of hydrazine synthase genes showed that the abundance of anammox bacteria ranged from 5.6u2009×u2009104 to 2.1u2009×u2009105 copies g−1 sediment in the examined ponds. The potential anammox rates ranged between 3.7 and 19.4xa0nmolxa0N2u2009g−1 sediment day−1, and the potential denitrification rates varied from 107.1 to 300.3xa0nmolxa0N2u2009g−1 sediment day−1. The anammox process contributed 1.2–15.3xa0% to sediment dinitrogen gas production, while the remainder would be due to denitrification. It is estimated that a total loss of 2.1–10.9xa0gxa0Nxa0m−2 per year could be attributed to the anammox process in the examined ponds, suggesting that this process could contribute to nitrogen removal in freshwater aquaculture ponds.

Cooccurrence and potential role of nitrite- and nitrate-dependent methanotrophs in freshwater marsh sediments

Nitrite- and nitrate-dependent anaerobic methane oxidation are mediated by the NC10 bacteria closely related to Candidatus Methylomirabilis oxyfera (M.xa0oxyfera) and the ANME-2d archaea closely related to Candidatus Methanoperedens nitroreducens (M.xa0nitroreducens), respectively. Here, we investigated the occurrence and activity of both M.xa0oxyfera-like bacteria and M.xa0nitroreducens-like archaea in the sediment of freshwater marshes in Eastern China. The presence of diverse M.xa0oxyfera-like bacteria (>87% identity to M.xa0oxyfera) and M.xa0nitroreducens-like archaea (>96% identity to M.xa0nitroreducens) was confirmed by using Illumina-based total bacterial and archaeal 16S rRNA gene sequencing, respectively. The recovered M.xa0oxyfera-like bacterial sequences accounted for 1.6-4.3% of the total bacterial 16S rRNA pool, and M.xa0nitroreducens-like archaeal sequences accounted for 0.2-1.8% of the total archaeal 16S rRNA pool. The detected numbers of OTUs of the 16S rRNA genes of M.xa0oxyfera-like bacteria and M.xa0nitroreducens-like archaea were 78 and 72, respectively, based on 3% sequence difference. Quantitative PCR showed that the 16S rRNA gene abundance of M.xa0oxyfera-like bacteria (6.1xa0×xa0106-3.2xa0×xa0107 copies g-1 sediment) was 2-4 orders of magnitude higher than that of M.xa0nitroreducens-like archaea (1.4xa0×xa0103-3.2xa0×xa0104 copies g-1 sediment). Stable isotope experiments showed that the addition of both nitrite and nitrate stimulated the anaerobic methane oxidation, while the stimulation by nitrite is more significant than nitrate. Our results provide the first evidence that the M.xa0oxyfera-like bacteria play a more important role than the M.xa0nitroreducens-like archaea in methane cycling in wetland systems.

Phosphate adsorption and precipitation on calcite under calco-carbonic equilibrium condition

Phosphate (PO43-) removal on calcite often entails two processes: adsorption and precipitation. Separating these two processes is of great importance for assessment of PO43- stability after removal. Thus, this study was aimed at finding a critical range of conditions for separating these two processes in calco-carbonic equilibrium, by adjusting PO43- concentration, reaction time and pH. PO43- removal kinetic results showed that: (I) At pH7.7, PO43- removal was mainly by adsorption at initial PO43- concentration ≤2.2xa0mgxa0L-1 and reaction time ≤24xa0h, with dominant precipitation occurring at initial PO43- concentration ≥3xa0mgxa0L-1 after 24xa0h reaction; (II) At pH8.3, adsorption was the key removal process at initial PO43- concentration ≤7.5xa0mgxa0L-1 and reaction time ≤24xa0h, whereas precipitation was observed at initial PO43- concentration of 10xa0mgxa0L-1 after 24xa0h reaction, (III) At pH 9.1 and 10.1, PO43- removal mechanism was mainly by adsorption at initial PO43- concentration ≤10xa0mgxa0L-1 within 24xa0h reaction. Based on the kinetic results, it is suggested that PO43- precipitation will occur after 24xa0h reaction when saturation index of amorphous calcium phosphate is between 1.97 and 2.19. Besides, increasing PO43- concentration does not cause a continuous decline of PO43- removal percentage. Moreover, experimental removal data deviated largely from the theoretical adsorption value by CD-MUSIC model. These indicate occurrence of precipitation which is in agreement with the kinetic result. Therefore our study will provide fundamental reference information for better understanding of phosphorous stabilization after removal by calcite.

Comparative study of phosphorus adsorption behaviors in lake sediments over short and long periods of time: implication for the prediction of the release of phosphorus by CaCl2 and NaHCO3 extraction

Ten sediments were collected from the northern part of Taihu Lake, China. They were incubated for 24xa0h and 80xa0days to analyze the adsorption characteristics. After adsorption, the residual sediments were extracted with 0.01xa0M CaCl2 and 0.5xa0M NaHCO3 separately. Maximum buffer capacities of the Langmuir and Freundlich functions of 80-day incubation were highly correlated with 24xa0h (R2xa0=xa00.97). A longer time would enhance the resistance of the sediments to P changes in the water. Adsorption and NaHCO3-P were highly linearly related with R2xa0>xa00.969, but the relationships between 24xa0h and 80xa0days were different. The relationships between adsorption and CaCl2-P could be better explained (97xa0%) by segmented line models, but the fitting results were affected by incubation time. An interesting finding is that when we plotted the NaHCO3-P and CaCl2-P together by a segmented line model, the data showed a uniform trend unrelated to the incubation time. NaHCO3-P is seldom used to evaluate P status in sediments in comparison with soils. Yet, our results suggested NaHCO3-P is a good bridge to link the sediments P retention ability and P release risk. Due to its simplicity, NaHCO3-P has promising potential in predicting the transfer of P from sediments.

Importance of anaerobic ammonium oxidation as a nitrogen removal pathway in freshwater marsh sediments

To explore the role of anaerobic ammonium oxidation (anammox) in nitrogen removal in freshwater marshes.

Comparative study of carboxylic acid adsorption on calcite: l-malic acid, d-malic acid and succinic acid

Succinic acid and l-malic acid are known to affect calcite dissolution/crystallization due to their tendency to adsorb on calcite’s surface. Taking into account the structural similarity among succinic acid, l-malic acid, and d-malic acid, a comparative study of their adsorption behavior on calcite was investigated for clarifying their adsorption mechanism. Kinetic results showed that l-malic acid adsorption reached equilibrium within 12xa0h, while succinic acid required 48xa0h. Results from the pH effect study showed that the strength of surface complex of succinic acid on calcite was weaker, even compared to its aqueous complex with Ca2+ ion. Alternately, l-malic acid exhibited a much stronger surface complex strength, even compared to its aqueous complex with Ca2+ ion. The adsorption isotherm results indicated that the saturated adsorption amount of l-malic acid was twice that of succinic acid, suggesting the surface complex of succinic acid may occupy a larger space on calcite surface compared to that of l-malic acid. Based on these results and those from previous studies, we proposed that succinic acid adsorption is through its two carboxyl groups binding to two adjacent surface sites (>xa0Ca+), and not only one. Also, l-malic acid adsorption occurs through one carboxyl group and one hydroxyl, which forms a “claw” on calcite surface. The similar adsorption behavior between l-malic acid and d-malic acid reinforces this proposition for l-malic acid adsorption mechanism. Our study will serve as good reference information to provide better understanding into the adsorption of other carboxylic acids on calcite.