Shifts in composition and function of bacterial communities reveal the effect of small barriers on nitrous oxide and methane accumulation in fragmented rivers.

Rivers are often blocked by barriers to form different habitats, but it is not clear whether this change will affect the accumulation of N2O and CH4 in rivers. Here, low barriers (less than 2 m, LB) increased N2O concentration by 1.13 times and CH4 decreased by 0.118 times, while high barriers (higher than 2 m, less than 5 m high, HB) increased N2O concentration by 1.19 times and CH4 by 2.76 times. Co-occurrence network analysis indicated LB and HB can promote the enrichment of Cyanobium and Chloroflexi, further limiting complete denitrification and increasing N2O accumulation. The LB promotes methanotrophs (Methylocystis, Methylophilus, and Methylotenera) to compete with denitrifiers (Pseudomonas) in water, and reduce CH4 accumulation. While the HB can promote the methanotrophs to compete with nitrifiers (Nitrosospira) in sediment, thus reducing the consumption of CH4. LB and HB reduce river velocity, increase water depth, and reduce dissolved oxygen (DO), leading to enrichment of nirS-type denitrifiers and the increase of N2O concentration in water. Moreover, the HB reduces DO concentration and pmoA gene abundance in water, which can increase the accumulation of CH4. In light of the changes in the microbial community and variation in N2O and CH4 accumulation, the impact of fragmented rivers on global greenhouse gas emissions merits further study.

Proteomics reveals the enhancing mechanism for eliminating toxic hydroxylamine from water by nanocompartments containing hydroxylamine oxidase.

Hydroxylamine (NH2OH) is a potentially toxic pollutant when it is present in water, as it can damage both bacteria and the human body. It is still difficult to eliminate the toxic NH2OH in water. Here, we showed that the model bacterium (Escherichia coli) with nanocompartments encapsulated with hydroxylamine oxidase (HAO) can remove NH2OH from water. In addition, the removal efficiency of NH2OH by genetically modified bacteria (with HAO-nanocompartments) was 3.87 mg N L-1 h-1, and that of wild-type bacteria (without HAO-nanocompartments) was only 1.86 mg N L-1 h-1. Label-free quantitative proteomics indicated that the nanocompartments containing HAO enhanced bacterial activity by inducing the up-regulation of proteins involved in stress and stimulus responses, and decreased their intracellular NH2OH concentration. Moreover, the synthesis of proteins involved in energy metabolism, gene expression, and other processes in bacterial was enhanced under hydroxylamine stress, and these changes increased the resistance of bacterial to NH2OH. This work can aid our understanding of the toxic effects of NH2OH on bacteria as well as the development of new approaches to eliminate NH2OH in water.

Encapsulins from Ca. Brocadia fulgida: An effective tool to enhance the tolerance of engineered bacteria (pET-28a-cEnc) to Zn2.

Zn2+ is largely discharged from many industries and poses a severe threat to the environment, making its remediation crucial. Encapsulins, proteinaceous nano-compartments, may protect cells against environmental stresses by sequestering toxic substances. To determine whether hemerythrin-containing encapsulins (cEnc) from anammox bacteria Ca. Brocadia fulgida can help cells deal with toxic substances such as Zn2+, we transferred cEnc into E.coli by molecular biology technologies for massive expression and then cultured them in media with increasing Zn2+ levels. The engineered bacteria (with cEnc) grew better and entered the apoptosis phase later, while wild bacteria showed poor survival. Furthermore, tandem mass tag-based quantitative proteomic analysis was used to reveal the underlying regulatory mechanism by which the genetically-engineered bacteria (with cEnc) adapted to Zn2+ stress. When Zn2+ was sequestered in cEnc as a transition, the engineered bacteria presented a complex network of regulatory systems against Zn2+-induced cytotoxicity, including functions related to ribosomes, sulfur metabolism, flagellar assembly, DNA repair, protein synthesis, and Zn2+ efflux. Our findings offer an effective and promising stress control strategy to enhance the Zn2+ tolerance of bacteria for Zn2+ remediation and provide a new application for encapsulins.

Bacterially self-assembled encapsulin nanocompartment for removing silver from water.

Compartmentalization can protect cells from the interference of external toxic substances by sequestering toxic products. We hypothesized that proteinaceous nanocompartments may be a feasible candidate material to be added to genetically modified bacteria for the sequestration of toxic environmental products, which would open up a new bioremediation pathway. Here, we showed that the model bacterium (Escherichia coli) with self-assembling nanocompartments can remove silver (Ag) from water. Transmission electron microscopy and energy dispersive X-ray (TEM-EDX) analysis showed that the nanocompartments combined stably with silver in vitro. In addition, when exposed to 30 µM AgNO3, the survival rate of genetically modified bacteria (with nanocompartments) was 86%, while it was just 59% in the wild-type bacteria (without nanocompartments). Label-free quantitative proteomics indicated that the nanocompartments enhanced bacterial activity by inducing the up-regulation of protein processing and secondary metabolites, and decreased their intracellular silver concentration, both of which contributed to their increased resistance to toxic silver. This study on nanocompartments has contributed to a deeper understanding of how bacteria respond to environmental stressors like heavy metal pollutants in water. The technology promises to provide a new strategy for recycling heavy metals from sewage.

[Effect of Hydroxylamine on Community of ANAMMOX Sludge].

At present, the anaerobic ammonium oxidation (ANAMMOX) process has the advantages of high efficiency, low energy consumption, and low sludge quantity, and it therefore has broad application prospects in sewage nitrogen removal. Hydroxylamine is not only an intermediate product of ANAMMOX metabolism but also an inhibitor. However, the effect of hydroxylamine on the activity of ANAMMOX is not clear. Therefore, we investigated the ANAMMOX activity under the condition of adding different concentrations of hydroxylamine (40-80 mg·L-1) through a hydroxylamine batch experiment. It was found that hydroxylamine can inhibit ANAMMOX activity. However, it was impossible to determine the threshold of ANAMMOX bacteria to hydroxylamine. Next, the mRNA levels of hydrazine oxidase (HZO) in different reactors were detected by real-time fluorescent quantitative polymerase chain reaction (RT-qPCR), and it was found that the expression levels of HZO peak and then decrease with an increase of hydroxylamine concentration. It was suggested that the tolerated hydroxylamine concentration was within 60-70 mg·L-1 for 3.12 g·L-1 ANAMMOX granular sludge. Moreover, a 16S rRNA high-throughput sequencing method was used to analyze the structure and function of ANAMMOX granules in microbial communities in the reactor. It was found that the addition of an appropriate concentration of hydroxylamine (50 mg·L-1) helped to enhance the cellular motility of bacteria and promoted the composition of ANAMMOX bacteria, providing a better ecological balance.

A self-assembled nanocompartment in anammox bacteria for resisting intracelluar hydroxylamine stress.

Anammox bacteria play an important role in the global nitrogen cycle, but research on anammoxosome structure is still in its initial stages. In particular, the anammox bacteria genome contains nanocompartments gene loci. However, the function and structure of the nanocompartments in anammox bacteria is poorly understood. We apply genetic engineering to demonstrate the self-assembled nanocompartments of anammox bacteria. The encapsulin shell protein (cEnc) and cargo protein hydroxylamine oxidoreductase (HAO) can self-assemble to form regular nanocompartments (about 128 nm in diameter) in vitro. Cell growth curve tests show that nanocompartments help model bacteria resist hydroxylamine (NH2OH) stress. Batch test results and transcriptional data show that cEnc and HAO are highly expressed in response to the negative effects of NH2OH on anammox efficiency, predicting a potential role of nanocompartments in helping anammox bacteria resist NH2OH stress. These findings improve our understanding of the mechanisms by which anammox bacteria respond to harmful environmental metabolites.