Toxic metals and metalloids: Uptake, transport, detoxification, phytoremediation, and crop improvement for safer food.

Agricultural soils are under threat of toxic metal/metalloid contamination from anthropogenic activities, leading to excessive accumulation of arsenic (As), cadmium (Cd), lead (Pb), and mercury (Hg) in food crops that poses significant risks to human health. Understanding how these toxic metals and their methylated species are taken up, translocated, and detoxified is prerequisite to developing strategies to limit their accumulation for safer food. Toxic metals are taken up and transported across different cellular compartments and plant tissues via various transporters for essential or beneficial nutrients, e.g. As by phosphate and silicon transporters, and Cd by manganese (Mn), zinc (Zn), and iron (Fe) transporters. These transport processes are subjected to interactions with nutrients and the regulation at the transcriptional and post-translational levels. Complexation with thiol-rich compounds, such as phytochelatins, and sequestration in the vacuoles are the common mechanisms for detoxification and for limiting their translocation. A number of genes involved in toxic metal uptake, transport, and detoxification have been identified, offering targets for genetic manipulation via gene editing or transgenic technologies. Natural variations in toxic metal accumulation exist within crop germplasm, and some of the quantitative trait loci underlying these variations have been cloned, paving the way for marker-assisted breeding of low metal accumulation crops. Using plants to extract and remove toxic metals from soil is also possible, but this phytoremediation approach requires metal hyperaccumulation for efficiency. Knowledge gaps and future research needs are also discussed.

[Performance and Microbial Characteristics of Ammonium-limited and Nitrite-limited ANAMMOX Systems].

The performance and microbial characteristics of ammonium-limited and nitrite-limited ANAMMOX reactors were studied in two continuously stirred tank reactors. The influent TN concentrations were controlled below 50 mg·L-1. The hydraulic retention time and water temperature were maintained at 2.0 h and 20℃, respectively. Results showed that though both ANAMMOX reactors demonstrated similar TN removal loading rates[0.45-0.5 kg·(m3·d)-1] and TN removal efficiencies (around 70%), the ΔNO3-/ΔNH4+ ratio of the ammonium-limited ANAMMOX reactor showed a faster upward trend. Batch tests and high-throughput sequencing results indicated that the ammonium-limited ANAMMOX reactor had more significant functional and population heterogeneity than the nitrite-limited ANAMMOX reactor. Candidatus_Brocadia was the predominant ANAMMOX bacteria in both reactors. The relative abundance of Candidatus_Brocadia in large granules (53.9%) was significantly higher than that in flocs (19.1%) under the ammonium-limited conditions, whereas only a small difference in relative abundance of Candidatus_Brocadia was observed between the granules (28.1%) and flocs (21.3%) in the nitrite-limited ANAMMOX reactor. Nitrospira-like NOB were detected in both ANAMMOX reactors, which primarily inhabited flocs, seemingly driven by the availability of oxygen. Moreover, the ammonium-limited (i.e., excess nitrite) conditions seemingly favored the growth of Nitrospira. Building upon these results, a control strategy for optimal operation of the ammonium-limited ANAMMOX reactor was proposed based on selective floc discharge.

[Realization Process of Nitritation and Changes in Sludge Characteristics in Granular Sludge Reactor for Low Strength Sewage Treatment].

The realization process of nitritation was studied in a CSTR reactor seeding with nitrification granular sludge to treat low ammonia sewage. During the operation period, the physical and chemical properties, the spatial distribution of functional microbes, and the activity of the granular sludge were also investigated to elaborate the main factors for the stability of nitritation. The results showed that nitritation can be successfully achieved and maintained by the cooperative controlling of nitrogen loading rate (NLR) and dissolved oxygen (DO) levels, and the nitrite accumulation rate was over 80%. The obtained nitritation granular sludge was brownish yellow, showing a smooth, full ellipsoid or sphere, and the microorganisms on the surface of the particles were mainly cocci; the average particle size was 1.3 mm, and the average sedimentation rate was 71.3 m·h-1. Batch tests showed that there was a significant stratified distribution structure in granular sludge (particle size >0.8 mm), the ammonia-oxidizing bacteria (AOB) mainly occupied the surface space of the particles, and the nitrite-oxidizing bacteria (NOB) were mainly distributed inside the particles. Flocs or small-size sludge (particle size<0.8 mm) and granular sludge (particle size >0.8 mm) exhibit different spatial distribution characteristics of microorganisms. In the granular sludge reactor, well stratification of the nitrifier guilds, high level of residual ammonia concentrations in effluent (15-33 mg·L-1), or low ratio between DO and NH4+-N concentrations (0.08-0.15) should be key influencing factors in the process of achieving nitritation.

[Characteristics of Organics Transformation and Sludge Morphology in an ABR for Sewage Treatment with Different HRTs].

The characteristics of organics transformation and sludge morphology of in an ABR(anaerobic baffled reactor) for sewage treatment with different HRTs were investigated based on reactor performance, particle size distribution, and scanning electron microscopy (SEM). Results showed that the COD removal rate was stably maintained above 90.0% when the HRT decreased from 15 h to 4 h. However, the first compartment of ABR contributed to 90%, 78.56%, 74.18%, and 58.91% of the total COD removal when the HRT was 10, 7.5, 5, and 4 h, respectively. When the HRT was reduced, the total amount of volatile fatty acids (VFAs) in the first compartment of ABR significantly increased, and the abundance of acetic acid, being the major constituent of VFAs, gradually increased from 51.36% to 58.77%; the concentrations of butyric acid and propionic acid were maintained and constituted a minority of the VFAs. The sludge morphology in ABR significantly changed in the wake of run time. On day 111, granulation of sludge was achieved. Additionally, the degree of sludge granulation showed a decreasing trend with the direction of water flow. SEM observations of granular sludge showed that the separation of biomass did occur in the ABR. Along the direction of water flow, filamentous bacteria, M. methane, monococci, and bacilli were the dominant microbes in each compartment of the ABR.

[Rapid Achievement of Nitrifying Micro-granular Sludge and Its Nitritation Function].

The rapid achievement of nitrifying micro-granular sludge and its nitritation function was studied in a continuously operated internal-loop airlift reactor seeding with floccular sludge. Results showed that the sludge micro-granulation was almost realized within three weeks by gradually reducing the hydraulic retention time from 5 h to 2.5 h. The color of the sludge first changed from yellowish-brown to creamy white, and then changed to pale yellow during the micro-granulation process. The settleability of the sludge first changed from good to bad, and then recovered to good. The value of the sludge settling velocity (SV) at SV5 and SV30 were both equal to 4%-5%, while SVI30 and SVI5 were both around 12-13 mL·g-1. The average size of the obtained nitrifying micro-granular sludge was 134 µm on day 27. Nearly 70% of the nitrifying micro-granular sludge was maintained in a relatively narrow range of 59-163 µm, thus indicating the largely homogeneous diameter distribution of these micro-granules. After sludge micro-granulation, the nitritation function was achieved within one week by progressively increasing the influent NH4 concentrations from 50 mg·L-1to 200 mg·L-1. The NO2- accumulation ratio and the nitritation loading rate reached up to 90% and 1.34 kg·(m3·d)-1, respectively. The high level of residual NH4 concentration in the effluent, or the low ratio of dissolved oxygen (DO) to NH4+-N concentrations (0.03-0.09), should be the primary cause of the rapid achievement of nitritation in the micro-granular sludge reactor.

[Relationship among pathological changes in Liver tissues and level of serum HBV DNA, HBeAg and ALT of 194 patients with chronic hepatitis B].

OBJECTIVE: To study the relationships among pathological and immunohistochemical changes in liver tissues, and the HBeAg, HBV DNA, ALT level in the patients with chronic hepatitis B. METHODS: Pathological and immunohistochemical examinations of liver tissue liver function tests, serum HBV and HBV DNA detection were performed in 194 patients with chronic hepatitis B. RESULTS: There was significant difference between the serum HBeAg positive group and the negative group in G2, G3-4 S2, S3-4 in liver tissues; The serum HBV DNA level of the groups S0 and S1-4, and the hepatic activity index between the groups G0-1 and G2-4 were significantly different. And the hepatic HBcAg positive group and HBcAg negative group were significantly different too. There was no significant difference between the HBsAg level in liver tissues as "+" group and the "++ - +++" group. The pathological diagnosis as S1 or (and) G2 is respectively 28.57%, 53.33%, 80.15%, 77.88% among the four groups with normal-mild-moderate-severe elevated serum ALT level. CONCLUSION: Serum HBV DNA correlated with HBcAg expression in liver tissue; the HBsAg level in liver tissues have no relationship with the serum HBV DNA level. The patients with low serum HBV DNA level may have high index of hepatic activity and hepatic fibrosis. Asymptomatic carriers and patients with low serum ALT level should be encouraged to accept liver biopsy. It can determine the degree of liver inflammation and fibrosis and timing of treatment.