不同形态有机碳的有效性在两种重金属污染水平下水稻土壤中的差异

调查分析了两块不同重金属污染水平下的水稻田土壤有机碳活性组分的含量,以评价重金属胁迫条件下有机碳基质的微生物有效性。结果显示,重污染水稻土的总有机碳(TOC)、0·5mol·L-1K2SO4溶解态有机碳(K2SO4-C)、微生物生物量碳(MBC)、1~7d(CO2-C1~7d)和8~28d矿化的有机碳(CO2-C8~28d)的含量均显著低于轻污染土壤(p<0·001)。碳有效性指标中,微生物商(MBC/TOC比)和8~28d的有机碳矿化率(CO2-C8~28d·TOC-1d-1))在轻污染土壤中较高,而K2SO4-C/TOC和代谢商(qCO2)在重污染土壤较高(p<0·001)。1~7d的有机碳矿化率(CO2-C1~7d·TOC-1d-1)在两种土壤中差异不显著。两种土壤培养初期的有机碳矿化率远高于培养后期(p<0·001)。逐步回归分析显示,CO2-C1~7d与活性组分K2SO4-C和MBC显著相关(r2=0·83,p<0·001),而CO2-C8~28d只与TOC显著相关(r2=0·70,p<0·001)。研究表明,尽管K2SO4溶解态有机碳在供试的重金属污染的水稻土中是较易被分解的活性碳基质,但重金属污染抑制了微生物数量及其呼吸活性,降低了活性有机碳库的矿化率,这是导致土壤中K2SO4溶解态碳积累的原因。溶解性有机碳又能提高重金属的有效性,进一步抑制微生物对有机碳的矿化。因此,评价重金属污染的水稻土有机碳的有效性,应当综合考虑不同有机碳库的活性、微生物的矿化能力和碳基质在不同阶段的供应潜力。     

Projecting the SARS-CoV-2 transition from pandemicity to endemicity: Epidemiological and immunological considerations

In this review, we discuss the epidemiological dynamics of different viral infections to project how the transition from a pandemic to endemic Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) might take shape. Drawing from theories of disease invasion and transmission dynamics, waning immunity in the face of viral evolution and antigenic drift, and empirical data from influenza, dengue, and seasonal coronaviruses, we discuss the putative periodicity, severity, and age dynamics of SARS-CoV-2 as it becomes endemic. We review recent studies on SARS-CoV-2 epidemiology, immunology, and evolution that are particularly useful in projecting the transition to endemicity and highlight gaps that warrant further research.     

Soil CO2 venting as one of the mechanisms for tolerance of Zn deficiency by rice in flooded soils

We sought to explain rice (Oryza sativa) genotype differences in tolerance of zinc (Zn) deficiency in flooded paddy soils and the counter‐intuitive observation, made in earlier field experiments, that Zn uptake per plant increases with increasing planting density. We grew tolerant and intolerant genotypes in a Zn‐deficient flooded soil at high and low planting densities and found (a) plant Zn concentrations and growth increased with planting density and more so in the tolerant genotype, whereas the concentrations of other nutrients decreased, indicating a specific effect on Zn uptake; (b) the effects of planting density and genotype on Zn uptake could only be explained if the plants induced changes in the soil to make Zn more soluble; and (c) the genotype and planting density effects were both associated with decreases in dissolved CO₂ in the rhizosphere soil solution and resulting increases in pH. We suggest that the increases in pH caused solubilization of soil Zn by dissolution of alkali‐soluble, Zn‐complexing organic ligands from soil organic matter. We conclude that differences in venting of soil CO₂ through root aerenchyma were responsible for the genotype and planting density effects.     

Assessment of early placental development in the cynomolgus monkey (Macaca fascicularis) using colour and pulsed wave Doppler sonography

Abstract: Colour flow mapping and pulsed wave Doppler were used to assess the process of placental growth and development in the cynomolgus monkey from 32 to 71 days gestational age. Fetal and maternal vessels were reliably visualised and insonated. Accurate longitudinal non-invasive assessment of placentation is possible using this technique.     

Mutational analysis of the Bordetella pertussis fim/fha gene cluster: identification of a gene with sequence similarities to haemolysin accessory genes involved in export of FHA

The chromosome of Bordetella pertussis harbours a region of 27 contiguous kb, which contains the bvg, fha and flm genes, involved in the co-ordinate regulation of virulence genes, FHA production and fimbriae production, respectively. The linkage of FHA and fimbrial genes has resulted in some confusion concerning the existence and location of genes required for the production of FHA and the function of the fimbrial genes fimB-D, which were proposed to be involved in both FHA and fimbriae biosynthesis. Through the use of non-polar mutations in each of these genes, we found that fimB-D are required for the production of both serotype 2 and 3 fimbriae, but not for FHA biosynthesis. Furthermore, a large open reading frame, designated fhaC, was identified downstream of fimD. It was shown that fhaC is essential for FHA production but not for fimbriae biogenesis. We propose that insertion mutations in fimB-D affect FHA production because of polar effects on fhaC expression. An insertion in the region downstream of fhaC had only a slight effect on FHA and fimbriae production. The fhaC gene product shows homology with ShIB and HpmB, two outer membrane proteins involved in export and activation of the haemolysins, ShIA and HpmA, of Serratia marcescens and Proteus mirabilis, respectively. Homology is also observed between the N-termini of FHA, ShIA and HpmA. Export of the haemolysins requires the Af-termini of these molecules, and when this region was removed from FHA by an in-frame deletion, FHA biosynthesis was abolished. These results suggest that the N-terminus of FHA interacts with FhaC, and that as a result FHA is transported across the outer membrane.