Simazine application inhibits nitrification and changes the ammonia-oxidizing bacterial communities in a fertilized agricultural soil

s-Triazine herbicides are widely used for weed control, and are persistent in soils. Nitrification is an essential process in the global nitrogen cycle in soil, and involves ammonia-oxidizing Bacteria (AOB) and ammonia-oxidizing Archaea (AOA). In this study, we evaluated the effect of the s-triazine herbicide simazine on the nitrification and on the structure of ammonia-oxidizing microbial communities in a fertilized agricultural soil. The effect of simazine on AOB and AOA were studied by PCR-amplification of amoA genes of nitrifying Bacteria and Archaea in soil microcosms and denaturing gradient gel electrophoresis (DGGE) analyses. Simazine [50?μg g(-1) dry weight soil (d.w.s)] completely inhibited the nitrification processes in the fertilized agricultural soil. The inhibition by simazine of ammonia oxidation observed was similar to the reduction of ammonia oxidation by the nitrification inhibitor acetylene. The application of simazine-affected AOB community DGGE patterns in the agricultural soil amended with ammonium, whereas no significant changes in the AOA community were observed. The DGGE analyses strongly suggest that simazine inhibited Nitrosobacteria and specifically Nitrosospira species. In conclusion, our results suggest that the s-triazine herbicide not only inhibits the target susceptible plants but also inhibits the ammonia oxidation and the AOB in fertilized soils.     

Germline mutations in BMPR1A/ALK3 cause a subset of cases of juvenile polyposis syndrome and of Cowden and Bannayan-Riley-Ruvalcaba syndromes

Juvenile polyposis syndrome (JPS) is an inherited hamartomatous-polyposis syndrome with a risk for colon cancer. JPS is a clinical diagnosis by exclusion, and, before susceptibility genes were identified, JPS could easily be confused with other inherited hamartoma syndromes, such as Bannayan-Riley-Ruvalcaba syndrome (BRRS) and Cowden syndrome (CS). Germline mutations of MADH4 (SMAD4) have been described in a variable number of probands with JPS. A series of familial and isolated European probands without MADH4 mutations were analyzed for germline mutations in BMPR1A, a member of the transforming growth-factor beta-receptor superfamily, upstream from the SMAD pathway. Overall, 10 (38%) probands were found to have germline BMPR1A mutations, 8 of which resulted in truncated receptors and 2 of which resulted in missense alterations (C124R and C376Y). Almost all available component tumors from mutation-positive cases showed loss of heterozygosity (LOH) in the BMPR1A region, whereas those from mutation-negative cases did not. One proband with CS/CS-like phenotype was also found to have a germline BMPR1A missense mutation (A338D). Thus, germline BMPR1A mutations cause a significant proportion of cases of JPS and might define a small subset of cases of CS/BRRS with specific colonic phenotype.     

氨氧化古菌的生态学研究进展

上百年来细菌一直被认为是地球氨氧化过程的主要驱动者,2005年海洋中分离到迄今唯一的非极端环境泉古菌,发现其氧化氨态氮获得能源生长,是氨氧化古菌。氨氧化古菌和细菌对地球氨氧化过程的相对贡献率,是目前全球氮循环研究最重要的微生物生态学问题之一。已有的证据表明古菌在海洋氨氧化过程中发挥了重要作用,细菌则是土壤氨氧化过程的主要驱动者。本文重点探讨了原位自然环境下氨氧化古菌的生态学研究进展。     

A combinatorial system to examine the enzymatic repair of multiply damaged DNA substrates

DNA damage drives genetic mutations that underlie the development of cancer in humans. Multiple pathways have been described in mammalian cells which can repair this damage. However, most work to date has focused upon single lesions in DNA. We present here a combinatorial system which allows assembly of duplexes containing single or multiple types of damage by ligating together six oligonucleotides containing damaged or modified bases. The combinatorial system has dual fluorescent labels allowing examination of both strands simultaneously, in order to study interactions or competition between different DNA repair pathways. Using this system, we demonstrate how repair of oxidative damage in one DNA strand can convert a mispaired T:G deamination intermediate into a T:A mutation. We also demonstrate that slow repair of a T:G mispair, relative to a U:G mispair, by the human methyl-binding domain 4 DNA glycosylase provides a competitive advantage to competing repair pathways, and could explain why CpG dinucleotides are hotspots for C to T mutations in human tumors. Data is also presented that suggests repair of closely spaced lesions in opposing strands can be repaired by a combination of short and long-patch base excision repair and simultaneous repair of multiply damage sites can potentially lead to lethal double strand breaks.     

LATERAL CYSTS AND FISTULAS OF THE NECK

The embryonic origin of lateral cysts and fistulas remains controversial. They are, however, located in the general anatomic pattern of the embryonic thymic duct, which starts in the lateral pharyngeal wall and passes under the sternomastoid muscle to enter the mediastinum. The cyst is a unilocular, semiattached, non-translucent mass which has a tendency to become infected in 30 per cent of cases.The preauricular sinus occurs in front of the ear and is due either to a branchial cleft or an inclusion of one of the six primitive buds which form the external ear.Cystic hygroma is due to sequestrated lymphatic channels. These are always multilocular and rather invasive and may extend into mediastinum and arms.Diagnosis and treatment are considered in this presentation.     

Environmental history and physiological state influence feeding responses of Atrina zelandica to suspended sediment concentrations

Epifaunal suspension-feeding bivalves can play important roles in marine ecosystems affecting macrobenthic communities, benthic boundary layers and benthic-pelagic coupling, not just by their presence but also by any changes in feeding behaviour. While seston quality and quantity have consistently been found to be important influences on the feeding rates of suspension-feeding bivalves, factors stressing individuals are also likely to be important, as they may affect energy-dependent thresholds of response. We postulated that (1) history of seston quantity would affect how suspension feeders deal with increases in total suspended particulates, and (2) high-seston concentrations would affect feeding rates more in individuals whose energy reserves were low after spawning. Three sites were selected for short-term (1 day) feeding experiments on the pinnid bivalve, Atrina zelandica. At one site, the experiment was run pre-and postspawning. Atrina exhibited high rejection of filtered particles (mostly 75% to 100%) and high organic absorption efficiencies (0.9-1) at all seston levels. Strong differences in the response of feeding behaviour to increased seston concentrations were observed between A. zelandica from the different sites, with lesser differences observed between times. The site-specific feeding responses to seston concentrations observed are likely to affect our ability to model responses of A. zelandica to sediment loading and to influence the importance of A. zelandica to benthic-pelagic coupling.     

Natural selection and the evolution of neutralism

The efficiency of evolutionary search increases as the density of acceptable proteins in a protein space increases. Populations caught in regions whose density is too low to support evolution can be pulled into high density regions by hitchhiking selection. As they move into such regions, the action of natural selection becomes more effective, yet these populations will satisfy conditions which lead to predictions made by neutral, so-called non-Darwinian models.     

Effect of various pre-treatments on the seedling growth performance of Tamarindus indica L.

ABSTRACT

Pre-treatment of seeds of Tamarindus indica L. with 95% sulphuric acid for 5, 10 or 15 min, methanol, ethanol, iso-propanol or butanol for 10 or 20 min, or boiling water for 10, 15, 20 or 30 min, was used to determine the effect of the various treatments on the development and vigour of the resultant seedlings. Seeds immersed in methanol, ethanol and sulphuric acid for 10 min produced seedlings with high vigour     

Microbial production and uptake of nitric oxide in soil

Abstract Fluxes of NO from three different soils have been studied by a flow-through system in the laboratory as a function of gas flow rate, of NO mixing ratio, and of incubation conditions. The dependence of net NO fluxes on gas flow rates and on NO mixing ratios could be described by a simple model of simultaneous NO production and NO uptake. By using this model, rates of gross NO production, rate constants of NO uptake, and NO compensation mixing ratios could be determined as function of the soil type and the incubation condition. Gross NO production rates were one to two orders of magnitude larger under anaerobic than under aerobic conditions. NO uptake rate constants, on the other hand, were only 5–8 times larger so that the compensation mixing ratios of NO were in a range of about 1600–2200 ppbv under anaerobic and of about 50–600 ppbv under aerobic conditions. The different soils exhibited similar NO uptake rate constants, but the gross NO production rate and compensation mixing ratio was significantly higher in an acidic (pH 4.7) sandy clay loam than in other less acidic soils. Experiments with autoclaved soil samples showed that both NO production and NO uptake was mainly due to microbial metabolism.