Formaldehyde-induced cytotoxicity and sister-chromatid exchanges in human lymphocyte cultures

The role of the error-prone misrepair pathway in mutagenesis was examined for a series of mutagens in umuC⁺ and umuC36 strains of Escherichia coli. Mutagenesis by ENU, MNU, MNNG and EMS was independent of the umuC⁺ gene function, while mutagenesis by MMS, 4NQO, γ-rays and UV was largely umuC⁺-dependent. Residual mutagenesis following UV-treatment of a umuC^? strain showed the same mutational specificity seen in the umuC⁺ strain. In contrast, the umuC mutation altered specificity substantially in an excision-repair-defective strain that showed a UV-spectrum strikingly different from that seen in an excision-repair-proficient strain. Only one of nine trpE frameshift mutations examined was reverted by UV-light and its reversion was umuC-dependent. In comparison, the dependence of frameshift mutagenesis following ICR 191 treatment was site-specific, suggesting at least two mechanisms of frameshift mutagenesis, one dependent upon misrepair, the other not.The results, together with those of previous reports (Kato and Nakano, 1981; Shinoura et al., 1983), suggest that the umuC⁺ gene exerts it's mutator activity via misrepair of DNA lesions provoking the induction of all types of mutational events, though following UV-irradiation mainly transition events are recovered.     

On the control between cell-mediated, IgM and IgG immunity

An hypothesis is proposed here describing some of the conditions that determine the type of response an antigen will induce, and explaining how the induction of one type of immunity affects the induction of other types of immunity. In more detail, the hypothesis attempts to account for the following observations: Some antigens induce only cell-mediated immunity, whereas others can, under different conditions, induce either cell-mediated or humoral immunity. The humoral response to most antigens consists of an initial period of IgM antibody synthesis, followed by a period of IgG synthesis. Some polymeric antigens induce the synthesis of only IgM antibody. There is a tendency for the immune response to an antigen, at a particular time, to be exclusively of the cell-mediated, IgM or IgG type.The hypothesis may also be relevant to some observations that, I believe, have been incorrectly interpreted to mean that “tolerance” to some antigens requires the presence of T (thymus-derived) cells specific for these antigens. The hypothesis suggests teleological reasons for the existence of the different types of immunity. It also suggests ways of controlling the type of response an antigen induces.     

Production and characterization of rabbit polyclonal sera against Shiga toxins Stx1 and Stx2 for detection of Shiga toxin-producing Escherichia coli

STEC has emerged as an important group of enteric pathogens worldwide. In this study, rabbit polyclonal Stx1 and Stx2 antisera were raised and employed in the standardization of immunoassays for STEC detection. Using their respective antisera, the limit of detection of the toxin was 35.0 pg for Stx1 and 5.4 pg for Stx2. By immunoblotting, these antisera recognized both toxin subunits. Cross-reactivity was observed in the A subunit, but only Stx2 antiserum was able to neutralize the cytotoxicity of both toxins in the Vero cell assay. Six stx-harboring E. coli isolates were analyzed for their virulence traits. They belonged to different serotypes, including the O48:H7, described for the first time in Brazil. Only three strains harbored eae, and the e-hly gene and hemolytic activity was detected in five strains. Three isolates showed new stx2 variants (stx(2v-ha) and stx(2vb-hb)). The ELISA assay detected all six isolates, including one VCA-negative isolate, while the immunodot assay failed to detect one isolate, which was VCA-positive. In contrast, the colony-immunoblot assay detected only one VCA-positive isolate. Our results demonstrate that among the immunoassays developed in this study, the immunodot, and particularly the ELISA, appear as perspective for STEC detection in developing countries.     

江米酒中凝乳酶产生菌的分离及产酶条件的优化

江米酒是我国南方的一种传统食品, 江米酒中微生物所产凝乳酶具有凝乳作用。从江米酒中分离纯化得到4株菌, 经菌落分离计数和酪蛋白平板实验研究确定产凝乳酶的优势菌为其中的霉菌, 并对该霉菌产凝乳酶条件进行了初步优化, 结果表明: 2倍浓度的PDA培养基中添加5%葡萄糖而不添加氮源是霉菌产凝乳酶的最佳培养基, 在此条件下其所产凝乳酶活力可比优化前提高144%。     

黄瓜霜霉病菌侵染若干因子的研究

研究了温、湿度条件对黄瓜霜霉病菌致病性的影响,结果表明,25～35℃最适宜黄瓜霜霉病的发生,15/35℃的交替温度变化最有利于霜霉病菌的侵染,但35℃以上的高温对霜霉病菌具有杀伤作用;2 h的湿度条件就足以引起侵染,一旦侵入寄主,环境湿度条件对病害的发展影响不大.-20℃低温冷冻保存10个月和干燥放置7 d的霜霉菌种仍具致病力.发病的黄瓜叶片可以连续产生孢子囊,但随着发病时间的延长产生孢子囊量逐渐减少.活体叶片单位面积上产生的孢子囊量比离体叶片大,且显症天数与叶片单位面积产生孢囊量呈抛物线型关系.     

Production of volatile organic compounds (VOCs) by yeasts isolated from the ascocarps of black (<Emphasis Type="Italic">Tuber melanosporum</Emphasis> Vitt.) and white (<Emphasis Type="Italic">Tuber magnatum</Emphasis> Pico) truffles

Twenty-nine yeast strains were isolated from the ascocarps of black and white truffles (Tuber melanosporum Vitt. and Tuber magnatum Pico, respectively), and identified using a polyphasic approach. According to the conventional taxonomic methods, MSP-PCR fingerprinting and sequencing of the D1/D2 domain of 26S rDNA, the strains were identified as Candida saitoana, Debaryomyces hansenii, Cryptococcus sp., Rhodotorula mucilaginosa, and Trichosporon moniliiforme. All isolates assimilated l-methionine as a sole nitrogen source and produced the volatile organic compounds (VOCs), 2-methyl butanol, 3-methyl butanol, methanethiol, S-methyl thioacetate, dimethyl sulfide, dimethyl disulfide, dimethyl trisulfide, dihydro-2-methyl-3(2H)-thiophenone and 3-(methylthio)-1-propanol (MTP). ANOVA analysis of data showed significant (P<0.01) differences in VOCs produced by different yeasts, with MTP as the major component (produced at concentrations ranging from 19.8 to 225.6 mg/l). In addition, since some molecules produced by the isolates of this study are also characteristic of truffle complex aroma, it is possible to hypothesize a complementary role of yeasts associated with this ecosystem in contributing to final Tuber spp. aroma through the independent synthesis of yeast-specific volatile constituents.     

产羧肽酶菌株的筛选及其产酶特性的研究*

从土壤中分离到28株产蛋白酶菌株,用其粗酶液水解多肽并经氨基酸自动分析仪测定产物中游离氨基酸的含量和种类,从中筛选到一株产羧肽酶的菌株。对该菌株的菌落和菌体形态进行观察,确定其属于曲霉菌属。该菌株在发酵至第48h时,发酵液中羧肽酶活性达到最大。此时发酵液pH值为7.46,菌体已处于衰败期,说明该酶的合成方式为延迟合成型。     

Lactobacillus ruminis is a predominant lactic acid producing bacterium in the caecum and rectum of the pig

AIMS: To identify the predominant lactic acid producing bacteria in the small intestine, caecum and the rectum of the healthy pig. METHODS AND RESULTS: Samples obtained from the large intestine of healthy pigs post-mortem were cultured using a modified agar-MRS medium in roll tubes. Thirteen isolates were selected on the basis of their morphological characteristics and Gram stain reaction for gene sequencing. These isolates were characterized by DNA sequence analysis of 16S rDNA. Eight isolates were identified as Lactobacillus ruminis, two as Enterococcus faecium, one as Mitsuokella multiacidus and two as Escherichia coli. CONCLUSION: This is the first report of Lact. ruminis as the dominant lactic acid bacteria in the large intestine of the pig. SIGNIFICANCE AND IMPACT OF THE STUDY: The results suggest that Lact. ruminis is a dominant bacterium in the large intestine of the healthy pig. Future work should focus on the role of this bacterium in relation to the physiological function of the intestine and the health of the animal.     

耐底物腈水合酶融合子的产酶条件优化

采用正交设计法对耐底物腈水合酶融合子的发酵条件进行优化,以发酵液起始pH,发酵周期,接种量,装料系数作为考察因素,最终确定最佳发酵条件为:起始pH8.0、发酵周期54h、接种量12％、装液系数12％.在此优化条件下融合子腈水合酶的活力达到1100万U/ml,较优化前提高了83.3％.通过响应面法对发酵培养基配方进行优化研究,采用Plackett-Burman法对8个因素进行了筛选,结果表明,葡萄糖、尿素、磷酸氢二钾、磷酸二氢钾是影响发酵液腈水合酶产量的主效应因子.用最陡爬坡试验及Central composite design设计进一步优化,利用Design-Expert软件进行二次回归分析,得到各因素的最佳浓度为:葡萄糖22.62g/L、尿素9.76g/L、K2HP04 1.22g/L、KH2PO41.268g/L.在此培养基优化配方下融合子腈水合酶的活力达到1280万U/ml,较原配方的酶活提高了16.4％.     

The third intracellular loop of D1 and D5 dopaminergic receptors dictates their subtype-specific PKC-induced sensitization and desensitization in a receptor conformation-dependent manner

We previously showed that phorbol-12-myristate-13-acetate (PMA) mediates a robust PKC-dependent sensitization and desensitization of the highly homologous human Gs protein and adenylyl cyclase (AC)-linked D1 (hD1R) and D5 (hD5R) dopaminergic receptors, respectively. Here, we demonstrate using forskolin-mediated AC stimulation that PMA-mediated hD1R sensitization and hD5R desensitization is not associated with changes in AC activity. We next employed a series of chimeric hD1R and hD5R to delineate the underlying structural determinants dictating the subtype-specific regulation of human D1-like receptors by PMA. We first used chimeric receptors in which the whole terminal region (TR) spanning from the extracellular face of transmembrane domain 6 to the end of cytoplasmic tail (CT) or CT alone were exchanged between hD1R and hD5R. CT and TR swaps lead to chimeric hD1R and hD5R retaining PMA-induced sensitization and desensitization of wild type parent receptors. In striking contrast, hD1R sensitization and hD5R desensitization mediated by PMA are correspondingly switched to PMA-induced receptor desensitization and sensitization following the IL3 swap between hD1R and hD5R. Cell treatment with the PKC blocker, Gö6983, inhibits PMA-induced regulation of these chimeric receptors in a similar fashion to wild type receptors. Further studies with chimeras constructed by exchanging IL3 and TR show that PMA-induced regulation of these chimeras remains fully switched relative to their respective wild type parent receptor. Interestingly, results obtained with the exchange of IL3 and TR also reveal that the D1-like subtype-specific regulation by PMA, while fully dictated by IL3, can be modulated in a receptor conformation-dependent manner. Overall, our results strongly suggest that IL3 is the critical determinant underlying the subtype-specific regulation of human D1-like receptor responsiveness by PKC.