腐乳毛霉蛋白酶菌株紫外线诱变育种

目的：选育酶活力高、耐热性好的毛霉蛋白酶菌株,用于腐乳发酵实验或生产。方法：从腐乳中分离毛霉蛋白酶菌株,对其出发菌株进行紫外线诱变,并经控温培养,选育优良变株。结果：获得一株酶活力高、耐热性强的优良变株SCLG—毛霉16,该菌株在32℃条件下,生长茂盛,其HE值为1.39、蛋白酶活力为180.375u/g,分别较出发菌株高出7.8%和51.4%。结论：将此优良变株用于腐乳发酵实验或生产,在缩短发酵时间,提升腐乳质量,延长生产季节等方面具有一定的应用价值。     

Growth promoting effect of a transgenic <Emphasis Type="Italic">Bacillus mucilaginosus</Emphasis> on tobacco planting

In this study, we have investigated the plant growth promoting effect of Bacillus mucilaginosus strain D₄B₁, a rhizosphere soil organism, and its transgenic strain NKTS-3 on tobacco planting. The transgenic strain contains a phytase expression cassette that can express high active phytase extracellularly and hydrolyze phytate in the soil to liberate inorganic phosphorus for the growth of tobacco plants. Greenhouse study and field experiments showed that both wild-type B. mucilaginosus and the transgenic strain could promote tobacco plant growth. Moreover, the transgenic strain promoted tobacco plant growth (235% more than control in pot experiments and 125% more than control in field experiments) was higher than the wild-type B. mucilaginosus (183% more than control in pot experiments and 108% more than control in field experiments). In addition, the inoculation with transgenic rhizobacteria could significantly improve root acquisition of phosphorus and increase the phosphorus content of the plant.     

Properties of the cured oncogenic strain 37400 ofAgrobacterium tumefaciens

The properties of the 37400 oncogenic strain ofAgrobacterium tumefaciens are described. This strain was derived from the VI lysogenic strain originally isolated by Hamilton from aZinnia elegans tumour. Strain 37400 has a number of properties which render it suitable for quantitative and genetic studies. It is cured of prophages and can serve as a universal sensitive indicator for a number of phages isolated from various lysogenic strains ofAgrobacterium tumefaciens. Its good growth properties in synthetic media and at elevated temperatures enable the isolation of auxotrophic mutants and temperature sensitive phage mutants. Preliminary experiments show that strain 37400 will serve as suitable starting material for conjugation experiments under defined conditions.     

Differences in the response of German cockroach (Dictyoptera: Blattellidae) field strains to vapors of pyrethroid formulations.

Late-instar German cockroaches from an insecticide-susceptible field strain (Fairbanks) and four pyrethroid-resistant field strains were exposed to vapors of a cyfluthrin flowable concentrate (FC) and the formulation blank (formulation without the active ingredient). Experiments with other pyrethroid formulations were done with the Fairbanks strain and an insecticide-resistant field strain (K-851) because these strains exemplified the maximum interstrain variation in experiments with the FC. In these experiments, I used a cyfluthrin wettable powder (WP) and its blank, a cyfluthrin emulsifiable concentrate (EC), and a permethrin aerosol and its blank. Vapors of the FC and its blank caused the most rapid dispersal. Dispersal induced by vapors of the WP, EC, and aerosol formulations was low and variable. In general, less of a dispersal response occurred in the resistant strains than in the susceptible strain. The strain mostly highly resistant to pyrethroids (K-851) dispersed slowly compared with the other resistant strains in experiments with the FC and its blank. When vapor-induced dispersal was relatively low (less than 50%), a trend was still evident towards less dispersal in the K-851 strain than in the Fairbanks strain. Although dispersal in experiments with the FC did not differ significantly from that in experiments with the FC formulation blank, mean percentage dispersal at the end of the experiments was higher with the formulation blanks than with the complete formulations in experiments with the WP and permethrin aerosol.     

The mechanical behaviour of brain tissue: large strain response and constitutive modelling

The non-linear mechanical behaviour of porcine brain tissue in large shear deformations is determined. An improved method for rotational shear experiments is used, producing an approximately homogeneous strain field and leading to an enhanced accuracy. Results from oscillatory shear experiments with a strain amplitude of 0.01 and frequencies ranging from 0.04 to 16 Hz are given. The immediate loss of structural integrity, due to large deformations, influencing the mechanical behaviour of brain tissue, at the time scale of loading, is investigated. No significant immediate mechanical damage is observed for these shear deformations up to strains of 0.45. Moreover, the material behaviour during complex loading histories (loading-unloading) is investigated. Stress relaxation experiments for strains up to 0.2 and constant strain rate experiments for shear rates from 0.01 to 1 s(-1) and strains up to 0.15 are presented. A new differential viscoelastic model is used to describe the mechanical response of brain tissue. The model is formulated in terms of a large strain viscoelastic framework and considers non-linear viscous deformations in combination with non-linear elastic behaviour. This constitutive model is readily applicable in three-dimensional head models in order to predict the mechanical response of the intra-cranial contents due to an impact.     

Comparative studies of the mosquito-larval toxin of Bacillus sphaericus SSII-1 and 1593

Two strains of Bacillus sphaericus. SSII-1 and 1593, were bioassayed for toxic activity against second-instar larvae of the mosquito Culex pipiens quinquefasciatus. It was found that strain 1593 developed a level of toxicity 3000 times that of strain SSII-1. Although the toxic activity of B. sphaericus SSII-1 was relatively unchanged throughout growth, an increase in activity of strain 1593 occurred as the bacteria began to sporulate. Strain differences were examined by (i) growth cycle experiments, (ii) bioassays of the toxicity of oligosporogenous mutants, and (iii) manganese limitation experiments. The toxin of strain 1593 was shown to be more stable than that of strain SSII-1. Unlike the spores of strain SSII-1, the spores of B. sphaericus 1593 were found to be highly toxic. Thin sections of SSII-1 or 1593 cells did not reveal the presence of any inclusion body that might be related to toxicity.     

Design and numerical implementation of a 3-D non-linear viscoelastic constitutive model for brain tissue during impact

Finite Element (FE) head models are often used to understand mechanical response of the head and its contents during impact loading in the head. Current FE models do not account for non-linear viscoelastic material behavior of brain tissue. We developed a new non-linear viscoelastic material model for brain tissue and implemented it in an explicit FE code. To obtain sufficient numerical accuracy for modeling the nearly incompressible brain tissue, deviatoric and volumetric stress contributions are separated. Deviatoric stress is modeled in a non-linear viscoelastic differential form. Volumetric behavior is assumed linearly elastic. Linear viscoelastic material parameters were derived from published data on oscillatory experiments, and from ultrasonic experiments. Additionally, non-linear parameters were derived from stress relaxation (SR) experiments at shear strains up to 20%. The model was tested by simulating the transient phase in the SR experiments not used in parameter determination (strains up to 20%, strain rates up to 8s(-1)). Both time- and strain-dependent behavior were predicted accurately (R2>0.96) for strain and strain rates applied. However, the stress was overestimated systematically by approximately 31% independent of strain(rate) applied. This is probably caused by limitations of the experimental data at hand.     

An Experimental Test of the Rhizopine Concept in Rhizobium meliloti

In some Rhizobium-legume symbioses, compounds known as rhizopines are synthesized by bacteroids and subsequently catabolized by free-living cells of the producing strain. It has been suggested than rhizopines act as proprietary growth substrates and enhance the competitive ability of the producing strain in its interactions with the diverse microbial community found within the rhizosphere. Wild-type, rhizopine-producing Rhizobium meliloti L5-30 and mutant L5-30 strains deficient for either rhizopine synthesis or catabolism were inoculated onto lucerne host plants in competition experiments. These experiments demonstrated that no apparent advantage resulted from the ability to synthesize a rhizopine, whereas the ability to catabolize rhizopine provided a clear advantage when an organism was in competition with a strain without this ability. The results suggest that when an organism is in competition with a catabolism-deficient mutant, the ability to catabolize rhizopine results in enhanced rates of nodulation. The results of the experiments were not consistent with the hypothesis that the sole role of rhizopines is to act as proprietary growth substrates for the free-living population of the producing strain.     

Effect of Diet and Strain Difference on the Virulence of Staphylococcus aureus for Mice

Years of intensive investigations in our laboratories on staphylococcal infections in mice have indicated a gradual decrease in the virulence of Staphylococcus aureus for this animal, particularly the strain we were using, the random-bred BT mouse. The present investigations, based on changes in diet and strain differences in mice, were undertaken in an attempt to improve susceptibility of our stock strain, on the one hand, and to determine whether susceptibility was influenced by genetic strain differences, on the other. In the first series of experiments, littermate mice of the BT strain were placed on different diets: one group received a commercial diet; the other, a basic diet previously established in our laboratories as adequate for growth requirements of the animals. An increase in the susceptibility of the animals to staphylococcal infection was noted in the mice receiving the basic diet. In the second series of investigations, three other strains of mice (the Swiss albino, the C3H/HeJ, and the C57B1) previously not used by our laboratories in staphylococcal experiments were studied for staphylococcal susceptibility. These experiments revealed that all of these strains of mice were highly susceptible to the infection, even though they were maintained on a commercial diet.     

Isolation and characterization of a Lactobacillus amylovorus mutant depleted in conjugated bile salt hydrolase activity: relation between activity and bile salt resistance

Growth experiments were conducted on Lactobacillus amylovorus DN-112 053 in batch culture, with or without pH regulation. Conjugated bile salt hydrolase (CBSH) activity was examined as a function of culture growth. The CBSH activity increased during growth but its course depended on bile salts type and culture conditions. A Lact. amylovorus mutant was isolated from the wild-type strain of Lact. amylovorus DN-112 053 after mutagenesis with N-methyl-N'-nitro-N-nitrosoguanidine. An agar plate assay was used to detect mutants without CBSH activity. In resting cell experiments, the strain showed reduced activity. Differences between growth parameters determined for wild-type and mutant strains were not detected. Comparative native gel electrophoresis followed by CBSH activity staining demonstrated the loss of proteins harbouring this activity in the mutant. Four protein bands corresponding to CBSH were observed in the wild-type strain but only one was detected in the mutant. The specific growth rate of the mutant strain was affected more by bile salts than the wild-type strain. Nevertheless, bile was more toxic for the wild-type strain. In viability studies in the presence of nutrients, it was demonstrated that glycodeoxycholic acid exerted a higher toxicity than taurodeoxycholic acid in a pH-dependent manner. No difference was apparent between the two strains. In the absence of nutrients, the wild-type strain died after 2 h whereas no effect was observed for the mutant. The de-energization experiments performed using the ionophores nigericin and valinomycin suggested that the chemical potential of protons (ZDeltapH) was involved in Lactobacillus bile salt resistance.     

Finite element modeling for strain rate dependency of fracture resistance in compact bone

Crack growths in compact bones driven by various strain rate levels were studied using finite element modeling. The energy resistance curves in bovine femur cortical bones were characterized, whereas the orthotropic viscoelasticity in bone materials was accounted for to assess the effect of strain rate on the energy resistance curve. The models were also used to justify the anticipated plane strain response as a result of rather thick specimens used in experiments. Similarities were found between the experimental and model results when crack resistance ability exhibited in bones with slow loading rates, while unstable crack growth existed in bones with rapid loading rates. The critical energy release rates slightly decreased with the increase in strain rates. The hybrid experimental and computational method introduced in this study could be beneficial for application in fracture study in which standard experiments cannot be validly performed.     

The effect of loading rate on the development of early damage in articular cartilage

Experimental reports suggest that cartilage damage depends on strain magnitude. Additionally, because of its poro-viscoelastic nature, strain magnitude in cartilage can depend on strain rate. The present study explores whether cartilage damage may develop dependent on strain rate, even when the presented damage numerical model is strain-dependent but not strain-rate-dependent. So far no experiments have been distinguished whether rate-dependent cartilage damage occurs in the collagen or in the non-fibrillar network. Thus, this research presents a finite element analysis model where, among others, collagen and non-fibrillar matrix are incorporated as well as a strain-dependent damage mechanism for these components. Collagen and non-fibrillar matrix stiffness decrease when a given strain is reached until complete failure upon reaching a maximum strain. With such model, indentation experiments at increasing strain rates were simulated on cartilage plugs and damage development was monitored over time. Collagen damage increased with increasing strain rate from 21 to 42 %. In contrast, damage in the non-fibrillar matrix decreased with increasing strain rates from 72 to 34 %. Damage started to develop at a depth of approximately 20 % of the sample height, and this was more pronounced for the slow and modest loading rates. However, the most severe damage at the end of the compression step occurred at the surface for the plugs subjected to 120 mm/min strain rate. In conclusion, the present study confirms that the location and magnitude of damage in cartilage may be strongly dependent on strain rate, even when damage occurs solely through a strain-dependent damage mechanism.     

Improvement of biological control capacity of Paenibacillus polymyxa E681 by seed pelleting on sesame

Sesame is an important vegetable crop for the production of oil in Korea. The main obstacle of sesame cultivation is the occurrence of damping-off diseases and wilt caused by a complex of soil-borne pathogens in fields cultivated for two or more successive years. To protect sesame seedlings against these diseases, Paenibacillus polymyxa E681, a plant growth-promoting rhizobacterium (PGPR) previously shown to suppress disease incidence and promote growth on cucumber and pepper in the greenhouse and field experiments, was evaluated for its capacity for biological control and growth promotion in vitro and in situ. Seed treatment with strain E681 alone did not show consistent protection. Therefore, seed pelleting with strain E681 was attempted to increase the seed size and improve the stability and effectiveness of biocontrol capacity by strain E681. Through screening of pelleting materials, a combination of clay and vermiculite was selected for further experiments to enhance seed germination and root colonization of strain E681 on sesame. In greenhouse trials, formulations of strain E681 reduced disease incidence in disease-conducive soil. In the field, pelleting of sesame seeds with strain E681 significantly reduced pre- and post-emergence damping-off compared to the non-treated or pelleting alone controls; pelleting also promoted the plant growth and the grain yield. Furthermore, the efficacy of strain E681 for biological control and plant growth promotion was improved by sesame seed pelleting compared to the treatment with strain E681 alone. Hence, the application of strain E681 via seed pelleting offers potential to overcome some of the problems associated with successive years of sesame cultivation.     

Screening of pectinase producer from alkalophilic bacteria and study on its potential application in degumming of ramie

Four strains designated as NT-2, NT-6, NT-33 and NT-82 were selected from alkalophilic bacteria. They all can produce pectinase and xylanase. The polygalacturonase (PGase) and xylanase activities of strain NT-33 were 1025 U ml^-1 and 26U ml^-1 respectively. The pH and temperature optimum for the activity of PGase were 10.5 and 70°C, respectively. From batch experiments, it was found that strain NT-33 had an excellent capacity for degumming ramie fibers. After 24 h fermentation this strain can remove 70% of the gum existing in ramie fibers. The experiments showed that a series of noncellulosic polysaccharide degrading enzymes were involved in the ramie degumming process.     

In vitro reconstitution of cdc25 regulated S. cerevisiae adenylyl cyclase and its kinetic properties.

The attenuated GTP regulation adenylyl cyclase (CDC35) lysates or membranes prepared from cells of a cdc25ts strain is enhanced 2.5- to 6-fold by mixing these lysates or membranes with lysates or membranes from a cdc35ts strain harboring wild-type CDC25. The kinetics of activation of the Saccharomyces cerevisiae adenylyl cyclase in vitro is first order, as is the activation of mammalian adenylyl cyclase. The rate of enzyme activation in the presence of non-hydrolysable analogs of GTP increases with the number of CDC25 gene copies present in the cell. When GppNHp was used the rate of activation of the cyclase in a strain harboring a multicopy plasmid of CDC25 was 7.0-fold higher than the rate in an isogenic strain with the cdc25-2 mutation. The rate of adenylyl cyclase activation from a strain with a disrupted CDC25 gene is 14.7-fold lower than the rate in an isogenic strain containing the CDC25 gene on a multicopy plasmid. The reconstitution experiments described provide direct biochemical evidence for the role of the CDC25 protein in regulating the RAS dependent adenylyl cyclase in S.cerevisiae. The reconstitution experiments and the kinetic experiments may also provide a biochemical assay for the CDC25 protein and can form the basis for its characterization. In this study we also show that adenylyl cyclase activity in ras1ras2byc1 cells is found in the soluble fraction, whereas in wild-type strain it is found in the membrane fraction. Overexpression of the gene CDC25 in the ras1ras2bcy1 strain relocalizes adenylyl cyclase activity to the membrane fraction. This finding suggests a biochemical link between CDC25 and CDC35 in the absence of RAS, in addition to its role in regulating RAS dependent adenylyl cyclase.     

紫外诱变改良柑橘采后病害拮抗菌柠檬形克勒克酵母研究

以柠檬形克勒克酵母(Kloeckera apiculata)为出发菌株, 采用紫外线(UV)、UV+LiCl等方法对其进行诱变改良。确定了处理的最佳剂量：紫外处理15 W 30 cm照射20 s, UV+LiCl处理UV照射20 s并在平板中加入LiCl 0.3% (W/V)。选育到一株生理特性有明显改善的变异菌株UV20-13, 果实试验中, 7 d后柑橘青、绿霉病的发病率分别比出发菌株降低25.56%和10.00%。生长动态测定和传代试验表明, 该菌株生长特性优于出发菌株, 连续传代10代, 该菌株没有出现退化、回复突变等, 在遗传上是稳定的。     

Improvement of biological control capacity of Paenibacillus polymyxa E681 by seed pelleting on sesame

Sesame is an important vegetable crop for the production of oil in Korea. The main obstacle of sesame cultivation is the occurrence of damping-off diseases and wilt caused by a complex of soil-borne pathogens in fields cultivated for two or more successive years. To protect sesame seedlings against these diseases, Paenibacillus polymyxa E681, a plant growth-promoting rhizobacterium (PGPR) previously shown to suppress disease incidence and promote growth on cucumber and pepper in the greenhouse and field experiments, was evaluated for its capacity for biological control and growth promotion in vitro and in situ. Seed treatment with strain E681 alone did not show consistent protection. Therefore, seed pelleting with strain E681 was attempted to increase the seed size and improve the stability and effectiveness of biocontrol capacity by strain E681. Through screening of pelleting materials, a combination of clay and vermiculite was selected for further experiments to enhance seed germination and root colonization of strain E681 on sesame. In greenhouse trials, formulations of strain E681 reduced disease incidence in disease-conducive soil. In the field, pelleting of sesame seeds with strain E681 significantly reduced pre- and post-emergence damping-off compared to the non-treated or pelleting alone controls; pelleting also promoted the plant growth and the grain yield. Furthermore, the efficacy of strain E681 for biological control and plant growth promotion was improved by sesame seed pelleting compared to the treatment with strain E681 alone. Hence, the application of strain E681 via seed pelleting offers potential to overcome some of the problems associated with successive years of sesame cultivation.     

紫外诱变改良柑橘采后病害拮抗菌柠檬形克勒克酵母研究

以柠檬形克勒克酵母(Kloeckera apiculata)为出发菌株,采用紫外线(UV)、UV LiCl等方法对其进行诱变改良.确定了处理的最佳剂量:紫外处理15 W 30 cm照射20 s,UV LiCl处理UV照射20 s并在平板中加入LiCl 0.3%(W/V).选育到一株生理特性有明显改善的变异菌株UV20-13,果实试验中,7 d后柑橘青、绿霉病的发病率分别比出发菌株降低25.56%和10.00%.生长动态测定和传代试验表明,该菌株生长特性优于出发菌株,连续传代10代,该菌株没有出现退化、回复突变等,在遗传上是稳定的.     

Mutagen sensitivity of Drosophila melanogaster. VI. Evidence from the excision-defective mei-9AT1 mutant for the timing of DNA-repair activity during spermatogenesis

The sex-linked recessive lethal test has been used to compare mutation induction by ethyl methanesulfonate and methyl methanesulfonate in spermatogenic stages of the DNA repair-deficient mei-9AT1 mutant and a repair-proficient control strain. For both agents, the data demonstrate that induced mutation rates are similar in both strains for the meiotic and post-meiotic broods. Conversely, for spermatogonial broods, the data indicate that the excision-deficient strain exhibits a 4-8 fold increase in induced mutation rate in comparison to the excision-proficient control strain. These experiments suggest that the low mutability of gonial cells normally observed for these agents is due to effective excision-repair processes which function until the commencement of meiosis. From alkylation mutagenesis experiments with repair-deficient E. coli strains, we note that the mei-9 strain exhibits pleiotropic mutant phenotypes very similar to those displayed by the uvr D mutant. By analogy with these studies, we speculate that mei-9, like uvr D, is deficient in a DNA unwinding protein.     

Draft Genome Sequence of the Quality Control Strain Enterococcus faecalis ATCC 29212

Enterococcus faecalis ATCC 29212, a vancomycin-sensitive strain, has been extensively used as a representative control strain for clinical and laboratory experiments. Here we report the draft genome and annotation of this strain, containing 3,027,060 bp, with a G+C content of 37.2% in 126 contigs (≥500 bp).