低温热处理对超高温灭菌乳中假单胞菌脂肪酶的活性影响

通过分析不同因素对假单胞菌脂肪酶活性的影响以及假单胞菌脂肪酶活性与超高温灭菌(UHT)乳脂肪上浮的关系,研究了控制UHT乳中假单胞菌脂肪酶活性和延缓脂肪上浮现象的措施。结果表明pH值对假单胞菌脂肪酶的活性有显著性影响(P<0.01),50、55、60℃(20min)的低温热处理能显著降低假单胞菌脂肪酶的活性(P<0.01)。贮藏试验表明低温热处理对控制UHT乳在贮存过程中的假单胞菌脂肪酶活性水平(P<0.01)和脂肪上浮现象(P<0.05)有明显的作用,而55℃和15min的低温热处理对缓解UHT乳在贮藏过程中的脂肪上浮现象最为有效。     

Suppression of root-knot disease by Pseudomonas fluorescens CHA0 in tomato: importance of bacterial secondary metabolite, 2,4-diacetylpholoroglucinol

The antimicrobial metabolites 2,4-diacetylphloroglucinol (2,4-DAPG) and pyoluteorin contribute to the ability of Pseudomonas fluorescens strain CHA0 to control plant diseases caused by soil-borne pathogens. P. fluorescens strain CHA0 and its derivatives CHA89 (antibiotics-deficient) and CHA0/pME3424 (antibiotics overproducing) were investigated as potential biocontrol agents against Meloidogyne javanica the root-knot nematode. Exposure of root-knot nematode to culture filtrates of P. fluorescens under in vitro conditions significantly reduced egg hatch and caused substantial mortality of M. javanica juveniles. Nutrient broth yeast extract (NBY) medium amended with 2% (w/v) glucose or 1 mM EDTA markedly repressed hatch inhibition activity of the strain CHA0 but not that of CHA0/pME3424 or CHA89. On the other hand, NBY medium amended with glucose significantly enhanced nematicidal activity of the strain CHA0/pME3424. Neither glucose nor EDTA had an influence on the nematicidal activity of the strains CHA0 and CHA89. Under in vitro conditions, antibiotic overproducing strain CHA0/pME3424 and CHA0 expressed phl‘-’lacZ reporter gene but strain CHA89 did not. Expression of the reporter gene reflects actual production of DAPG. In general, CHA0/pME3424 expressed reporter gene to a greater extent compared to its wild type counterpart CHA0. Regardless of the bacterial strains, reporter gene expression was markedly enhanced when NBY medium was amended with glucose but EDTA had no such effect. A positive correlation between the degree of juvenile mortality and extent of phl‘-’lacZ reporter gene expression was also observed in vitro. Strain CHA0 produced zones of 4-6 mm on MM medium containing gelatin while strain CHA0/pME3424 and CHA89 did not. When MM medium containing gelatin was amended with 2% glucose of 1 mM EDTA size of haloes produced by the strain CHA0 reduced to 2 mm. Under glasshouse conditions aqueous cell suspension of the strains CHA0 or CHA0/pME3424 at various inoculum levels (10⁷, 10⁸ or 10⁹ cfu ml⁻¹) significantly reduced root-knot development. CHA89 caused significant reduction in galling when applied at 10⁹ cfu ml⁻¹. To better understand the mechanism of nematode suppression, split root bioassay was performed. Split-root experiments, that guarantee a spatial separation of inducing agent and a challenging pathogen, showed that soil treatment of one half of the root system with cell suspension of CHA0 or CHA0/pME3424 resulted in a significant systemic induced resistance leading to reduction of M. javanica infection of tomato roots in the non-baterized nematode treated half. The results clearly suggest that the antibiotic 2,4-DAPG from P. fluorescens CHA0 act as the inducing agents of systemic resistance in tomato roots. Populations of CHA0 and its derivatives declined progressively by 10-fold between first and fourth harvests (0-21 days after inoculation). However, bacterial populations increased at final harvest (28 days after application).     

Colonization of wheat seedling (Triticum aestivum) roots by Pseudomonas fluorescens and Bacillus subtilis

Summary Colonization patterns of Pseudomonas fluorescens and Bacillus subtilis on roots of wheat seedlings growing on water agar were studied qualitatively by replica printing and quantitatively by the plate count method. The results indicated a stronger colonization potential for P. fluorescens (up to 10⁷ cfu/cm root) than for B. subtilis (up to 10⁵ cfu/cm root). Although the numbers of both species were lower when inoculated together, the observed colonization patterns on the roots were comparable to those found with single inoculations. For none of these bacteria was active migration along the root surface in any direction observed, indicating that distal positions are reached mainly by a passive displacement on the root tip and elongating cells. Ecological implications of the observed phenomena are discussed.     

Fate, tree growth effect and potential impact on soil microbial communities of mycorrhizal and bacterial inoculation in a forest plantation

The knowledge of the survival of inoculated beneficial fungal and bacterial strains in the field and the effects of their release on the indigenous microbial communities has been of great interest since the practical use of selected natural or genetically modified microorganisms has been developing. The aim of this study was to monitor, 4 years after plantation into the field site, the effects of Douglas fir (Pseudotsuga menziesii) co-inoculation with the mycorrhiza helper bacterial strain Pseudomonas fluorescens BBc6R8 and/or the fungal strain Laccaria bicolor S238N on seedling growth and on the indigenous bacterial and ectomycorrhizal communities using quantitative and qualitative approaches. The field persistence of the inoculated strains was also monitored. The seedling shoot volume estimate was statistically significantly higher in the fungal inoculated plots in comparison to the non-inoculated plots but no treatment-related changes in the quantitave or qualitative microbial measurements were observed and the inoculated strains could not be detected after 4 years.     

Influence of temperature on the motility of Pseudomonas oryzihabitans and control of Globodera rostochiensis

The motility and efficacy of Pseudomonas oryzihabitans as a biocontrol agent against the potato cyst nematode Globodera rostochiensis were studied with respect to temperature. The influence of soil moisture on bacterial movement was also tested. In a closed container trial, P. oryzihabitans significantly reduced invasion of second stage juveniles (J2) of G. rostochiensis in potato roots, its effect being more marked at 25 and 21 °C than at 17 °C. P. oryzihabitans motility in vitro was optimal at 26 °C and inhibited at temperatures below 18 °C. In soil, both temperature and matric potential affected bacterial movement. At 16 °C its movement and survival were suppressed, but they were unaffected at 25 °C. At both temperatures the biocontrol agent moved faster in the wetter (−0.03 MPa) than in the drier soil (−0.1 MPa). These results suggest that temperature is a key factor in determining the potential of P. oryzihabitans as a biocontrol agent.     

Soil bacterial community response to sulfadiazine in the soil–root zone

Sulfonamide antibiotics reach soil via manure and adversely affect microbial diversity. Clear effects of these bacteriostatic, growth‐inhibiting antibiotics occur in the presence of a parallel input of microbial activity stimulating manure. Natural hot spots with already increased soil microbial activity are located in the rhizosphere, comprising microorganism such as Pseudomonas with plant growth promoting and pathogenic strains. The hypothesis was therefore that the antibiotic activity of sulfonamides is promoted in the rhizosphere even in the absence of manure, followed by shifts of the natural plant‐specific microbial community structure. This was evaluated by a laboratory experiment with Salix fragilis L. and Zea mays L. After 40 d of incubation, sub‐areas such as non‐rhizosphere soil, rhizosphere soil and plant roots were sampled. Effects on microbial community structure were analyzed using 16S rRNA gene fragment patterns of total bacteria community and Pseudomonas. Selected exoenzymes of N‐, P‐, and C‐cycling were used to test effects on microbial functions. Compared to the factors soil sub‐area and sulfadiazine (SDZ) content, plant species had the largest influence on the bacterial community structure and soil exoenzyme activity pattern. This was also reflected by an up to 1.5‐fold higher acid phosphatase activity in samples from maize‐ compared to willow‐planted soil. We conclude that antibiotic effects on the bacterial community structures are influenced by the antibiotic concentration and root influence.     

Luteoforol,a flavan 4-ol,is induced in pome fruits by prohexadione-calciumand shows phytoalexin-like properties against <Emphasis Type="Italic">Erwinia amylovora</Emphasis>and other plant pathogens

Treatments with prohexadione-calcium led to lowered incidence of fire blight, scab and other diseases in pome fruit trees and other crop plants. In addition to acting as a growth regulator, prohexadione-calcium interferes with flavonoid metabolism and induces the accumulation of the 3-deoxycatechin luteoliflavan in shoots of pome fruit trees. Luteoliflavan does not possess any remarkable antimicrobial activity. Therefore luteoforol, its unstable and highly reactive precursor, has been tested in vitro for its bactericidal and fungicidal activities. Luteoforol was found to be highly active against different strains of Erwinia amylovora, the causal agent of fire blight, and all other bacterial and fungal organisms tested. Phytotoxic effects were also observed in pear plantlets. The results obtained indicate that prohexadione-calcium induces luteoforol as an active principle with non-specific biocidal properties. It is proposed that luteoforol is released upon pathogen attack from its cellular compartment and inhibits further disease development by destroying pathogen cells as well as by inducing a hypersensitive-like reaction in the host plant tissue. This mechanism would be closely analogous to the one known for structurally related phytoalexins in sorghum.     

组成型脱硫工程菌的构建及其脱硫性能分析

[目的]研究组成型脱硫工程菌的构建及其脱硫性能。[方法]以专一性脱硫菌德氏假单胞菌Pseudomonas delafieldii R-8为出发菌株,将该菌的脱硫质粒中的脱硫基因dszABC和组成型gap基因启动子克隆到表达载体pPR9TT中,获得的组成型重组质粒pRT-C后电转化R-8-0菌,得到了组成型工程菌R-8-C,并对其脱硫性能进行了比较研究。[结果]R-8-C菌在含0.10 mmol/L Na2SO4的BSM培养基中仍然具有较高脱硫活性,在72 h内,是以二苯并噻吩(DBT)为唯一硫源时R-8脱硫活性的93%;而对照组(即原始菌R-8)几乎不能脱硫。以DBT为唯一硫源时,在不同生长时期内,R-8-C菌生长细胞的脱硫活性均高于R-8菌,且在24 h内,R-8-C菌的脱硫活性约为R-8菌的1.3倍。[结论]该研究为进一步了解脱硫基因调控机制及构建高活性脱硫工程菌奠定了基础。     

一株丁草胺降解菌的分离鉴定

通过富集培养技术结合高效液相色谱法检测,从长期受丁草胺污染的污泥中筛选出1株丁草胺降解菌,命名为Y-1。经形态特征、生理生化特征和16S rDNA序列同源性分析,将该菌株鉴定为假单胞菌属(Pseudomonas sp.)。通过研究Y-1在不同条件下的降解特性发现,降解丁草胺的最优条件为:丁草胺初始浓度20 mg/L、接种量5%、pH值7、培养温度30℃。在最优环境条件下培养7 d,Y-1能降解培养液中76%的丁草胺,显示了良好的降解能力。