银杏外种皮提取物对病原菌Cylindrocladium colhounii的抑制作用

采用菌丝生长抑制法,研究了银杏外种皮3种不同提取物对病原菌(Cylindroc ladium col-hounii)的抑制作用并测定了这些提取物的MIC/MBC。结果表明,在相同实验天数内,抑菌效果(最小抑菌率)由高到低依次为银杏外种皮乙醇提取物(37.4%)、石油醚提取物(23.7%)和新鲜外种皮汁液(18.4%)。当提取物的浓度提升到一定程度时,三者的抑菌率均可达到100%;三种提取物的MIC/MBC分别为:86.25/86.25,172.5/276,293.25/345mg·mL-1。可见银杏外种皮具有明显抑制该病原菌生长的作用,且抑菌成分在乙醇中的溶解度较大。这为进一步研究该抑菌成分乃至生物农药的开发奠定了基础。     

Antibacterial activity of herbal extracts against five plant pathogenic bacteria

The present study was designed to evaluate in vitro antibacterial activity of herbal extracts against five plant pathogenic bacteria (viz. Xanthomonas campestris, Xanthomonas axonopodis pv. punicae, Erwinia spp., Pseudomonas syringae and Xanthomonas citri). Herbal extracts of leaves and rinds of Garcinia indica, rhizomes of Curcuma aromatica, roots of Glyccyrrhiza glabra, leaves of Nyctanthes arbor-tristis and seeds of Vernonia anthelmintica were used for screening. Screening was done using agar well diffusion method. Relatively potent extracts were shortlisted from this study and were further studied to find out their minimum bactericidal concentration (MBC). From the studies, it was observed that extracts of C. aromatica, G. indica and G. glabra have shown lowest MBC values among other tested plant extracts. This study indicates the potential of these potent plant extracts in the management of diseases caused by plant pathogenic bacteria.     

Trypanosoma cruzi: Synergistic cytotoxicity of multiple amphipathic anti-microbial peptides to T. cruzi and potential bacterial hosts

The parasite Trypanasoma cruzi is responsible for Chagas disease and its triatomine vector, Rhodnius prolixus, has a symbiotic relationship with the soil bacterium, Rhodococcus rhodnii.R. rhodnii that was previously genetically engineered to produce the anti-microbial peptide, cecropin A was co-infected with T. cruzi into R. prolixus resulting in clearance of the infectious T. cruzi in 65% of the vectors. Similar anti-microbial peptides have been isolated elsewhere and were studied for differential toxicity against T. cruzi and R. rhodnii. Of the six anti-microbial peptides tested, apidaecin, magainin II, melittin, and cecropin A were deemed potential candidates for the Chagas paratransgenic system as they were capable of killing T.cruzi at concentrations that exhibit little or no toxic effects on R. rhodnii. Subsequent treatments of T. cruzi with these peptides in pair-wise combinations resulted in synergistic killing, indicating that improvement of the 65% parasite clearance seen in previous experiments may be possible utilizing combinations of different anti-microbial peptides.     

Redox state and gender differences in vascular smooth muscle cells

Vascular smooth muscle cells (VSMC) have been isolated from male and female rat aorta and studied to assess their susceptibility to ultraviolet radiation-induced oxidative stress. Interestingly, a gender difference, in terms of reactive oxygen species production, was detected in both basal and irradiated VSMC. Namely, VSMC from male rats were more susceptible to radiation-induced stress and easier underwent apoptosis in comparison to cells from female rats. Conversely, the latter, in the same experimental conditions, clearly displayed signs of premature senescence. These results indicate that a sort of "gender memory" can be conserved in VMSC in primary culture.     

An ATPase inhibitory peptide with antibacterial and ion current effects

An 84-residue bactericidal peptide, PSK, was purified from a Chrysomya megacephala fly larvae preparation. Its amino acid sequence is similar to that of a previously reported larval peptide of the Drosophila genus (SK84) noticed for its anticancer and antimicrobial properties. The PSK sequence is also homologous to mitochondrial ATPase inhibitors from insects to humans (35–65% sequence identity), indicating an intracellular protein target and possible mechanism for PSK. It contains a cluster of six glycine residues, and has several two- and three-residue repeats. It is active against both Gram-positive and Gram-negative bacteria via a mechanism apparently involving cell membrane disintegration and inhibition of ATP hydrolysis. In addition, PSK induces an inward cationic current in pancreatic β cells. Together, the findings identify a bioactive peptide of the ATPase inhibitor family with specific effects on both prokaryotic and mammalian cells.     

Bacteriostatic effects of cerium-humic acid complex

The bacteriostatic potency of the cerium-humic acid complex was evaluated by experimental measurement of this complex interaction with E. coli, Bacillus pyocyaneus, Staphylococcus aureus, Leuconostoc and Streptococcus faecalis, and by comparison bacteriostatic effects with the cerium-citrate complex. The experimental results indicated that the cerium-humic acid complex strongly inhibited growth of all five bacterial strains, and its diameter of bacteriostatic circles were more than 30 mm. The minimal bacteria-inhibiting concentration were 1×10⁻³, 2×10⁻³ and 1×10⁻² mol/L for E. coli and Bacillus pyocyaneus, Staphylococcus aureus, and Leuconostoc and Streptococcus faecalis individually, and the measured minimal bactericidal concentrations were 2×10⁻³ and 1×10⁻² mol/L for Bacillus pyocyaneus, E. coli, and Leuconostoc. To kill Staphylococcus aureus and Streptococcus faecalis, the concentration had to be more than 1×10⁻² mol/L. On the contrary, we found that cerium-citrate complex did not inhibit the growth of the above five bacteria, but stimulated bacterial growth. The completely different bacteriostatic results of two cerium complexes may hint that the association and chemical properties of the two complexes were different.     

Novel fungicidal benzylsulfanyl-phenylguanidines

A series of substituted benzylsulfanyl-phenylamines was synthesized, of which four substituted benzylsulfanyl-phenylguanidines (665, 666, 667 and 684) showed potent fungicidal activity (minimal fungicidal concentration, MFC ? 10 μM for Candida albicans and Candida glabrata). A benzylsulfanyl-phenyl scaffold with an unsubstituted guanidine resulted in less active compounds (MFC = 50-100 μM), whereas substitution with an unsubstituted amine group resulted in compounds without fungicidal activity. Compounds 665, 666, 667 and 684 also showed activity against single C. albicans biofilms and biofilms consisting of C. albicans and Staphylococcus epidermidis (minimal concentration resulting in 50% eradication of the biofilm, BEC50 ? 121 μM for both biofilm setups). Compounds 665 and 666 combined potent fungicidal (MFC = 5 μM) and bactericidal activity (minimal bactericidal concentration, MBC for S. epidermidis ? 4 μM). In an in vivo Caenorhabditis elegans model, compounds 665 and 667 exhibited less toxicity than 666 and 684. Moreover, addition of those compounds to Candida-infected C. elegans cultures resulted in increased survival of Candida-infected worms, demonstrating their in vivo efficacy in a mini-host model.     

Antimicrobial activity and phytochemical screening of Ocimum americanum L extracts against pathogenic microorganisms

The aim of the present study is to assess the antimicrobial activities of various leaf extracts of Ocimum americanum were tested against pathogenic microorganisms. Preparation of different extracts viz., aqueous, acetone, ethyl acetate and methanol through soxhlet extraction method. Various extracts were investigated against MTCC strains of Bacillus cereus, Clostridium penfrigens, Klebsilla pnemoniae, Salmonella paratyphi, Candida albicans and Aspergillus niger by agar well diffusion and disc diffusion methods. Minimum inhibitory concentration (MIC), Minimum Bactericidal/Fungicindal Concentration (MBC/MFC) were determined through micro dilution method. Elucidation of phytochemicals and functional groups were observed by HPLC and FT-IR respectively. Ethyl acetate leaf extract of O.americanum showed significant antimicrobial activity against the all tested pathogens in agar well diffusion method in which B.cereus (17 mm) was observed high zone of inhibition. Whereas lowest inhibition was observed in aqueous extract against C.pentrigens (7 mm). The ranges of MIC values from 0.78 μg/ml to 50 μg/ml and MBC/MFC 1.56 μg/ml to 50 μg/ml were observed. Phytochemicals such as alkaloids, steroids, saponins, flavonoids, tannins, terepenes, phenolic compounds cardiac glycosides were detected. Saponinns, flavonoids, tannins, phenolic compounds were observed in only ethyl acetate leaf extracts. Functional group of the leaf extracts was exhibited by FTIR and HPLC analysis of the ethyl acetate leaf extract was elutated at six peaks. Based on the results we concluded that ethyl acetate leaf extract of O.americanum has proved to be potentially effective than the other extracts. Therefore, ethyl acetate leaf extract of O.americanum could act as antimicrobial agent and further studies are recommended for isolation of compounds and toxicological studies.     

Spatial heterogeneity of soil nutrients and aboveground biomass in abandoned old-fields of Loess Hilly region in Northern Shaanxi, China

The responses of soil enzyme activity of freshwater marsh, microbial biomass carbon (MBC), dissolved organic carbon (DOC) and aboveground biomass to water gradients were studied with Carex lasiocarpa pot culture experiment. The relationships between soil enzyme activity and MBC, DOC and aboveground biomass were discussed. The water gradients were W1, 15 cm; W2, ?5 cm; W3, ?5–5 cm; W4, submerged. The results indicated that acid phosphatase, invertase and urease activities were decreased with the increase of water level, while catalase activity was increased with moisture content increasing. Drying-wetting alternation (W3) increased soil enzyme activities if compared with W1. MBC content followed the order of W3 > W1 > W2 > W4, and the activities of invertase, urease and catalase were significantly positively correlated with MBC (p < 0.05). DOC content presented the order of W4 > W1 > W3 > W2, and the activities of urease and acid phosphatase were most significantly negatively correlated with DOC (p < 0.01). In addition, drying-wetting alternation promoted the growth of Carex lasiocarpa. When water submerged plants, the growth of Carex lasiocarpa was significantly inhibited. The aboveground biomass was positively related to soil enzyme activities. There were close relationships between the activities of invertase, urease and catalase and the growth situation of Carex lasiocarpa.     

施肥对板栗林地土壤N2O通量动态变化的影响

2011年6月—2012年6月期间,在浙江省临安市典型板栗林地进行施肥对土壤N2O通量变化影响的试验研究。目的在于探明不同施肥处理下板栗林地土壤N2O通量的动态变化规律,并探讨土壤N2O通量和土壤环境因子之间的关系。试验设置4个处理:对照(不施肥)、无机肥、有机肥、有机无机混合肥。采用静态箱-气相色谱法测定了板栗林地土壤N2O通量,并测定了土壤温度、水分、水溶性有机碳(WSOC)和微生物量碳(MBC)含量。结果表明:板栗林土壤N2O通量呈显著季节性变化,最大值出现在夏季,最小值出现在冬季;而且,施肥处理显著提高土壤N2O年均通量和年累积量;在整个试验期间,无机肥、有机肥和有机无机混合肥处理下土壤N2O的排放系数分别达到0.96%、1.45%和1.29%。此外,施肥也显著增加了土壤WSOC和MBC的含量(P<0.05)。不同施肥处理条件下,土壤N2O通量与土壤5 cm处温度、WSOC含量间均呈极显著正相关(P<0.01),但与MBC含量之间的相关性不显著。土壤N2O排放与土壤含水量间除对照处理外均没有显著相关性。综上所述,施肥引起土壤WSOC含量的增加可能是施肥增加板栗林地土壤N2O排放速率的主要原因之一。