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1.
The total numbers of actinomycetes found in three horizons of forest soil (L, F and H, after Babel 1971) were lower in areas treated with the herbicide Labuctril 25 than in untreated control. The highest inhibition effect (a decrease in actinomycete numbers by 50%) was observed in horizon L after a one-year post-treatment period, in horizon F after two years. In contrast, in horizon H the occurrence of actinomycetes was only reduced by 16–18% after both time intervals. 相似文献
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Three post-emergence herbicides (2,4-D, picloram and glyphosate) were applied to samples of an Alberta agricultural soil at
concentrations of 0, 2, 20, and 200 μg g−1. The effects of these chemicals on certain microbial variables was monitored over 27 days. All herbicides caused enhancement
of basal respiration but only for 9 days following application, and only for concentrations of 200 μg g−1. Substrate-induced respiration was temporarily depressed by 200 μg g−1 picloram and 2,4-D, and briefly enhanced by 200 μg g−1 glyphosate. It is concluded that because changes in microbial variables only occurred at herbicide concentrations of much
higher than that which occurs following field application, the side-effects of these chemicals is probably of little ecological
significance. 相似文献
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Chadha B.S. Jaswinder K. Rubinder K. Saini H.S. Singh S. 《World journal of microbiology & biotechnology》1999,15(2):217-221
Thermomyces lanuginosus strains from different culture collections, namely ATCC 26909, ATCC 22083, DEN 1457, IMI 84400 and BS1 were compared for xylanase production, and isozyme profile. Of all the strains of T. lanuginosus, BS1 a soil isolate produced the largest amount of xylanase. All strains were found to produce two forms of xylanase (I & II) with molecular mass corresponding to 25.0 and 54.0 KDa. The u.v/NTG mutagenesis of T. lanuginosus BS1 aleurospores/protoplasts resulted in xylanase-hyperproducing mutants. A morphological colour mutant RB 524 produced approximately 2.5-fold higher xylanase (2506.0 units/ml) as compared to the parent strain (1018.1 units/ml). 相似文献
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A total of 90 different Streptomyces isolates were recovered from 36 soil samples and assessed for their antibacterial activity. Nine isolates were identified by the absence of an aerial mycelium. The rest were grouped into six colour series, namely grey, white, yellow, green, red and polymorphic colours (pink, orange or violet) with total numbers of 29, 18, 14, 8, 3 and 9, respectively. The isolates (68%) showed a reverse side culture pigmentation, 30% produced melanin and 25% produced other soluble pigments. Isolates (48%) were characterized by flexuous spore chains, 21% with spiral and 10% for each of the rectus and retinaculum apertum arrangement. The antibiotic activity against a wide range of bacteria was exhibited by 54% of the isolates which were effective against Bacillus subtilis (57%), Staphylococcus aureus (47%), Escherichia coli (24%), Klebsiella spp (16%), and Shigella spp (12%). The lowest activity (8%) was exhibited against Pseudomonas spp and Salmonella spp. The antibacterial activity of the isolates was divided into four groups according to the diameter of the inhibition zone produced. Groups 3 and 4 with larger inhibition zones indicated their potential as a possible source of novel antibiotics. 相似文献
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2,4-D (2,4-dichlorophenoxyacetio acid) when applied to the soil at three doses (1.9, 7.6 and 15.2 mg per kg dry soil) had a stimulating effect on the total count of soil fungi and on several fungal species especially between 5 and 20 d after treatment. When the herbicide was incorporated in the agar medium it had a stimulating effect on the counts of total fungi, Aspergillus sp., A. niger, A.fumigatus and Fusarium app. at the low dose (6.3 ppm), but wag toxic at this dose toward Humicola grisea and Myrothecium verrucaria at the medium and high doses (25.2 and 50.4 ppm), it was toxic to the total count of fungi and to the majority of fungal species. VCS-438 [2-(3,4-dichlorophenyl)-4-methyl-l,2,4-oxadiazolidine-3,5-dione] was beneficial to the total count of fungi 2 and 5 d after soil treatment with the medium dose (8.0 mg per kg dry soil). Some fungal species could benefit from the low and the high doses (2.0 and 16.0 mg per kg dry soil) after these experimental periods. In the agar medium the counts of total fungi, Aspergillus sp., A. niger and A.fumigatus were almost significantly reduced by the three doses (6.8, 27.2 and 54.8 ppm). Planavin (4-methylsulphonyl-2,6-dinitro-N,N-dipropylaniline) was stimulating for the total count of fungi, Aspergillus, A.niger and A.ochraceus 2 and 5 d after treatment with the medium dose (8.0 mg per kg dry soil), and was also stimulating to Fusarium population at the medium dose after 2 d and at the high dose (16 mg per kg dry soil) after 20 d. In the agar medium Planavin at the low dose (6.8 ppm) was stimulating to A.terreus and inhibitory to A.nidulans and A.fumigatus. The medium and high doses (27.2 and 54.8 ppm) were generally toxic to the total count of fungi. 相似文献
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The ability of released proteins (Yops) and surface lipopolysaccharides (LPS) from the wild-type strain Yersinia enterocolitica 8081-L2, serotype 0:8 to influence the complement activity was determined. Yops and LPS from wild-type and mutant strains showed different ability to affect the classical pathway (CP) functional complement activity in vitro. The serum CP activity was inhibited during the infection induced with six Y. enterocolitica and three Y. pseudotuberculosis strains in rabbits. The changed complement activity might be of importance for the course of Yersinia infections. 相似文献
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Inclusion of benzimidazole or cobalt in the growth medium causes considerably increases in the free cystine levels of wild type and a cell division mutant strain of Chlamydomonas reinhardi. Homocystine levels are reduced slightly. Since benzimidazole and cobalt also markedly affect the expression of the mutation, it is suggested as a tentative hypothesis that this may be achieved via the rise in free cystine. Cysteine in the growth medium does not increase the internal free cystine or the expression of the mutation in a similar way to benzimidazole or cobalt. 相似文献
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Summary Samples of a sandy loam soil were supplied with normal, 10-fold and 100-fold rates of ioxynil, dalapon, mecoprop, dichlorprop,
MCPA + dichlorprop, picloram, and amitrole-T and incubated at 29°C at 65 per cent of the waterholding capacity. Treated soil
samples were compared with untreated samples. Samples supplied with (NH4)2SO4 and herbicides were used to investigate the effect of the herbicides on the rate of nitrification and the production of nitrite.
In several cases higher numbers of bacteria were found for a longer or shorter period in soil treated with herbicides. There
was some evidence that certain groups of bacteria had adapted to ioxynil in a soil sample supplied with the 100-fold rate
of this chemical.
After 2 or 4 weeks lower numbers ofAzotobacter chroococcum were found at the normal rate of ioxynil, dalapon, mecoprop, and dichlorprop. At the 100-fold rate of application the numbers
of Azotobacter were unfavourably affected by all herbicides.
The production of mineral nitrogen was hardly affected by the normal and 10-fold rates of application.
In the first week the rate of nitrification was slightly depressed in soil samples treated with the normal rates of dichlorprop
and amitrole-T and with the 10-fold rates of dalapon, mecoprop, and MCPA + dichlorprop. Strong inhibition of the nitrification
for at least 7 weeks was shown by the 10-fold rate of amitrole-T. At the 100-fold rate all herbicides, with the exception
of picloram, depressed the rate of nitrification for a longer or shorter period.
During the second week a very small increase of nitrite was found in the samples treated with the normal and 10-fold rates
of dalapon, mecoprop, dichlorprop, and amitrole-T. A small increase of nitrite was noted for 26 weeks in samples treated with
the 100-fold rates of amitrole-T.
A highly significant depression of CO2 evolution was found in the first week in samples treated with the normal rates of ioxynil, dalapon, mecroprop, dichlorprop,
and amitrole-T, also in samples treated with the 10-fold rates of dalapon, mecoprop, dichlorprop, MCPA + dichlorprop, picloram,
and amitrole-T. A highly significant depression of CO2 production was found after 8 weeks in all the samples treated with herbicides at the 100-fold rate with the exception of
the sample treated with picloram.
The decomposition of the herbicides was studied in soil samples treated with the 100-fold rates of herbicides. Only traces
of dalapon and mecoprop were found after 9 months, but 7.2% ioxynil, 29.8% dichlorprop, 39% (MCPA + dichlorprop), 52.1% picloram
and 52.2% amitrole-T were still present in active form. 相似文献
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Heavy metal pollution in aquatic ecosystems is a far reaching environmental problem. The possible influences of heavy metal exposure and the potential harm to organisms when combined with other environmental stressors such as temperature have been largely unexplored. An aquatic toxicity test of Caenorhabditis elegans was performed to estimate the 24 h median lethal concentration (LC50) of different zinc concentrations at different temperatures (15 °C, 20 °C, 25 °C, and 30 °C). We also examined the time course thermotolerance on wild type (N2) and daf-21 null (JT6130) adults exposed to 6.1 mM zinc at 37 °C. Hsp90 protein expression level in response to the combined effect of temperature and zinc toxicity was also investigated by both Western blots and ELISA. Our results show that C. elegans wild type nematodes exhibit severe lethal toxicity after a 24 h exposure to zinc at higher temperatures. In addition, the expression level of Hsp90 was highly inhibited in adult worms subjected to zinc stress. This toxicity assay at different temperatures provides insight into organism response to combined effects of temperature and zinc toxicity. 相似文献
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Phytostimulatory effect of Azospirillum brasilense wild type and mutant strains altered in IAA production on wheat 总被引:2,自引:0,他引:2
Dobbelaere Sofie Croonenborghs Anja Thys Amber Vande Broek Ann Vanderleyden Jos 《Plant and Soil》1999,212(2):153-162
Auxin production by Azospirillum is believed to play a major role in the observed plant growth promoting effect. By using
different genetically modified strains, the contribution of auxin biosynthesis by A. brasilense in altering root morphology
was evaluated in a plate assay. Inoculation with the wild type strains A. brasilense Sp245 and Sp7 resulted in a strong decrease
in root length and increase in root hair formation. This effect was abolished when inoculating with an ipdC mutant of A. brasilense.
The ipdC gene encodes a key enzyme in the IPyA pathway of IAA synthesis by A. brasilense. On the other hand, the observed
auxin effect was further enhanced by adding tryptophan, a precursor of IAA, to the plates and could be mimicked by replacing
the Azospirillum cells by a particular concentration of IAA. Furthermore, particular mutants (rpoN, scrp) and transconjugants
(extra copy of ipdC) of A. brasilense were tested in the plate assay. Together, these results confirm the important role of
IAA produced by Azospirillum in altering root morphology and illustrate the power of combining genetic tools and bioassays
to elucidate the mechanism of a beneficial Azospirillum-plant interaction.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
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Biochemical studies of melibiose metabolism in wild type and mel mutant strains of Salmonella typhimurium 总被引:6,自引:4,他引:2
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M Levinthal 《Journal of bacteriology》1971,105(3):1047-1052
I identified two enzyme activities, alpha-galactosidase and a galactoside permease, required for melibiose metabolism by Salmonella typhimurium. These activities are very low under normal growth conditions, but their production can be induced by melibiose and gratuitously by melibiitol. Melibiose induction is severely inhibited by glucose, but the glucose effect can be countered by 3', 5' cyclic adenosine monophosphate. I isolated two phenotypic classes of mutants not able to utilize melibiose as a carbon source. One class, Car(-), is deficient in the phosphotransferase system. The other, Mel, lacks either alpha-galactosidase, galactoside permease, or both functions. 相似文献
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T. CSERHÁTI, Z. ILLÉS AND S. NEMES-KÓSA. 1992. The effect of some benzonitrile ester herbicides on the growth of Bacillus megaterium, B. cereus var. mycoides, B. polymyxa, B. subtilis, Pseudomonas fluorescens and Azotobacter chrooccum was investigated in the concentration range 20–640 ppm by the agar diffusion method. The zones of inhibition, restricted growth and eventual stimulation were determined. The data matrix was evaluated by principal component analysis. Azotobacter chroococcum was the most resistant to the benzonitrile esters. The influence of benzonitrile esters on the growth of micro-organisms depended equally on the species and on the chemical structure of the herbicides. Chloro substitution considerably modified the effect whereas bromo and iodo substitution resulted in similar biological activity. 相似文献
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Five fresh soil Streptomyces spp. strains were isolated, phylogenetically characterized on the basis of 16S rDNA sequences and analyzed for the presence
of restriction modification systems. Three type II site-specific endonucleases were detected and partially purified. Two isolated
enzymes were isoschizomers of SacI restriction endonuclease recognizing 5′-GAGCTC-3′ sequence; the third one recognised 5′-CCGCGG-3′
sequence and it was an isoschizomer of SacII. SacII like modification was observed in other two isolates having no detectable
restriction activity. The lack of correlation between restriction and modification phenotypes and phylogenetic classification
of the isolates indicates efficient gene transfer mechanism in the Streptomyces genus. 相似文献
20.
Ninety-three wild-type isolates identified as actinomycetes were tested against 11 organochlorine pesticides (OPs): aldrin, chlordane, DDD, DDE, DDT, dieldrin, heptachlor, and heptachlor epoxides, lindane, and methoxychlor. Qualitative screening agar assays displayed 62-78% tolerance of strains to OPs. Four strains designed M4, M7, M9 and M15 were selected based on multi-OP-tolerance, and identified as members of the streptomycetes group. Different growth profiles were observed in cultures of the four selected streptomycetes cultured in synthetic medium containing 5-50 microg x l(-1) aldrin or chlordane or lindane. Increase of aldrin removal by the selected microorganisms was concomitant with the 4.8-36.0 microg x l(-1) pesticide concentration range. After 72 h of streptomycete M7 growth in synthetic medium containing 48.0 microg x l(-1) aldrin, the remaining OP concentration in the supernatant was approximately 10% of the initial concentration. Also, in stationary growth phase less than 2.5 microg x l(-1) aldrin residual concentration was detected in the medium. 相似文献