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1.
 A large collection of cowpea rhizobia strains was obtained from soil samples collected from either a semi-arid or a tropical rain forest area located at about the same latitude in the north-eastern region of Brazil and evaluated for their intrinsic antibiotic resistance to eight commercial antibiotics. The aim of this study was to correlate antibiotic resistance of native rhizobia strains to edaphic-climatic factors as a way to establish suitable inoculants for specific areas. A large diversity regarding intrinsic antibiotic resistance was found, and 17 clusters were identified as varying from sensitive to gradually resistant up to 500 μg·ml–1 of the antibiotics tested. Clustering analysis did not show any pattern related to the geographic region where isolates have been obtained. On the other hand, an increase in the antibiotic-resistant rhizobia population was associated with an increase in soil P and Al contents. lsolates which were sensitive to spectinomycin, ampicillin, streptomycin, chloramphenicol and tetracycline were present at higher rates in soils devoid of Al. Rhizobia bacteria producing mucus type I (fluid and capable of spreading over the solid media) were found preferentially in soil with Al concentrations up to 36 mg·kg–1, diminishing quickly at higher levels. Received: 2 May 1997  相似文献   

2.
In acid soil, low pH, reduced availability of nutrients, and toxicity of Al and Mn limit plant growth and the survival and effectiveness of rhizobia. The symbiosis between legumes and rhizobia is particularly sensitive to acid soil stress. A pot experiment evaluated whether Bradyrhizobium japonicum strain growth on acidic agar media would predict ability to colonize the rhizosphere and form effective nodules in acidic soils. Three Indonesian strains of B. japonicum with similar effectiveness at neutral pH in sand culture but with different tolerance of acid soil stress factors in agar media, and an acid-tolerant commercial strain (CB1809) of comparable effectiveness, were tested in three acid soils using the Al tolerant soybean (Glycine max cv PI 416937). At 7 days after inoculation all strains had achieved large rhizosphere populations, but by day 14 the rhizosphere population of the acid-sensitive strain had decreased, while the more acid-tolerant strains increased. The acid-tolerant strains had significantly greater nodulation and symbiotic effectiveness than plants inoculated with the acid-sensitive strain. Laboratory prescreening of B. japonicum for acid, Al and Mn tolerance in acid media successfully identified strains which were symbiotically competent in low pH soils.  相似文献   

3.
This study tested the competitive ability of three locally isolated Cyclopia rhizobia and strain PPRICI3, the strain currently recommended for the cultivation of Cyclopia, a tea-producing legume. Under sterile glasshouse conditions, the three locally isolated strains were equally competitive with strain PPRICI3. In field soils, the inoculant strains were largely outcompeted by native rhizobia present in the soil, although nodule occupancy was higher in nodules growing close to the root crown (the original inoculation area). In glasshouse experiments using field soil, the test strains again performed poorly, gaining less than 6% nodule occupancy in the one soil type. The presence of Cyclopia-compatible rhizobia in field soils, together with the poor competitive ability of inoculant strains, resulted in inoculation having no effect on Cyclopia yield, nodule number or nodule mass. The native rhizobial population did not only effectively nodulate uninoculated control plants, they also out-competed introduced strains for nodule occupancy in inoculated plants. Nonetheless, the Cyclopia produced high crop yields, possibly due to an adequate supply of soil N.  相似文献   

4.
Summary Previous laboratory and greenhouse studies have shown that phages significantly reduce soil populations of homologous rhizobia. Reductions in nodulation and N2 fixation have also been observed. The purpose of the current study was to examine the effect of a phage specific ofBradyrhizobium japonicum USDA 117 on nodulation, nodule occupancy, N2 fixation and soybean growth and yield under field conditions. The phage was inoculated in combination withB. japonicum USDA 117 and/orB. japonicum USDA 110 (resistant strain) into a rhizobia-free sandy loam soil and planted toGlycine max (L.) Merr. Williams. When the phage was applied to soil inoculated withB. japonicum USDA 117 alone, significant reductions in nodule weight and number, shoot weight, foliar N, nitrogenase activity, and seed index were observed. When, however, the soil also contained the non-homologous strain,B. japonicum USDA 110, no significant effects on any of these parameters were found. Nodule occupancy by competing strains ofB. japonicum USDA 110 and USDA 117 was also affected by the phage. In soil which did not contain the phage, 46% and 44% of the identified nodules were occupied by USDA 110 and 117, respectively. When the phage was present in the soil, nodule occupancy byB. japonicum USDA 117 was reduced to 23%, while occupancy byB. japonicum USDA 110 was increased to 71%. These results suggest that nodulation by selected strains of rhizobia can be restricted and nodulation by more effective, inoculated strains can be increased through the introduction of a homologous phage to soils.  相似文献   

5.
Summary Six fast-growing soybean rhizobia (Rhizobium fredii) and thirteen slow-growing soybean rhizobia (Bradyrhizobium japonicum) were examined for resistance to 10 antibiotics. Axenic studies were carried out to determine the competitiveness of dual-strain inocula consisting of fast- and slow-growing rhizobia isolated from subtropical-tropical soils for nodule occupancy on a hybrid of Asian and US soybean cultivars. Nodule occupancy was determined by intrinsic resistance to erythromycin and neomycin. The results showed wide variability in resistance to 10 antibiotics for fast- and slow-growing rhizobia. The intrinsic antibiotic resistance of fast- and slow-growing rhizobia was extremely high against nalidixic acid (400 g ml–1) and penicillin (200 g ml–1). The competitive ability of inoculant strains for nodule occupancy varied for different combination sets and with the plant growing media. Our results show that fast-growing rhizobia nodulate a hybrid of Asian and US soybean cultivars. Fast-growing soybean rhizobia did not completely exclude nodulation by the slow-growing strains, which formed 0–79% nodules, depending on the strain used in the inoculum.  相似文献   

6.
Only four antibiotics (kanamycin, spectinomycin, ampicillin and novobiocin) of ten tested were capable of discriminating between root nodule isolates of Rhizobium meliloti obtained from uninoculated field-grown alfalfa (Medicago sativa L.). The 300 isolates in the collection were subdivided into seven groups based on their intrinsic antibiotic resistance characteristics with 204 and 55 isolates placed into two groups, C and F, respectively. Isolates from group C dominated the root nodule population on plants in eight of the nine quadrats analyzed. Furthermore they were one of the two dominant groups found in nodules formed on plants grown in a plant infection-soil dilution experiment and challenged with a composite soil sample from the field site. Antiserum raised to a group C isolate (No. 31) cross-agglutinated with 46 of 55 group C isolates to a titer identical with that of the parent antigen. There were no cross-reactions between isolates from any of the other six groups. Only 9 of 34 isolates from group F cross-agglutinated with antiserum raised to a group F isolate (No. 17). Thirty-three of 35 cross-agglutinating field isolates from group C had the same sodium dodecyl sulphate-polyacrylamide-gel electrophoretic protein-profile pattern as isolate No. 31 whereas non-agglutinating isolates from the same group had distinctly different protein profile patterns. The data suggest that intrinsic antibiotic resistance characteristics can be a useful complementary tool to be used in conjunction with other methods to identify and discriminate isolates of R. meliloti. It should not be used on its own as a strain identification method.  相似文献   

7.
Rhizobia isolated from cowpeas (Vigna unguiculata (L.) Walp.) grown in three west African soils were examined for intrinsic resistance to five antibiotics and were scored for one of two colony morphologies. Half of the strains tested had a “wet”, slimy colony morphology and half had small discrete “dry”, non-slimy colonies. The populations as a whole were resistant to gentamicin (87%) but varied in their resistance to streptomycin, rifampicin, kanamycin and penicillin. Thirteen patterns of resistance were found for the 128 strains screened and strains within the same pattern usually had the same colony type. The most common pattern (32%) was resistance to all five antibiotics. Associations between resistances were random within populations and colony type. Each population was diverse, expressing from 6 to 8 patterns of resistance, but one population was relatively homogeneous, with 68% of its members exhibiting the same pattern. Correlations between intrinsic antibiotic resistance and colony type were demonstrated both for the west African cowpea rhizobia and for a broader group of cowpea miscellany rhizobia. The method was practical, rapid and reliable for identification of groups within populations.  相似文献   

8.
Summary We assessed the effectiveness of three locally made lignite, subbituminous coal and cowmanure-based cowpea Bradyrhizobium inoculants in comparison with a peat-based imported Bradyrhizobium incoculant in a two-field plot investigation. The local inoculants were prepared by incorporating three rhizobia strains (Ife CR9, Ife CR15 and Bradyrhizobium japonicum) into each of the above carrier materials and were used to inoculate three cowpea seed varieties: TVU 1190, IT 82E-60 and Ife brown. With lignite-based He CR9 inoculated into TVU 1190 seeds, total N content of the plants was 178.6 mg/plant compared with only 64.3 mg/plant for the uninoculated nitrate-free control plants. With Nigerian lignite, sub-bituminous coal and cow manure as carriers for cowpea rhizobia, the cowpea yield of the inoculated plants increased by 72%, 54% and 10%, respectively, compared with uninoculated plants, while the peat-based inoculant gave a 25% increase in cowpea yield. With lignite-based Ife CR9 inoculated into Ife brown seeds, total N content of the plants was 149.1 mg/plant, but with inoculation by lignite-based B. japonicum, total N content of the treated Ife brown plant was 132.4 mg/plant. Thus, the native Ife CR9 strain seems to be slightly better adapted to tropical conditions than the imported B. japonicum.  相似文献   

9.
Clover rhizobia (55 strains) were screened for tolerance of acidity and Al, using the technique of Keyser and Munns (1979). Assessment of visible turbidity after 14 days indicated three strains tolerant of pH 4.5 (although growth rate was reduced), 25 strains tolerant of 5μm Al and no strains tolerant of 50 μ m Al at pH 5.5.50 μmAl caused a decrease in the numbers of acid-tolerant strains at pH 4.5. Tolerance of acidity or Al was not associated with the pH or Al status of the soil from which a strain was isolated.Screening of eight strains of clover rhizobia and nine strains of Lotus rhizobia using turbidity assessment and viable counts indicated seven strains of clover rhizobia with different degrees of tolerance of 20 μm Al but none tolerant of 50 μm Al at pH 5.5. All Lotus rhizobia (both slow- and fast-growers) were tolerant of 20 and 50 μm Al at pH 5.5, with 50 μm Al causing a reduction in growth rate.Subculturing of strains in non-stressed and stressed media had no effect on the response to 50 μmAl at pH 5.5.  相似文献   

10.
Rhizobium trifolii were isolated from soils along a transect covering a range of soil pH (3.6–5.6) using two varieties of white clover by either growing seedlings directly in soil or in nutrient solution in tubes inoculated with soil. Rhizobia were present at pH 4.5 but absent at pH 3.9. Neither nodule number nor effectiveness were influenced by the method of isolation and the clover variety on which the strain was isolated. There was no relationship between the pH of the soils and either the number of nodules or the effectiveness of the isolates from those soils. Screening the isolates for tolerance of acidity and Al showed that multiplication was unaffected at pH 5.0 but was slowed for all strains at pH 4.5. Multiplication at pH 5.5 was unaffected by 10 μM Al but was inhibited by 50 μM Al. At pH 4.5 all but 16% of the isolates were inhibited by 10 μM Al; none multiplied with 50 μM Al. The strains which multiplied at pH 4.5 with and without Al were isolated equally from soils in the range pH 4.5–5.6. They were also isolated in almost equal proportions from the two varieties of clover and by the two isolation methods. Overall there was little variation in the effectiveness and acid- and Al-tolerance of isolates from these soils of different pH.  相似文献   

11.
The role of cobalt in the processes leading to nodule initiation in Lupinus angustifolius L. cv. Uniharvest was studied. Survival and multiplication of Rhizobium lupini were examined in Lancelin soil and in the rhizosphere of L. angustifolius grown in it, with or without inoculation with antibiotic-resistant derivatives of R. lupini strain WU425. A clearing and staining technique was then used to record the incidence of nodule initiation in L. angustifolius seedlings.Within the constraints of experimental techniques, soil and rhizosphere numbers of R. lupini were unaffected by the cobalt status of the soil. Cobalt limitation was, however, inhibitory to nodule initiation in L. angustifolius, with reductions of up to 13 and 30% in nodule initiation for inoculated and uninoculated seedlings respectively.The severity of cobalt deficiency in L. angustifolius seems to be due solely to the plant's inability to provide cobalt to the rhizobia within the plant and not to any external limitation on their growth in soil or rhizosphere.  相似文献   

12.
为研究牛粪厌氧发酵沼渣中多重耐药细菌的环境污染风险，选用畜禽养殖中常用的5种抗生素(红霉素、氨苄青霉素、金霉素、链霉素、环丙沙星)对牛粪沼渣中可培养抗生素抗性细菌进行筛选。结果表明：多重耐药细菌的比例高达76.5%,其中，抗5种和4种抗生素的细菌分别有11,21株。所有多重耐药细菌均对氨苄青霉素具有抗性，抗红霉素、金霉素和链霉素的细菌分别占总多重耐药细菌数的92.0%,89.3%,61.3%。通过细菌16S rRNA测序鉴定，32株具有4种以上抗性的细菌分别属于福氏志贺氏菌、摩根氏菌和假中间苍白杆菌，均为重要的临床致病菌。使用全基因组测序对7株典型多重耐药细菌携带的抗性基因进行分析，共检测出28种抗生素抗性基因，对应9种抗生素抗性类型。通过分析抗性基因及插入序列所在位点信息发现，多重耐药细菌普遍携带含有抗性基因和插入序列共存的质粒，表明抗性基因具有高度的可移动性和较强的传播风险。综上所述，牛粪沼渣中含有大量的多重耐药细菌，可视作抗生素抗性基因的储存库，应重视沼渣农业资源化利用过程中的环境风险监测与评估。  相似文献   

13.
Five strains of Rhizohium trifolii were used to inoculate Trifolium subterraneum cv. Woogenellup sown into two soils with naturally-occurring populations of R. trifolii. In the 1st year all inoculant strains used singly were present at high frequency in the sampled nodule populations from the inoculated plots. Where an inoculant containing a mixture of equal parts of the 5 strains was used. one strain (WU95) predominated at both sites.The persistence of the strains was followed for a further 3 years at one site. Three of the strains WU95, CC2480a and WU290, were maintained at a high frequency (>75% of nodules sampled) for the entire period, but the other two strains showed poor persistence in this environment. Highly effective strains of rhizobia, not identifiable as inoculant strains, nor present in the nodule population at the first sampling, appeared during the course of the study. One strain. WU290, showed a high degree of variation in symbiotic effectiveness between single colony isolates from the stock culture and also between field isolates that were serologically identical with this strain.  相似文献   

14.
《Applied soil ecology》2001,16(3):275-282
Legume trees are symbiotically associated with rhizobia and mycorrhizal fungi, microorganisms that improve their growth. The objective of this work was to characterize 61 rhizobial isolates from eight species of native legume trees: Acacia caven, Inga urugüensis, Lonchocarpus nitidus, Prosopis nigra, Sesbania virgata, Peltophorum dubium, Enterolobium contortisiliquum and Erythrina crista-galli. The strains were isolated from nodules with high nitrogenase activity and their growth rate, antibiotic, salinity and acidity resistances were determined. Their relationships were analyzed building a matrix with the resistance characteristics. Most of the isolates were fast growers and acid-producing with high level of exopolysaccharides. In general, isolates were erythromycin resistant but sensitive to rifampicin. All the isolates grew well at pH 5.5 while 75% did so at pH 4.4. More than 60% of the isolates grew in 2% of NaCl but this declined to 21% of the isolates in 3% NaCl. This population showed high antibiotic, salinity and pH resistance, suggesting adaptability to major ecological environment stresses, and great saprohytic competence within soil environments. Isolates from the same host showed high homology between them.  相似文献   

15.
Compatible rhizobia strains are essential for nodulation and biological nitrogen fixation (BNF) of hairy vetch (Vicia villosa Roth, HV). We evaluated how past HV cultivation affected nodulation and BNF across host genotypes. Five groups of similar HV genotypes were inoculated with soil dilutions from six paired fields, three with 10-year HV cultivation history (HV+) and three with no history (HV?), and used to determine efficiency of rhizobia nodulation and BNF. Nodulation was equated to nodule number and mass, BNF to plant N and Rhizobium leguminosarum biovar viceae (Rlv) soil cell counts using qPCR to generate an amplicon of targeted Rlv nodD genes. Both HV cultivation history and genotype affected BNF parameters. Plants inoculated with HV+ soil dilutions averaged 60 and 70 % greater nodule number and mass, respectively. Such plants also had greater biomass and tissue N than those inoculated with HV? soil. Plant biomass and tissue N were strongly correlated to nodule mass (r 2?=?0.80 and 0.50, respectively), while correlations to nodule number were low (r 2?=?0.50 and 0.31, respectively). Although hairy vetch rhizobia occur naturally in soils, past cultivation of HV was shown in this study to enhance nodulation gene-carrying Rlv population size and/or efficiency of rhizobia capable of nodulation and N fixation.  相似文献   

16.
We examined water quality indicators (pH, temperature, turbidity, total phosphorus, and fecal coliform density) and bacterial antibiotic resistance (prevalence, conjugative transfer, and genetic linkage of resistance elements) at locations impacted by confined animal feeding operations (CAFOs) and compared them to nearby reference sites. Sites located upstream and downstream of two wastewater treatment facilities were also compared. Sites near CAFO farms had poor water quality (elevated total phosphorus and turbidity), while water quality remained relatively good downstream of wastewater treatment plants. High proportions of antibiotic-resistant bacteria were observed at all study sites, and frequent conjugative transfer of resistance was observed in laboratory assays. Out of a total of 830 environmental bacterial isolates, 77.1% were resistant to only ampicillin, while 21.2% were resistant to combinations of antibiotics including ampicillin (A), kanamycin (K), chlorotetracycline (C), oxytetracycline (O), and streptomycin (S). Multi-drug-resistant bacteria were significantly more common at sites impacted by CAFO farms. In conjugation assays, 83.3% of the environmental isolates transferred one or more antibiotic resistance genes to a laboratory strain of Salmonella typhimurium. A subset of multi-drug-resistant (A, C, and O) isolates was screened for specific tetracycline resistance genes and class I and II integrons. None of the screened isolates (n?=?22) were positive for integrons, while 13 isolates contained resistance genes for tet (B) and tet (C). Our results indicate that CAFO farms not only impair traditional measures of water quality but may also increase the prevalence of multi-drug-resistant bacteria in natural waters.  相似文献   

17.
The spread of antibiotic-resistant bacteria in the environment is raising serious public health concerns, and manure is being increasingly recognized as a major source of antibiotic-resistant bacteria. In this research, we isolated Escherichia coli and enterococci from manure produced in a Wisconsin, USA family dairy farm to determine their resistance to six representative antibiotics. The average densities for E. coli and enterococci were 6.37(±4.38)?×?107 colony formation units (CFU)?g?1 and 1.60(±1.57)?×?104 CFU g?1, respectively. The E. coli isolates were found to be resistant to cephalothin, ampicillin, tetracycline, and erythromycin. In addition to these four antibiotics, the Enterococcus isolates were also resistant to gentamicin and ciprofloxacin. Additionally, we examined the survival and growth of E. coli and enterococci in dairy manure over a period of ~3 days. While the densities of enterococci remained stable over the study period, the concentrations of E. coli on average increased by 1.5 log10 units. Further tests of the bacterial antibiotic resistance over time showed no significant changes in the prevalence of antibiotic resistance. This result indicated that slightly aged manure could represent a larger source of antibiotic-resistant E. coli than fresh manure and the accumulation of antibiotic-resistant E. coli and enterococci in the agricultural fields must be accounted for in the modeling of the spread of antibiotic-resistant bacteria in the environment.  相似文献   

18.
Abstract

Soybean cultivation in Ethiopia is dominated by smallholder farmers who use little or no inputs, often resulting in low yields. The use of effective rhizobia strains was considered as an ecologically and environmentally sound approach for soybean production. Field experiments were conducted during 2015/16 cropping seasons at two different agro-climatic regions in Ethiopia to investigate the effectiveness of local soybean isolates for improving nodulation, growth, yield and quality of soybean. Ten treatments comprising of seven indigenous rhizobia isolates, one exotic strain, nitrogen fertilized treatment and uninoculated control were arranged in randomized complete block design in three replications. Results of the experiment revealed that nodule number and nodule dry weight significantly increased from nil in the uninoculated control to 14–34 and 110–521?mg plant?1, respectively due to inoculation with different isolates. Furthermore, inoculation significantly increased shoot dry weight by 24–46%, shoot nitrogen concentration by 20–30%, shoot N content by 29–49%, plant height by 14–41%, pods per plant by 12–38%, seeds per pod by 7–19%, thousand seed weight by 15–24%, grain yield by 22–115% and protein content by 7–39% compared with the uninoculated control. Generally, isolates Jm-1-Bo, As-5-Aw, Bk-3-Aw, Cw-6-Aw and MAR 1495 performed better than the others in most yield parameters at both locations of which Jm-1-Bo and As-5-Aw were the local isolates performing best irrespective of location, and were superior to the effective exotic standard strain. Therefore, isolates Jm-1-Bo, As-5-Aw and Bk-3-Aw could be utilized as candidates for inoculant production at large scale in areas with similar agroecology.  相似文献   

19.
The shoot dry weight of alfalfa inoculated with an effective strain of Rhizobium meliloti mixed with an ineffective strain in different ratios was found to be directly proportional to the log of the number of effective nodules. Consequently the comparison of the shoot dry weight of plants inoculated with a mixture of effective and ineffective strains with the shoot dry weight of plants inoculated with the effective strain should allow the estimation of the relative competitiveness of the effective strains. To check this. the competitiveness of 14 antibiotic-resistant strains of R. leguminosarum was evaluated in this way and compared with the ability of the strains to form nodules when inoculated to seeds of Vicia faba planted in a soil containing indigenous R. leguminosarum. The percentage of recovery of the inoculum strains in the nodules of field-grown fababeans was positively correlated with the competitiveness of the strains as estimated by the greenhouse test. This simple way of evaluating the nodulating competitiveness of strains of rhizobia being indicative of their competitive behaviour with indigenous rhizobia in the field could therefore be useful for screening a large number of strains for competitiveness.  相似文献   

20.
This study assesses the impact of antibiotics used in clinical and veterinary practices, on the incidence of antibiotic- heavy metal resistant enterics in fresh water and sediment from agricultural and harbor sample sites. A total of 848 bacterial strains of the familyEnterobacteriaceae was isolated from agricultural and lake harbor samples and identified to genus level. These were examined for antibiotic-heavy metal resistance. A select smaller number of these isolates were also examined for the presence of plasmids and ability to transfer antibiotic resistance via conjugation or transformation. More than 85 % of the 848 isolates from all four sites were resistant to Ph, Zn, and Co while 5.6% to 16% were resistant to Te and 2.4% to 5.7% to Hg. The ranking of metal resistance according to frequency was the same as the frequency of metal occurrence in sediment samples. Of the total isolates tested, 87% were resistant to six or more antibiotics and 74% were also simultaneously resistant to Co, Zn, and Ph. Testing the resistance of the water isolates to antibiotics used solely in animal husbandry-veterinary medicine indicated that 55.6% of the agricultural isolates possessed resistance to these antibiotics while only 31.9% of the isolates from harbor water showed resistance to the same antibiotics. Of 41 ampicillin resistant isolates examined, 16 (39%)were capable of transferring antibiotic-heavy resistance markers via conjugation. From this same group, plasmid DNA preparations were made. Of these latter preparations, 67% transformed recipientE. coli cells while 58% possessed discernible, often multiple plasmids when examined by gel electrophoresis.  相似文献   

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