摘要:

The survival of genetically alteredPseudomonas putidastrains harboring an inducible plasmid, pRO101, or a constitutive plasmid, pRO103, was compared. These plasmids encode for the degradation of 2,4-dichlorophenoxyacetate (TFD) to 2-chloromaleylacetate, and the maintenance of either plasmid did not alter survival ofP.putidaPPO301(pRO101) or PPO301(pRO103) in an unamended agricultural soil. Moreover, in TFD-amended soil, survival of PPO301, PPO301(pRO101), and PPO301(pRO103) was statistically the same after 50 days. Reapplication of TFD to soil 50 days after the original application did not change the numbers of PPO301(pRO101) or PPO301(pRO103), which cannot use TFD as a sole source of carbon. However, a mutant strain, PPO301KS(pRO101), which is able to use TFD as a sole source of carbon, was stimulated by the second addition of TFD: PPO301KS(pRO101) cfu/g soil increased by greater than 20-fold. Although the microbiota indigenous to the study soil was capable of degrading TFD, the addition of plasmid-bearing PPO301 had a dramatic effect on TFD degradation. After 10 days, the concentration of TFD in soil inoculated with plasmid-bearing PPO301 was approximately five times lower (84 ppm) than that in uninoculated soil (435 ppm). In a parallel study,Raphanus sativus(radish) seeds failed to germinate in uninoculated and PPO301-inoculated soil amended with 500 ppm TFD. Seed germination was 53 and 80% in soils inoculated with PPO301(pRO101) and PPO301(pRO103), respectively (P < 0.001). However, the difference in the rate of TFD degradation between the native soil and soil inoculated with plasmid-bearingP.putidawas probably related to the relatively high inoculum density ofP.putidastrains (108 cfu) and the relatively low population density of TFD metabolizers indigenous to the soil.Key words: survival, degradation, plasmid, 2,4-dichlorophenoxyacetate, soil.

ISSN:0008-4166    

DOI:10.1139/m90-142

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

A temperature-sensitive mutation in themurHgene ofEscherichia coliconfers a lysis phenotype at the restrictive temperature. An extragenic suppressor ofmurHapparently representing a new locus at 12.5 min on the linkage map and designatedsmhBis described. ThesmhBmutation by itself also conferred a temperature-sensitive lysis phenotype. A mutation in another new locus designatedlytDwhich arose spontaneously in thesmhBmutant was mapped close tosmhBat 12.7 min on the linkage map. ThelytDmutation by itself conferred a temperature-sensitive lysis phenotype indistinguishable from that of themurHmutant. Thus, the suppression of lysis in thesmhB murHand thesmhB lytDdouble mutants suggests a mechanism involving the reciprocal suppression of the two individual lysis-causing mutant alleles. The suppressor activity ofsmhBwas apparently relatively specific in thatsmhBfailed to prevent lysis induced by either mutational (murEormurF) or antibiotic-induced blocks in peptidoglycan synthesis. This suggests thatmurH,smhB, andlytDmay be functionally related.Key words: temperature-sensitive mutation,Escherichia coli, lysis phenotype, suppression.

ISSN:0008-4166    

DOI:10.1139/m90-143

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The degradation of dimethyl nitrosoamine (DMNA) by a methanotroph,Methylosinus trichosporiumOB3b, was studied using14C-labelled DMNA. The organism was capable of assimilating DMNA-carbon and converting it to CO2. The rates of CO2productionfrom DMNA and its cellular uptake (VP) were linearly correlated with DMNA concentrations of 0.03–10 mM, which corresponded to approximately 3% of added DMNA metabolized in 24 h. These rates were two to three orders of magnitude less than the rate of uptake of methane,was suppressed when the concentrations of DMNA exceeded 0.3 mM. In the presence of 0.1 mM DMNA,VPandwere essentially the same in the presence or absence of methane in the first 8 h of incubation, but declined sharply thereafter only when methane was absent. These observations suggest that the metabolism of DMNA was carried out by methane monooxygenase (MMO), and that NADH, a cofactor for MMO, may be provided by the oxidation of the stored compounds in the cells when methane is not available.Key words: dimethyl nitrosamine, degradation,Methylosinus trichosporium, methane monooxygenase.

ISSN:0008-4166    

DOI:10.1139/m90-144

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The population dynamics of six introducedBradyrhizobium japonicumstrains were measured over three growing seasons in a Wisconsin soil with a low incidence of indigenousB.japonicum(10 cells/gm). Four antibiotic-resistant members of the 123 serocluster (which were either spectinomycin resistant or streptomycin resistant), USDA 110, and USDA 138 were inoculated using liquid inoculum, at a rate of 1 × 108 cells per 2.5-cm row, on two soybean cultivars in 1985. Nodule occupants were identified using an enzyme-linked immunosorbent assay (ELISA), fluorescent antibodies, and antibiotic-resistant mutants. In the first growing season, 100% of the nodules were formed by the introduced strains. The nodules from the uninoculated plots were occupied by an indigenous 110 serogroup. In the second and the third season at the same site (without further inoculation), a high percentage (> 60%) of the nodules from all the plots were nodulated by the 123 serocluster (either alone or as mixed infections). However, < 25% of the nodules in the 123-inoculated plots and < 9% in the other plots were formed by any of the antibiotic-marked 123 inoculum strains introduced in 1985. The main conclusions are (i) that it is possible to successfully introduce inoculum strains in soils where the indigenousBradyrhizobiumpopulation is low and to obtain 100% nodule occupancy in the first growing season, and (ii) that successful inoculation in one year in soils with a low incidence ofBradyrhizobiumdoes not ensure that the introduced inoculum strains will form nodules in subsequent years.Key words:Bradyrhizobium japonicum, indigenous bradyrhizobia, interstrain competition, field trials.

ISSN:0008-4166    

DOI:10.1139/m90-145

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

A charcoal–soil mixture, paddy straw compost, and wheat bran were tested to explore their possible use as carriers for phosphate-solubilizing bacteria and fungi. The charcoal–soil mixture was found to be the best carrier for phosphate-solubilizing bacteria, and wheat bran, for phosphate-solubilizing fungi. Higher temperatures during storage markedly influenced the shelf life of phosphate-solubilizing microorganisms. Thermotolerant strains, such asBacillus subtilis,Bacillus circulans, andAspergillus niger, were found to survive not only at high storage temperatures (40 and 45 °C), but also at low moisture status in the carrier.Key words: inoculum carriers, thermotolerant strains, shelf life.

ISSN:0008-4166    

DOI:10.1139/m90-146

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Three N2-fixing yellow bacteria (5AJ, 5ATR, and 29AJ) isolated from the rhizosphere of rice, previously found to be related toFlavobacterium capsulatumby DNA–rRNA hybridization, were compared on the basis of 115 morphological, physiological, biochemical, and nutritional characters. The bacteria were nonfermentative, irregular motile rods with polar flagella. They exhibited a gram-negative reaction and yellow pigmentation. A numerical analysis using these phenotypic characteristics showed that the bacteria were more closely related toPseudomonas paucimobilisthan toF.capsulatum. A relationship to theP.paucimobiliscluster was also supported by the presence of the pigment nostoxanthin. This pigment was also found inF.capsulatumand could be used as a distinctive marker for this group of yellow bacteria. Their phenotypic properties, protein patterns, and serological tests (ELISA) showed that two of the isolates (5AJ and 5ATR) were identical and had originated from the same parental strain. On the other hand, the serological tests indicated that both N2-fixing yellow bacteria (5AJ or 5ATR and 29AJ) differed from the reference strains,F.capsulatumandP.paucimobilis.Key words: N2-fixing bacteria, taxonomic study, nostoxanthin,Pseudomonas.

ISSN:0008-4166    

DOI:10.1139/m90-147

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

In 38 yeast genera tested, utilization ofD-glucarate was uncommon, occurring with only 10 strains out of 373. The ability was prominent amongCryptococcusstrains, with 8 out of 8 tested being positive, including the pathogenCryptococcus neoformans. The ability was present also inTrichosporonwhere 2 out of the 4 strains tested were positive. There was a correlation between ability to utilizeD-glucarate, galactarate,L-tartarate, andD-glucuronate. Use ofL-ascorbate occurred in more genera than use ofD-glucarate, but all strains that grew onD-glucarate grew onL-ascorbate. The utilization of certain hydroxylated carboxylates by strains, mainly found in two genera, is of interest in identifying the catabolic pathways involved, in taxonomic studies, and in developing rapid methods of yeast identification.Key words:Cryptococcus,Trichosporon, glucarate, galactarate, tartarate.

ISSN:0008-4166    

DOI:10.1139/m90-148

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The role of protozoan grazing in controlling bacterial populations was examined in four microbial habitats in Halifax Harbor, Canada: the water column, setting particles, the sediment–water interface, and the sediment. Large numbers of protozoans were found in all habitats although most (>56%) were small (<5 μm) flagellates. Protozoans larger than 10 μm were rarely observed; protozoans >20 μm were never observed. Protozoans were also observed to a depth of 9 cm below the sediment surface although efforts to culture viable protozoa failed except for the top 1 cm. The use of the metabolic inhibitor cycloheximide with and without colchicine to selectively inhibit eucaryotic metabolism was shown to severely affect procaryotic metabolism in sediment (and presumably particle and water) samples. Using fluorescently labelled bacteria as food, and under optimum conditions, up to 42% of the Protozoa population exhibited active grazing within 7 h. Using protozoan and bacterial community sizes and doubling times, it was calculated that each protozoan in Halifax Harbor would have to consume 13–118 bacteria per hour for the enumerated nanoplanktonic (<20 μm) Protozoa to be the sole control of the size of the bacterial community.Key words: marine, Protozoa, bacterivory, particles, bacteria.

ISSN:0008-4166    

DOI:10.1139/m90-149

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Analysis of plasmid profiles was used to typeRhizobium leguminosarumbiovarviciaestrains isolated from nodules of peas, lentils and faba beans grown in two different soils. One soil was from a native pasture with no previous history of cultivation, the other was from a plot in a rotation study which included lentils every 2 years. The results indicated a strong preference of both peas and faba beans for strains having certain specific plasmid profiles. Strains belonging to one plasmid profile group (group 2) formed over half the nodules on peas grown in soil from the rotation plot but were never found on faba beans grown in the same soil, while strains from another group (group 5) formed nearly all of the nodules on faba beans grown in soil from the rotation plot, but no nodules on peas. Competitiveness for pea nodulation was correlated with an ability to catabolize homoserine, an amino acid found in large quantities in pea root exudate. Strains having plasmid profiles corresponding to those of strains that have been used in commercial inoculants over the last few years were isolated only rarely, regardless of the soil and host plant studied.Key words:Rhizobium, competition, plasmids, legumes, nodulation.

ISSN:0008-4166    

DOI:10.1139/m90-150

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Genes for 51.4- and 41.9-kDa insecticidal proteins ofBacillus sphaericuswere separately cloned and expressed inEscherichia coli. Both proteins were required for toxicity. Approximately equal numbers of cells containing the 51.4- and 41.9-kDa proteins produced the greatest toxicity; excess 41.9-kDa protein did not affect toxicity, whereas excess 51.4-kDa protein reduced activity. Larvae were killed when 41.9-kDa protein was fed up to 24 h after the 51.4-kDa protein, but not when the order of feeding was reversed. Radiolabelled toxins bound in approximately equal amounts to the gastric caecum and posterior midgut ofCulex quinquefasciatuslarvae. Radiolabelled 51.4-kDa protein was rapidly degraded by ca. 12–13 kDa in the larval gut, while 41.9-kDa protein was degraded by 1–2 kDa. Nonreduced toxin extracted fromB.sphaericusproduced a band on SDS–PAGE of ca. 68–74 kDa that contained both 51.4- and 41.9-kDa proteins based on sequence analysis, and a band of ca. 51 kDa that contained primarily 41.9-kDa protein.Escherichia colicontaining 51.4-kDa protein enhanced toxicity of the latter eluted SDS-PAGE band. These proteins may associate very strongly, and trace amounts of 51.4-kDa protein in preparations of 41.9-kDa protein fromB.sphaericusmay be responsible for the previously reported toxicity of the latter.Key words:Bacillus sphaericus, toxin, mosquito, cloning.

ISSN:0008-4166    

DOI:10.1139/m90-151

出版商:NRC Research Press    

年代:1990

数据来源: NRC