摘要:

InEscherichia coli, the transcription factor sigmaS, encoded byrpoS, controls the expression of a large number of genes involved in cellular responses to a diverse number of stresses, including starvation, osmotic stress, acid shock, cold shock, heat shock, oxidative DNA damage, and transition to stationary phase. A list of over 50 genes under the control ofrpoShas been compiled. The transcription factor sigmaSacts predominantly as a positive effector, but it does have a negative effect on some genes. The synthesis and accumulation of sigmaSare controlled by mechanisms affecting transcription, translation, proteolysis, and the formation of the holoenzyme complex. Transcriptional control ofrpoSinvolves guanosine 3',5'-bispyrophosphate (ppGpp) and polyphosphate as positive regulators and the cAMP receptor protein - cAMP complex (CRP-cAMP) as a negative regulator. Translation ofrpoSmRNA is controlled by a cascade of interacting factors, including Hfq, H-NS,dsrARNA, LeuO, andoxySRNA that seem to modulate the stability of a region of secondary structure in the ribosome-binding region of the gene's mRNA. The transcription factor sigmaSis sensitive to proteolysis by ClpPX in a reaction that is promoted by RssB and inhibited by the chaperone DnaK. Despite the demonstrated involvement of so many factors, arguments have been presented suggesting that sensitivity to proteolysis may be the single most important modulator of sigmaSlevels. The activity of sigmaSmay also be modulated by trehalose and glutamate, which activate holoenzyme formation and promote holoenzyme binding to certain promoters.Key words: transcription, translation, regulation, sigma factor, starvation.

ISSN:0008-4166    

DOI:10.1139/w98-069

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Numerous strains of an unusual asexual yeast species were isolated from flowers of morning glory (Ipomoeaspp., Convolvulaceae) and associated drosophilids and sap beetles of the genusConotelussampled in Hawaii and in Brazil. The nutritional profile of this yeast is similar to those ofMetschnikowia hawaiiensisandMetschnikowia continentalis, which share the same habitats. The cells are large, hydrophobic, and tend to remain attached after budding, causing the colonies on agar media to have a convoluted appearance, reminiscent of popcorn. The sequences of the D1/D2 domain of large subunit rDNAs of strains from three different localities confirmed that a single species is involved, and that it is related to large-sporedMetschnikowiaspecies. The type strain is UWO(PS)91-672.1 (CBS 8466).Key words:Candida ipomoeae, yeast, new species, rDNA.

ISSN:0008-4166    

DOI:10.1139/w98-067

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Thermophilic heterotrophic nitrifiers were isolated for the first time from deep-sea hydrothermal vents. Fluid and chimney samples were taken at Snakepit (Mid-Atlantic Ridge) and nitrifiers were isolated from various parts of the hydrothermal ecosystem. However, most of these isolates originated from chimney samples and seemed to be mainly located in the inner and outer parts of the upper layers. All of them were rod-shaped cells, with or without spores, that grew aerobically at 65°C. Under aerobic conditions, they were able to produce nitrite from organic matter via ammonia (heterotrophic nitrification) but also from nitrate (reduction). Thus, they could largely contribute to the nitrogen cycle. These thermophilic heterotrophic nitrifiers were characterized by a considerable diversity and a phenotypic study has shown that they were closely related to the generaThermusandBacillus.Key words: thermophilic bacteria, heterotrophic nitrification, hydrothermal vents, deep-sea

ISSN:0008-4166    

DOI:10.1139/w98-059

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Pseudomonas mendocinaMC2, able to use 9-fluorenone but not fluorene as its sole source of carbon and energy, was isolated. Identification of metabolites in growth media and washed cell suspensions indicated that strain MC2 metabolizes 9-fluorenone via angular dioxygenation of the ketone, to give 1,1a-dihydroxy-1-hydro-9-fluorenone, followed by the opening of the five-membered ring and further degradation of the resulting biphenyl derivative by reactions akin to those of biphenyl metabolism, which produce phthalate as an intermediate. The aim of this research was to study the biodegradation of fluorene by a co-culture of strain MC2 andArthrobactersp.strain F101, which grows on fluorene and simultaneously transforms a fraction of the substrate to 9-fluorenone, which accumulates as a dead-end product. Growing with 0.1 g fluorene/L,Arthrobactersp. strain F101 caused the total removal of this compound from the cultures, but when this strain was grown with 1g fluorene/L, only 16% of the fluorene was used. The addition of 9-fluorenone to cultures growing on fluorene showed that 9-fluorenone inhibits fluorene degradation. Finally, whenPseudomonas mendocinaMC2 andArthrobactersp. strain F101 were co-cultured with 1g fluorene/L as a sole source of carbon and energy, the growth of the strains completely removed fluorene in 2 days. 9-Fluorenone did not accumulate and the carbon assimilation into cell biomass was estimated as approximately 46%.Key words: microbial consortium, fluorene, 9-fluorenone, biodegradation.

ISSN:0008-4166    

DOI:10.1139/w98-066

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Ten bacterial strains were isolated from seven contaminated soils by enrichment with phenanthrene as the sole carbon source. These isolates and another phenanthrene-degrading strain were examined for various characteristics related to phenanthrene degradation and their ability to metabolize 12 other polycyclic aromatic hydrocarbons (PAH), ranging in size from two to five rings, after growth in the presence of phenanthrene. Fatty acid methyl ester analysis indicated that at least five genera (Agrobacterium,Bacillus,Burkholderia,Pseudomonas, andSphingomonas) and at least three species ofPseudomonaswere represented in this collection. All of the strains oxidized phenanthrene according to Michaelis-Menten kinetics, with half-saturation coefficients well below the aqueous solubility of phenanthrene in all cases. All but one of the strains oxidized 1-hydroxy-2-naphthoate following growth on phenanthrene, and all oxidized at least one downstream intermediate from either or both of the known phenanthrene degradation pathways. All of the isolates could metabolize (oxidize, mineralize, or remove from solution) a broad range of PAH, although the exact range and extent of metabolism for a given substrate were unique to the particular isolate. Benz[a]anthracene, chrysene, and benzo[a]pyrene were each mineralized by eight of the strains, while pyrene was not mineralized by any. Pyrene was, however, removed from solution by all of the isolates, and the presence of at least one significant metabolite from pyrene was observed by radiochromatography for the five strains in which such metabolites were sought. Our results support earlier indications that the mineralization of pyrene by bacteria may require unique metabolic capabilities that do not appear to overlap with the determinants for mineralization of phenanthrene or other high molecular weight PAH.Key words: kinetics, polycyclic aromatic hydrocarbons, phenanthrene, mineralization, benzo[a]pyrene.

ISSN:0008-4166    

DOI:10.1139/w98-065

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Spontaneous mutants (3/parental strain) of soybean bradyrhizobia resistant to streptomycin and erythromycin were selected from strains isolated from bradyrhizobial populations indigenous to Cape Fear and Dothan soils. These were used to evaluate (i) the validity of using antibiotic-resistant mutants to make inferences about the competitiveness of parental strains in soil environments and (ii) the recovery of strains in nodules after inoculation of soybeans grown in soils with indigenous bradyrhizobial populations. Streptomycin and erythromycin resistances of all mutants were stable after approximately 27 generations of growth in yeast extract - mannitol medium, but 33% of the mutants lost resistance to erythromycin upon passage through nodules. Only 17% of the mutants were as competitive as their parental strain when inoculated in a ratio near 1:1 in vermiculite. Four of 10 mutants, which differed in competitiveness from their parental strain in vermiculite, had competitiveness against the soil populations equal to that of their parental strain. Therefore, assessment of competitiveness of mutants and parental strains in non-soil media may not accurately reflect their competitiveness in soil systems. For both the Cape Fear and Dothan soils, recovery of a given mutant from nodules of field-grown plants was always lower than from nodules of plants grown in the greenhouse. Inoculation of the entire rooting zone in the greenhouse experiment and of only a portion of the rooting zone in the field experiments may account for this difference in recovery. Techniques that increase the volume of soil inoculated may enhance nodulation by inoculant strains.Key words:Bradyrizobium, antibiotic resistance, competition.

ISSN:0008-4166    

DOI:10.1139/w98-063

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The enzymatic activity of phosphoglycerate mutase (Pgm) from three gram-positive endospore-forming bacteria (Bacillus subtilis, Clostridium perfringens, andSporosarcina ureae) requires Mn2+and is very sensitive to pH; at low concentrations of Mn2+, a pH change from 8 to 6 resulted in greater than 30- to 200-fold decreases in the activity of these Pgms. However, Pgm deactivation at pH 6 was reversed by shifting the enzyme to pH 7 or 8. Free Mn2+was not directly involved in Pgm catalysis, although enzyme-bound Mn2+may be involved. The rate of catalysis by Mn2+-containing Pgm was also slightly pH dependent, although theKmfor 3-phosphoglyceric acid appeared to be the same at pH 6, 7, and 8. These findings suggest that Mn2+binds to catalytically inactive Pgm and converts it to a catalytically competent form, and further, that pH influences the efficiency with which the enzyme binds Mn2+. The extreme pH sensitivity of the Mn2+-dependent Pgms supports a model in which this enzyme is inhibited during sporulation by acidification of the forespore, thus allowing accumulation of the spore's large depot of 3-phospho-glyceric acid. The activity of Pgm from two closely related gram-positive bacteria that do not form spores (Planococcus citreusandStaphylococcus saprophyticus) also requires Mn2+and is pH sensitive. In contrast, the Pgm activities from two more distantly related non-endospore-forming gram-positive bacteria (Micrococcus luteusandStreptomyces coelicolor) are neither dependent on metal ions nor particularly sensitive to pH.Key words:Bacillus, Clostridium, Mn2+, phosphoglycerate mutase, sporulation.

ISSN:0008-4166    

DOI:10.1139/w98-060

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Thaxtomin A production in culture, potato common scab severity (percentage of tuber surface infected or number of lesions per tuber), and fatty acid profiles were determined for 78Streptomycesisolates. Only pathogenicStreptomycesspp. (n= 17) produced thaxtomin A in culture. Thaxtomin A production in culture (µg/mL) was significantly positively correlated with the percentage of tuber surface infected (R= 0.60;p= 0.017) but not with the number of lesions per tuber (R= 0.37;p= 0.17). An increase of 1 µg/mL in thaxtomin A production corresponded to an 11% increase in disease severity (percentage of tuber surface infected). The data indicate that quantitative information on the ability of a particular pathogen isolate or population to produce thaxtomin A may be critical to understanding and predicting the disease potential of that population. Using cluster analysis of fatty acid data, 94% of 67 unknown field isolates grouped with other field isolates having the same pathogenicity (plus or minus).Key words: thaxtomin A, phytotoxin, potato sca

ISSN:0008-4166    

DOI:10.1139/w98-061

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Antimicrobial substances were produced byBacillus subtilisBS 107 in a defined medium and isolated from culture filtrate by precipitation at pH 2.5. Active fractions were extracted in ethyl acetate, acetone, and 80% ethanol and purified by thin-layer chromatography (TLC) on silica gel plates developed with an ethanol-water mixture (2:1, v/v). In each case, a band with aRfof 0.75 formed an inhibitory zone when the TLC plates were placed in contact with agar seeded with test cultures of theErwiniaspp. The antibiotic was released into the culture medium during early stages of growth ofBacillus subtilisBS 107 but higher amounts were released in older cultures. The antibiotic was resistant to the action of nucleases, proteases, and lipase. It was stable when autoclaved twice for 35 min at 2 atm (1 atm = 101.325 kPa) in acidic, neutral, and alkaline solutions. It remained active over the pH range of 1-14 during 1 month of observation and exhibited no loss of antimicrobial activity when stored at 4°C for over 1 year.Bacillus subtilisBS 107 showed activity in vitro and in vivo againstErwinia carotovorasubsp.atrosepticaandErwinia carotovorasubsp.carotovora, the causal agents of potato blackleg and tuber soft rot. The application of an antagonist or its antibiotic to cut potato tissues prevented or reduced symptoms of the diseases. The antibiotic was active in vitro against a broad spectrum of bacterial and fungal species.Key words: antagonist,Bacillus subtilisBS 107,Erwinia carotovora, potato

ISSN:0008-4166    

DOI:10.1139/w98-064

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

A gene locusabpwas identified immediately upstream of the CAMP factor genecfuinStreptococcus uberis.An open reading frame capable of coding for a 277-residue protein was identified. On the basis of sequence characteristics, theabpgene product is potentially a polar amino acid and opine binding component of an ATP-binding cassette type (ABC-type) transport system similar to those of Gram-negative bacteria. This membrane protein is likely lipid modified at its amino terminus and was present in fiveS. uberisstrains and oneStreptococcus parauberisstrain examined.Key words: bovine mastitis,Streptococcus uberis, amino acid transport.

ISSN:0008-4166    

DOI:10.1139/w98-058

出版商:NRC Research Press    

年代:1998

数据来源: NRC