摘要:

DNA-mediated gene transformation of mouseLtk−aprt−hprt−cells was used to obtain stable, doubly selected transformants simultaneously expressing herpes virus thymidine kinase (TK) and mammalian adenine phosphoribosyltransferase (APRT). Cotransformants occurred at a frequency of 5 × 10−6, a similar frequency for the transfer of theaprtmarker has been previously observed. Isozyme and Southern blot analysis show that the TK and APRT expressed in these transformants resulted from gene transfer. For one stable cotransformant, [3H]thymidine ([3H]TdR) selection against TK activity resulted in the loss of APRT activity as well, suggesting that these genes had become genetically linked together. Similarly selection against APRT expression resulted in the loss of a subset of the transferred herpes simplex virustkgenes. 5-Bromodeoxyuridine (BUdR) selected TK−variants differed from [3H]TdR selected TK−variants, in that they retainedtkgenes. However, BUdR-selected variants expressed full levels of APRT. Therefore, even though the transferredtkandaprtgenes had become genetically linked together, they were, in this case, independently expressed since these cells were phenotypically TK−and APRT+.

ISSN:0008-4166    

DOI:10.1139/m85-059

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Hydrogen-dependent chemolithotrophic nitrogen fixation ofPseudomonassp. strains H8 and KLH76 andAzospirillum lipoferumstrain 34H was confirmed by acetylene-reduction assay (ARA) and15N2incorporation. Glucose at lower than 2 mMdid not significantly repress H2-dependent acetylene reduction of chemolithotrophically grownPseudomonassp. H8 andAzospirillum lipoferum. H2(10%) stimulated ARA associated with the root of 4-week-old rice seedlings but not ARA of bacteria associated with etiolated seedlings of rice. A difference in ARA was found among rice varieties both in the presence and absence of H2. It was, however, more pronounced in the absence of H2.

ISSN:0008-4166    

DOI:10.1139/m85-060

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Sensitivity to polyene antibiotics, e.g., nystatin, amphotericin B, and filipin, was determined in phosphatidylcholine (PC) or phosphatidylethanolamine (PE) or phosphatidylserine (PS) enrichedSaccharomyces cerevisiaecells, using glutamic acid, phenylalanine, glycine, and lysine transport as an index of polyene antibiotic action. As compared with normal cells, phospholipid-enriched cells acquired resistance towards different polyenes. However, the sensitivity of glutamic acid transport towards nystatin remained unaffected in PC-, PE-, or PS-enriched cells. In contrast to nystatin, the other two polyenes were more effective in checking the influx of amino acids. Results demonstrated that the specific enrichment of PC, PE, or PS could selectively protectS.cerevisiaecells from polyene antibiotic action.

ISSN:0008-4166    

DOI:10.1139/m85-061

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Nitrogen fixation as measured by acetylene conversion to ethylene was found to be common for duckweed blooms on ponds, lakes, and streams in Michigan. Twenty-six of 29 sites with duckweed sampled over a 2-year period showed acetylene reduction activity (ARA). These activities corresponded to N inputs of 3.7–7.5 kg N∙ha−1per annual cycle for typical blooms but denseLemna trisulcablooms could be 10 times greater. The ARA was stimulated five- to six-fold by light, was not removed when plants were shaken in water, and was usually associated with the leaves and not the roots. Colonies of heterocyst-bearing cyanobacteria of the generaNostoc,Gloeotrichia,Anabaena,Calothrix, andCylindrospermumwere observed attached to the lower epidermis or in the reproductive pockets of leaves ofSpirodelaandLemnaplants but not onWolffiaplants. The ARA correlated reasonably well with the density of cyanobacterial colonies observed. The duckweed appeared to provide a more favorable environment for the cyanobacteria which should result in enhanced nitrogen inputs to aquatic and sediment environments harboring duckweed. The N2fixation was not sufficient, however, to meet all the nitrogen needs of the duckweed bloo

ISSN:0008-4166    

DOI:10.1139/m85-062

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The recovery ofStaphylococcus aureusfrom swimming-pool water by membrane filtration was studied in model experiments. On the nonselective medium tryptone soya agar (TSA) there was no difference in counts of noninjuredS.aureuswith all membrane filters tested and with pour plates. Chlorine-injuredS.aureuswas enumerated most efficiently on TSA by Gelman Tuffryn HT-450 and Sartorius SM 13806 filters. Tuffryn filters were also most productive when used in combination with the selective medium rabbit plasma – bovine fibrinogen agar (RPFA). Other filters, particularly Gelman GN-6 and Millipore HAWP, when used on RPFA were shown to have a synergistic inhibitory effect on both noninjured and chlorine-injuredS.aureus. This effect was not found on Baird-Parker agar. Using Tuffryn filters, counts on RPFA were equal to those on TSA for noninjuredS.aureusand 0.1–2.0 log units less for chlorine-injuredS.aureus. Despite this, the possibility for reading thein situcoagulase reaction for individual colonies on RPFA is considered such an advantage of this medium that its general use for enumeration ofS.aureusin swimming pools is recommended. Further studies should be carried out to allow better resuscitation.

ISSN:0008-4166    

DOI:10.1139/m85-063

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

A total of 200 beta-hemolytic streptococci, isolated from clinical specimens submitted to our laboratory, were identified as group A versus non-A using the fluorescent antibody technique (FA), bacitracin susceptibility (BBL, Difco, and Raven disks), SeroSTAT, Streptex, Phadebact, and the API 20S system. Of the 122 group A isolates, all methods except SeroSTAT and Phadebact yielded 92–99% agreement when compared with the Lancefield precipitin test. Phadebact yielded an 84% agreement and SeroSTAT changed from 83 to 98% after trypsinization. Numerous false positives were obtained and only FA (91%) and API 20S (96%) yielded better than 90% agreement on non-A identification when compared with the Lancefield test. The most false positives were obtained (45%) using the SeroSTAT reagents. Considering accuracy, our data suggests the FA technique to be the method of choice for identifying group A streptococci.

ISSN:0008-4166    

DOI:10.1139/m85-064

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Four antibiotic-resistance plasmids isolated from thermophilic bacilli were characterized in detail. Three tetracycline-resistance (Tcr) plasmids were designated as pTHT9 (7.7 kilobases (kb)), pTHT15 (4.5 kb) and pTHT22 (8.4 kb). From the results of restriction endonuclease analysis and the subsequent Southern hybridization, these were found to possess extensive genetic homology in the regions that include the replication origin and the Tcrgene. Detailed restriction maps of the smallest Tcrplasmid pTHT15 and a kanamycin-resistance (Kmr) plasmid pTHN1 (4.8 kb) were constructed. The positions of antibiotic-resistance loci and regions essential for plasmid replication were determined by cloning plasmid fragments inBacillus subtilis. These four plasmids were found to replicate and express the resistance genes stably in bothB.subtilisandB.stearothermophilus.

ISSN:0008-4166    

DOI:10.1139/m85-065

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The wild-typeAspergillus niger(V35) does not require fatty acids for growth. Four unsaturated fatty acid auxotrophs designated as UFA1, UFA2, UFA3, and UFA4have been produced from this organism by treating the conidia of the wild-type strain with a mutagen,N-methyl-N′-nitro-N-nitrosoguanidine, followed by isolation on media containing monounsaturated fatty acids and the nonionic detergent, Brij 58. Optimal growth of the mutants comparable with that of the wild type was achieved with medium supplemented with C16or C18unsaturated fatty acids containing at least onecisdouble bond at the Δ9position. Some other fatty acids (18:1 Δ11cisand 16:1 Δ9trans) support growth to some extent. The mutants do not grow at all in the presence of saturated fatty acids. Fatty acid analyses of the mutant, UFA2, grown in the presence of different fatty acid supplements reveal that it may be defective in a desaturase system. Experiments with unlabeled and [1-14C]palmitoyl-CoA have shown that the microsomes of the mutant (UFA2) contain a partially defective Δ9-desaturase system.

ISSN:0008-4166    

DOI:10.1139/m85-066

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

A comparative study of the mycelial lipid composition of a wild strain (V35) and one unsaturated fatty acid auxotroph (UFA2) ofAspergillus nigerhas been performed. The lipid composition of both strains are qualitatively the same but quantitatively different. All the strains contain the following phospholipids: cardiolipin, phosphatidylethanolamine, phosphatidylcholine, lysophosphatidylethanolamine, lysophosphatidylcholine, and phosphatidylserine; and triglycerides, diglycerides, mono-glycerides, ergosterol, and sterol esters as the neutral lipids; mono- and di-galactosyl diglyceride as the major glycolipids along with small amounts of the corresponding mannose analogs. Phosphatidylethanolamine and phosphatidylcholine constitute the bulk of the phospholipids. The mutant (UFA2) contains a higher level of glycerides and lower levels of sterol (both free and esterified form), phospholipids, and glycolipids than the wild type.Aspergillus nigercontains C16to C18saturated and unsaturated fatty acids. Small amounts of long-chain (C20to C24) and short-chain (C10to C14) saturated and unsaturated acids are also present. Linoleic, oleic, and palmitic are the major acids, stearic and linolenic acids being minor ones. UFA2grows only in the presence of unsaturated fatty acid (C16or C18) and accumulates a higher concentration of supplemented acid which influences its fatty acid profile.

ISSN:0008-4166    

DOI:10.1139/m85-067

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The ability of chymotrypsin-treated (chymo+) and untreated (chymo−) polyoma virus to transform cultured hamster embryo fibroblasts was examined. The data show that exposure to this protease reduces the ability of the virus to transform non-permissive cells to essentially the same extent as it reduces its ability to replicate in permissive cells. Twenty-five lines of transformed cells were established from colonies growing in soft agar, and after 20in vitropassages, cells of all lines were characterized with respect to their ability to form colonies in soft agar and their tumorigenicity in hamsters. While the studies showed that there are striking differences among the lines with respect to colony-forming ability, and real, though less striking differences in tumorigenicity, they failed to reveal any obvious differences between the groups of cell lines transformed by chymo−and chymo+polyoma virus. Of 13 lines examined, all were found to express both middle and small polyoma T antigens, none express significant levels of large T antigen, and 11 express some form of what is probably a truncated large T antigen, the most common species having a molecular weight of 67 000.

ISSN:0008-4166    

DOI:10.1139/m85-068

出版商:NRC Research Press    

年代:1985

数据来源: NRC