Biomedical subjects

J D Owens

Publications and source records attributed to J D Owens.

At least 19 recordsLinked to original sources

PubMed2002

Effects of temperature, pH, water activity and CO2 concentration on growth of Rhizopus oligosporus NRRL 2710.

AIMS: To investigate the effects of temperature, pH, water activity (aw) and CO2 concentration on the growth of Rhizopus oligosporus NRRL 2710. METHODS AND RESULTS: Hyphal extension rates from mycelial and spore inocula were measured on media with different aw (approximately 1.0, 0.98 and 0.96) and pH (3.5, 5.5 and 7.5) incubated at 30, 37 or 42 degrees C in atmospheres containing 0.03, 12.5 or 25% (v/v) CO2. The effects of environmental conditions on hyphal extension rate were modelled using surface response methodology. The rate of hyphal extension was very sensitive to pH, exhibiting a pronounced optimum at pH 5.5-5.8. The hyphal extension rate was less sensitive to temperature, aw or CO2, exhibiting maximum rates at 42 degrees C, a(w) approximately 1.0 and 0.03% (v/v) CO2. CONCLUSIONS: The fastest hyphal extension rate (1.7 mm h(-1)) was predicted to occur at 42 degrees C, pH 5.85, a(w) approximately 1.0 and 0.03% CO2. SIGNIFICANCE AND IMPACT OF THE STUDY: The present work is the first to model the simultaneous effects of temperature, pH, aw and CO2 concentration on mould growth. The information relates to tempe fermentation and to possible control of the microflora in Tanzanian cassava heap fermentations.

Carbon Dioxide↗

PubMed2000

Effect of ammonia on the growth of Bacillus species and some other bacteria.

The tolerance of 26 Bacillus species isolated from alkaline fermented foods, five other bacilli and nine non spore-forming bacteria to alkaline pH and ammonia was determined. All grew at pH 7, 8 and 9 in the presence of 930 mmol l-1 NH4 + at pH 7.0, and in the presence of NH3 concentrations up to 5 mmol l-1 at pH 7.0 and 8.0. At higher NH3 concentrations, growth of some of the bacteria was inhibited and at 500 mmol l-1 only B. pasteurii and B. pumilus grew. Bacteria from alkaline food fermentations included strains relatively sensitive to NH3 (inhibited by 50 mmol l-1) and relatively tolerant strains (grew in the presence of 300 mmol l-1) and there was no evidence that they were more tolerant to NH3 than bacteria not associated with these fermentations.

Ammonia↗

PubMed1999

Glucosamine content of tempe mould, Rhizopus oligosporus.

The glucosamine content of Rhizopus oligosporus NRRL 2710 mycelium grown in different media was determined. In Sabouraud dextrose broth the glucosamine content ranged from 51 g (kg dry biomass)(-1) for mycelial pellets less than 5 mm diameter to 107 g kg(-1) for pellets 16-35 mm diameter. Mycelium grown on Sabouraud dextrose agar contained 111 g glucosamine (kg dry biomass)(-1) while that grown on soymilk agar, used to simulate growth on soybeans in tempe, contained 82 g kg(-1). The estimation of glucosamine was reproducible, with a mean coefficient of variation of 4% for mycelial pellets and 11% for mycelium from agar media. It is suggested that a conversion factor of 12 g dry biomass (g glucosamine)(-1) is applicable to determine fungal biomass in tempe fermentation.

Biomass↗

PubMed1999

Protein utilization during soybean tempe fermentation.

The aim was to identify to what extent proteins were utilized during the fermentation of bacteria-free tempe prepared with acidified soybean cotyledons and Rhizopus oligosporus NRRL 2710 at 30 degrees C. Dry matter declined continuously during the fermentation to 980 g/(kg of initial dry cotyledons) at 28 h, 910 g at 46 h (when the tempe was judged mature), and 835 g at 72 h. The decrease in dry matter was due mainly to reduction in crude lipid, amounting to 65 g/(kg of initial dry cotyledons) at 46 h and 135 g/(kg of initial dry cotyledons) at 72 h and representing approximately 70% and 80%, respectively, of the total dry matter loss. Protein oxidation (estimated from ammonia production) was 5 g at 28 h,10 g at 46 h, and 20 g/(kg of initial dry cotyledons) at 72 h. The total amount of soy protein hydrolyzed, including that incorporated into mold biomass, was estimated to be 80 g/(kg of initial dry cotyledons) at 28 h incubation, 95 g at 46 h, and 100 g at 72 h. The hydrolyzed protein at 46 h represented 25% of the initial protein. Of this hydrolyzed protein, it is suggested that approximately 65% remained in the tempe as amino acids and peptides, 25% was assimilated into mold biomass, and 10% was oxidized.

Fermentation↗

PubMed1997

Munkoyo beverage, a traditional Zambian fermented maize gruel using Rhynchosia root as amylase source.

A typical munkoyo beverage was made by fermenting Rhynchosia heterophylla root extract-cooked maize meal mixture with Lactobacillus confusus LZI and Saccharomyces cerevisiae YZ20. The fermented munkoyo beverage had a pH of 3.3, lactic acid content of 60 mmol/l, ethanol 320-410 mmol/l and a characteristic 'munkoyo' aroma. L. confusus, used alone, produced a beverage with a faint munkoyo flavour note whilst beverage produced with S. cerevisiae alone seemed not to have a typical munkoyo note. R. heterophylla root extract converted 75% of the starch in sterile cooked maize meat to maltose (80% of total sugars), maltotriose (17%) and glucose (3%) in I h at 45 degrees C. During fermentation by the mixed culture or the yeast alone most of the maltose was utilised but little or none of the maltotriose. The ratio of yeast to lactic acid bacteria in the starter culture affected the rate of production of ethanol but had no effect on the growth or acid production by the bacterium. To obtain a munkoyo beverage with the desired low alcohol concentration (< 100 mmol/l), the ratio of yeast concentration (cfu/ml) to Lactobacillus concentration in the starter culture should be 1:1000 or less and the beverage should be fermented for 24 h only.

Amylases↗

PubMed1997

Decoupling of DNA excision repair and RNA transcription in translocation breaksite regions of plasmacytoma-susceptible BALB/cAnPt mice.

Preferential repair of pyrimidine dimers in rodent cells is thought to be directly coupled to the RNA transcription machinery. The most compelling evidence for this notion is the finding that excision repair occurs more rapidly in the template strand of DNA of transcribed genes than in the non-template strand. A thorough test of this coupling concept by careful comparison of the rate of repair to the rate of transcription of a gene and its regulatory region has not been reported. In the present study, we used nuclear run-on as a measure of transcription in the c-myc and Pvt1 genes in normal B-lymphoblasts from plasmacytoma-susceptible (BALB/cAnPt) and plasmacytoma-resistant (DBA/2N) strains of mice. Previous studies have shown that these loci, but not c-abl or Dhfr are repaired differently in mouse strains: poorly in BALB/cAnPt but efficiently in DBA/2N. The results presented here indicate that in DBA/2N cells, run-on transcription from both DNA strands can be readily detected in the regions of c-myc and Pvt1 that were efficiently repaired. Unexpectedly, however, in BALB/cAnPt lymphoblasts, transcription was equivalent to that of DBA/2N, despite a dramatic reduction in efficiency of excision repair. This finding indicates that, in BALB/cAnPt lymphoblasts, DNA repair 5' to c-myc and in Pvt1 is decoupled from the RNA transcription machinery. We postulate that this dissociation of repair and transcription represents a BALB/cAnPt-specific defect in a component of the transcription/repair complex that specifically compromises repair activity but not transcription. This defect may be responsible for the inability of normal BALB/cAnPt lymphoblasts to repair DNA sequences in the c-myc 5' flank and the Pvt1 gene, inducing gene-specific instability that predisposes these loci to genetic accidents, including chromosomal translocation, retroviral integration and other mutations.

Animals↗

PubMed1996

Sapal: a traditional fermented taro [Colocasia esculenta (L.) Schott] corm and coconut cream mixture from Papua New Guinea.

Sapal is a traditional fermented food made by mixing cooked, grated taro [Colocasia esculenta (L.) Schott] corm with coconut cream and allowing it to ferment at ambient temperature. The fermentation was primarily due to heterofermentative lactic acid bacteria, which reached 10(10) cfu/ml. Seven out of 10 isolated bacterial strains were identified as Leuconostoc mesenteroides or Leuc. paramesenteroides. The initial microbial flora was derived from the coconut cream. Yeasts grew on the surface of the sapal in the later stages of the fermentation. Overnight storage of the grated taro corm resulted in the glucose concentration increasing from 1.1 to about 5 g/l. During the fermentation the glucose concentration decreased to undetectable levels. The pH value fell from an initial value of 6.1 to 4.1 after 24 h.

Cocos↗

PubMed1996

Control of ammonia formation during Bacillus subtilis fermentation of legumes.

The control of ammonia formation during the Bacillus subtilis fermentation of autoclaved, roasted soybean cotyledons (Glycine max) and of autoclaved African locust bean cotyledons (Parkia spp.) was investigated. Addition of NaCl, 1.5 mol (kg wet cotyledons)-1, part way through the fermentation inhibited ammonia formation and softening of the cotyledons. Addition of glycerol, 1.7 mol (kg wet cotyledons)-1 part way through the fermentation inhibited alkalinisation and ammonia formation while allowing enzymic activity and softening of the cotyledons to continue. Restriction of the oxygen supply by incubating the cotyledons in a sealed container also prevented excessive ammonia production and increase in pH value. Fermentations conducted in sealed containers with an air to cotyledons ratio of approximately 130-175 ml air (g wet cotyledons)-1 supported good microbial growth and proteolysis without the formation of detectable ammonia aroma.

Ammonia↗

PubMed1993

Retroviral enhancer insertion 5' of c-myc in two translocation-negative mouse plasmacytomas upregulates c-myc expression to different extents.

Essentially all murine plasmacytomas have deregulated c-myc expression that is typically brought about by chromosomal translocations between the c-myc/Pvt-1 locus and one of the immunoglobulin loci. ABPC 22 and RFPC 2782 are BALB/c plasmacytomas that lack chromosomal translocations yet have Southern blot evidence of c-myc gene rearrangements. In this report we show that proviral integrations 5' of the c-myc gene can deregulate c-myc expression in mouse plasmacytomas. Analysis of DNA sequences 5' of the c-myc genes from both tumors demonstrated that rearrangements were caused by retroviral integrations 5' of c-myc exon 1. The proviral insertion in RFPC 2782 was associated with a high steady-state c-myc mRNA level comparable to that seen in plasmacytomas with typical translocations. An analogous proviral insertion in ABPC 22 was associated with a c-myc RNA level that was only 38% of that of RFPC 2782. Nuclear run-on studies of c-myc transcription showed that ABPC 22 has both a lower rate of transcription and a greater degree of transcriptional attenuation than RFPC 2782. DNA sequencing of the long terminal repeat of each tumor provirus showed that the ABPC 22 provirus harbors a deletion of one of the two direct repeats in the viral enhancer, whereas both repeats are present in the RFPC 2782 provirus. These data indicate that maximum LTR enhancer effectiveness in plasmacytomas in vivo requires the presence of both LTR direct repeats. The documentation of the low level of steady-state c-myc mRNA in ABPC 22 supports the notion that deregulated c-myc expression, even at low steady state levels, is effective in supporting the development of plasmacytomas.

Animals↗

PubMed1992

Causes of conductance change in yeast cultures.

The conductance change due to growth of Saccharomyces cerevisiae Y112, Zygosaccharomyces bailii M and Rhodotorula rubra NCYC 63 in culture media containing glucose, tartrate pH buffer and ammonium ions as sole nitrogen source was compared with that in a medium containing L-asparagine as sole nitrogen source. Decreases in conductance were observed in glucose-ammonium cultures of all three yeasts while little change occurred in cultures with L-asparagine as sole nitrogen source. This supports the hypothesis that the metabolic activity primarily responsible for conductance change in yeast cultures is the uptake of charged ammonium ions as nitrogen source and the reaction of protons with pH buffer compounds. Rhodotorula rubra cultures with L-asparagine as sole carbon source caused large increases in conductance with growth. Chemical analyses of culture filtrates showed that this increase in conductance was due to use of L-asparagine as carbon source and the excretion of nitrogen surplus to biosynthetic needs as ammonium. In addition, the production of aspartate, acetate and bicarbonate contributed to the increase in conductance.

Asparagine↗

PubMed1991

Nonhomologous recombination at sites within the mouse JH-C delta locus accompanies C mu deletion and switch to immunoglobulin D secretion.

Plasma cells secrete immunoglobulins other than immunoglobulin M (IgM) after a deletion and recombination in which a portion of the immunoglobulin heavy-chain locus (IgH), from the 5'-flanking region of the mu constant-region gene (C mu) to the 5'-flanking region of the secreted heavy-chain constant-region gene (CH), is deleted. The recombination step is believed to be targeted via switch regions, stretches of repetitive DNA which lie in the 5' flank of all CH genes except delta. Although serum levels of IgD are very low, particularly in the mouse, IgD-secreting plasmacytomas of BALB/c and C57BL/6 mice are known. In an earlier study of two BALB/c IgD-secreting hybridomas, we reported that both had deleted the C mu gene, and we concluded that this deletion was common in the normal generation of IgD-secreting cells. To learn how such switch recombinations occur in the absence of a switch region upstream of the C delta 1 exon, we isolated seven more BALB/c and two C57BL/6 IgD-secreting hybridomas. We determined the DNA sequences of the switch recombination junctions in eight of these hybridomas as well as that of the C57BL/6 hybridoma B1-8. delta 1 and of the BALB/c, IgD-secreting plasmacytoma TEPC 1033. All of the lines had deleted the C mu gene, and three had deleted the C delta 1 exon in the switch recombination event. The delta switch recombination junction sequences were similar to those of published productive switch recombinations occurring 5' to other heavy-chain genes, suggesting that nonhomologous, illegitimate recombination is utilized whenever the heavy-chain switch region is involved in recombination.

Animals↗

PubMed1990

The in vivo generation of murine IgD-secreting cells is accompanied by deletion of the C mu gene and occasional deletion of the gene for the C delta 1 domain.

Mature, resting rodent, and primate B lymphocytes express two membrane Ig isotypes, IgM and IgD. Although membrane IgD production by these cells is regulated at a transcriptional level, and does not require deletion of the C mu gene, C mu has been deleted in all of the IgD-secreting tumor cells that have been studied. These IgD-secreting tumors, which include two mineral oil-induced plasmacytomas and three IgD-switch variants of an IgM-secreting hybridoma, might not, however, be representative of the rare IgD-secreting cells generated in response to an immune stimulus. A recent study of mice injected with a goat antibody to mouse IgD has demonstrated the generation of a relatively large secretory IgD response in these animals. We have now produced hybridomas by fusing spleen cells from these mice with a non-Ig-secreting plasmacytoma. Two of these hybridomas, KWD-1 and KWD-2, secrete IgD and express cell membrane IgD. Both of these hybridomas were found to have deleted the C mu gene. KWD-2 produces a delta-chain mRNA and a delta-chain protein similar in size to those previously reported for normal secreted mouse IgD; however, KWD-1 synthesizes a secretory delta-chain mRNA that is approximately 0.25 kb smaller than the KWD-2 secretory delta-chain mRNA and secretes IgD with a delta-chain that is approximately 21 kDa smaller than the secretory delta-chain of KWD-2. ELISA studies with epitope-defined anti-delta mAb indicate that KWD-2 has both delta Fc (C delta 3) [corrected] and delta Fd (C delta 1) [corrected] determinants, whereas KWD-1 has delta Fc but not delta Fd. These studies also demonstrate that the Ag-binding site of KWD-1 is not deleted because KWD-1 specifically binds goat IgG. Northern blot analyses with exon-specific probes indicate that while both KWD-1 and KWD-2 synthesize kappa-chain mRNA and delta-chain mRNA that includes the VH, C delta hinge, and C delta 3 exons, the C delta 1 exon is present only on the KWD-2 delta-chain mRNA. Southern blot analysis confirms that the C delta 1 exon has been deleted in KWD-1, but not KWD-2. We have previously noted that a secretory delta-chain mRNA that is similar in size to that produced by KWD-1 accounts for approximately 25% of the splenic secretory delta-chain mRNA produced by goat anti-mouse IgD antibody-injected mice.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1990

Alternative splicing of RNAs transcribed from the human c-myb gene.

An alternative splicing event in which a portion of the intron bounded by the vE6 and vE7 exons with v-myb homology is included as an additional 363-nucleotide coding exon (termed E6A or coding exon 9A) has been described for normal and tumor murine cells that express myb. We show here that this alternative splicing event is conserved in human c-myb transcripts. In addition, another novel exon (termed E7A or coding exon 10A) is identified in human c-myb mRNAs expressed in normal and tumor cells. Although the myb protein isoform encoded by murine E6A-containing mRNA is larger than the major c-myb protein, the predicted products of both forms of human alternatively spliced myb transcripts are 3'-truncated myb proteins that terminate in the alternative exons. These proteins are predicted to lack the same carboxy-terminal domains as the viral myb proteins encoded by avian myeloblastosis virus and E26 virus. The junction sequences that flank these exons closely resemble the consensus splice donor and splice acceptor sequences, yet the alternative transcripts are less abundant than is the major form of c-myb transcripts. The contribution that alternative splicing events in c-myb expression may make on c-myb function remains to be elucidated.

Amino Acid Sequence↗

PubMed1989

Altered myc gene transcription and intron-induced stabilization of myc RNAs in two mouse plasmacytomas.

Accumulation of unusually high amounts of larger-than-normal c-myc mRNAs occurs in two mouse plasmacytomas, TEPC 1165 and TEPC 2027. Southern blot and DNA sequence analyses showed that both tumors have undergone translocations of immunoglobulin heavy chain loci to positions 5' of the c-myc gene promotors resulting in removal of DNA sequences encoding a negative transcriptional regulatory element. In contrast to other mouse plasmacytomas, TEPC 1165 and TEPC 2027 rearranged myc genes show increased transcription, partially explaining their abundance of myc RNA. Similar to other mouse plasmacytomas, the abundance of myc RNA in TEPC 1165 and TEPC 2027 is also influenced by increased stability of structurally atypical myc RNAs. Two myc mRNAs are found in TEPC 2027, a 2.4 kb species including all 3 myc exons and a 4.0 kb species with the 3 exons plus the first intron. The two major myc mRNAs in TEPC 1165, 3.0 and 3.9 kb species, also include all three myc exons plus portions of the first intron. S1 nuclease protection analyses show that the 5' initiation and 3' untranslated (UT) regions of the unusual TEPC 1165 RNAs are normal showing that the size differences arise solely from inclusion of first intron sequences in the large myc RNAs. DNA sequence analysis showed that the presence of first intron sequences in the large myc RNAs is due to mutations affecting the splice donor region at the 3' end of exon 1 in both tumors. SDS-PAGE analysis of immunoprecipitated TEPC 1165 and TEPC 2027 myc proteins showed them to be of normal electrophoretic mobility but no more abundant than in a pre-B cell line 18-81 that contains at least 10 fold less myc RNA. The 4.0 kb myc mRNA of TEPC 2027 is atypically stable while the 2.4 kb myc mRNA undergoes normal rapid turnover within the same cell, demonstrating that the presence of first intron sequences in the large myc RNA stabilizes it despite the presence of 3' UT and putative exon 1 destabilizing sequences. These results show that myc intron 1 sequences can counteract the effect of 3' UT region destabilizing sequences in myc RNA and suggest that the increased myc RNA stability noted in TEPC 1165 and TEPC 2027 is largely due to the presence of the intron 1 sequences.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1987

Amino acids at the site of V kappa-J kappa recombination not encoded by germline sequences.

Murine V kappa-J kappa recombination is characterized by a maintenance of size at the site of recombination and the use of nucleic acids found only in germline sequences. This is in contrast to heavy chain VH-D-JH assembly where random nucleotides are added at the recombination sites to produce considerable size variation, even though the heptamer/nonomer recombination sequences are identical in both kappa and heavy chain genes. We have examined the origin of an unusual amino acid, Ile, found at the site of V kappa-J kappa recombination in antigalactan antibodies, by sequence analysis of the corresponding rearranged and germline genes. Results indicate that the Ile codon can be generated by use of a single nucleotide 3' of the V kappa segment in combination with the second and third nucleotides of the first codon of J kappa 5 or J kappa 4. However, several antigalactan antibodies express Ile in combination with J kappa 2. An Ile codon cannot be generated by recombination in any reading frame between germline V kappa and J kappa 2 segments. These results suggest that the origin of the Ile codon in lines using J kappa 2 may represent a novel even in murine light chain assembly, possibly similar to the de novo addition of nucleotides observed in heavy chain gene recombination.

Amino Acid Sequence↗

PubMed1986

Selection of pH buffers for use in conductimetric microbiological assays.

Many metabolic activities of micro-organisms lead to changes in the pH value of cultures and consequently pH buffer compounds are potentially a major source of conductivity changes in cultures. To maximize changes in conductivity associated with microbial growth the pH buffer-associated changes should occur in a direction that reinforces those due to other metabolic activities. In agreement with this, studies with Escherichia coli showed that fermentation of glucose and aerobic growth on L-alanine yielded greater changes in the conductivity of media containing Tris(hydroxymethyl)aminomethane or L-histidine buffers than in a medium containing phosphate buffer, whereas aerobic growth on glucose or succinate yielded greater changes with phosphate buffer than with Tris(hydroxymethyl)aminomethane or L-histidine buffers. Criteria for the selection of appropriate pH buffer compounds are presented.

Aerobiosis↗

PubMed1985

Sources of conductance changes during bacterial reduction of trimethylamine oxide to trimethylammonium in phosphate buffer.

The sources of conductance changes during reduction of trimethylamine oxide to trimethylamine by Escherichia coli with formate as electron donor and in the presence of phosphate buffer were investigated. Theoretical considerations and experimental results suggest that the major source of conductance change is the conversion of dihydrogen phosphate to hydrogen phosphate. This transformation contributes almost twice as much to the total conductance change as does the conversion of uncharged trimethylamine oxide to charged trimethylammonium.

Buffers↗

PubMed1985

Prevention of autoimmune uveitis by competitive immunization with bovine gamma globulin.

The effect of antigenic competition on the development of autoallergic experimental uveitis and autoallergy to ocular antigens was studied. Strain 13 guinea pigs were immunized with adjuvants containing either National Institutes of Health strain retina-uvea extract or retina-uvea extract plus bovine gamma globulin (BGG). They were later reimmunized with ocular extract and BGG or ocular extract alone, in adjuvant. They were observed weekly by slit-lamp examination. At the end of the study, they were skin tested using strain 13 retina-uvea extract. The eyes of certain groups were examined histologically. Immunization and reimmunization with ocular extract produced uveitis. The addition of BGG to the initial immunization prevented the development of uveitis even after reimmunization with ocular extract alone. It did not, however, necessarily prevent the development of delayed type skin sensitivity to retina-uveal extract.

Animals↗