Biomedical subjects

D A Webster

Publications and source records attributed to D A Webster.

80 records · Page 5Linked to original sources

PubMedDate not supplied

Production of alpha-amylase in fed-batch cultures of vgb+ and vgb- recombinant Escherichia coli: some observations.

Synthesis and excretion of Bacillus stearothermophilus alpha-amylase is analyzed in fed-batch cultivations of Escherichia coli JM103[pMK79] and E. coli JM103[pMK57], the former strain containing the plasmid-encoded Vitreoscilla hemoglobin (VHb) gene (vgb) and the latter strain being devoid of this gene. Fed-batch operation is observed to be substantially superior to batch operation as concerns the alpha-amylase production rate and the extent of excretion of the enzyme. Faster feeding of a nutrient medium (LB or M9) discourages synthesis of alpha-amylase. While synthesis of alpha-amylase in the vgb(-) strain is discouraged when oxygen availability is reduced, the reverse is the case with the vgb(+) strain, the promotion of alpha-amylase synthesis in the latter strain being linked to the synthesis of VHb. Increased availability of the principal carbon source (glucose) in a defined medium leads to overproduction of both alpha-amylase and VHb under oxygen limitation, which may be responsible for the segregational instability observed with the vgb(+) strain. The very high extents of excretion of alpha-amylase attained in fed-batch cultures are encouraging for downstream processing of the recombinant protein.

Bioreactors↗

PubMedDate not supplied

Cloning and expression of Vitreoscilla hemoglobin gene in Burkholderia sp. strain DNT for enhancement of 2,4-dinitrotoluene degradation.

The gene (vgb) encoding the hemoglobin (VHb) of Vitreoscilla sp. was cloned into a broad host range vector and stably transformed into Burkholderia (formerly Pseudomonas) sp. strain DNT, which is able to degrade and metabolize 2,4-dinitrotoluene (DNT). Vgb was stably maintained and expressed in functional form in this recombinant strain (YV1). When growth of YV1, in both tryptic soy broth and minimal salts broth containing DNT and yeast extract, was compared with that of the untransformed strain, YV1 grew significantly better on a cell mass basis (A(600)) and reached slightly higher maximum viable cell numbers. YV1 also had roughly twice the respiration as strain DNT on a cell mass basis, and in DNT-containing medium, YV1 degraded DNT faster than the untransformed strain. YV1 cells pregrown in medium containing DNT plus succinate showed the fastest degradation: 100% of the initial 200 ppm DNT was removed from the medium within 3 days.

Bacterial Proteins↗

PubMedDate not supplied

Primary sequence of a dimeric bacterial haemoglobin from Vitreoscilla.

Vitreoscilla, a filamentous bacterium in the Beggiatoa family, synthesizes a soluble haem-protein which has two identical subunits of relative molecular mass 15,775 and two b haems per molecule. It is synthesized in relatively large quantities when the organism, a strict aerobe, is grown under hypoxic conditions. It forms a relatively stable oxygenated form which is spectrally similar to oxymyoglobin (oxyHb) and oxyhaemoglobin (oxyHb). The amino acid sequence of this protein has been determined and aligned to fit the helical regions of several animal and plant globins. This alignment is consistent with its being a structural homologue of the eucaryotic haemoglobins although it diverged from the others in the N-terminal region and may lack an A-helix. It showed the maximum sequence homology (24%) with lupin leghaemoglobin (Lb). Vitreoscilla Hb is the first bacterial haemoglobin to be sequenced. It may function to enable the organism to survive in oxygen-limited environments by acting as an oxygen storage-trap or to facilitate oxygen diffusion.

Amino Acid Sequence↗

PubMedDate not supplied

Cloning and expression of the Vitreoscilla hemoglobin gene in Enterobacter aerogenes: effect on cell growth and oxygen uptake.

The hemoglobins found in unicellular organisms show a greater chemical reactivity, protect cells against oxidative stress and hence have been implicated in a wider variety of potential functions than those traditionally associated with animal and plant hemoglobins. There are well-documented studies showing that bacteria expressing Vitreoscilla hemoglobin (VHb), the first prokaryotic hemoglobin characterized, have better growth and oxygen uptake rates than VHb counterparts.

Bacterial Proteins↗

PubMedDate not supplied

Antibacterial and osteoinductive properties of demineralized bone matrix treated with silver.

The problems incurred by storage of demineralized bone allograft material and its potential use in contaminated operative sites make an antibacterial property desirable. Silver was considered for this role because of its wide spectrum of antibacterial susceptibility, low incidence of resistance, and its ability to persistently inhibit bacteria after binding to collagen matrices. Demineralized bone matrix prepared from rat diaphyseal bone segments was treated by exposure fo AgCl, AgNO3 and NaNO3 solutions prior to lyophilization. The resulting material was tested for bacterial inhibition after incubation in saline solutions for various times and showed inhibition persisting for at least four weeks (Ag-treated material only). Silver treating the matrix was found to partially inhibit the osteoinductive capacity at 10(-3) and 10(-2) M but not at 10(-5) M as measured by intramuscular implantation in the rat for six weeks. Control and NaNo3-treated specimens showed normal bone growth as measured by ashing and by 99mTc binding, and confirmed by radiologic densities. Histologic sections showed dense microdeposits on dense material predominately near the decalcified bone surfaces, but also within the matrix. The results suggest that pretreatment with silver at concentrations in the 10(-4) range would render the implant material antibacterial, protect its sterility, and leave the osteoinductive capacity intact.

Animals↗

PubMedDate not supplied

Silver anode treatment of chronic osteomyelitis.

Twenty-five patients with active, chronic osteomyelitis, resistant to conventional management, were treated with surgical debridement and daily application of electrically activated silver dressings. Sixteen (64%) cases resulted in closed, stable, pain-free wounds, with the remainder resulting in persistent drainage or amputation. Nine of 12 cases complicated by nonunion achieved union. In 13 patients an open-bone graft was performed and silver treatment continued: these tended to remain free of purulent drainage but fared no better than average in the long-term follow-up. The silver anode dressing seems to be an effective aid in the treatment of chronic bone infection when combined with adequate surgical debridement, thereby reducing the need for prolonged systemic antibiotics.

Adult↗

PubMedDate not supplied

Late reduction of bilateral traumatic hip dislocations in a child.

A 5-year-old girl with bilateral traumatic hip dislocations neglected for 6 weeks was successfully managed by skeletal traction for reduction and cast immobilization for 6 weeks. The delay in reduction did not preclude a good result. Osteoporosis of the femoral head was noted to be a favorable prognostic sign relative to its vascularity. Skeletal traction is an optimum method of reduction for neglected hip dislocations, while open reduction is rarely indicated. Prolonged restriction of weight bearing is unnecessary following soft-tissue healing.

Casts, Surgical↗

PubMedDate not supplied

Restoration deterioration related to later failure.

The purpose of this study was to determine the relationship between the deterioration and the later failure of a very large number of amalgams and anterior resin composites examined over periods of up to 16 years. Assessments were made of the deterioration of various clinical factors or characteristics of the restorative materials that were thought to predict later failures. True failures, which were directly related to the restorative materials, accounted for 7.5% of the amalgam and 30.4% of the composite restorations. For the amalgams, there was a significant association found between the failures and surface tarnishing. Marginal fracture and marginal staining were not associated significantly with any of the three different failure modes. For the composites there were significant associations found between the failures and surface roughness, marginal fracture, and color mismatch. Surface staining and marginal staining were not associated significantly with any of the three different failure modes. Many restorations assessed as being unsatisfactory continued to function for a further 2.5 to 3.5 years on average before being replaced, often for unrelated reasons. There is a need to define unsatisfactory restorations more clearly in terms of actual adverse effects on dental health, rather than merely in terms of restoration deterioration.

Color↗