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J R Lawrence

Publications and source records attributed to J R Lawrence.

At least 37 records · Page 2Linked to original sources
PubMed1999

Physiological adaptations involved in alkane assimilation at a low temperature by Rhodococcus sp. strain Q15.

We examined physiological adaptations which allow the psychrotroph Rhodococcus sp. strain Q15 to assimilate alkanes at a low temperature (alkanes are contaminants which are generally insoluble and/or solid at low temperatures). During growth at 5 degrees C on hexadecane or diesel fuel, strain Q15 produced a cell surface-associated biosurfactant(s) and, compared to glucose-acetate-grown cells, exhibited increased cell surface hydrophobicity. A transmission electron microscopy examination of strain Q15 grown at 5 degrees C revealed the presence of intracellular electron-transparent inclusions and flocs of cells connected by an extracellular polymeric substance (EPS) when cells were grown on a hydrocarbon and morphological differences between the EPS of glucose-acetate-grown and diesel fuel-grown cells. A lectin binding analysis performed by using confocal scanning laser microscopy (CSLM) showed that the EPS contained a complex mixture of glycoconjugates, depending on both the growth temperature and the carbon source. Two glycoconjugates [beta-D-Gal-(1-3)-D-GlcNAc and alpha-L-fucose] were detected only on the surfaces of cells grown on diesel fuel at 5 degrees C. Using scanning electron microscopy, we observed strain Q15 cells on the surfaces of octacosane crystals, and using CSLM, we observed strain Q15 cells covering the surfaces of diesel fuel microdroplets; these findings indicate that this organism assimilates both solid and liquid alkane substrates at a low temperature by adhering to the alkane phase. Membrane fatty acid analysis demonstrated that strain Q15 adapted to growth at a low temperature by decreasing the degree of saturation of membrane lipid fatty acids, but it did so to a lesser extent when it was grown on hydrocarbons at 5 degrees C; these findings suggest that strain Q15 modulates membrane fluidity in response to the counteracting influences of low temperature and hydrocarbon toxicity.

Adaptation, Physiological↗
PubMed1998

The identification of salicylates as normal constituents of serum: a link between diet and health?

AIM: To examine sera for the presence of salicylic acid and 2,3- and 2,5-dihydroxybenzoic acids (2,3- and 2,5-DHBA), in individuals not taking salicylate drugs. METHODS: Extracts of acidified serum samples were analysed by high performance liquid chromatography with electro-chemical detection. The chromatographic conditions were altered, and the retention times of the unknown compounds compared against authentic salicylic acid, 2,3-DHBA, and 2,5-DHBA. Serum samples (some spiked with salicylic acid) were incubated with salicylate hydroxylase and analyses undertaken. An extract of acidified serum was derivatised using N-methyl-N-trimethylsilyltrifluoroacetamide and the salicylic acid derivative identified by gas chromatography-mass spectrometry. RESULTS: Salicylic acid, 2,3-DHBA, and 2,5-DHBA were identified as being normal constituents of serum. CONCLUSIONS: Salicylic acid, 2,3-DHBA, and 2,5-DHBA possess anti-inflammatory properties. The finding that these compounds are present as normal constituents of serum, possibly arising from diet, raises important questions as to their role in the promotion of health.

Chromatography, High Pressure Liquid↗
PubMed1998

Clinical and biochemical determinants of plasma lipid peroxide levels in type 2 diabetes.

The enhanced risk and increased severity of atheroma in diabetes is well recognized but, as yet, incompletely explained. A cross-sectional study of vascular disease risk factors in a group of type 2 diabetic patients from South West Scotland has revealed an association between glycaemic control, assessed by HbAl level and plasma lipid peroxides measured by a specific high-performance liquid chromatography method. Duration of diabetes appeared to be a subsidiary contributor to lipid peroxidation. We suggest this evidence supports the importance of glycaemic control in modulating glyco-oxidative mechanisms probably crucial to production of diabetic complications. Atherosclerosis prevention in diabetes may hinge on exemplary simultaneous control of both hyperglycaemia and hyperlipidaemia.

Chromatography, High Pressure Liquid↗
PubMed1995

Bioaccumulation of the Herbicide Diclofop in Extracellular Polymers and Its Utilization by a Biofilm Community during Starvation.

Continuous-flow cell systems were used to cultivate a degradative biofilm community with the herbicide diclofop methyl as the sole carbon and energy source. The aromatic character of this compound and its breakdown products enabled direct visualization of their accumulation in the biofilm matrix. This accumulation could be inhibited by addition of a more labile carbon source to the culture medium or by inhibition of cell activity. The fluorescence of diclofop-grown biofilms remained constant after 14 to 21 days but decreased with time when diclofop was omitted from the irrigation solution. However, this decrease was inhibited by cyanide, indicating either utilization or release of accumulated diclofop when the cells were viable. Subsequent experiments with [(sup14)C]diclofop also indicated that decreased fluorescence in the absence of an exogenous carbon source resulted from degradation of adsorbed diclofop and its breakdown products by the biofilm bacteria. These results demonstrate that biofilm exopolymers can facilitate storage of nutrients for subsequent mineralization during periods of carbon limitation.

Journal Article↗
PubMed1995

In Situ Localization of Azospirillum brasilense in the Rhizosphere of Wheat with Fluorescently Labeled, rRNA-Targeted Oligonucleotide Probes and Scanning Confocal Laser Microscopy.

The colonization of wheat roots by Azospirillum brasilense was used as a model system to evaluate the utility of whole-cell hybridization with fluorescently labeled, rRNA-targeted oligonucleotide probes for the in situ monitoring of rhizosphere microbial communities. Root samples of agar- or soil-grown 10- and 30-day-old wheat seedlings inoculated with different strains of A. brasilense were hybridized with a species-specific probe for A. brasilense, a probe hybridizing to alpha subclass proteobacteria, and a probe specific for the domain Bacteria to identify and localize the target bacteria. After hybridization, about 10 to 25% of the rhizosphere bacteria as visualized with 4(prm1),6-diamidino-2-phenylindole (DAPI) gave sufficient fluorescence signals to be detected with rRNA-targeted probes. Scanning confocal laser microscopy was used to overcome disturbing effects arising from autofluorescence of the object or narrow depth of focus in thick specimens. This technique also allowed high-resolution analysis of the spatial distribution of bacteria in the rhizosphere. Occurrence of cells of A. brasilense Sp7 and Wa3 was restricted to the rhizosphere soil, mainly to the root hair zone. C-forms of A. brasilense were demonstrated to be physiologically active forms in the rhizosphere. Strain Sp245 also was found repeatedly at high density in the interior of root hair cells. In general, the combination of fluorescently labeled oligonucleotide probes and scanning confocal laser microscopy provided a very suitable strategy for detailed studies of rhizosphere microbial ecology.

Journal Article↗
PubMed1994

Effects of erythropoietin therapy on the lipid profile in end-stage renal failure.

To evaluate the effects of erythropoietin (EPO) therapy on the lipid profile in end-stage renal failure, we undertook a prospective study in patients on both hemodialysis (HD) and continuous ambulatory peritoneal dialysis (CAPD). One hundred and twelve patients (81 HD, 31 CAPD) were enrolled into the study. Lipid parameters [that is, total cholesterol and the LDL and HDL subfractions, triglycerides, lipoprotein (a), apoproteins A and B], full blood count, iron studies, B12, folate, blood urea, aluminium and serum parathyroid hormone were measured prior to commencement of EPO therapy. Ninety-five patients were reassessed 5.2 +/- 0.3 (mean +/- SEM) months later and 53 patients underwent a further assessment 13.1 +/- 0.6 months after the commencement of EPO, giving an overall follow-up of 10.0 +/- 0.6 months in 95 patients. As expected, EPO treatment was associated with an increase in hemoglobin (7.7 +/- 0.1 vs. 9.9 +/- 0.2 g/dl; P < 0.001) and a decrease in ferritin (687 +/- 99 vs. 399 +/- 69 micrograms/liter; P < 0.01). A significant fall in total cholesterol occurred (5.8 +/- 0.1 vs. 5.4 +/- 0.2 mmol/liter; P < 0.05) in association with a fall in apoprotein B (1.15 +/- 0.04 vs. 1.04 +/- 0.06; P < 0.05) and serum triglycerides (2.26 +/- 0.14 vs. 1.99 +/- 0.21; P < 0.05) during the course of the study. Other lipid parameters did not change, although there was a trend towards improvement.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1994

Multicellular organization in a degradative biofilm community.

Diclofop methyl, a commercial herbicide, was used as the sole carbon source to cultivate diclofop-degrading biofilms in continuous-flow slide culture. The biofilms were analyzed by using scanning confocal laser microscopy and image analysis. Spatial relationships among members of the community were distinctive to diclofop-grown biofilms. These relationships did not develop when the biofilms were grown on more labile substrates but were conserved when the biofilms were cultivated with other chlorinated ring compounds. The structures included conical bacterial consortia rising to 30 mum above the surrounding biofilm, grape-like clusters of cocci embedded in a matrix of perpendicularly oriented bacilli, and other highly specific patterns of intra- and intergeneric cellular coaggregation and growth. These unique consortial relationships indicated that syntrophic interactions may be necessary for optimal degradation of diclofop methyl and other chlorinated ring compounds.

Journal Article↗
PubMed1994

Determination of diffusion coefficients in biofilms by confocal laser microscopy.

Microbial exopolymer may hinder the diffusion of nutrients, antibiotics, and other materials to the cell surface. Studies of diffusion in biofilms have been limited to indirect measurements. This study demonstrated the use of fluorescein and size-fractionated fluor-conjugated dextrans in conjunction with scanning confocal laser microscopy to directly monitor and determine diffusion coefficients within biofilms. The monitoring approaches were simple and, when combined with computerized image collection, allowed assembly of a data set suitable for calculation of one-dimensional diffusion coefficients for biofilm regions. With these techniques, it was shown that regional variability in the mobility of the dextrans occurred within mixed-species biofilms. Some regions exhibited rapid diffusion of all test molecules, while adjacent regions were only penetrated by the lower-molecular-weight compounds. The effective diffusion coefficients (D(e)) determined in a mixed-species biofilm were a function of the molecular radius of the probe (i.e., fluorescein, D(e) = 7.7 x 10 cm s; 4,000 molecular weight, D(e) = 3.1 x 10 cm s; and 2,000,000 molecular weight, D(e) = 0.7 x 10 cm s). These results demonstrated that diffusion in the biofilm was hindered relative to diffusion in the bulk solution. The study indicated that in situ monitoring by scanning laser microscopy is a useful approach for determining the mobility of fluorescently labeled molecules in biofilms, allowing image acquisition, appropriate scales of study, both xy and xz monitoring, and calculation of D(e) values.

Journal Article↗
PubMed1994

Effect of Motility on Surface Colonization and Reproductive Success of Pseudomonas fluorescens in Dual-Dilution Continuous Culture and Batch Culture Systems.

The colonization of glass surfaces by motile and nonmotile strains of Pseudomonas fluorescens was evaluated by using dual-dilution continuous culture (DDCC), competitive and noncompetitive attachment assays, and continuous-flow slide culture. Both strains possessed identical growth rates whether in the attached or planktonic state. Results of attachment assays using radiolabeled bacteria indicated that both strains obeyed first-order (monolayer) adsorption kinetics in pure culture. However, the motile strain attached about four times more rapidly and achieved higher final cell densities on surfaces than did the nonmotile strain (2.03 x 10 versus 5.57 x 10 cells vial) whether evaluated alone or in cocultures containing motile and nonmotile P. fluorescens. These kinetics were attributed to the increased transport of motile cells from the bulk aqueous phase to the hydrodynamic boundary layer where bacterial attachment, growth, and recolonization could occur. First-order attachment kinetics were also observed for both strains by using continuous-flow slide culture assays analyzed by image analysis. The DDCC system contained both aqueous and particulate phases which could be diluted independently. DDCC results indicated that when cocultures containing motile and nonmotile P. fluorescens colonized solid particles, the motile strain replaced the nonmotile strain in the system over time. Increasing the aqueous-phase rates of dilution decreased the time required for extinction of the nonmotile strain while concurrently decreasing the overall carrying capacity of the DDCC system for both strains. These results confirmed that bacterial motility conveyed a selective advantage during surface colonization even in aqueous-phase systems not dominated by laminar flow.

Journal Article↗
PubMed1994

The role of interactions, sessile growth and nutrient amendments on the degradative efficiency of a microbial consortium.

A degradative microbial consortium consisting of at least nine bacterial and one algal species was isolated from soil with diclofop methyl as the sole carbon source. In continuous flow culture, the presence of the algae increased diclofop methyl degradation and removal by 36%. Batch culture experiments with 14C-labeled diclofop methyl confirmed algal involvement in the mineralization of diclofop methyl as there was no significant difference in the amount of 14CO2 evolved by the bacterial consortium with and without the algal activity when the consortium was cultivated in the dark to inhibit algal growth, while 11% more 14CO2 was produced in the light by the algal-bacterial consortium. Pure cultures isolated from the bacterial consortium could not individually mineralize diclofop methyl as the sole carbon source. However, when supplied with an additional carbon source, two strains could mineralize diclofop methyl. Addition of either the complex growth medium, or a cell-free filtrate from the algal-bacterial consortium to batch systems containing 14C-labeled diclofop methyl resulted in a significant increase in the production of 14CO2 by the bacterial consortium, suggesting co-metabolism of diclofop methyl in the presence of a labile carbon source. Removal of diclofop methyl by the bacterial consortium was increased by 36% when a larger surface to volume ratio was provided by glass beads that allowed extensive biofilm formation. The requirement for exogenous carbon sources and the inability of isolated pure cultures to degrade diclofop methyl indicated that interspecies interactions are necessary for degradation. The positive effect of sessile growth suggested that spatial organization of cells may also be important for degradation.

Bacteria↗
PubMed1994

The evolution of the end-stage renal disease program in Australia.

Australia was an early pioneer of national integrated programs for the management of end-stage renal disease (ESRD). From being a leader in numbers of patients per population treated, it is now in the top 15. The Australian program has a high proportion of living patients with functioning transplants and a high proportion of out-of-hospital dialysis. The proportion of elderly patients is increasing but lower than expected. A particular problem is the treatment of Aboriginal people. The ANZ Data surveys give accurate complete data for the national program. Unique features of the Australian patients are the high incidence of analgesic nephropathy and the low incidence of primary hypertension as a cause of renal failure. Surveys show that it is possible to improve transplantation rates 2 to 3 times. Analysis of Australian data raises the question of whether dialysis and transplantation should be offered to all potential patients regardless of comorbidity or quality of life when health resources are inevitably finite.

Adult↗
PubMed1993

Development of steady-state diffusion gradients for the cultivation of degradative microbial consortia.

A diffusion gradient plate was constructed and evaluated for its potential use in the isolation of degradative microbial consortia from natural habitats. In this model, a steady-state concentration gradient of diclofop methyl, established by diffusion through an agarose gel, provided the carbon for microbial growth. Colonization of the gel surface was observed with epifluorescence and scanning confocal laser microscopy to determine microbial responses to the diclofop gradient. A detectable gradient developed over a narrow band (<10 mm). Consequently, quantitative analyses of the microbial response to the gradient were difficult to obtain. A two-dimensional, finite-element numerical transport model for advective-diffusive transport was used to simulate concentration and flux profiles in the physical model. The simulated profiles were correlated with the measured concentration gradient (R = 0.89) and the cell numbers on the gel surface (R = 0.85). The numerical model was subsequently used to redesign the physical model. The detectable concentration gradient in the modified physical model extended over the length of the gel (38 mm). The simulated profile again showed a good correlation with the measured profile (R = 0.96) and the microbial responses to the concentration gradient (R = 0.99). It was concluded that these gradients provide the steady-state environments needed to sustain steady-state consortia. They also provide a physical pathway for the development of degradative biofilms from low to high concentrations of toxicants and simulate conditions under which low concentrations of toxicant are supplied at a constant flux over long periods of time, such as the conditions that could occur in natural environments.

Journal Article↗
PubMed1992

Behavioral analysis of Vibrio parahaemolyticus variants in high- and low-viscosity microenvironments by use of digital image processing.

Digital image analysis and light microscopy were used to study and quantify the growth and behavior of two variants and selected flagellar mutants of Vibrio parahaemolyticus in glass flow cells under high- and low-viscosity conditions. The observations showed a series of surface-associated behaviors, including attachment, microcolony formation, migration, chemotactic movements, and aggregation, indicating a substantial degree of adaptive flexibility and multicellular behavior during growth of V. parahaemolyticus at interfaces.

Bacterial Adhesion↗
PubMed1991

Upholsterers' glue associated with myocarditis, hepatitis, acute renal failure and lymphoma.

A 20-year-old man with heavy exposure to upholsterers' glue presented with life-threatening acute myocarditis, and then rapidly developed acute hepatic necrosis and acute renal failure. He made a rapid and complete recovery from this florid acute illness, only to present three months later with supradiaphragmatic non-Hodgkin's lymphoma. These illnesses have all been described in association with solvent exposure. The unique feature of this case is the occurrence of multiple manifestations which might be attributed to solvent exposure, both acute and chronic, in the same individual.

Acute Kidney Injury↗
PubMed1991

Proteus mirabilis biofilm protection against struvite crystal dissolution and its implications in struvite urolithiasis.

Proteus mirabilis biofilm formation, struvite (MgNH4PO4.6H2O) crystal formation and dissolution in an artificial urine mixture were monitored using computer-enhanced microscopy (CEM) and a 1 x 3 mm. glass flow cell. Image analysis showed that P. mirabilis biofilm formation did not occur to any extent at macroenvironment flow rates greater than two mL/h (equivalent to a microenvironment flow rate of less than 5 microns./sec). Essentially, cells attached to glass surfaces, grew slowly and divided. Daughter cells were generally released directly into the medium where they could then presumably colonize other regions. Microcolonies formed by the adhesion of aggregates of cells from the medium, and over time grew into biofilms. Struvite crystallization due to urease activity and pH elevation above neutrality, was preceded by the deposition of organic matter on the glass surface, followed by the appearance of a number of tiny (one to two microns.) crystals. Crystals forming within a biofilm at low dilution rates took on a characteristic twinned or "X-shaped" appearance (crystal habit) indicative of a rapid growth rate. Those forming outside the biofilm took on a more tabular appearance reflecting their slower growth. When the macroenvironment flow rate of artificial urine (initial pH 5.8) in the glass flow cell was increased from two mL/h to four mL/h, struvite crystals not associated with biofilms dissolved within five to 10 min. Crystals entrapped within the P. mirabilis biofilm withstood flow rates up to 200 mL/h presumably due to the maintenance of an alkaline Mg-saturated microenvironment within the biofilm. These observations may suggest a mechanism by which struvite calculi can grow in spite of neutral or acidic urine pH and resist mild acidification therapy.

Bacterial Adhesion↗
PubMed1991

Optical sectioning of microbial biofilms.

Scanning confocal laser microscopy (SCLM) was used to visualize fully hydrated microbial biofilms. The improved rejection of out-of-focus haze and the increased resolution of SCLM made it preferable to conventional phase microscopy for the analysis of living biofilms. The extent of image improvement was dependent on the characteristics of individual biofilms and was most apparent when films were dispersed in three dimensions, when they were thick, and when they contained a high number of cells. SCLM optical sections were amenable to quantitative computer-enhanced microscopy analyses, with minimal interference originating from overlying or underlying cell material. By using SCLM in conjunction with viable negative fluorescence staining techniques, horizontal (xy) and sagittal (xz) sections of intact biofilms of Pseudomonas aeruginosa, Pseudomonas fluorescens, and Vibrio parahaemolyticus were obtained. These optical sections were then analyzed by image-processing techniques to assess the distribution of cellular and noncellular areas within the biofilm matrices. The Pseudomonas biofilms were most cell dense at their attachment surfaces and became increasingly diffuse near their outer regions, whereas the Vibrio biofilms exhibited the opposite trend. Biofilms consisting of different species exhibited distinctive arrangements of the major biofilm structural components (cellular and extracellular materials and space). In general, biofilms were found to be highly hydrated, open structures composed of 73 to 98% extracellular materials and space. The use of xz sectioning revealed more detail of biofilm structure, including the presence of large void spaces within the Vibrio biofilms. In addition, three-dimensional reconstructions of biofilms were constructed and were displayed as stereo pairs. Application of the concepts of architectural analysis to mixed- or pure-species biofilms will allow detailed examination of the relationships among biofilm structure, adaptation, and response to stress.

Image Processing, Computer-Assisted↗
PubMed1991

Tubular sodium handling and tubuloglomerular feedback in experimental diabetes mellitus.

Tubular Na handling and tubuloglomerular feedback (TGF) activity were assessed using micropuncture techniques during the hyperfiltration phase of streptozotocin-induced diabetes mellitus in Sprague-Dawley rats. Three animal groups were studied, designated as having severe diabetes [blood sugar level (BSL) 18-25 mmol/l], moderate diabetes (BSL 13-18 mmol/l) and control (BSL less than 10 mmol/l). Single-nephron glomerular filtration rate (SNGFR) measured at both late proximal (LP) and early distal (ED) sites was elevated in severe diabetes compared with both other groups. TGF activity, determined as the difference between LP and ED measurements of SNGFR, was significantly increased in severe diabetes (46.4 +/- 6.6 vs. 30.1 +/- 6.5 vs. 14.8 +/- 1.9 nl/min). Tubular Na transport was higher in severe diabetes compared with control, as demonstrated by a decrease in fractional delivery of Na to the LP (42.9 +/- 3.0 vs. 52.9 +/- 1.9%), as well as to the ED site (4.5 +/- 0.4 vs. 12.3 +/- 0.9%). Administration of phlorizin to severely diabetic animals resulted in a BSL comparable to that observed in moderate diabetes, and whole animal GFR, as well as SNGFR, TGF activity, and tubular Na handling were also similar to those found in moderate diabetes. Studies performed during mannitol infusion demonstrated that osmotic diuresis alone was not associated with the changes in TGF and tubular Na handling observed in the diabetic state. These data suggest that the hyperfiltration occurring in early diabetes is associated with enhanced proximal and loop resorption of Na independent of Na-glucose cotransport and osmotic diuresis. Activation of TGF serves to limit the rise in GFR, which results from factors as yet unrecognized in the diabetic state.

Animals↗