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Sets of time lapse sequences (movies) of pseudomonad cells attaching in each of six flowcells operated at Reynolds numbers from 96 – 2220 were obtained over a 3-d period. The interval between images varied between 1 s and 24 min, which allowed a range of different cell behaviours to be observed. The rate of accumulation of the cells on the surface was determined for each flowrate. Analysis of the images showed that the residence time distributions of the attaching cells were of the same form as those recorded previously in the literature. This showed that up to 50% of the cells that arrived sufficiently close to the surface to be considered temporarily attached, left the surface within 1 s of arrival. Use of an analytically derived algorithm allowed the rate of arrival of the cells to be estimated. Data showed that for every cell attaching on a relatively permanent basis, between 20 and 35 cells arrived at the surface.

Fluid flow has been shown to be important in influencing biofilm morphology and causing biofilms to flow over surfaces in flow cell experiments. However, it is not known whether similar effects may occur in porous media. Generally, it is assumed that the primary transport mechanism for biomass in porous media is through convection, as suspended particulates (cells and flocs) carried by fluid flowing through the interstices. However, the flow of biofilms over the surfaces of soils and sediment particles, may represent an important flux of biomass, and subsequently affect both biological activity and permeability. Mixed species bacterial biofilms were grown in glass flow cells packed with 1 mm diameter glass beads, under laminar or turbulent flow (porous media Reynolds number = 20 and 200 respectively). The morphology and dynamic behavior reflected those of biofilms grown in the open flow cells. The laminar biofilm was relatively uniform and after 23 d had inundated the majority of the pore spaces. Under turbulent flow the biofilm accumulated primarily in protected regions at contact points between the beads and formed streamers that trailed from the leeward face. Both biofilms caused a 2 to 3-fold increase in friction factor and in both cases there were sudden reductions in friction factor followed by rapid recovery, suggesting periodic sloughing and regrowth events. Time-lapse microscopy revealed that under both laminar and turbulent conditions biofilms flowed over the surface of the porous media. In some instances ripple structures formed. The velocity of biofilm flow was on the order of 10 mum h(-1) in the turbulent flow cell and 1.0 mum h(-1) in the laminar flow cell.

After a needs assessment indicated that male students underutilized campus health services, the San Francisco State University Student Health Service developed a coordinated complement of outpatient health services for men. The authors review their experience in developing, implementing, operating, and evaluating this ongoing clinical service. The needs assessment and subsequent program evaluation data suggest that male students on a large, culturally diverse, urban campus would respond favorably to targeted, multidisciplinary health initiatives that incorporate the principles of health promotion and disease prevention.

Summary Four aquatic hyphomycetes and one terrestrial fungus were examined for their responses to the phenoxy herbicides (±)-MCPP and 2,4-D as both single and binary preparations with respect to hyphal extension, sporulation and respiration. Hyphal extension of all species was unaffected at concentrations less than 100 mg l−1. At higher concentrations there was a variable inhibitory response to the herbicides but no clear pattern was observed between the five fungi. The binary herbicide mixture had a weak synergistic effect on inhibition of growth rate. For the four aquatic hyphomycetes sporulation was reduced at several herbicide concentrations, but there was no consistent reduction over the experimental period. Flagellospora curvula and Clavariopsis aquatica showed increased sporulation at 100 and 1000 mg l−1 for only some herbicide combinations. The respiration rates of the fungi varied with species and herbicide concentration and ranged between stimulation at 100 mg l−1 to inhibition at 4000 mg l−1. T...

The application of confocal scanning laser microscopy (CSLM) to biofilm research has provided detailed new information on the structural complexity of fully hydrated living biofilms. Biofilms studied by CSLM are widely reported to be heterogeneous and consist of micro‐colonies or cell clusters (aggregates of microbial cells in an extracellular polysaccharide matrix) separated by interstitial voids and channels. CSLM combined with molecular probing can identify the distribution of individual species within biofilms, while CSLM combined with microelectrodes and particle tracking has demonstrated the significance of structural heterogeneity on mass transfer in biofilms. In this review the contribution that CSLM has made towards the development of conceptual and mathematical biofilm models over the last decade is discussed. The significance of biofilm structural heterogeneity to understanding of mass transfer processes in biofilm systems and the fundamental significance of hydrodynamics in shaping biofilm str...

A bacterial consortium containing thermophilic sulfidogens was obtained from filtration of produced fluids from a North Sea oil production facility. It was subjected to two distinct starvation regimes considered to be representative of those that might be experienced by such organisms surviving either (a) in open seawater prior to injection into the formation with secondary recovery fluids, or (b) in secondary recovery water‐floods deep in the reservoir. Metabolic activity measurements and resuscitation data together with scanning electron microscopy indicate survival for 21 months with no available carbon source. Survival was measured by the starved cells’ ability to reduce intracellularly the metabolic indicator INT to INT‐formazan. By this method, starvation survival was demonstrated in all samples tested over the experimental period (up to 21 months). The indication of such ability was not consistently accompanied by resuscitation and growth in media previously used for culture maintenance and propaga...

Sulphidogenic bacteria in oil reservoirs are of great economic importance in terms of souring, fouling and corrosion. Mixed cultures containing these bacteria were isolated from chalk formations in North Sea oil reservoirs. These were thermophilic cultures, growing optimally at 60°C. Oil formations are porous matrices, providing a very large surface area and ideal conditions for bacterial attachment, survival and growth. This study included assessments of sulphide production rates of thermophilic (t-)sulphidogen consortia with and without additional surfaces. The availability of a surface contributed significantly to the rate and extent of sulphide generation. Surfaces were offered in varying amounts to growing planktonic cultures: significantly more sulphide was produced from cultures in contact with a surface than from identical cultures in the absence of a surface. In another series of experiments, t-sulphidogens were added to chalk rock chips in the presence of nutrients and incubated for several months. This resulted in rapid sulphide generation, the final concentration being related to the initial nutrient concentration. Subsequent nutrient addition resulted in renewed sulphide generation. It is suggested that bacteria in reservoirs can withstand long periods of nutrient deprivation while attached within the porous rock matrix and opportunistically utilise nutrients when they become available.