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Biofilms of bacteria, indigenous to oil field produced water, were grown in square section, glass capillary flow cells at 45 degrees C. Initially, in situ image analysis microscopy revealed predominantly coccoid bacteria (length-to-width ratio measurements (l (c):w (c)) of bacterial cells gave a mean value of 1.1), while chemical measurements confirmed sulphate reduction and sulphide production. After nitrate ion addition at 100 and 80 mg/l, in the two repeat experiments respectively, the dominance of rod-shaped bacteria (mean l (c):w (c) = 2.8) was observed. This coincided with the occurrence of nitrate reduction in the treated flow cells. Beneficially, no significant increase in biofilm cover was observed after the addition of nitrate. The dominant culturable nitrate-reducing bacterium was Marinobacter aquaeolei. The l (c):w (c) ratio measured here concurs with previously reported cell dimensions for this organism. Several Marinobacter strains were also isolated from different oil fields in the North Sea where nitrate treatment has been applied to successfully treat reservoir souring, implying that this genus may play an important role in nitrate treatment.

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Sporocytophaga myxococcoides NCIB 8639 utilized a number of cellulosic substrates and produced extracellular carboxymethylcellulase and activity towards Avicel (a milled microcrystalline cellulose powder). Both types of enzyme were synthesized in media containing glucose but the activity was influenced by the nature and concentration of the carbon source. The ratio of carboxymethylcellulase activities measured by reducing sugar production and by viscosity decrease was also influenced by the nature of the cellulosic substrate supplied to cultures. The greatest extracellular enzyme production occurred in cultures grown on microcrystalline cellulose powders such as Avicel and Whatman CC3 1 at concentrations up to 4 % (w/v). The greatest degradation rate observed was in cultures supplied with Avicel where 60y0 of the substrate was degraded in 4 d.