Browsing by Author "Okabe, Satoshi"

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Anaerobic srb biofilms in industrial water systems: a process analysis
(1993) Okabe, Satoshi; Jones, Warren L.; Lee, Whonchee; Characklis, William G.
Corrosion of mild steel underneath aerobic biofilms containing sulfate-reducing bacteria. part i: at low dissolved oxygen concentration
(1993-11) Lee, Whonchee; Lewandowski, Zbigniew; Okabe, Satoshi; Characklis, William G.; Avci, Recep; Nielsen, P. H.
The sulfate‐reducing bacteria (SRB)‐enhanced corrosion of mild steel in the presence of 1.5 mg·l−1 dissolved oxygen (DO) in bulk liquid was investigated. The biofilm process analysis was combined with microelectrode measurements, electrochemical measurements, and surface analysis. In the early stages of biofilm accumulation, the cathodic polarization and the decreasing corrosion rate were attributed to DO consumption by aerobic bacteria. During that time, limited SRB activity was observed. The DO concentration near the steel surface was between 0.6 and 1 mg·l−1. After total depletion of dissolved oxygen near the steel surface, the cathodic depolarization and the increased corrosion rate were associated with the proliferation of SRB near the steel surface. Auger electron spectroscopy analysis indicated localized sulfide attack. High pit density appeared where the coincidence of oxygen and sulfur occurred. The bottom of the pit was enriched with sulfur.
Effects of temperature and phosphorous concentration on microbial sulfate reduction by desulfovibrio desulfuricans
(1992-04) Okabe, Satoshi; Characklis, William G.
The effects of temperature and phosphorous concentration on the rate and the extent of microbial sulfate reduction with lactate as carbon and energy source were investigated for Desulfovibrio desulfuricans. The continuous culture experiments (chemostat) were conducted at pH 7.0 from 12 to 48°C. The maximum specific growth rate (μmax) was relatively constant in the range 25°C–43°C and dramatically decreased outside this temperature range. The half-saturation coefficient was minimum at 25°C. Cell yield was highest in the optimum temperature range (35°C–43°C) for growth. Maintenance energy requirements for D. desulfuricans were not significant. Two moles of lactate is consumed for every mole of sulfate reduced, and this stoichiometric ratio is not temperature dependent. Steady state rate and stoichiometric coefficients accurately predicted transient behavior during temperature shifts. The extent of extracellular polymeric substance (EPS) is related to the concentration of phosphorous in the medium. EPS production rate increased with decreased phosphorous loading rate. Failure to discriminate between cell and EPS formation by D. desulfuricans leads to significant overestimates of the cell yield. The limiting C:P ratio for D. desulfuricans was in the range of 400:1 to 800:1.
Estimation of cellular and extracellular carbon contents in sulfate-reducing bacteria biofilms by lipopolysaccharide assay and epifluorescence microscopic techni
(1994-11) Okabe, Satoshi; Nielsen, P. H.; Jones, Warren L.
Measurement of cellular and extracellular carbon contents of sulfate-reducing bacteria (SRB) is essential and important in studies of the role of SRB in corrosion and biofouling. An epifluorescence (EPI) microscopic technique and a lipopolysaccharide (LPS) assay were used to quantify cellular and extracellular carbon contents in Desulfovibrio desulfuricans biofilms. The average contents of lipopolysaccharide (LPS) and cellular carbon were 7.3 ± 2.8 (fg LPS) cell−1 and 39.9 ± 9.9 (fg cellular-C) cell−1, respectively, in a D. desulfuricans chemostat culture. A ratio of cellular carbon content to LPS content was 6.5 ± 2.8, and was used to estimate cellular carbon contents in a D. desulfuricans biofilm. The LPS and EPI methods gave comparable results for suspended samples, but not for biofilm samples.
Factors affecting microbial sulfate reduction by desulfovibrio desulfuricans in continuous culture: limiting nutrients and sulfide concentration
(1992-09) Okabe, Satoshi; Nielsen, P. H.; Characklis, William G.
The effects of sulfate and nitrogen concentrations of the rate and stoichiometry of microbial sulfate reduction were investigated for Desulfovibrio desulfuricans grown on lactate and sulfate in a chemostat at pH 7.0. Maximum specific growth rates (μmax), half-saturation coefficients (Ksul), and cell yield (Yc/Lac) of 0.344 ± 0.007 and 0.352 ± 0.003 h −1, 1.8 ± 0.3 and 1.0 ± 0.2 mg/L, and 0.020 ± 0.003 and 0.017 ± 0.003 g cell/g lactate, respectively, were obtained under sulfate-limiting conditions at 35°C and 43°C. Maintenance energy requirements for D. desulfuricans were significant under sulfate-limiting conditions. The extent of extracellular polymeric substance (EPS) produced was related to the carbon: nitrogen ratio in the medium. EPS production rate increased with decreased nitrogen loading rate. Nitrogen starvation also resulted in decreased cell size of D. desulfuricans. The limiting C : N ratio (w/w) for D. desulfuricans was in the range of 45 : 1 to 120 : 1. Effects of sulfide on microbial sulfate reduction, cell size, and biomass production were also ivestigated at pH 7.0. Fifty percent inhibition of lactate utilization occurred at a total sulfide concentration of approximately 500 mg/L. The cell size of D. desulfuricans decreased with increasing total sulfide concentration. Sulfide inhibition of D. desulfuricans was observed to be a reversible process.
Rate and stoichiometry of sulfate reducing bacteria in suspended and biofilm cultures
(Montana State University - Bozeman, College of Engineering, 1992) Okabe, Satoshi
Sulfide product inhibition of desulfovibrio desulfuricans in batch and continuous cultures
(1995-02) Okabe, Satoshi; Nielsen, P. H.; Jones, Warren L.; Characklis, William G.
Sulfide product inhibition kinetics for growth and activity of Desulfovibrio desulfuricans was investigated in batch and continuous cultures at pH = 7.0. A non-competitive inhibition model adequately described sulfide product inhibition kinetics. Inhibition coefficient (Ki) for maximum specific growth rate (μinhmax) was 251 mg l−1 S in a batch experiment. Cell yield determined in a chemostat was reduced in half by a sulfide concentration of about 250 mg l−1 S, which was very close to the Ki value for the batch growth. Maximum specific growth rate (μinhmax) and cell yield (YcLac) were strongly inhibited by high levels of sulfide concentrations, whereas specific lactate utilization rate increased with increasing sulfide concentrations. The results indicated an increase in the relative energy needed for maintenance to overcome sulfide inhibition and uncoupling growth from energy production. However, D. desulfuricans to some extent could recover from the shock of high sulfide concentrations. Stoichiometry for catabolic reactions (energy producing) did not change at high sulfide concentrations, while anabolic reactions (cellular synthesis) were strongly inhibited by high sulfide concentrations. These results suggested that separation of sulfide product inhibition into growth (cell yield) and activity (substrate utilization rate) was important to incorporate the sulfide product inhibition kinetics in a variety of applications.