Jean-Michel Lebeault

High efficiency styrene biodegradation in a biphasic organic/water continuous reactor

Styrene was degraded as sole source of carbon and energy by a selected bacterial community in a two-phase aqueous-organic medium (80%:20%, vol/vol). Silicone oil was used to solubilize styrene, which is sparingly soluble in water and to prevent its toxicity toward microorganisms. Preliminary studies with the mixed population in batch cultures indicate that the specific activity and the maximum growth rate at optimal 3H 6.0 were 46 mg·g−1·h−1 and 0.15 h−1, respectively. In pH-regulated chemostat cultures, styrene was degraded at dilution rates ranging from 0.05 to 0.20 h−1. Kinetic parameters and the proportion of each strain in the mixed culture were followed. At 0.20 h−1, only one strain as compared to four initially present, remained in the medium. This strain Pseudomonas aeruginosa, degrades styrene with a specific activity of 293 mg·g−1·h−1. Such results could lead to industrial treatment of waste gas or water polluted with styrene.

Interfacial area effects of a biphasic aqueous/organic system on growth kinetic of xenobiotic-degrading microorganisms

The activity of xenobiotic-degrading microorganisms is generally high in a biphasic aqueous/organic system. Therefore, the influence of interfacial area variation on kinetic parameters of Candida sp. growing on ethyl butyrate was evaluated. Interfacial areas of both aseptic and cultured biphasic systems were utilized. Substrate transport measurements in aseptic system (where the interface varied with the organic-phase fraction and agitator speed) showed that the substrate concentration in the aqueous phase was constant at different agitation speeds and decreased as the organic phase increased. Kinetic measurements of the cultured system showed that kinetic parameters vary as functions of their respective aseptic interfacial areas. Higher µmax and Ki and lower Ks values were obtained with larger interfacial areas. Measurements of the cultured system showed that the interfacial area increased as the biomass increased, and that about 50% of the biomass was attached to the interface as an interfacial biofilm at the end of the culture. Results suggest that the growth and selection of xenobiotic-degrading microorganisms in a biphasic aqueous/organic system should be evaluated mainly on the basis of the activity of adhering biomass (forming a biofilm) at the interfacial area rather than on substrate transport to the aqueous phase

Improvement of Escherichia coli strains overproducing lysine using recombinant DNA techniques

SummarySeveral genes of the lysine biosynthetic pathway were cloned separately on the high copy number plasmid pBR322 (Richaud et al. 1981). These hybrid plasmids were used to transform an Escherichia coli strain TOC R 21 that overproduces lysine due to mutations altering the aspartokinase reaction. The synthesis of lysine was studied in these different strains. It appears that only plasmids containing the dapA gene (encoding dihydrodipicolinate synthetase) lead to an increase in lysine production. This result allows us to identify this reaction as the limiting biosynthetic step in strain TOC R 21 and indicates that such a method of gene amplification can be used to improve strains overproducing metabolites.

Production of gallic acid from tara tannin by bacterial strains

SummaryBacterial strains identified as Klebsiella pneumonia and Corynebacterium sp. degraded in few hours a great part of pure tara (Caesalpinia spinosa) tannin or crude water extract of tara pods powder. Large amounts of gallic acid were recovered during some experiments reaching 55 % of the theoretical yield in the best case. The feasibility of gallic acid production by a biotechnological process is discussed.

Optimisation of the indirect impedancemetry technique; a handy technique for microbial growth measurement

In the indirect impedancemetry technique, the CO2 produced during biological activity reacts with potassium hydroxide (KOH) solution, providing negative conductance variation. In this work, this technique was optimized, on a rapid automated bacterial impedance technique (RABIT) apparatus, developed by Don Whitley Sc. Ltd (UK). The KOH concentration and volume, as well as the temperature were tested. The dynamics of CO2 absorption and the ratio between the conductance variation and the amount of CO2 produced were examined. After injection of CO2 either directly in the KOH solution, or above the KOH solution, the best results were obtained with a KOH volume corresponding to immersion of the electrodes (0.7–1.2 ml), and with KOH concentrations of up to 7 g/1, although 5–6 g/l is preferred. Decrease of 280 μS/μmol CO2 was obtained at 27°C for a KOH concentration ranging from 0.5 to 8 g/1. All these results were slightly affected by temperature. However, it would be preferable for the CO2 produced to be bubbled directly into the KOH solution, in order to decrease the dynamic response of the system (gaseous transfer).

Automatic method for evaluating the activity of sourdough strains based on gas pressure measurements

Abstract. A new method is proposed for the evaluation of the activity of sourdough strains, based on gas pressure measurements in closed air-tight reactors. Gas pressure and pH were monitored on-line during the cultivation of commercial yeasts and heterofermentative lactic acid bacteria on a semi-synthetic medium with glucose as the major carbon source. Relative gas pressure evolution was compared both to glucose consumption and to acidification and growth. It became obvious that gas pressure evolution is related to glucose consumption kinetics. For each strain, a correlation was made between maximum gas pressure variation and amount of glucose consumed. The mass balance of CO2 in both liquid and gas phase demonstrated that around 90% of CO2 was recovered. Concerning biomass production, a linear relationship was found between log colony-forming units/ml and log pressure for both yeasts and bacteria during the exponential phase; and for yeasts, relative gas pressure evolution also followed optical density variation.

An on-line technique for monitoring propionic acid fermentation.

An on-line technique, based on measuring the increase in pressure due to CO2 release in a closed air-tight reactor, was used to evaluate the fermentation of lactate by propionibacteria. The method was applied to batch cultures of Propionibacterium shermanii grown in yeast extract/sodium lactate medium containing lactate as a carbon source under micro-aerophilic conditions. Gas pressure evolution was compared both with substrate consumption and metabolites production and with acidification and growth. Linear relationships were found between gas pressure variation, lactate consumption and propionate and acetate production. The technique also enabled the evaluation of total CO2 produced, by taking account of pressure, oxygen and pH measurements. These results tend to show that this simple and rapid method could be useful to monitor propionic acid bacteria growth.

High efficiency of a coupled aerobic-anaerobic recycling biofilm reactor system in the degradation of recalcitrant chloroaromatic xenobiotic compounds

Abstract Chloroaromatic compounds are xenobiotics that cause great concern. The degradation of a model molecule, 3,4-dichlorobenzoate (3,4-DCB), was studied using three aerobic (AE)-anaerobic (AN) biofilm reactor systems: a coupled aerobic-anaerobic recycle biofilm reactor (CAR) system, an in-series anaerobic-aerobic biofilm reactor (SAR) system; and an independent aerobic and anaerobic biofilm reactor (IAR) system. In all three systems the inlet substrate concentration was 2.0 g/l and the dilution rates ranged from 0.045 to 0.142 per hour. The results show that the degradation efficiency of the CAR system (expressed as dechlorination and xenobiotic disappearance efficiencies, and biomass yield), was higher at all dilution rates tested than in both SAR and IAR systems. Moreover, dechlorination and xenobiotic disappearance efficiencies for resting suspended aerobic and anaerobic cells or mixed aerobic-anaerobic growing cells under anaerobic conditions were higher than under aerobic conditions. These results suggest that a “cooperative metabolism” between aerobic and anaerobic bacteria (caused by an exchange of cells and metabolites between AE and AN reactors) in the CAR system overcame the metabolic and kinetic limitations of aerobic and anaerobic bacteria in the AE and AN reactors of IAR and SAR systems. Therefore, the degradation efficiency of persistent and recalcitrant chloroaromatic xenobiotic compounds could be enhanced by using a CAR system.

Determination of Cellulose Surface Energy by Imbibition Experiments in Relation to Bacterial Adhesion

Abstract Bacterial adhesion is an important initiating step of microbial contamination in the paper and board industry. The adhesion process results from interactions between the cell surface, the liquid, and the fibers. In this context, we determined the cellulose pulp surface energy to better understand these interactions. As contact angles cannot be directly measured on cellulose fibers, experiments involving liquid imbibition into cellulose pulp sheets were performed. The results were interpreted in terms of Lifshitz–van der Waals (γs LW), electron‐donor (γs −), and electron‐acceptor (γs +) components of the surface energy. Results evidenced that cellulose fiber surface is characterized by significant electron‐donor capacity, as is the cell surface of the bacteria. These results suggests that hydrophobic, non‐specific type of interactions between the cell surface and cellulose are involved in this case.

Pressure measurement to evaluate ethanol or lactic acid production during glucose fermentation by yeast or heterofermentative bacteria in pure and mixed culture

Abstract. A rapid and simple technique to follow CO2 release during fermentation of glucose by heterofermentative bacteria or yeasts was used in order to evaluate ethanol and lactate production in pure and mixed cultures of yeast and bacteria. In pure cultures, good correlations were found between gas pressure variations (ΔP) and ethanol or lactate production by yeasts or heterofermentative bacteria, and ratios between ΔP and ethanol or lactate produced could be established. In mixed cultures, ratios between maximal ΔP and total amount of glucose consumed were determined. It was thus possible to evaluate the amount of glucose that was consumed by each strain and then deduce the bacterial lactate production. Good results were obtained for mixed cultures of yeast and homofermentative bacteria. This technique may be useful to evaluate the activity of strains in mixed cultures of yeast and lactic acid bacteria.