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The growth curve of Azotobacter vinelandii was biphasic when the organism was grown in a medium containing a mixture of galactose and glucose. Galactose was the primary carbon source; glucose was also consumed, but the rate at which it was consumed was lower than the rate at which galactose was consumed during the first phase of growth. Metabolic pathways for both sugars were induced. Cell cultures exhibited a second lag period as galactose was depleted. The length of this lag phase varied from 2 to 10 h depending on the pregrowth history of the cells. The second log growth phase occurred at the expense of the remaining glucose in the medium and was accompanied by induction of the high-maximum rate of metabolism glucose-induced glucose permease and increases in the levels of glucose metabolic enzymes. The second lag phase of diauxie may have been due to the time required for induction of the glucose-induced glucose permease.

In this work, the establishment of material balances and stoichiometry of the growth of Bacillus sp. was undertaken. This strain produces high quantities of a xylanase suitable for use as bleach boost agent in chlorine-free bleaching sequences of paper pulp. As carbon dioxide plays an important role as a growth factor, bacterial growth in two fermentations, one fed with air and another fed with carbon-dioxide-enriched air, were compared. For this purpose, a method permitting the determination of the consumption of the two carbon sources, xylan and peptone, was proposed. The material balances revealed that in both cases, the bacteria first use peptone as their carbon source, and then xylan in the second part of the growth phase. The aerated culture showed diauxic growth on these two substrates, whereas carbon-dioxide-enriched air caused disappearance of the metabolic adaptation phase, and rendered biomass production more economic. The fermentation fed with air needed 30% more xylan than the fermentation fed with carbon-dioxide-enriched air for the same quantity of biomass produced.Key words: Bacillus sp., carbon dioxide, material balances, diauxic growth.

Clostridium acetobutylicum, a promising organism for biomass transformation, has the capacity to utilize a wide variety of carbon sources. During pre-treatments of (ligno) cellulose through thermic and/or enzymatic processes, complex mixtures of oligo saccharides with beta 1,4-glycosidic bonds can be produced. In this paper, the capability of C. acetobutylicum to ferment glucose and cellobiose, alone and in mixtures was studied. Kinetic studies indicated that a diauxic growth occurs when both glucose and cellobiose are present in the medium. In mixtures, d-glucose is the preferred substrate even if cells were pre grown with cellobiose as the substrate. After the complete consumption of glucose, the growth kinetics exhibits an adaptation time, of few hours, before to be able to use cellobiose. Because of this diauxic phenomenon, the nature of the carbon source deriving from a cellulose hydrolysis pre-treatment could strongly influence the kinetic performances of a fermentation process with C. acetobutylicum.

We studied the following two aspects of the glucose effect on galactose operon expression in Escherichia coli K-12: catabolite repression and inducer exclusion. Using both inducible and constitutive strains and measuring the rate of promoter-proximal enzyme synthesis, we found that the galactose operon did not seem to exhibit catabolite repression. The only glucose effect on galactose operon expression which we observed was inducer exclusion, as shown by the existence of diauxic growth in the presence of glucose and galactose. This diauxie was not relieved by cyclic adenosine 3',5'-monophosphate. Cyclic adenosine 3',5'-monophosphate did not seem to be an antagonist of any glucose effect on galactose operon expression; its only effect was to stimulate promoter-distal gene expression.

Maximum L-asparaginase activity was obtained when 1.0% lactose and 1.5% yeast extract were supplied as carbon and nitrogen sources, respectively. Glucose inhibited the enzyme formation. The diauxie phenomenon was observed with Erwinia aroideae NRRL B-138 grown in a medium containing glucose and lactose.

A MUTANT of Salmonella typhimurium has been obtained by Engelsberg (unpublished) which was characterized as ‘diauxie-resistant’ since, in contrast to the wild type, it could adapt itself to normally inducing substrates in the presence of glucose. The mutant was found by Engelsberg and Entner (unpublished) to contain three times as much glucose-6-phosphatase as the wild type. This enzyme difference suggests that the diauxie phenomenon can be explained by an extension of the hypothesis of Racker et al. 1 concerning the Crabtree effect, where it was suggested that glucose inhibits the utilization of endogenous materials by competing for the phosphate-nucleotide (adenylate) pool.

The transport, fate and effects of many toxic chemicals in aquatic ecosystems are largely mediated by microbial transformations. In our research, we have assumed that the transformations are a result of enzymatic reactions, and thus follow Michaelis-Menten kinetics. Using diverse field-collected and laboratory microcosm microbiota, we obtained sufficient experimental data to reach some general conclusions concerning the strengths and weaknesses of using Michaelis-Menten kinetics in making environmental predictions. We concluded that this approach is best suited to predicting microbial transformations for pollutant concentrations of approximately 10−7 M or lower. The approach also is applicable to high pollutant concentrations (saturated systems), provided that toxic effects of the pollutant and adaptation are considered. Unfortunately, most experiments have been conducted in the upper 10−7 to 10−4 M pollutant concentration range, which may approach saturation for a portion of enzymatic systems in a mixed population. This range is ideal for analytical purposes, but could be confounded by mixed-order and multiphasic kinetics, toxic effects of the pollutant and adaptation. Adaptation, mass-transport effects, multiphasic kinetics of pollutant uptake and transformation, and suppression of transformation by diauxie, biologically produced inhibitors, and other xenobiotic chemicals are some of the factors that we believe need to be more thoroughly evaluated to improve predictive modeling capabilities.