The production of crystals and spores ofBacillus thuringiensis var.israelensis was studied under different aeration conditions. The results with 4 l batch cultures showed that for O2 non-limited, cultures cell yield, toxin production and spore count were constant for all oxygen transfer rates (OTR). Under O2 limitation, °-endotoxin concentrations and spore counts were lower than those obtained in non-limited cultures. In addition, δ-endotoxin yields diminished under O2 limitation, suggesting that the toxin synthesis mechanism could have been affected.

Acetobacter diazotrophicus is a diazotrophic bacterium that colonizes sugarcane tissues. Glucose is oxidized to gluconate in the periplasm prior to uptake and metabolism. A membrane-bound glucose dehydrogenase quinoenzyme [which contains pyrroloquinoline quinone (PQQ) as the prosthetic group] is involved in that oxidation. Gluconate is oxidized further via the hexose monophosphate pathway and tricarboxylic acid cycle. A. diazotrophicus PAL3 was grown in a chemostat with atmospheric nitrogen as the sole N source provided that the dissolved oxygen was maintained at 1.0-2.0% air saturation. The biomass yields of A. diazotrophicus growing with glucose or gluconate with fixed N were very low compared with other heterotrophic bacteria. The biomass yields under N-fixing conditions were more than 30% less than with ammonium as the N source using gluconate as the carbon source but, surprisingly, were only about 14% less with glucose. The following scheme for the metabolism of A. diazotrophicus through the different pathways emerged: (1) the respiratory chain of this organism had a different efficiency of ATP production in the respiratory chain (P:O ratio) under different culture conditions; and (2) N fixation was one (but not the sole) condition under which a higher P:O ratio was observed. The other condition appears to be the expression of an active PQQ-linked glucose dehydrogenase.

Geotrichum klebahnii ATCC 42397 produces a protopectinase ( PPase -SE ) with polygalacturonase ( PGase ) activity. The microorganism was aerobically cultivated in synthetic media. Glucose, fructose and xylose yielded the highest enzyme levels ( 10 ± 11 PGase units ml À 1 ) . Galacturonic acid repressed enzyme production and no growth was obtained with disaccharides and pectin. Specific enzyme activity obtained in an O 2 -limited culture was similar to that found in nonlimited ones. A growth yield ( Y x / s ) of 0.49 g of cell dry weight per gram of glucose consumed was obtained in a typical batch bioreactor culture. Enzyme production was growth associated, and no major products other than biomass and CO 2 were detected. The volumetric enzyme activity reached a maximum around D = 0.3 ± 0.4 h À 1 in glucose -limited continuous cultures. However, it varied strongly ( together with microorganism morphology ) even after retention times ! ! ! ! ! !8 at any D tested ( 0.035 ± 0.44 h À 1 ) though the rest of the culture variables remained fairly constant. No correlation between morphology and enzyme activity could be obtained. Enzyme production was poor in urea -and vitamin -limited continuous cultures. In all cases, biomass and CO 2 accounted for 100% of carbon recovery though Y x / s values were different.

The glucose carbon fluxes in continuous cultures of Bacillus thuringiensis grown in a complex medium have been studied as a function of the growth rate. The results are discussed in the light of a growth model. From reduced nicotinamide adenine dinucleotide (NADH) and carbon balances it was determined that the fraction of glucose consumed for biomass synthesis decreased with the growth rate, while the glucose flux through the tricarboxylic acid (TCA) cycle diminished after a threshold value of D"0.34 h~1, where D"dilution rate. At the highest growth rate tested, glucose was used almost exclusively as the energy source, via fermentative pathways, which indicates that the yeast extract was used as the carbon source. The specific rate of oxygen consumption increased with growth even after the beginning of the accumulation of acids, indicating that the respiratory chain was not saturated. The results suggest that there is a mismatch between glycolysis and TCA cycle capacity, depending on the growth rate. Furthermore, values of (P/O) ratio and m ATP are presented, where (P/O) is mole of ATP formed per gram atom oxygen consumed by the respiratory chains and m ATP is the maintenance requirement for ATP.