Succinic acid-producing biofilms of Actinobacillus succinogenes: reproducibility, stability and productivity.

Continuous anaerobic fermentations were performed in a biofilm reactor packed with Poraver® beads. Dilution rates (D) varied between 0.054 and 0.72 h(-1), and D-glucose and CO2 gas were used as carbon substrates. Steady-state conditions were shown to be repeatable and independent of the operational history. Production stability was achieved over periods exceeding 80 h at values of D below 0.32 h(-1). In these situations, steady-state variation (expressed as fluctuations in NaOH neutralisation flow rates) exhibited a standard deviation of less than 5 % while no indication of biofilm deactivation was detected. The total biomass amount was found to be independent of the dilution rate with an average dry concentration of 23.8 ± 2.9 g L(-1) obtained for all runs. This suggests that the attachment area controls the extent of biofilm accumulation. Specific succinic acid (SA) productivities, based on the total biomass amount, exhibited a substantial decrease with decreasing D. An SA volumetric productivity of 10.8 g L(-1) h(-1) was obtained at D = 0.7 h(-1)-the highest value reported to date in Actinobacillus succinogenes fermentations. SA yields on glucose increased with decreasing D, with a yield of 0.90 ± 0.01 g g(-1) obtained at a D of 0.054 h(-1). Production of formic acid approached zero with decreasing D, while the succinic to acetic acid ratio increased with decreasing D, resulting in an increasing SA yield on glucose.

Effect of nighttime temperature on tomato plant defensive chemistry.

Given that the amplitude of diurnal temperature fluctuations has been decreasing, mainly via warmer night temperatures, we examined the effects of nighttime temperature on concentration of the catecholic phenolics chlorogenic acid and rutin in tomato plants. A two-factor design, with carbon dioxide (350 ppm and 700 ppm) and nighttime temperature (14, 15, 16, 17, and 18 degrees C, with a 26 degrees C daytime temperature) was used. Compared to the lower carbon dioxide level, for whole plants the concentration of phenolics was lower at the higher carbon dioxide level, but patterns for plant parts differed. Nighttime temperature did not affect concentration of phenolics for whole plants, but it did influence concentration of the phenolics for plant parts, although not in predictable ways. Furthermore, the pattern of concentration of chlorogenic acid was somewhat different from that of rutin. The amount of change in concentration of these allelochemicals is likely sufficient to have substantial effects on insect herbivores. We conclude that nighttime temperature affects concentration of allelochemicals in tomato plants in significant ways.