Acetone-butanol-ethanol (ABE) fermentation in an immobilized cell trickle bed reactor

Acetone-butanol-ethanol (ABE) fermentation was successfully carried out in an immobilized cell trickle bed reactor. The reactor was composed of two serial columns packed with Clostridium acetobutylicum ATCC 824 entrapped on the surface of natural sponge segments at a cell loading in the range of 2.03-5.56 g dry cells/g sponge. The average cell loading was 3.58 g dry cells/g sponge. Batch experiments indicated that a critical pH above 4.2 is necessary for the initiation of cell growth. One of the media used during continuous experiments consisted of a salt mixture alone and the other a nutrient medium containing a salt mixture with yeast extract and peptone. Effluent pH was controlled by supplying various fractions of the two different types of media. A nutrient medium fraction above 0.6 was crucial for successful fermentation in a trickle bed reactor. The nutrient medium fraction is the ratio of the volume of the nutrient medium to the total volume of nutrient plus salt medium. Supplying nutrient medium to both columns continuously was an effective way to meet both pH and nutrient requirement. A 257-mL reactor could ferment 45 g/L glucose from an initial concentration of 60 g/L glucose at a rate of 70 mL/h. Butanol, acetone, and ethanol concentrations were 8.82, 5.22, and 1.45 g/L, respectively, with a butanol and total solvent yield of 19.4 and 34.1 wt %. Solvent productivity in an immobilized cell trickle bed reactor was 4.2 g/L h, which was 10 times higher than that obtained in a batch fermentation using free cells and 2.76 times higher than that of an immobilized CSTR. If the nutrient medium fraction was below 0.6 and the pH was below 4.2, the system degenerated. Oxygen also contributed to the system degeneration. Upon degeneration, glucose consumption and solvent yield decreased to 30.9 g/L and 23.0 wt %, respectively. The yield of total liquid product (40.0 wt %) and butanol selectivity (60.0 wt %) remained almost constant. Once the cells were degenerated, they could not be recovered.     

Characterization of an HSP70 Cognate Gene Family in Arabidopsis

Analysis of the polypeptide composition of extracts from heat-shocked leaves of Arabidopsis indicated the presence of at least 12 HSP70-related polypeptides, most of which were constitutively expressed. In vitro translation of mRNA from heat-shocked and control leaves indicated that the amount of mRNA encoding four HSP70 polypeptides was increased strongly by heat-shock. Three Arabidopsis genes which exhibit homology to a Drosophila HSP70 gene were cloned. Two of the three genes are arranged in direct orientation approximately 1.5 kilobases apart. The third gene is not closely linked to the other two. Nucleotide sequence analysis of the 5′ regions of the two linked genes revealed that both contain a TATA box, the CAAT motif, and several short sequences which are homologous to the Drosophila heat-shock consensus sequence. The deduced partial amino acid sequence of the open reading frames were 79 and 72% homologous to the corresponding regions of the Drosophila HSP70-cognate and HSP70 sequences, respectively. As with the two maize HSP70 genes which have been characterized, and the Drosophila HSP70-cognate genes, the Arabidopsis genes contained a putative intron in the codon specifying amino acid 72. Analysis of mRNA levels with gene-specific oligonucleotide probes indicated that two of the genes were not expressed or were expressed at very low levels in leaves during normal growth or after heat-shock, whereas the other gene was constitutively expressed. By analogy with the results of similar studies of other organisms, it appears that the three cloned genes are members of a small family which are most closely related to the HSP70-cognate genes found in other species.     

Translational alterations in maize leaves responding to pathogen infection, paraquat treatment, or heat shock : polysome dissociation and accumulation of a 57 kilodalton protein

Translational alterations occur in maize (Zea mays L.) leaves stressed by pathogen infection or herbicide paraquat treatment. These translational changes include: (a) dissociation of large polysomes to small polysomes, monosomes, and subunits; (b) a decreased rate of total protein synthesis; and (c) a reduced synthesis of several proteins by polysomes in vitro. The polysome dissociation was neither due to an extraction artifact nor to degradation of RNA by RNase. The protein patterns of polysomes isolated from leaves inoculated with Bipolaris maydis at 6 to 48 hours showed an increase in the intensity of a 57 kilodalton protein. When inoculated with less virulent pathogens, such as B. zeicola, Exserohilum turcicum, or Colletotrichum graminicola, the protein was accumulated in polysomes of leaves at 24 to 48 hours after inoculation. The 57 kilodalton protein was also accumulated in polysomes of maize leaves responding to heat shock or herbicide paraquat treatments. The purified 57 kilodalton protein reassociated with polysomes isolated from healthy leaves and inhibited polysomal translation in vitro. Since the 57 kilodalton protein is rapidly accumulated in maize polysomes in response to various biological and environmental stresses and may affect protein synthesis, it may be involved in translational regulation of maize leaves during stress response.     

Action Spectrum for Resetting the Circadian Phototaxis Rhythm in the CW15 Strain of Chlamydomonas: II. Illuminated Cells

The action spectrum for resetting the phase of the circadian clock in Chlamydomonas reinhardtii is different depending upon whether the light stimuli are presented to cells that were in darkness versus dim illumination before stimulation. In this report, we show that phase resetting of illuminated cells appears to be mediated by components of the photosynthetic apparatus. This conclusion is based upon the action spectrum for phase-shifting illuminated cells (which looks like that for photosynthesis) and upon the fact that inhibitors of photosynthetic electron transport also inhibit the light-induced phase shift of illuminated cells. Both of these characteristics differ from that of cells taken from darkness. We, therefore, believe that at least two resetting pathways for this circadian clock exist and that both of these pathways are ecologically significant.