The transcriptional activator XlnR from Aspergillus niger is a zinc binuclear cluster transcription factor that belongs to the GAL4 superfamily. Several putative structural domains in XlnR were predicted using database and protein sequence analysis. Thus far, only the functionality of the N-terminal DNA-binding domain has been determined experimentally. Deletion mutants of the xlnR gene were constructed to localize the functional regions of the protein. The results showed that a putative C-terminal coiled-coil region is involved in nuclear import of XlnR. After deletion of the C-terminus, including the coiled-coil region, XlnR was found in the cytoplasm, while deletion of the C-terminus downstream of the coiled-coil region resulted in nuclear import of XlnR. The latter mutant also showed increased xylanase activity, indicating the presence of a region with an inhibitory function in XlnR-controlled transcription. Previous findings had already shown that a mutation in the XlnR C-terminal region resulted in transcription of the structural genes under non-inducing conditions. A regulatory model of XlnR is presented in which the C-terminus responds to repressing signals, resulting in an inactive state of the protein.

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Clostridium thermocellum is a thermophilic, cellulolytic anaerobe that is a candidate microorganism for industrial biofuels production. Strains with mutations in genes associated with production of L-lactate (Δldh) and/or acetate (Δpta) were characterized to gain insight into the intracellular processes that convert cellobiose to ethanol and other fermentation end-products. Cellobiose-grown cultures of the Δldh strain had identical biomass accumulation, fermentation end-products, transcription profile, and intracellular metabolite concentrations compared to its parent strain (DSM1313 Δhpt Δspo0A). The Δpta-deficient strain grew slower and had 30 % lower final biomass concentration compared to the parent strain, yet produced 75 % more ethanol. A Δldh Δpta double-mutant strain evolved for faster growth had a growth rate and ethanol yield comparable to the parent strain, whereas its biomass accumulation was comparable to Δpta. Free amino acids were secreted by all examined strains, with both Δpta strains secreting higher amounts of alanine, valine, isoleucine, proline, glutamine, and threonine. Valine concentration for Δldh Δpta reached 5 mM by the end of growth, or 2.7 % of the substrate carbon utilized. These secreted amino acid concentrations correlate with increased intracellular pyruvate concentrations, up to sixfold in the Δpta and 16-fold in the Δldh Δpta strain. We hypothesize that the deletions in fermentation end-product pathways result in an intracellular redox imbalance, which the organism attempts to relieve, in part by recycling NADP⁺ through increased production of amino acids.

Botryococcus braunii can produce both long-chain hydrocarbons as well as carbohydrates in large quantities, and is therefore a promising industrial organism for the production of biopolymer building blocks. Many studies describe the use of different strains of Botryococcus braunii but differences in handling and cultivation conditions make the comparison between strains difficult. In this study, 16 B. braunii strains obtained from six culture collections were compared for their biomass productivity and hydrocarbon and carbohydrate content. Biomass productivity was highest for AC768 strain with 1.8gLday, while hydrocarbon production ranged from none to up to 42% per gram biomass dry weight, with Showa showing the highest hydrocarbon content followed by AC761. The total carbohydrate content varied from 20% to 76% per gram of the biomass dry weight, with CCALA777 as the highest producer. Glucose and galactose are the main monosaccharides in most strains and fucose content reached 463mgL in CCALA778.