Anaerobic growth of Pseudomonas aeruginosa PAO1 was affected by quorum sensing. Deletion of genes that produce N -acyl- l -homoserine lactone signals resulted in an increase in denitrification activity, which was repressed by exogenous signal molecules. The effect of the las quorum-sensing system was dependent on the rhl quorum-sensing system in regulating denitrification.

Background: Bioethanol isolated from lignocellulosic biomass represents one of the most promising renewable and carbon neutral alternative liquid fuel sources. Enzymatic saccharification using cellulase has proven to be a useful method in the production of bioethanol. The filamentous fungi Acremonium cellulolyticus and Trichoderma reesei are known to be potential cellulase producers. In this study, we aimed to reveal the advantages and disadvantages of the cellulase enzymes derived from these fungi. Results: We compared A. cellulolyticus and T. reesei cellulase activity against the three lignocellulosic materials: eucalyptus, Douglas fir and rice straw. Saccharification analysis using the supernatant from each culture demonstrated that the enzyme mixture derived from A. cellulolyticus exhibited 2-fold and 16-fold increases in Filter Paper enzyme and β-glucosidase specific activities, respectively, compared with that derived from T. reesei. In addition, culture supernatant from A. cellulolyticus produced glucose more rapidly from the lignocellulosic materials. Meanwhile, culture supernatant derived from T. reesei exhibited a 2-fold higher xylan-hydrolyzing activity and produced more xylose from eucalyptus (72% yield) and rice straw (43% yield). Although the commercial enzymes Acremonium cellulase (derived from A. cellulolyticus, Meiji Seika Co.) demonstrated a slightly lower cellulase specific activity than Accellerase 1000 (derived from T. reesei, Genencor), the glucose yield (over 65%) from lignocellulosic materials by Acremonium cellulase was higher than that of Accellerase 1000 (less than 60%). In addition, the mannan-hydrolyzing activity of Acremonium cellulase was 16-fold higher than that of Accellerase 1000, and the conversion of mannan to mannobiose and mannose by Acremonium cellulase was more efficient. Conclusion: We investigated the hydrolysis of lignocellulosic materials by cellulase derived from two types of filamentous fungi. We found that glucan-hydrolyzing activity of the culture supernatant from A. cellulolyticus was superior to that from T. reesei, while the xylan-hydrolyzing activity was superior for the cellulase from T. reesei. Moreover, Acremonium cellulase exhibited a greater glucan and mannan-hydrolyzing activity than Accellerase 1000.

Although branched-chain amino acids are synthesized as building blocks of proteins, we found that the fungus Aspergillus nidulans excretes them into the culture medium under hypoxia. The transcription of predicted genes for synthesizing branched-chain amino acids was upregulated by hypoxia. A knockout strain of the gene encoding the large subunit of acetohydroxy acid synthase (AHAS), which catalyzes the initial reaction of the synthesis, required branched-chain amino acids for growth and excreted very little of them. Pyruvate, a substrate for AHAS, increased the amount of hypoxic excretion in the wild-type strain. These results indicated that the fungus responds to hypoxia by synthesizing branched-chain amino acids via a de novo mechanism. We also found that the small subunit of AHAS regulated hypoxic branched-chain amino acid production as well as cellular AHAS activity. The AHAS knockout resulted in higher ratios of NADH/NAD ⁺ and NADPH/NADP ⁺ under hypoxia, indicating that the branched-chain amino acid synthesis contributed to NAD ⁺ and NADP ⁺ regeneration. The production of branched-chain amino acids and the hypoxic induction of involved genes were partly repressed in the presence of glucose, where cells produced ethanol and lactate and increased levels of lactate dehydrogenase activity. These indicated that hypoxic branched-chain amino acid synthesis is a unique alternative mechanism that functions in the absence of glucose-to-ethanol/lactate fermentation and oxygen respiration.

Acremonium cellulolyticus is one of several fungi that offer promise as an alternative to Trichoderma reesei for use in industrial cellulase production. However, the mechanism of cellulase production has not been studied at the molecular level because adequate genetic engineering tools for use in A. cellulolyticus are lacking. In the present study, we developed a gene disruption method for A. cellulolyticus, which needs a longer homologous region length. We cloned a putative A. cellulolyticus creA gene that is highly similar to the creA genes derived from other filamentous fungi, and isolated a creA disruptant strain by using the disruption method. Growth of the creA disruptant on agar plates was slower than that of the control strain. In the wild-type strain, the CreA protein was localized in the nucleus, suggesting that the cloned gene encodes the CreA transcription factor. Cellulase and xylanase production by the creA disruptant were higher than that of the control strain at the enzyme and transcription levels. Furthermore, the creA disruptant produced cellulase and xylanase in the presence of glucose. These data suggest both that the CreA protein functions as a catabolite repressor protein, and that disruption of creA is effective for enhancing enzyme production by A. cellulolyticus.

We propose that the cellulose-degrading fungus Acremonium cellulolyticus nomen nudum is a new species, Talaromyces cellulolyticus, on the basis of morphology an