Increased intestinal mucosal PCO2 is used to detect the condition of inadequate O2 delivery, i.e., "dysoxia." However, mucosal PCO2 (PmCO2) can arise from oxidative phosphorylation, in which case it would detect metabolism that persists as blood stagnates, and/or from HCO3- neutralization by anaerobically produced metabolic acid, in which event it could represent dysoxia. We measured portal venous PCO2 (PVCO2) directly and PmCO2 indirectly with saline-filled CO2-permeable Silastic balloon tonometers in the intestinal lumen during progressive lethal cardiac tamponade in six pentobarbital-anesthetized dogs. PVCO2 and PmCO2 were relatively constant, differing by approximately 10 Torr until an O2 delivery (DO2) of approximately 1.3 ml.kg-1.min-1 was reached, below which PVCO2 and PmCO2 diverged strikingly, achieving a final difference of 78.7 +/- 35.81 (SD) Torr. To determine whether PCO2 arose from aerobic or anaerobic metabolism, we used the Dill nomogram to predict venous oxyhemoglobin (HbO2v) saturation (%HbO2v) from PVCO2. Portal venous %HbO2 predicted by the Dill nomogram agreed well with measured portal venous %HbO2 during all but the final values, indicating primarily aerobic appearance of PCO2 in venous blood, suggesting that portions of intestine that remained perfused at very low flow produced dissolved CO2 mainly by oxidative phosphorylation. As PmCO2 increased below critical DO2, however, predicted mucosal %HbO2v became strikingly negative, achieving a final value of -192 +/- 106.1%, indicating anaerobic dissolved CO2 production in mucosa. We conclude that PCO2 measured in intestinal lumen can be used to detect dysoxia.

Burnettiene A is a novel cytotoxic tridecaketide decalin polyketide from Aspergillus burnettii. Its biosynthesis was elucidated by heterologous expression in fungi.

Chemical exploration of the recently described Australian fungus, Aspergillus burnettii, uncovered a new metabolite, burnettiene A. Here, we characterise the structure of burnettiene A as a polyene-decalin polyketide. Bioinformatic analysis of the genome of A. burnettii identified a putative biosynthetic gene cluster for burnettiene A (bue), consisting of eight genes and sharing similarity to the fusarielin gene cluster. Introduction of the reassembled bue gene cluster into Aspergillus nidulans for heterologous expression resulted in the production of burnettiene A under native promoters. Omission of bueE encoding a cytochrome P450 led to the production of preburnettiene A, confirming that BueE is responsible for catalysing the regiospecific multi-oxidation of terminal methyl groups to carboxylic acids. Similarly, bueF was shown to encode an ester-forming methyltransferase, with its omission resulting in the production of the tricarboxylic acid, preburnettiene B. Introduction of an additional copy of the transcription factor bueR under the regulation of the gpdA promoter significantly improved the heterologous production of the burnettienes. Burnettiene A displayed strong in vitro cytotoxicity against mouse myeloma NS-1 cells (MIC 0.8 µg/mL).