A continuous single organic phase process for the lipase catalyzed synthesis of peroxy acids increases productivity.

The design of an optimal process is particularly crucial when the reactants deactivate the biocatalyst. The reaction cascades of the chemo-enzymatic epoxidation where the intermediate peroxy acid is produced by an enzyme are still limited by enzyme inhibition and deactivation by hydrogen peroxide. To avoid additional effects caused by interfaces (aq/org) and to reduce the process limiting deactivation by the substrate hydrogen peroxide, a single-phase concept was applied in a fed-batch and a continuous process (stirred tank), without the commonly applied addition of a carrier solvent. The synthesis of peroxyoctanoic acid catalyzed by Candida antarctica lipase B was chosen as the model reaction. Here, the feasibility of this biocatalytic reaction in a single-phase system was shown for the first time. The work shows the economic superiority of the continuous process compared to the fed-batch process. Employing the fed-batch process reaction rates up to 36 mmol h-1 per gramcat, and a maximum yield of 96 % was achieved, but activity dropped quickly. In contrast, continuous operation can maintain long-term enzyme activity. For the first time, the continuous enzymatic reaction could be performed for 55 h without any loss of activity and with a space-time yield of 154 mmol L-1 h-1, which is three times higher than in the fed-batch process. The higher catalytic productivity compared to the fed-batch process (34 vs. 18 gProd g-1 cat) shows the increased enzyme stability in the continuous process.

Application of gas diffusion electrodes in bioelectrochemical syntheses and energy conversion.

Combining the advantages of biological components (e.g., reaction specificity, self-replication) and electrochemical techniques in bioelectrochemical systems offers the opportunity to develop novel efficient and sustainable processes for the production of a number of valuable products. The choice of electrode material has a great impact on the performance of bioelectrochemical systems. In addition to the redox process at the electrodes, interactions of biocatalysts with electrodes (e.g., enzyme denaturation or biofouling) need to be considered. In recent years, gas diffusion electrodes (GDEs) have proved to be very attractive electrodes for bioelectrochemical purposes. GDEs are porous electrodes, that posses a large three-phase boundary surface. At this interface, a solid catalyst supports the electrochemical reaction between gaseous and liquid phase. This mini-review discusses the application of GDEs in microbial and enzymatic fuel cells, for microbial electrolysis, in biosensors and for electroenzymatic synthesis reactions.

Engineering Methylobacterium extorquens for de novo synthesis of the sesquiterpenoid α-humulene from methanol.

Over the last 10 to 15 years, metabolic engineering of microbes has become a versatile tool for high-level de novo synthesis of terpenoids, with the sesquiterpenoids armopha-1,4-diene, farnesene and artemisinic acid as prime examples. However, almost all cell factory approaches towards terpenoids to date have been based on sugar as the raw material, which is mainly used as a food resource and subject to high price volatilities. In this study we present de novo synthesis of the sesquiterpenoid α-humulene from the abundantly available non-food carbon source methanol by metabolically engineered Methylobacterium extorquens AM1. Expression of α-humulene synthase from Zingiber zerumbet in combination with farnesyl pyrophosphate (FPP) synthase from Saccharomyces cerevisiae led to concentrations of up to 18 mg/L α-humulene. Introduction of a prokaryotic mevalonate pathway from Myxococcus xanthus in combination with ribosome binding site optimization of α-humulene and FPP synthases increased product concentration 3-fold. This value was additionally raised by 30% using a carotenoid synthesis deficient mutant strain. Final product concentrations of up to 1.65 g/L were obtained in methanol limited fed-batch cultivations, which is the highest titer of de novo synthesized α-humulene reported to date. This study demonstrates the potential of M. extorquens as a future platform strain for the production of high-value terpenoids from the alternative carbon source methanol.

Age-dependent dissociation of ATP synthase dimers and loss of inner-membrane cristae in mitochondria.

Aging is one of the most fundamental, yet least understood biological processes that affect all forms of eukaryotic life. Mitochondria are intimately involved in aging, but the underlying molecular mechanisms are largely unknown. Electron cryotomography of whole mitochondria from the aging model organism Podospora anserina revealed profound age-dependent changes in membrane architecture. With increasing age, the typical cristae disappear and the inner membrane vesiculates. The ATP synthase dimers that form rows at the cristae tips dissociate into monomers in inner-membrane vesicles, and the membrane curvature at the ATP synthase inverts. Dissociation of the ATP synthase dimer may involve the peptidyl prolyl isomerase cyclophilin D. Finally, the outer membrane ruptures near large contact-site complexes, releasing apoptogens into the cytoplasm. Inner-membrane vesiculation and dissociation of ATP synthase dimers would impair the ability of mitochondria to supply the cell with sufficient ATP to maintain essential cellular functions.