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Bioproduction of renewable chemicals is considered as an urgent solution for fossil energy crisis. However, despite tremendous efforts, it is still challenging to generate microbial strains that can produce target biochemical to high levels. Here, we report an example of biosynthesis of high-value and easy-recoverable derivatives built upon natural microbial pathways, leading to improvement in bioproduction efficiency. By leveraging pathways in solventogenic clostridia for co-producing acyl-CoAs, acids and alcohols as precursors, through rational screening for host strains and enzymes, systematic metabolic engineering-including elimination of putative prophages, we develop strains that can produce 20.3 g/L butyl acetate and 1.6 g/L butyl butyrate. Techno-economic analysis results suggest the economic competitiveness of our developed bioprocess. Our principles of selecting the most appropriate host for specific bioproduction and engineering microbial chassis to produce high-value and easy-separable end products may be applicable to other bioprocesses.

Langmuir probe diagnostics in a multi-dipole confined hot cathode discharge has been revisited with an improved sheath expansion model with fitted expansion parameters. The results show a three-Maxwellian EEDF composition also observed in previous studies using a very similar system. The dependence on neutral pressure and discharge current of each electron species are consistent with known physical processes in a multi-dipole confined hot cathode discharge. This shows that the employment of the new ion saturation fitting method does not eliminate the contribution of the high energy degraded primaries to the Langmuir probe I-V trace, as sheath expansion and high energy electron current contributes differently on an I-V trace. The result remains supportive to the existence of a very hot (Tdp >15eV) degraded primary electron species separate from the typical hot electron (Thot ~ 3eV) species. Thus it is recommended to sweep the Langmuir probe beyond the bias voltage of the hot cathode, whenever possible, in order to properly resolve the contribution to the I-V trace of the degraded primaries.

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