Current microbial cell factory methods for producing chemicals from renewable resources primarily rely on (fed-)batch production systems, leading to the accumulation of the desired product. Industrially relevant chemicals like 2-phenylethanol (2PE), a flavor and fragrance compound, can exhibit toxicity at low concentrations, inhibit the host activity, and negatively impact titer, rate, and yield. Batch liquid-liquid (L-L) In Situ Product Removal (ISPR) was employed to mitigate inhibition effects, but was not found sufficient for industrial-scale application. Here, we demonstrated that continuous selective L-L ISPR provides the solution for maintaining the productivity of de novo produced 2PE at an industrial pilot scale. A unique bioreactor concept called “Fermentation Accelerated by Separation Technology” (FAST) utilizes hydrostatic pressure differences to separate aqueous- and extractant streams within one unit operation, where both production and product extraction take place - allowing for the control of the concentration of the inhibiting compound. Controlled aqueous 2PE levels (0.43 ± 0.02 g kg−1) and extended production times (>100 h) were obtained and co-inhibiting by-product formation was reduced, resulting in a twofold increase of the final product output of batch L-L ISPR approaches. This study establishes that continuous selective L-L ISPR, enabled by FAST, can be applied for more economically viable production of inhibiting products.@en

Medium-chain-length polyhydroxyalkanoate (mcl-PHA) production by using microbial enrichments is a promising but largely unexplored approach to obtain elastomeric biomaterials from secondary resources. In this study, several enrichment strategies were tested to select a community with a high mcl-PHA storage capacity when feeding octanoate. On the basis of analysis of the metabolic pathways, the hypothesis was formulated that mcl-PHA production is more favorable under oxygen-limited conditions than short-chain-length PHA (scl-PHA). This hypothesis was confirmed by bioreactor experiments showing that oxygen limitation during the PHA accumulation experiments resulted in a higher fraction of mcl-PHA over scl-PHA (i.e., a PHA content of 76 wt% with an mcl fraction of 0.79 with oxygen limitation, compared to a PHA content of 72 wt% with an mcl-fraction of 0.62 without oxygen limitation). Physicochemical analysis revealed that the extracted PHA could be separated efficiently into a hydroxybutyrate-rich fraction with a higher M_w and a hydroxyhexanoate/hydroxyoctanoate-rich fraction with a lower M_w. The ratio between the two fractions could be adjusted by changing the environmental conditions, such as oxygen availability and pH. Almost all enrichments were dominated by Sphaerotilus sp. This is the first scientific report that links this genus to mcl-PHA production, demonstrating that microbial enrichments can be a powerful tool to explore mcl-PHA biodiversity and to discover novel industrially relevant strains.

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