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Cheap and renewable feedstocks such as the one-carbon substrate formate are emerging for sustainable production in a growing chemical industry. We investigated the acetogen Acetobacterium woodii as a potential host for bioproduction from formate alone and together with autotrophic and heterotrophic co-substrates by quantitatively analyzing physiology, transcriptome, and proteome in chemostat cultivations in combination with computational analyses. Continuous cultivations with a specific growth rate of 0.05 h−1 on formate showed high specific substrate uptake rates (47 mmol g−1 h−1). Co-utilization of formate with H2, CO, CO2 or fructose was achieved without catabolite repression and with acetate as the sole metabolic product. A transcriptomic comparison of all growth conditions revealed a distinct adaptation of A. woodii to growth on formate as 570 genes were changed in their transcript level. Transcriptome and proteome showed higher expression of the Wood-Ljungdahl pathway during growth on formate and gaseous substrates, underlining its function during utilization of one-carbon substrates. Flux balance analysis showed varying flux levels for the WLP (0.7–16.4 mmol g−1 h−1) and major differences in redox and energy metabolism. Growth on formate, H2/CO2, and formate + H2/CO2 resulted in low energy availability (0.20–0.22 ATP/acetate) which was increased during co-utilization with CO or fructose (0.31 ATP/acetate for formate + H2/CO/CO2, 0.75 ATP/acetate for formate + fructose). Unitrophic and mixotrophic conversion of all substrates was further characterized by high energetic efficiencies. In silico analysis of bioproduction of ethanol and lactate from formate and autotrophic and heterotrophic co-substrates showed promising energetic efficiencies (70–92%). Collectively, our findings reveal A. woodii as a promising host for flexible and simultaneous bioconversion of multiple substrates, underline the potential of substrate co-utilization to improve the energy availability of acetogens and encourage metabolic engineering of acetogenic bacteria for the efficient synthesis of bulk chemicals and fuels from sustainable one carbon substrates.

In this study, continuous cultivations of C.carboxidivorans to study heterotrophic and mixotrophic conversion of glucose and H

Photosynthetic Poly-β-hydroxybutyrate (PHB) productivity in cyanobacteria needs to be increased to make cyanobacterial derived bioplastics economically feasible and competitive with petroleum-based plastics. In this study, high PHB yielding mutants of Synechocystis sp. PCC 6714 have been generated by random mutagenesis, using UV light as a mutagen. The selection of strains was based on PHB content induced by nitrogen and phosphorus starvation. The fast growing mutant MT_a24 exhibited more than 2.5-fold higher PHB productivity than that of the wild-type, attaining values of 37 ± 4% dry cell weight PHB. The MT_a24 was characterized for phenotypes, CO2 uptake rate and gene expression levels using quantitative PCR. Genome sequencing showed that UV mutagenesis treatment resulted in a point mutation in the ABC-transport complex, phosphate-specific transport system integral membrane protein A (PstA). The MT_a24 shows potential for industrial production of PHB and also for carbon capture from the atmosphere or point sources.

Adaptation to highly saline conditions required halophilic organisms to develop unique features. The mounting interest in those features has resulted in a number of potential applications for moderate and extreme halophiles. However, industrial exploitation has been reported only for few instances. With the aim to bring concepts from laboratory to pilot-scale a customized bioreactor for halophilic cultures was developed. The setup combined a bubble column reactor (BCR) with a membrane module for cell retention. The BCR was compared to a conventional stirred tank reactor (STR) in terms of physiological and hydro-dynamical parameters. The results showed that the BCR is preferable in terms of energy efficiency. The BCR reached a maximum kLa of 84 h−1 at ambient pressure, which equals an oxygen transfer rate (OTR) of 6 mmol/(L*h) in medium with 150 g/L NaCl. To reach this mass transfer a STR required more than 3-fold the amount of energy. Cultivation of the extreme halophilic archaeon Haloferax mediterranei showed suitability of the BCR for continuous halophilic processes. To reduce cost and ecological impact of this process a highly saline industrial waste stream from a chemical production process was used as source for NaCl. The BCR presented in this study allows continuous and competitive cultivation of halophilic organisms at high volumetric rates and high biomass productivities as required for large scale industrial applications.

In this study, the impact of gas composition (i.e. CO, CO2 and H2 partial pressures) on CO2 utilization, growth, and acetate production was investigated in batch and continuous cultures of A. woodii. Based on an industrial blast furnace gas, H2 blending was used to study the impact of H2 availability on CO2 fixation alone and together with CO using idealized gas streams. With H2 available as an additional energy source, net CO2 fixation and CO, CO2 and H2 co-utilization was achieved in gas-limited fermentations. Using industrial blast furnace gas, up to 15.1 g l−1 acetate were produced in continuous cultures. Flux balance analysis showed that intracellular fluxes and total ATP production were dependent on the availability of H2 and CO. Overall, H2 blending was shown to be a suitable control strategy for gas fermentations and demonstrated that A. woodii is an interesting host for CO2 fixation from industrial gas streams.