SummaryIn large‐scale production processes, metabolic control is typically achieved by limited supply of essential nutrients such as glucose or ammonia. With increasing bioreactor dimensions, microbial producers such as Escherichia coli are exposed to changing substrate availabilities due to limited mixing. In turn, cells sense and respond to these dynamic conditions leading to frequent activation of their regulatory programmes. Previously, we characterized short‐ and long‐term strategies of cells to adapt to glucose fluctuations. Here, we focused on fluctuating ammonia supply while studying a continuously running two‐compartment bioreactor system comprising a stirred tank reactor (STR) and a plug‐flow reactor (PFR). The alarmone ppGpp rapidly accumulated in PFR, initiating considerable transcriptional responses after 70 s. About 400 genes were repeatedly switched on/off when E. coli returned to the STR. E. coli revealed highly diverging long‐term transcriptional responses in ammonia compared to glucose fluctuations. In contrast, the induction of stringent regulation was a common feature of both short‐term responses. Cellular ATP demands for coping with fluctuating ammonia supply were found to increase maintenance by 15%. The identification of genes contributing to the increased ATP demand together with the elucidation of regulatory mechanisms may help to create robust cells and processes for large‐scale application.

Several genes for chromatin proteins are known in Archaea. These include histones and histone-like proteins in Euryarchaeota, and a DNA binding protein, Alba, which was first detected in the crenarchaeote Sulfolobus solfataricus and is thought to be involved in transcriptional regulation. The methanogenic archaeon Methanococcus voltae harbors four genes coding for all these three types of chromatin proteins. Deletion mutants for the two histone genes ( hstAand hstB), the gene encoding the histone-like protein ( hmvA) and the gene for the Alba homologue ( albA) have now been constructed in this organism. Although all single mutants were viable, deletion of hstA resulted in slow growth. Two transcripts were detected for each of the two histone genes. These were expressed in different relative amounts, which were correlated with different growth phases. Cell extracts obtained from the different mutants exhibited altered protein patterns, as revealed by 2D gel electrophoresis, indicating that the chromatin proteins are involved in gene regulation in M. voltae.

Summary Background Vigorous chromosome movements driven by cytoskeletal assemblies are a widely conserved feature of sexual differentiation to facilitate meiotic recombination. In fission yeast, this process involves the dramatic conversion of arrays of cytoplasmic microtubules (MTs), generated from multiple MT organizing centers (MTOCs), into a single radial MT (rMT) array associated with the spindle pole body (SPB), the major MTOC during meiotic prophase. The rMT is then dissolved upon the onset of meiosis I when a bipolar spindle emerges to conduct chromosome segregation. Structural features and molecular mechanisms that govern these dynamic MT rearrangements are poorly understood. Results Electron tomography of the SPBs showed that the rMT emanates from a newly recognized amorphous structure, which we term the rMTOC. The rMTOC, which resides at the cytoplasmic side of the SPB, is highly enriched in γ-tubulin reminiscent of the pericentriolar material of higher eukaryotic centrosomes. Formation of the rMTOC depends on Hrs1/Mcp6, a meiosis-specific SPB component that is located at the rMTOC. At the onset of meiosis I, Hrs1/Mcp6 is subject to strict downregulation by both proteasome-dependent degradation and phosphorylation leading to complete inactivation of the rMTOC. This ensures rMT dissolution and bipolar spindle formation. Conclusions Our study reveals the molecular basis for the transient generation of a novel MTOC, which triggers a program of MT rearrangement that is required for meiotic differentiation.

Zero-growth processes are a promising strategy for the production of reduced molecules and depict a steady transition from aerobic to anaerobic conditions. To investigate the adaptation of Corynebacterium glutamicum to altering oxygen availabilities, we conceived a triple-phase fermentation process that describes a gradual reduction of dissolved oxygen with a shift from aerobiosis via microaerobiosis to anaerobiosis. The distinct process phases were clearly bordered by the bacteria’s physiologic response such as reduced growth rate, biomass substrate yield and altered yield of fermentation products. During the process, sequential samples were drawn at six points and analyzed via RNA-sequencing, for metabolite concentrations and for enzyme activities. We found transcriptional alterations of almost 50% (1421 genes) of the entire protein coding genes and observed an upregulation of fermentative pathways, a rearrangement of respiration, and mitigation of the basic cellular mechanisms such as transcription, translation and replication as a transient response related to the installed oxygen dependent process phases. To investigate the regulatory regime, 18 transcriptionally altered (putative) transcriptional regulators were deleted, but none of the deletion strains showed noticeable growth kinetics under an oxygen restricted environment. However, the described transcriptional adaptation of C. glutamicum resolved to varying oxygen availabilities provides a useful basis for future process and strain engineering.

This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. Eicosapentaenoic acid (EPA) and fucoxanthin, a carotenoid, provide a broad variety of health benefits in human nutrition. In this study, an up-and downstream process for the coproduction of EPA and fucoxanthin using the diatom Phaeodactylum tricornutum in flat-panel airlift photobioreactors is proposed. The approach represents a promising alternative to conventional sources for both compounds, viz. marine fish and macroalgae. The productivity as well as the biomass-specific product content were optimized during cultivation. Subsequently, both compounds were extracted, separated and purified using pressurized liquids.