Background: Poly-3-hydroxybutyrate (PHB) is a polyester with thermoplastic properties that is naturally occurring and produced by such bacteria as Ralstonia eutropha H16 and Bacillus megaterium. In contrast to currently utilized plastics and most synthetic polymers, PHB is biodegradable, and its production is not dependent on fossil resources making this bioplastic interesting for various industrial applications. Results: In this study, we report on introducing the bacterial PHB pathway of R. eutropha H16 into the diatom Phaeodactylum tricornutum, thereby demonstrating for the first time that PHB production is feasible in a microalgal system. Expression of the bacterial enzymes was sufficient to result in PHB levels of up to 10.6% of algal dry weight. The bioplastic accumulated in granule-like structures in the cytosol of the cells, as shown by light and electron microscopy. Conclusions: Our studies demonstrate the great potential of microalgae like the diatom P. tricornutum to serve as solar-powered expression factories and reveal great advantages compared to plant based production systems.

Summary: Upon iron limitation, Bacillus subtilis secretes the catecholic trilactone (2,3‐dihydroxybenzoate‐glycine‐threonine)₃ siderophore bacillibactin (BB) for ferric iron scavenging. Here, we show that ferri‐BB uptake is mediated by the FeuABC transporter and that YuiI, a novel trilactone hydrolase, catalyses ferri‐BB hydrolysis leading to cytosolic iron release. Among several Fur‐regulated ABC transport mutants, only ΔfeuABC exhibited impaired growth during iron starvation. Quantification of intra‐ and extracellular (ferri)‐BB in iron‐depleted ΔfeuABC cultures revealed a fourfold increase of the extracellular siderophore concentration, confirming a blocked ferri‐BB uptake in the absence of FeuABC. Ferri‐BB was found to bind selectively to the periplasmic binding protein FeuA (K_d = 57 ± 1 nM), proving high‐affinity transport of the iron‐charged siderophore. During iron starvation, a ΔyuiI mutant displayed impaired growth and strong intracellular (30‐fold) and extracellular (6.5‐fold) (ferri)‐BB accumulation. Kinetic studies in vitro revealed that YuiI hydrolyses both BB and ferri‐BB. While BB hydrolysis led to strong accumulation of the tri‐ and dimeric reaction intermediates, ferri‐BB hydrolysis yielded exclusively the monomeric reaction product and occurred with a 25‐fold higher catalytic efficiency than BB single hydrolysis. Thus, ferri‐BB was the preferred substrate of the YuiI esterase whose gene locus was designated besA.

Significance: We report an intersubunit interaction within the coronavirus replication–transcription complex that is critical for replication and evolutionarily conserved. We provide evidence that the nsp12-associated NiRAN domain has nucleoside monophosphate (NMP) transferase activity in trans and identified nsp9, an RNA-binding protein, as its target. NiRAN catalyzes the covalent attachment of an NMP moiety to the conserved nsp9 amino terminus in a reaction dependent on Mn ²⁺ ions and an adjacent conserved Asn residue. NiRAN activity and nsp9 NMPylation were found to be essential for coronavirus replication. The data lead us to connect this activity of a nidovirus enzymatic marker with previous observations within a functionally and evolutionarily coherent hypothesis on the initiation of RNA synthesis in a class of RNA viruses.

Although it is generally accepted that dietary fiber is health promoting, the underlying immunological and molecular mechanisms are not well defined, especially with respect to cellulose, the most ubiquitous dietary fiber. Here, the impact of dietary cellulose on intestinal microbiota, immune responses and gene expression in health and disease was examined. Lack of dietary cellulose disrupted the age-related diversification of the intestinal microbiota, which subsequently remained in an immature state. Interestingly, one of the most affected microbial genera was Alistipes which is equipped with enzymes to degrade cellulose. Absence of cellulose changed the microbial metabolome, skewed intestinal immune responses toward inflammation, altered the gene expression of intestinal epithelial cells and mice showed increased sensitivity to colitis induction. In contrast, mice with a defined microbiota including A. finegoldii showed enhanced colonic expression of intestinal IL-22 and Reg3γ restoring intestinal barrier function. This study supports the epidemiological observations and adds a causal explanation for the health promoting effects of the most common biopolymer on earth.

The NF-κB signaling system plays an important regulatory role in the control of many biological processes. The activities of NF-κB signaling networks and the expression of their target genes are frequently elevated in pathophysiological situations including inflammation, infection, and cancer. In these conditions, the outcome of NF-κB activity can vary according to (i) differential activation states, (ii) the pattern of genomic recruitment of the NF-κB subunits, and (iii) cellular heterogeneity. Additionally, the cytosolic NF-κB activation steps leading to the liberation of DNA-binding dimers need to be distinguished from the less understood nuclear pathways that are ultimately responsible for NF-κB target gene specificity. This raises the need to more precisely determine the NF-κB activation status not only for the purpose of basic research, but also in (future) clinical applications. Here we review a compendium of different methods that have been developed to assess the NF-κB activation status in vitro and in vivo. We also discuss recent advances that allow the assessment of several NF-κB features simultaneously at the single cell level.