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Discovery of the Asgard superphylum of archaea provides new evidence supporting the two-domain model of life: eukaryotes originated from an Asgard-related archaeon that engulfed a bacterial endosymbiont. However, how eukaryotes acquired bacterial-like membrane lipids with a sn-glycerol-3-phosphate (G3P) backbone instead of the archaeal-like sn-glycerol-1-phosphate (G1P) backbone remains unknown. In this study, we reconstituted archaeal lipid production in Saccharomyces cerevisiae by expressing unsaturated archaeol-synthesizing enzymes. Using Golden Gate cloning for pathway assembly, modular gene replacement was performed, revealing the potential biosynthesis of both G1P- and G3P-based unsaturated archaeol by uncultured Asgard archaea. Unexpectedly, hybrid neutral lipids containing both archaeal isoprenoids and eukaryotic fatty acids were observed in recombinant S. cerevisiae. The ability of yeast and archaeal diacylglycerol acyltransferases to synthesize such hybrid lipids was demonstrated.

In conventional views, the bacterial adaptation is characterized by strong purifying selection as well as rapid evolution in changing environments. However, the genomic GC content varies greatly but has some degree of phylogenetic stability. Using 11,083 representative genomes, we report a phylogenetically constrained bimodal distribution of the genomic GC. Results suggest that such divergence of the genomic GC can be well explained by the DNA replication and repair (DRR) system, in which multiple pathways are observed correlated to the genomic GC. The biased conservations of various stress-related genes especially the DRR-related ones imply distinct adaptive evolution of the ancestral lineages of high or low GC clades which may be induced by major environmental changes in early evolution. Furthermore, our findings support that the mutational biases resulted from these legacies of adaptation have changed the course of adaptive evolution in bacteria thus causing great variation in the genomic GC. This study demonstrates the importance of indirect effects from natural selection which may be easily misinterpreted as neutral processes.

Malic acid is a valuable organic acid and important acidulant in food and pharmaceutical industries and can be produced using electrodialysis with bipolar membrane (EDBM). The aim of this study was to investigate the possibility of malic acid production using a system integrating EDBM and biochemical process, i.e., the microbial electrodialysis and chemical-production cell (MEDCC). With an applied voltage of 1.0 V, the MEDCC successfully conversed 0.3 M malate into 0.23 M malic acid, which was about four times as that produced in the EDBM (0.06 M). The maximum current density in the MEDCC was five times higher than that in the EDBM (10 vs. 1.9 A/m2). The specific electric consumption for the malic acid production in the MEDCC was 0.34 kWh/kg, which was only 10–30% of that in the reported EDBMs. In the MEDCC, the energy from the anode biodegradation provided about 50% of the total energy demand (0.68 kWh/kg) during the malic acid production. Our results show that the MEDCC should be a promising method for organic acid production with advantages of lower electrical consumption and diverse substrates utilized by exoelectrogens.

The aim of this study was to develop microbial electrolysis cell (MEC) with a novel acidophilic and autotrophic biocathode for treatment of acid wastewater. A biocathode was developed using acidophilic sulfate-reducing bacteria as the catalyst. Artificial wastewater with 200mgL(-1) sulfate and different Zn concentrations (0, 15, 25, and 40 mg L(-1)) was used as the MEC catholyte. The acidophilic biocathode dominated by Desulfovibrio sp. with an abundance of 66% (with 82% of Desulfovibrio sequences similar to Desulfovibrio simplex) and achieved a considerable sulfate reductive rate of 32 gm(-3)d(-1). With 15 mg L(-1) Zn added, the sulfate reductive rate of MEC improved by 16%. The formation of ZnS alleviated the inhibition from sulfide and sped the sulfate reduction. With 15 and 25 mgL(-1) Zn added, more than 99% of Zn was removed from the wastewater. Dissolved Zn ions in the catholyte were converted into insoluble Zn compounds, such as zinc sulfide and zinc hydroxide, due to the sulfide and elevated pH produced by sulfate reduction. The MEC with acidophilic and autotrophic biocathode can be used as an alternative to simultaneously remove sulfate and metals from acid wastewaters, such as acid mine drainage.

The aim of this study was to investigate different microbial electrolysis desalination cells for malic acid production. The systems included microbial electrolysis desalination and chemical-production cell (MEDCC), microbial electrolysis desalination cell (MEDC) with bipolar membrane and anion exchange membrane (BP-A MEDC), MEDC with bipolar membrane and cation exchange membrane (BP-C MEDC), and modified microbial desalination cell (M-MDC). The microbial electrolysis desalination cells performed differently in terms of malic acid production and energy consumption. The MEDCC performed best with the highest malic acid production rate (18.4 ± 0.6 mmol/Lh) and the lowest energy consumption (0.35 ± 0.14 kWh/kg). The best performance of MEDCC was attributable to the neutral pH condition in the anode chamber, the lowest internal resistance, and the highest Geobacter percentage of the anode biofilm population among all the reactors.