Production of Specifically Labeled Compounds by Methanobacterium espanolae Grown on H 2 -CO 2 plus [ 13 C]Acetate

Effects of set cathode potentials on microbial electrosynthesis system performance and biocathode methanogen function at a metatranscriptional level

Microbial electrosynthesis exploits the catalytic activity of microorganisms to utilize a cathode as an electron donor for reducing waste CO2 to valuable fuels and chemicals. Electromethanogenesis is the process of CO2 reduction to CH4 catalyzed by methanogens using the cathode directly as a source of electrons or indirectly via H2. Understanding the effects of different set cathode potentials on the functional dynamics of electromethanogenic communities is crucial for the rational design of cathode materials. Replicate enriched electromethanogenic communities were subjected to different potentials (- 1.0 V and - 0.7 V vs. Ag/AgCl) and the potential-induced changes were analyzed using a metagenomic and metatranscriptomic approach. The most abundant and transcriptionally active organism on the biocathodes was a novel species of Methanobacterium sp. strain 34x. The cathode potential-induced changes limited electron donor availability and negatively affected the overall performance of the reactors in terms of CH4 production. Although high expression of key genes within the methane and carbon metabolism pathways was evident, there was no significant difference in transcriptional response to the different set potentials. The acetyl-CoA decarbonylase/synthase (ACDS) complex were the most highly expressed genes, highlighting the significance of carbon assimilation under limited electron donor conditions and its link to the methanogenesis pathway.

Biochemical and genetic characterization of an early step in a novel pathway for the biosynthesis of aromatic amino acids and p-aminobenzoic acid in the archaeon Methanococcus maripaludis

Methanococcus maripaludis is a strictly anaerobic, methane-producing archaeon and facultative autotroph capable of biosynthesizing all the amino acids and vitamins required for growth. In this work, the novel 6-deoxy-5-ketofructose-1-phosphate (DKFP) pathway for the biosynthesis of aromatic amino acids (AroAAs) and p-aminobenzoic acid (PABA) was demonstrated in M. maripaludis. Moreover, PABA was shown to be derived from an early intermediate in AroAA biosynthesis and not from chorismate. Following metabolic labelling with [U-(13)C]-acetate, the expected enrichments for phenylalanine and arylamine derived from PABA were observed. DKFP pathway activity was reduced following growth with aryl acids, an alternative source of the AroAAs. Lastly, a deletion mutant of aroA', which encodes the first step in the DKFP pathway, required AroAAs and PABA for growth. Complementation of the mutants by an aroA' expression vector restored the wild-type phenotype. In contrast, a deletion of aroB', which encodes the second step in the DKFP pathway, did not require AroAAs or PABA for growth. Presumably, methanococci contain an alternative activity for this step. These results identify the initial reactions of a new pathway for the biosynthesis of PABA in methanococci.

Archaeobacterial ether lipid liposomes (archaeosomes) as novel vaccine and drug delivery systems

Liposomes are artificial, spherical, closed vesicles consisting of one or more lipid bilayer(s). Liposomes made from ester phospholipids have been studied extensively over the last 3 decades as artificial membrane models. Considerable interest has been generated for applications of liposomes in medicine, including their use as diagnostic reagents, as carrier vehicles in vaccine formulations, or as delivery systems for drugs, genes, or cancer imaging agents. The objective of this article is to review the properties and potential applications of novel liposomes made from the membrane lipids of Archaeobacteria (Archaea). These lipids are unique and distinct from those encountered in Eukarya and Bacteria. Polar glycerolipids make up the bulk of the membrane lipids, with the remaining neutral lipids being primarily squalenes and other hydrocarbons. The polar lipids consist of regularly branched, and usually fully saturated, phytanyl chains of 20, 25, or 40 carbon length, with the 20 and 40 being most common. The phytanyl chains are attached via ether bonds to the sn-2,3 carbons of the glycerol backbone(s). It has been shown only recently that total polar lipids of archaeobacteria, and purified lipid fractions therefrom, can form liposomes. We refer to liposomes made with any lipid composition that includes ether lipids characteristic of Archaeobacteria as archaeosomes to distinguish them from vesicles made from the conventional lipids obtained from eukaryotic or eubacterial sources or their synthetic analogs. In general, archaeosomes demonstrate relatively higher stabilities to oxidative stress, high temperature, alkaline pH, action of phospholipases, bile salts, and serum proteins. Some archaeosome formulations can be sterilized by autoclaving, without problems such as fusion or aggregation of the vesicles. The uptake of archaeosomes by phagocytic cells can be up to 50-fold greater than that of conventional liposome formulations. Studies in mice have indicated that systemic administration of several test antigens entrapped within certain archaeosome compositions give humoral immune responses that are comparable to those obtained with the potent but toxic Freund's adjuvant. Archaeosome compositions can be selected to give a prolonged, sustained immune response, and the generation of a memory response. Tissue distribution studies of archaeosomes administered via various systemic and peroral routes indicate potential for targeting to specific organs. All in vitro and in vivo studies performed to date indicate that archaeosomes are safe and do not invoke any noticeable toxicity in mice. The stability, tissue distribution profiles, and adjuvant activity of archaeosome formulations indicate that they may offer a superior alternative to the use of conventional liposomes, at least for some biotechnology applications.