Tryptophan auxotrophs were obtained by random transposon insertions in the Methanococcus maripaludis tryptophan operon

Teaching old dogs new tricks: genetic engineering methanogens

Methanogenic archaea, which are integral to global carbon and nitrogen cycling, currently face challenges in genetic manipulation due to unique physiology and limited genetic tools. This review provides a survey of current and past developments in the genetic engineering of methanogens, including selection and counterselection markers, reporter systems, shuttle vectors, mutagenesis methods, markerless genetic exchange, and gene expression control. This review discusses genetic tools and emphasizes challenges tied to tool scarcity for specific methanogenic species. Mutagenesis techniques for methanogens, including physicochemical, transposon-mediated, liposome-mediated mutagenesis, and natural transformation, are outlined, along with achievements and challenges. Markerless genetic exchange strategies, such as homologous recombination and CRISPR/Cas-mediated genome editing, are also detailed. Finally, the review concludes by examining the control of gene expression in methanogens. The information presented underscores the urgent need for refined genetic tools in archaeal research. Despite historical challenges, recent advancements, notably CRISPR-based systems, hold promise for overcoming obstacles, with implications for global health, agriculture, climate change, and environmental engineering. This comprehensive review aims to bridge existing gaps in the literature, guiding future research in the expanding field of archaeal genetic engineering.

Transposon Insertion Mutagenesis in Hyperthermophilic Crenarchaeon Sulfolobus islandicus

Transposon insertion mutagenesis is a forward genetic approach that has been widely utilized for genetic characterization of bacteria and single-celled eukaryotes, and its applications are being rapidly expanded into a few archaeal model organisms for gene function analysis. Previously, we developed a Tn5-based in vivo transposon insertion mutagenesis system in the hyperthermophilic crenarchaeon S. islandicucs M.16.4 and defined the essential gene set under laboratory growth conditions. In this chapter, we will mainly focus on presenting details regarding the generation of a near-saturating transposon insertion mutant library in this crenarchaeal model. We envision that the traditional transposon-based forward mutagenesis screening paired with next generation sequencing will greatly speed up the exploration of archaeal genomic features.

Methanogens: biochemical background and biotechnological applications

Since fossil sources for fuel and platform chemicals will become limited in the near future, it is important to develop new concepts for energy supply and production of basic reagents for chemical industry. One alternative to crude oil and fossil natural gas could be the biological conversion of CO2 or small organic molecules to methane via methanogenic archaea. This process has been known from biogas plants, but recently, new insights into the methanogenic metabolism, technical optimizations and new technology combinations were gained, which would allow moving beyond the mere conversion of biomass. In biogas plants, steps have been undertaken to increase yield and purity of the biogas, such as addition of hydrogen or metal granulate. Furthermore, the integration of electrodes led to the development of microbial electrosynthesis (MES). The idea behind this technique is to use CO2 and electrical power to generate methane via the microbial metabolism. This review summarizes the biochemical and metabolic background of methanogenesis as well as the latest technical applications of methanogens. As a result, it shall give a sufficient overview over the topic to both, biologists and engineers handling biological or bioelectrochemical methanogenesis.

A Flexible System for Cultivation of Methanococcus and Other Formate-Utilizing Methanogens

Many hydrogenotrophic methanogens use either H₂ or formate as the major electron donor to reduce CO₂ for methane production. The conventional cultivation of these organisms uses H₂ and CO₂ as the substrate with frequent replenishment of gas during growth. H₂ is explosive and requires an expensive gassing system to handle safely. Formate is as an ideal alternative substrate from the standpoints of both economy and safety but leads to large changes in the culture pH during growth. Here, we report that glycylglycine is an inexpensive and nontoxic buffer suitable for growth of Methanococcus maripaludis and Methanothermococcus okinawensis. This cultivation system is suitable for growth on liquid as well as solid medium in serum bottles. Moreover, it allows cultivation of liter scale cultures without expensive fermentation equipment. This formate cultivation system provides an inexpensive and flexible alternative for the growth of formate-utilizing, hydrogenotrophic methanogens.

Genome-scale analysis of gene function in the hydrogenotrophic methanogenic archaeon Methanococcus maripaludis

A comprehensive whole-genome analysis of gene function by transposon mutagenesis and deep sequencing methodology has been implemented successfully in a representative of the Archaea domain. Libraries of transposon mutants were generated for the hydrogenotrophic, methanogenic archaeon Methanococcus maripaludis S2 using a derivative of the Tn5 transposon. About 89,000 unique insertions were mapped to the genome, which allowed for the classification of 526 genes or about 30% of the genome as possibly essential or strongly advantageous for growth in rich medium. Many of these genes were homologous to eukaryotic genes that encode fundamental processes in replication, transcription, and translation, providing direct evidence for their importance in Archaea. Some genes classified as possibly essential were unique to the archaeal or methanococcal lineages, such as that encoding DNA polymerase PolD. In contrast, the archaeal homolog to the gene encoding DNA polymerase B was not essential for growth, a conclusion confirmed by construction of an independent deletion mutation. Thus PolD, and not PolB, likely plays a fundamental role in DNA replication in methanococci. Similarly, 121 hypothetical ORFs were classified as possibly essential and likely play fundamental roles in methanococcal information processing or metabolism that are not established outside this group of prokaryotes.

Genetic Confirmation of the Role of Sulfopyruvate Decarboxylase in Coenzyme M Biosynthesis inMethanococcus maripaludis

Coenzyme M is an essential coenzyme for methanogenesis. The proposed biosynthetic pathway consists of five steps, of which the fourth step is catalyzed by sulfopyruvate decarboxylase (ComDE). Disruption of the gene comE by transposon mutagenesis resulted in a partial coenzyme M auxotroph, which grew poorly in the absence of coenzyme M and retained less than 3% of the wild type level of coenzyme M biosynthesis. Upon coenzyme M addition, normal growth of the mutant was restored. Moreover, complementation of the mutation with the wild type comE gene in trans restored full growth in the absence of coenzyme M. These results confirm that ComE plays an important role in coenzyme M biosynthesis. The inability to yield a complete CoM auxotroph suggests that either the transposon insertion failed to completely inactivate the gene or M. maripaludis possesses a promiscuous activity that partially complemented the mutation.

Model organisms for genetics in the domain Archaea: methanogens, halophiles, Thermococcales and Sulfolobales

The tree of life is split into three main branches: eukaryotes, bacteria, and archaea. Our knowledge of eukaryotic and bacteria cell biology has been built on a foundation of studies in model organisms, using the complementary approaches of genetics and biochemistry. Archaea have led to some exciting discoveries in the field of biochemistry, but archaeal genetics has been slow to get off the ground, not least because these organisms inhabit some of the more inhospitable places on earth and are therefore believed to be difficult to culture. In fact, many species can be cultivated with relative ease and there has been tremendous progress in the development of genetic tools for both major archaeal phyla, the Euryarchaeota and the Crenarchaeota. There are several model organisms available for methanogens, halophiles, and thermophiles; in the latter group, there are genetic systems for Sulfolobales and Thermococcales. In this review, we present the advantages and disadvantages of working with each archaeal group, give an overview of their different genetic systems, and direct the neophyte archaeologist to the most appropriate model organism.

Studying gene regulation in methanogenic archaea

Methanogenic archaea are a unique group of strictly anaerobic microorganisms characterized by their ability, and dependence, to convert simple C1 and C2 compounds to methane for growth. The major models for studying the biology of methanogens are members of the Methanococcus and Methanosarcina species. Recent development of sophisticated tools for molecular analysis and for genetic manipulation allows investigating not only their metabolism but also their cell cycle, and their interaction with the environment in great detail. One aspect of such analyses is assessment and dissection of methanoarchaeal gene regulation, for which, at present, only a handful of cases have been investigated thoroughly, partly due to the great methodological effort required. However, it becomes more and more evident that many new regulatory paradigms can be unraveled in this unique archaeal group. Here, we report both molecular and physiological/genetic methods to assess gene regulation in Methanococcus maripaludis and Methanosarcina acetivorans, which should, however, be applicable for other methanogens as well.