Genetic manipulation of giant viruses and their host, Acanthamoeba castellanii.

Giant viruses (GVs) provide an unprecedented source of genetic innovation in the viral world and are thus, besides their importance in basic and environmental virology, in the spotlight for bioengineering advances. Their host, Acanthamoeba castellanii, is an accidental human pathogen that acts as a natural host and environmental reservoir of other human pathogens. Tools for genetic manipulation of viruses and host were lacking.

Evolution of giant pandoravirus revealed by CRISPR/Cas9.

Giant viruses (GVs) are a hotspot of unresolved controversies since their discovery, including the definition of "Virus" and their origin. While increasing knowledge of genome diversity has accumulated, GV functional genomics was largely neglected. Here, we describe an experimental framework to genetically modify nuclear GVs and their host Acanthamoeba castellanii using CRISPR/Cas9, shedding light on the evolution from small icosahedral viruses to amphora-shaped GVs.

Virus-encoded histone doublets are essential and form nucleosome-like structures.

The organization of genomic DNA into defined nucleosomes has long been viewed as a hallmark of eukaryotes. This paradigm has been challenged by the identification of "minimalist" histones in archaea and more recently by the discovery of genes that encode fused remote homologs of the four eukaryotic histones in Marseilleviridae, a subfamily of giant viruses that infect amoebae. We demonstrate that viral doublet histones are essential for viral infectivity, localize to cytoplasmic viral factories after virus infection, and ultimately are found in the mature virions.

Exploration of the propagation of transpovirons within Mimiviridae reveals a unique example of commensalism in the viral world.

Acanthamoeba-infecting Mimiviridae are giant viruses with dsDNA genome up to 1.5 Mb. They build viral factories in the host cytoplasm in which the nuclear-like virus-encoded functions take place.

Pandoravirus Celtis Illustrates the Microevolution Processes at Work in the Giant Genomes.

With genomes of up to 2.7 Mb propagated in μm-long oblong particles and initially predicted to encode more than 2000 proteins, members of the family display the most extreme features of the known viral world. The mere existence of such giant viruses raises fundamental questions about their origin and the processes governing their evolution.

Diversity and evolution of the emerging Pandoraviridae family.

With DNA genomes reaching 2.5 Mb packed in particles of bacterium-like shape and dimension, the first two Acanthamoeba-infecting pandoraviruses remained up to now the most complex viruses since their discovery in 2013. Our isolation of three new strains from distant locations and environments is now used to perform the first comparative genomics analysis of the emerging worldwide-distributed Pandoraviridae family.

The chimeric nature of the genomes of marine magnetotactic coccoid-ovoid bacteria defines a novel group of Proteobacteria.

Magnetotactic bacteria (MTB) are a group of phylogenetically and physiologically diverse Gram-negative bacteria that synthesize intracellular magnetic crystals named magnetosomes. MTB are affiliated with three classes of Proteobacteria phylum, Nitrospirae phylum, Omnitrophica phylum and probably with the candidate phylum Latescibacteria. The evolutionary origin and physiological diversity of MTB compared with other bacterial taxonomic groups remain to be illustrated.

In Vivo Evolution of Bacterial Resistance in Two Cases of Enterobacter aerogenes Infections during Treatment with Imipenem.

Infections caused by multidrug resistant (MDR) bacteria are a major concern worldwide. Changes in membrane permeability, including decreased influx and/or increased efflux of antibiotics, are known as key contributors of bacterial MDR. Therefore, it is of critical importance to understand molecular mechanisms that link membrane permeability to MDR in order to design new antimicrobial strategies.

Genome analysis of the first Marseilleviridae representative from Australia indicates that most of its genes contribute to virus fitness.

Unlabelled: The family Marseilleviridae consists of Acanthamoeba-infecting large DNA viruses with icosahedral particles ∼ 0.2 μm in diameter and genome sizes in the 346- to 380-kb range. Since the isolation of Marseillevirus from a cooling tower in Paris (France) in 2009, the family Marseilleviridae has expanded rapidly, with representatives from Europe and Africa.

Pandoraviruses: amoeba viruses with genomes up to 2.5 Mb reaching that of parasitic eukaryotes.

Ten years ago, the discovery of Mimivirus, a virus infecting Acanthamoeba, initiated a reappraisal of the upper limits of the viral world, both in terms of particle size (>0.7 micrometers) and genome complexity (>1000 genes), dimensions typical of parasitic bacteria. The diversity of these giant viruses (the Megaviridae) was assessed by sampling a variety of aquatic environments and their associated sediments worldwide.

Comparative genomic analysis provides insights into the evolution and niche adaptation of marine Magnetospira sp. QH-2 strain.

Magnetotactic bacteria (MTB) are capable of synthesizing intracellular organelles, the magnetosomes, that are membrane-bounded magnetite or greigite crystals arranged in chains. Although MTB are widely spread in various ecosystems, few axenic cultures are available, and only freshwater Magnetospirillum spp. have been genetically analysed.

Preliminary crystallographic analysis of the Megavirus superoxide dismutase.

Megavirus chilensis, a close relative of the Mimivirus giant virus, is able to replicate in Acanthamoeba castellanii. The first step of viral infection involves the internalization of the virions in host vacuoles. It has been experimentally demonstrated that Mimivirus particles contain many proteins capable of resisting oxidative stress, as encountered in the phagocytic process.

ppGpp is the major source of growth rate control in E. coli.

It is widely accepted that the DNA, RNA and protein content of Enterobacteriaceae is regulated as a function of exponential growth rates; macromolecular content increases with faster growth regardless of specific composition of the growth medium. This phenomenon, called growth rate control, primarily involves regulation of ribosomal RNA and ribosomal protein synthesis. However, it was uncertain whether the global regulator ppGpp is the major determinant for growth rate control.

An MCP-like protein interacts with the MamK cytoskeleton and is involved in magnetotaxis in Magnetospirillum magneticum AMB-1.

Magnetotactic bacteria have the unique capacity of aligning and swimming along geomagnetic field lines, a behavior called magnetotaxis. Although this behavior has been observed for 40 years, little is known about its mechanism. Magnetotactic bacteria synthesize unique organelles, magnetosomes, which are magnetic crystals enveloped by membrane.

A second actin-like MamK protein in Magnetospirillum magneticum AMB-1 encoded outside the genomic magnetosome island.

Magnetotactic bacteria are able to swim navigating along geomagnetic field lines. They synthesize ferromagnetic nanocrystals that are embedded in cytoplasmic membrane invaginations forming magnetosomes. Regularly aligned in the cytoplasm along cytoskeleton filaments, the magnetosome chain effectively forms a compass needle bestowing on bacteria their magnetotactic behaviour.

Evolution of penicillin-binding protein 2 concentration and cell shape during a long-term experiment with Escherichia coli.

Peptidoglycan is the major component of the bacterial cell wall and is involved in osmotic protection and in determining cell shape. Cell shape potentially influences many processes, including nutrient uptake as well as cell survival and growth. Peptidoglycan is a dynamic structure that changes during the growth cycle.

Death and cannibalism in a seasonal environment facilitate bacterial coexistence.

Bacterial populations can evolve and adapt to become diverse niche specialists, even in seemingly homogeneous environments. One source of this diversity arises from newly 'constructed' niches that result from the activities of the bacteria themselves. Ecotypes specialized to exploit these distinct niches can subsequently coexist via frequency-dependent interactions.

Evolution of global regulatory networks during a long-term experiment with Escherichia coli.

Evolution has shaped all living organisms on Earth, although many details of this process are shrouded in time. However, it is possible to see, with one's own eyes, evolution as it happens by performing experiments in defined laboratory conditions with microbes that have suitably fast generations. The longest-running microbial evolution experiment was started in 1988, at which time twelve populations were founded by the same strain of Escherichia coli.

Long-term experimental evolution in Escherichia coli. XII. DNA topology as a key target of selection.

The genetic bases of adaptation are being investigated in 12 populations of Escherichia coli, founded from a common ancestor and serially propagated for 20,000 generations, during which time they achieved substantial fitness gains. Each day, populations alternated between active growth and nutrient exhaustion. DNA supercoiling in bacteria is influenced by nutritional state, and DNA topology helps coordinate the overall pattern of gene expression in response to environmental changes.