MicrobiologyBytes

Traditional treatment of bacterial infections relies heavily on the use of antibacterial compounds that either kill bacteria (bactericidal) or inhibit their growth (bacteriostatic). Typically, the targets for the main conventional antibiotics are essential cellular processes such as bacterial cell wall biosynthesis, bacterial protein synthesis, and bacterial DNA replication and repair. However, resistance to these drugs arises and spreads very rapidly, even to such an extent that bacteria have been identified that are simultaneously resistant to all available antibiotics. The increasing occurrence of resistant bacteria gradually renders antibiotics ineffective in treating infections and has enormous human and economic consequences worldwide. As a result, the identification of novel drug targets and the development of novel therapeutics constitute an important area of current scientific research. An alternative to killing or inhibiting growth of pathogenic bacteria is the specific attenuation of bacterial virulence, which can be attained by targeting key regulatory systems that mediate the expression of virulence factors. One of the target regulatory systems is quorum sensing (QS), or bacterial cell-to-cell communication. QS is a mechanism of gene regulation in which bacteria coordinate the expression of certain genes in response to the presence or absence of small signal molecules. As the importance of QS in virulence development of pathogenic bacteria became clear, about a decade ago, QS disruption was suggested as a new anti-infective strategy.

Although at this moment it is difficult to accurately estimate the risk of resistance development, this paper argues that scientists need to pay attention to the possibility that it will evolve. Once we have better knowledge of the risk of resistance development to QS disruption, it might be possible to direct further research on QS inhibition preferentially towards strategies that include a lower risk of resistance development.

Can Bacteria Evolve Resistance to Quorum Sensing Disruption? 2010 PLoS Pathog 6(7): e1000989. doi:10.1371/journal.ppat.1000989

Recent research has revealed that some plant viruses, like many animal viruses, have measurably evolving populations. Most of these viruses have single-stranded positive-sense RNA genomes, but a few have single-stranded DNA genomes. The studies show that extant populations of these virus species are only decades to centuries old, and the genera in which they are placed have diverged since agriculture was invented, and spread around the world during the Holocene. We suggest that this is not mere coincidence but evidence that the conditions generated by agriculture during this era have favoured particular viruses. There is also evidence, albeit less certain, that some plant viruses, including a few shown to have measurably evolving populations, have much more ancient origins. We discuss the possible reasons for this clear discordance between short-term and long-term evolutionary rate estimates, and how it might result from a large timescale dependence of the evolutionary rates. We also discuss briefly why it is useful to know the rates of evolution of plant viruses.

Time – the emerging dimension of plant virus studies. J Gen Virol. Nov 4 2009

Related:

• Plant viruses: master explorers of evolutionary space. Curr Opin Genet Dev. 1993 3(6): 873-877
• Experimental evolution of plant RNA viruses. Heredity. 2008 100(5): 478-483
• Resistance to Plant Viruses

New mass sequencing techniques are revealing that the diversity of viruses is much greater than ever imagined. In this article in Microbiology Today (pdf) Peter Simmonds shows that some recent “new” viruses are providing clues to how viruses evolve:

One of the immediate problems facing evolutionary studies of viruses is the evident fact that viruses are hugely diverse in size, appearance, even the nature of their genetic material (DNA or RNA). From this, it is reasonably clear that they are a not a single evolutionary group, and cannot be easily added as a single unit to the tree of life with its three main divisions (Bacteria, Archaea and Eukarya). By the same token, it seems likely that different virus groups (e.g. animal RNA viruses, retroviruses, large DNA viruses, bacteriophages) may indeed have entirely separate evolutionary origins. In this article I will describe two areas where recent discoveries have produced tantalizing new insights into the origin and ubiquity of some of these groups. Through the application of new, mass-sequencing techniques and scope for large-scale environmental sampling for virus genomic sequences, we may finally be able to understand the extent and complexity of the “virosphere” in which we live, and the extraordinary diversity of viruses that infect us.

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Related:

• Evolutionary history and phylogeography of human viruses
• One virus particle can be enough to cause infection
• Coevolution with viruses drives bacterial mutations

Some canyons in Israel have north and south-facing slopes that have completely different environments, despite their close proximity. In this article in Microbiology Today (pdf) Johannes Sikorski looks at the micro-organisms that live in these habitats and come to some surprising conclusions that might help us understand micro-evolution rather better:

Bacteria and archaea are genetically, phylogenetically and physiologically very diverse. But how does such diversity start to evolve? How do the first subtle and tender lineages begin to accrue? Oh, you might say, that’s trivial. Have a look at the textbooks and you will find everything there about the evolutionary interplay of mutation, recombination, natural selection and genetic drift. The theoretical framework of population genetics is extremely well-developed. Even more, you insist, microbial microevolution has and still is being analysed in very elegant laboratory experiments, where microbes are allowed to mutate, adapt and evolve in test tubes under very stringent and therefore reproducible and adjustable conditions. But may I remind you that the majority of bacteria are neither evolving in a computer, nor are they living in the pencils of mathe-maticians and theoretical population geneticists, nor in laboratory test tubes, although all these approaches yield tremendous results. Most bacteria live outside in the environment, in water, soil, rocks, plants, etc. Here, where they face a great plethora of biotic and abiotic challenges, they evolve and speciate. Shouldn’t we look at how evolution happens in nature, even though as passive observers, we researchers cannot control this process? What are the decisive factors? Is it possible to catch a glimpse of such a natural evolutionary experiment?

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Related:

• What is a bacterial species?
• Genomic islands in bacterial evolution
• Evolution of root nodule symbiosis with nitrogen-fixing bacteria

A cockatrice was a flamboyant sight at medieval banquets, featuring a roasted chimera of rooster fused to a suckling pig. In this article in Microbiology Today (pdf) Ed Bolt and Stephane Delmas suggest that there are similarities with archaea, ancient micro-organisms that have features of both bacteria and eukaryotes within their genomes:

Archaea and bacteria are micro-organisms that are similar, yet different. Archaea are evolutionarily ancient organisms that have soaked up diverse ecosystems for at least 2.5 billion years. They are, like bacteria, unencumbered by various complex sub-cellular structures (e.g. mitochondria, a membrane-bound nucleus) and as such have been for most of their long exist- ence, or at least from when microbiologists started looking at them, considered to be bacteria that had evolved to thrive in extreme environments (e.g. at high temperature or salinity). For this reason they were often called archeabacteria. However, DNA sequencing experiments in the 1970s drove a wedge through the bacteria, splitting it into two separate domains of cellular life: the Bacteria and the Archaea. The genetic distinction between bacteria and archaea is now generally accepted since its original proposal in 1977, but has its evolutionary root much earlier, probably pre-dating the emergence of oxygen 2.5 billion years ago. Therefore, the classification of cellular organisms is now usually represented in a tree of life consisting of three domains, Bacteria, Archaea and Eukarya…

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Related:

• Unique cell division machinery in the Archaea