Myxobacteria: Historical aspects, current discoveries, genomics and bioinformaticsMyxobacteria represent the epitome of complex prokaryotic behaviour. Their predatory swarms move over solid surfaces utilizing two distinct motility machineries: one driven by retractable pili, and the other by a novel gliding machinery. Furthermore, under nutrient limitation, myxobacteria enter a developmental program featuring distinct cell fates and culminating in the formation of multicellular fruiting bodies filled with dormant spores (Yang and Higgs, 2014).
For well over a century, the myxobacteria have been the premiere example of prokaryotes with fascinating 'eukaryotic-like' behaviours because of their social lifestyle. During vegetative or active growth, myxobacteria spread or move over solid surfaces as multicellular swarms. This allows them to hunt and feed on prey microorganisms cooperatively as they share secreted antimicrobials and hydrolytic enzymes. When faced with nutrient limitation, myxobacteria may enter a developmental programme with the formation of dormant spores within beautiful and macroscopic multicellular fruiting bodies. The complex multicellular behaviours of these supposedly unicellular microorganisms have had biologists spellbound for many generations.
The earliest work on myxobacteria was pioneered by Roland Thaxter around 1900. He published elegant illustrations of the macroscopic fruiting bodies as well as careful description of microscopic morphologies of vegetative and differentiated cells of various myxobacteria. Like a spore, however, the field largely laid dormant with few signs of life for quite a period. A renaissance started in the 1960s, led by Martin Dworkin, David White, Eugene Rosenberg and Hans Reichenbach. Among many notable accomplishments, they attained new techniques of isolation and cultivation, and provided insights into the physiology and self-organization of these amazing bacteria. Development and application of tools in genetics and molecular biology around the 1980s sparked a booming era of scientific progress on Myxococcus xanthus, the reigning model for this bacterial group. Dale Kaiser and David Zusman deserve the most credit as leaders of this era and they rooted family trees which have produced many a myxobiologist in recent history. Some hallmarks of this period include the discovery of the two motility systems of M. xanthus, insights into the sensory regulation of gliding motility and the establishment of the molecular framework for fruiting body development. The genomics and post-genomics era was launched by the complete sequencing of M. xanthus and Sorangium cellulosum genomes which remain two of the largest among bacteria to this date. Bioinformatic analyses revealed that these genomes encoded record numbers of proteins for signal transduction, transcriptional regulations, secondary metabolite production and of unknown function (Yang and Higgs, 2014). As a sign of the new age, we can now investigate myxobacteria at the level of systems biology instead of individual genes. In more recent years, tools in computational biology and cell biology including advanced imaging are being increasingly applied to myxobacteria to reveal their secrets. As the saying goes, the rest is history.
New discoveries and insights on on the model M. xanthus are streaming out in quickened pace and more depth (Yang and Higgs, 2014). With tools in functional genomics and the increasing power of technology, it is now possible to study myxobacteria by comparative genomics as well as global transcriptomics and proteomics. Quantitative approaches and high-resolution imaging are providing insights into regulatory networks and promising to unravel many mechanistic mysteries.
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