MicrobiologyBytes

Following the success of the MicrobiologyBytes Page on Facebook, I’m blogging about the creation of the new edition of Principles of Molecular Virology on the same platform. This is a public page, so you don’t need a Facebook account to read it – you don’t need to be my “friend” on Facebook. Facebook Pages do not reveal the content of your personal Facebook Wall to other people who are not your Facebook “friends”. I won’t be sending you “friend” requests on Facebook and will not respond to “friend” requests from you (sorry ;-)

If you want to stay up to date with my progress, click the “Like” button on the PoMV page and you get all the updates directly on your Facebook wall.

Related: More microbiology on Facebook

• American Society for Microbiology
• Society for Applied Microbiology
• Society for General Microbiology

Air conditioning systems are present in many modern cars. The advantages of air conditioning such as comfort in the summer time are well-known. However, the potential risk of contamination of the air in the cabin by microorganisms by the air conditioning system has yet rarely been examined. A new study looked at influence of AC systems in cars on the quality of filtered air from the outside and air re-circulating from the car’s cabin under various conditions. The result?

The microbiological quality of air improves when using air conditioning systems in cars. BMC Infectious Diseases 2010, 10: 146 doi:10.1186/1471-2334-10-146
Air conditioning systems are a common feature in automobiles these days. However, its impact on the number of particles and microorganisms inside the vehicle – and by this its impact on the risk of an allergic reaction – is yet unknown. Over a time period of 30 months, the quality of air was investigated in three different types of car that were all equipped with a automatic air conditioning system. Operation modes using fresh air from outside the car as well as circulating air from inside the car were examined. The total number of microorganisms and the number of mold spores were measured by impaction in a high flow air sampler. Particles of 0.5 to 5.0 µm diameter were counted by a laser particle counter device. Overall 32 occasions of sampling were performed. The concentration of microorganisms outside the cars was always higher than it was inside the cars. Few minutes after starting the air conditioning system the total number of microorganisms was reduced by 81%, the number of mold spores was reduced by 83.3%, and the number of particles was reduced by 87%. There were no significant differences neither between the types of cars nor between the types of operation mode of the air conditioning system (fresh air vs. circulating air). All parameters that were looked for in this study improved during utilization of the car’s air conditioning system. We believe that the risk of an allergic reaction will be reduced during use also. Nevertheless, we recommend regular maintenance of the system and replacement of older filters after defined changing intervals.

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• Dirty Money

Most viruses are either helical or icosahedral in structure. The two highly symmetric shapes permit viruses to use the same component protein multiple times to create large structures from a minimum number of distinct protein species. The strategy conserves the amount of genetic material viruses need to encode structural proteins. Although the two basic shapes serve the needs of viruses more or less equally well, structural biologists have had a much easier time determining the structures of the icosahedra. For example, while more than one hundred high resolution structures of icosahedral viruses are now available, the number of comparable helical virus structures is limited to helical plant viruses such as tobacco mosaic virus and filamentous bacteriophage such as E. coli phage f1. It’s not as though helical animal and human viruses are of limited interest. Just the opposite. They include influenza virus plus members of the paramyxo-, rhabdo- bunya-, corona, filo- and arenavirus families, all of which contain important human pathogens. The problem is that structural analysis of these viruses is unusually difficult. The protein-RNA complex is often disordered or weakly ordered in the virion, and the viruses have a membrane, a structure that complicates both crystallization and electron microscopic analysis.

To advance our knowledge of helical virus structure, investigators have focused their attention on the rhabdoviruses, a family of bullet-shaped viruses that includes rabies and vesicular stomatitis viruses (VSV). Rhabdoviruses have a helical nucleocapsid that is well ordered over most of the virion length. Although a membrane is present, it is tightly wrapped around the nucleocapsid, and does not obscure the helix in electron micrographs of the virion. With such excellent images, one would think it would be a simple matter to compute a three-dimensional reconstruction of the particle. No structure has been forthcoming, however, despite the best efforts of many highly talented structural biologists – until now.

Helical Virus Structure: The Case of the Rhabdovirus Bullet. Viruses 2010 2(4), 995-1001; doi:10.3390/v2040995

Related:

• Cryo-EM Model of the Bullet-Shaped Vesicular Stomatitis Virus. 2010 Science 327 (5966) 689-693 doi:10.1126/science.1181766
  Assembly of a virus particle is generally presumed to be a stochastic process. However, assembly of VSV appears to follow a well-orchestrated program. It begins with RNA and N as a nucleocapsid ribbon. The ribbon curls into a tight ring and then is physically forced to curl into larger rings that eventually tile the helical trunk. M subunits bind on the outside of the nucleocapsid, rigidify the bullet tip and then the trunk, and create a triangularly packed platform for binding G trimers and envelope membrane, all in a coherent operation during budding.

Chlamydia pneumoniae is an intracellular bacterial pathogen with an extremely diverse host range (humans, amphibians, reptiles and marsupials). C. pneumoniae exposure is widespread in humans, with sero-prevalence studies reporting 50% infection levels by age 20 and reaching 80% in the elderly. In humans, C. pneumoniae infections can range from asymptomatic to severe respiratory disease, including pneumonia. Less common presentations include bronchitis, pharyngitis, laryngitis and sinusitis, making up 5% of cases. In addition to respiratory infections in humans, C. pneumoniae has also been associated with atherosclerosis and stroke, myocarditis, multiple sclerosis and Alzheimer’s disease.

Despite the widespread prevalence of C. pneumoniae in humans, all isolates studied to date are extremely similar at the DNA level. Four C. pneumoniae human isolates have had their full genome sequenced. Genomic comparisons revealed a highly conserved (>99.9%) gene order and organisation, with few deletions and less than 300 single nucleotide polymorphisms (SNPs) distinguishing the isolates. This near clonality of C. pneumoniae human isolates that are temporally and geographically separate, has been taken to indicate that human infections are a relatively recent event and that the efficient respiratory spread of the agent explains how 60–80% of adults worldwide have been infected at least once in their lifetime .

Researchers selected 23 target genes in this organism to investigate genetic diversity: seven of these had been lost or gained by C. pneumoniae, a further six were conserved, four were polymorphic, and six were truncated or length polymorphic in one strain or the other. The results highlights that C. pneumoniae animal isolates are much more genetically diverse than C. pneumoniae human isolates, and have crossed the host barrier to humans on at least two occasions. This study provides new insights into the evolution of this complex pathogen.

Chlamydia pneumoniae Is Genetically Diverse in Animals and Appears to Have Crossed the Host Barrier to Humans on (At Least) Two Occasions. 2010 PLoS Pathog 6(5): e1000903. doi:10.1371/journal.ppat.1000903

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• Chlamydia use proteolysis to evade host defences