Fungal physiology

N -acetylglucosamine induces white to opaque switching, a mating prerequisite in Candida albicans Huang, G. et al. PLoS Pathog. 6, e1000806 (2010) (doi: 10.1371/journal.ppat.1000806)

The pathogenic fungus Candida albicans must switch from a white form to an opaque form to mate. This switch is regulated by an elaborate genetic programme, but the signals that initiate it were poorly understood. Soll and colleagues now show that the percentage of cells that undergo switching is more than 25-fold higher in cells grown on the monosaccharide N-acetylglucosamine (GlcNAc) than in cells grown on glucose. GlcNAc-induced upregulation of switching required cyclic AMP, Ras1, the protein kinase A subunit Tpk2 and the master regulator of switching, Wor1. Furthermore, an increased level of CO2, which also induces switching, acts synergistically with GlcNAc. As GlcNAc is produced mainly by bacteria, this signal is probably encountered along with increased CO2 levels in the human intestinal tract, ensuring high levels of switching to the opaque state and, hence, high levels of mating.

Viral immune evasion

Antagonism of the complement component C4 by flavivirus nonstructural protein NS1 Avirutnam, P. et al. J. Exp. Med. 22 Mar 2010 (doi: 10.1084/jem.20092545)

Many pathogens have developed mechanisms to evade elimination by the complement system, which has an important role in the clearance of pathogens in the host. It has now been discovered that flaviviruses (including West Nile virus, yellow fever virus and dengue virus) have a unique means of preventing the action of the complement system. The viral protein NS1 can form a complex with complement component C1 in solution and can also then bind complement component C4. This leads to the cleavage of C4 to C4a and C4b. As C4b is rapidly hydrolysed in solution, virus-directed cleavage of C4 in solution inhibits the complement system downstream of C4, increasing the survival of the virus.

Metagenomics

Bacterial diversity in the oral cavity of 10 healthy individuals Bik, E.M. et al. ISME J. 25 Mar 2010 (doi:10.1038/ismej.2010.30)

A large metagenomic study has shown that the microbiome of the human mouth differs between individuals. In this study, samples were collected from the mouths of 10 healthy individuals, and a total of 11,368 16S ribosomal RNAs were cloned and sequenced. This revealed a total of 247 operational taxonomic units covering 9 bacterial phyla, including 24 sequences with < 99% identity to known species. The prevalence of the different bacteria varied between individuals: eight genera were detected in all individuals, but the most abundant genus was Streptococcus in five individuals, Prevotella in two individuals and Neisseria, Haemophilus and Veillonella each in one individual. Analysis of co-occurrence and exclusion at the genus level showed that some bacteria were more likely to be found together, whereas others were more likely to compete. The composition of the oral microbiome was found to differ from that of other sites, such as the intestine, suggesting that the mouth contains its own unique ecosystem.