Viral immune evasion

Retroviral infection in vivo requires an immune escape virulence factor encrypted in the envelope protein of oncoretroviruses Schlecht-Louf, G. et al. Proc. Natl Acad. Sci. USA 107, 3782–3787 (2010)

Retroviral envelope (Env) proteins have an immunosuppressive activity that can be removed by the deletion of specific residues. The authors 'switched off' the immunosuppressive capacity of the Friend murine leukaemia virus (FrMLV) Env and assessed its importance in virus physiology in vivo. Wild-type virus causes high viraemia, whereas mice infected with mutant FrMLV had barely detectable or undetectable viraemia 7 and 14 days after infection, respectively. The Env residues suppress immune responses mediated by natural killer cells and T cells at early and late stages of infection, respectively. Injection with the mutated virus protected the mice against subsequent infections with wild-type virus, suggesting that deletion of the immunosuppressive domain of Env could be a retroviral vaccine strategy.

Biofilms

Treponema denticola biofilm-induced expression of a bacteriophage, toxin-antitoxin systems and transposases Mitchell, H. L. et al. Microbiology 156, 774–788 (2010)

In this study the authors developed a continuous culture system that allows the parallel growth of biofilm and planktonic forms of Treponema denticola to assess differences in the expression of proteins involved in the persistence of T. denticola in biofilms. Many genes were upregulated in the biofilm T. denticola, including the major virulence factor cystalysin, outer sheath proteins, several toxin–antitoxin systems and a family of transposases. The increased expression of virulence factors indicates that T. denticola might be more virulent when growing in a biofilm. They also identified for the first time a lysogenic phage (ϕtd1) that is incorporated in the T. denticola genome and found that its lytic genes are upregulated during biofilm growth, producing excised and circularized phages. These data suggest that when T. denticola grows in mixed-species biofilms there is high potential for gene transfer to increase virulence and facilitate biofilm persistence.

Bacterial physiology

Acetylation of metabolic enzymes coordinates carbon source utilization and metabolic flux Wang, Q. et al. Science 327, 1004–1007 (2010)

Lysine acetylation controls many processes in eukaryotes, including metabolism, and now this study shows that it also has an integral role in Salmonella enterica metabolism. The authors show that 90% of the acetylated proteins in S. enterica have metabolic functions. These include three central metabolic enzymes (GapA, AceA and AceK), the function of which was regulated by the S. enterica major acetyltransferase, PatA, and the NAD+-dependent deacetylase CobB. Furthermore, the protein acetylation status depended on the carbon source, as mutants lacking PatA grew better on citrate medium, whereas those lacking CobB grew better on glucose medium. PatA and CobB levels were in fact found to be differentially regulated on the basis of carbon source, revealing an important regulatory circuit that controls metabolism through acetylation.