Environmental microbiology

Phage community dynamics in hot springs Breitbart, M. et al. Appl. Environ. Microbiol. 70, 1633–1640 (2004)

Breitbart et al. report the abundance of phage in extreme thermal environments (up to 1 million viruses ml−1) and the corresponding lysis of a large proportion of the resident bacterial species, which shows that these phage have a clear role in community dynamics. As some of these phage were robust at lower temperatures, lateral DNA transfer from these extreme environments is plausible.

Anti-infectives

Inhibition of hepatitis B virus replication by APOBEC3G Turelli, P. et al. Science 303, 1829 (2004)

Human APOBEC3G is a cytidine deaminase that has antiretroviral activity. It is packaged into virions and deaminates deoxycytidine residues to yield deoxyuridine during viral DNA synthesis, which generates non-functional proviruses. Replication of hepatitis B virus involves reverse transcription, and expression of APOBEC3G reduced the amount of released HBV DNA by 50-fold. This effect was reversed by supplying HIV-1 Vif protein. Vif prevents virion incorporation of the deaminase. APOBEC3G catalytic activity was not required to inhibit HBV DNA replication. Instead, it seemed to block pre-genomic RNA packaging — so the mechanisms of inhibition of retroviruses and HBV by this molecule are different.

Bacterial pathogenesis

Auto, a surface-associated autolysin of Listeria monocytogenes required for entry into eukaryotic cells and virulence Cabanes, D. et al. Mol. Microbiol. 51, 1601–1614 (2004)

Cabanes et al. used subtractive genomics to identify Listeria monocytogenes surface proteins that were not shared with a non-pathogenic Listeria strain. They identified an autolysin (Auto) and showed that it is required for cell entry in vitro and in vivo. This new determinant for L. monocytogenes entry into eukaryotic cells is expressed independently of the master virulence-gene regulator PrfA and might function to reorganize bacterial surface architecture during infection.

Fungal physiology

Inoculum size effect in dimorphic fungi: extracellular control of yeast-mycelium dimorphism in Ceratocystis ulmi Hornby, J. M. et al. Appl. Environ. Microbiol. 70, 1356–1359 (2004)

Ceratocystis ulmi is a dimorphic fungus. Yeast predominate when C. ulmi is grown in vitro using a large inoculum but, with a low inoculum size, mycelia develop. This was attributed to the production of a quorum-sensing signalling molecule, which mediates the developmental switch from mycelial to yeast cell growth.