Phage biology

Independent virus development outside a host Häring, M. et al. Nature 436, 1101–1102 (2005)

All viruses require a host cell for functional activity, right? Wrong, according to a paper recently published in Nature. The authors report their discovery of an archaeal virus that develops a long tail from both ends only once it has been released from the host cell. The virus was isolated from an acidic hot spring at Pozzuoli, Italy, and was detected in enrichment culture as lemon-shaped particles bearing appendages of varying lengths at both ends. The virus, named ATV, could be cultured in the hyperthermophilic archaeon Acidanius convivator but, surprisingly, tails were only observed after infected cell cultures had been maintained at 75°C for 8 days. Analyses confirmed that the tail development is an active biological process. As ATV causes a lytic infection, the host-independent development of tails could be a useful strategy for survival in the external environment.

Environmental microbiology

Computational improvements reveal great bacterial diversity and high metal toxicity in soil Gans, J. et al. Science 309, 1387–1390 (2005)

Accurate measurements of the species abundance of microorganisms in environments such as soil are extremely difficult to obtain. In a recent issue of Science, researchers from Los Alamos National Laboratory have published details of a new analytical approach, based on reassociation kinetics, which allows different species-abundance models to be quantitatively compared. The authors then reanalysed three reassociation data sets from a study that had assessed the impact of metal pollution on bacterial diversity and abundance. The analysis revealed that in the original study, the abundance of microorganisms had been underestimated by two orders of magnitude. The effects of metal pollution had also been underestimated — although the overall bacterial biomass was unaffected, bacterial diversity was reduced by >99.9%.

Phage biology

The single-stranded genome of phage CTX is the form used for integration into the genome of Vibrio cholerae Val, M. -E. et al. Mol. Cell 19, 559–566 (2005)

The Vibrio cholerae positive single-stranded (ss) DNA phage CTXΦ integrates into the V. cholerae genome using the host-encoded tyrosine recombinases XerC and XerD. Now, new work published in Molecular Cell by Val et al. provides more molecular details on the integration reaction. The new data reveal that folding of the phage ssDNA genome between the XerC- and XerD-binding sites into a hairpin structure creates the reaction substrate for XerCD, allowing integration into the host genome while at the same time preventing inappropriate excision. This reaction differs greatly from the classical model of ssDNA integration and creates a new paradigm for tyrosine recombinase action.