Bacterial communities in pigmented biofilms formed on the sandstone bas-relief walls of the Bayon Temple, Angkor Thom, Cambodia.

The Bayon temple in Angkor Thom, Cambodia has shown serious deterioration and is subject to the formation of various pigmented biofilms. Because biofilms are damaging the bas-reliefs, low reliefs engraved on the surface of sandstone, information about the microbial community within them is indispensable to control biofilm colonization. PCR-denaturing gradient gel electrophoresis (DGGE) analysis of biofilm samples from the pigmented sandstone surfaces showed that the bacterial community members in the biofilms differed clearly from those in the air and had low sequence similarity to database sequences. Non-destructive sampling of biofilm revealed novel bacterial groups of predominantly Rubrobacter in salmon pink biofilm, Cyanobacteria in chrome green biofilm, Cyanobacteria and Chloroflexi in signal violet biofilm, Chloroflexi in black gray biofilm, and Deinococcus-Thermus, Cyanobacteria, and Rubrobacter in blue green biofilm. Serial peeling-off of a thick biofilm by layers with adhesive sheets revealed a stratified structure: the blue-green biofilm, around which there was serious deterioration, was very rich in Cyanobacteria near the surface and Chloroflexi in deep layer below. Nitrate ion concentrations were high in the blue-green biofilm. The characteristic distribution of bacteria at different biofilm depths provides valuable information on not only the biofilm formation process but also the sandstone weathering process in the tropics.

Complete inhibition of tobamovirus multiplication by simultaneous mutations in two homologous host genes.

The TOM1 gene of Arabidopsis thaliana encodes a putative multipass transmembrane protein which is necessary for the efficient multiplication of tobamoviruses. We have previously shown that mutations severely destructive to the TOM1 gene reduce tobamovirus multiplication to low levels but do not impair it completely. In this report, we subjected one of the tom1 mutants (tom1-1) to another round of mutagenesis and isolated a new mutant which did not permit a detectable level of tobamovirus multiplication. In addition to tom1-1, this mutant carried a mutation referred to as tom3-1. Positional cloning showed that TOM3 was one of two TOM1-like genes in Arabidopsis. Based on the similarity between the amino acid sequences of TOM1 and TOM3, together with the results of a Sos recruitment assay suggesting that both TOM1 and TOM3 bind tobamovirus-encoded replication proteins, we propose that TOM1 and TOM3 play parallel and essential roles in the replication of tobamoviruses.