Inhibition of Escherichia coli precursor-16S rRNA processing by mouse intestinal contents

The correlation between ribosome content and growth rate found in many bact erial species has proved useful for estimating the growth activity of indiv idual cells by quantitative in situ rRNA hybridization. However, in dynamic environments, the stability of mature ribosomal RNA causes problems in usi ng cellular rRNA contents for direct monitoring of bacterial growth activit y in situ. In a recent paper, Cangelosi and Brabant suggested monitoring th e content of precursors in rRNA synthesis (pre-rRNAs) as an alternative app roach. These are rapidly broken down after the cessation of bacterial growt h. We have applied fluorescence in situ hybridization of pre-16S rRNA to Es cherichia coil cells growing in vitro in extracts from two different compar tments of the mouse intestine: the caecal mucus layer, where E. coil grew r apidly, and the contents of the caecum, which supported much slower bacteri al growth. The amounts of 23S rRNA and pre-16S rRNA measured for E. coil gr owing in intestinal mucus corresponded to that expected for bacteria with t he observed growth rate. In contrast, the slow-growing E. coil cells presen t in intestinal contents turned out to have an approximately ninefold highe r content of pre-16S rRNA than cultures of the same strain growing rapidly in rich media. We present results suggesting that the mouse intestinal cont ents contain an agent that inhibits the growth of E. coil by disturbing its ability to process pre-16S rRNA.