Monitoring precursor 16S rRNAs of Acinetobacter spp. in activated sludge wastewater treatment systems

Recently, Cangelosi and Brabant used oligonucleotide probes targeting the p recursor 16S rRNA of Escherichia coli to demonstrate that the levels of pre cursor rRNA were more sensitive to changes in growth phase than the levels of total rRNA (G. A. Cangelosi and W. H. Brabant, J, Bacteriol. 179:4457-44 63, 1997), In order to measure changes in the levels of precursor rRNA in a ctivated sludge systems, we designed oligonucleotide probes targeting the 3 ' region of the precursor 16S rRNA of Acinetobacter spp. We used these prob es to monitor changes in the level of precursor 16S rRNA during batch growt h of Acinetobacter spp. in Luria-Bertani (LB) medium, filtered wastewater, and in lab- and full-scale wastewater treatment systems. Consistent with th e previous reports for E. coli, results obtained with membrane hybridizatio ns and fluorescence in situ hybridizations with Acinetobacter calcoaceticus grown in LB medium showed a more substantial and faster increase in precur sor 16S rRNA levels compared to the increase in total 16S rRNA levels durin g exponential growth. Diluting an overnight culture of A. calcoaceticus gro wn in LB medium with filtered wastewater resulted in a pattern of precursor 16S rRNA levels that appeared to follow diauxic growth. In addition, fluor escence in situ hybridizations with oligonucleotide probes targeting total 16S rRNA and precursor 16S rRNA showed that individual cells of A. calcoace ticus expressed highly variable levels of precursor 16S rRNA when adapting from LB medium to filtered sewage. Precursor 16S rRNA levels of Acinetobact er spp. transiently increased when activated sludge was mixed with influent wastewater in lab- and full-scale wastewater treatment systems. These resu lts suggest that Acinetobacter spp. experience a change in growth activity within wastewater treatment systems.