Temporal changes in bacterial rRNA and rRNA genies in Delaware (USA) coastal waters

The diversity and abundance of bacterial 16S rRNA genes (rDNA) and associated 16S rRNA were assessed to examine community structure and potential activity in a 2 yr seasonal study of marine surface waters along the Delaware (USA) coast. The majority of the ribotypes appearing as rRNA or rDNA were present at least 50% of the time, and their variation over time was less than that of most biotic and abiotic factors. Even though there were no predictable seasonal patterns in community structure, environmental parameters explained between 40 and 50% of the observed variation in community structure, In general, summer communities correlated positively with temperature, light, bacterial production, and phosphate levels, while winter communities correlated with dissolved organic carbon concentrations. The abundance of 3 select ribotypes (SAR11, a Cytophaga subgroup, SAR116-like) varied some over time as measured by quantitative PCR (qPCR). The SAR11 clade was 10 times more abundant than the other 2 groups. However, the 16S rRNA to rDNA ratios, as measured by qPCR and reverse transcription-qPCR, varied greatly over time and were highest in the SAR11 population and the Cytophaga subgroup. The rRNA to rDNA ratio of the Cytophaga subgroup and SAR116-like group significantly correlated with some environmental parameters. Taken together, these results suggest that the community composition of the major members does not change much over time, but individual members do vary in abundance and activity and can be influenced by environmental factors.