Marine bacteria are essential links in marine productivity and biogeochemical cycles. Although the species composition of marine bacteria is largely unknown, evidence suggests that most marine bacteria are members of the Purple bacteria phylum of the Eubacterial kingdom. The phylum contains photosynthetic, heterotrophic, and lithotrophic bacteria. Many members are capable of either the oxidation or reduction of nitrogen and sulfur which are extremely important in the marine environment. This project seeks to ascertain if a general relationship between RNA/DNA ratios and growth rate exists for the Purple bacteria. New evidence from the marine Purple bacterium, Pseudomonas perfectomarina, indicates that the relationship between RNA/DNA ratio and growth rate extends to the low growth rates believed to occur in the ocean. Furthermore, the Ps. perfectomarina data is in agreement with the RNA/DNA ratios measured on enteric bacteria at near maximal growth rates. However, it has not been widely established that this predictive relationship between RNA/DNA ratio and growth rate is valid for other Purple bacteria over the complete range of growth rates that can exist in the natural environment. In order to expand the repertoire of rRNA probes that can be used to measure microbial growth rate in the ocean, a five-step approach will be undertaken to: 1) clone the marine rRNA genes and create marine rRNA promoter-reporter gene fusions to assess if there is regulation in a growth rate-dependent manner; 2) empirically measure the RNA-DNA ratio vs growth rate for six marine bacteria (representing three subdivisions of the Purple bacteria) using previously established methods; 3) investigate the mechanisms controlling rRNA synthesis in the marine bacteria; 4) screen the marine bacteria's genomes for the presence of novel genes regulating rRNA synthesis; 5) clone and sequence the 23 S rRNA subunit of each marine bacterium and identify species-specific regions which will be used to assay the in situ growth rate in seawater samples from the Southern California Bight. If a general relationship between RNA/DNA ratios and growth rates are found to exist for these purple bacteria, investigators could routinely determine the presence and measure the growth rates of large numbers of Purple bacteria in natural samples. In conclusion, it is extremely important for the future use of rRNA probes in the ocean that the relationship between rRNA and growth rate be investigated. No other macromolecule can provide the genetic and metabolic information necessary to evaluate the growth rate of a single species of micro-organism in a complex assemblage without the risk of contamination.
