Physiological Structure and Single-cell Activity in Marine Bacterioplankton

Generations of microbiologists have pondered over the issue of bacterial activity and whether most bacteria in the environment are “active,” “inactive,” or “dormant” (Stevenson 1978). This is a question with clear practical implications, in terms of food, sanitary, and clinical microbiology, as well as profound ecological implications. The issue started to be debated in earnest within the aquatic microbial community roughly at the time researchers were developing new methods to estimate the total abundance of aquatic bacteria, since some of the first stains used were thought to respond differently depending on the RNA content of single bacterial cells (see, e.g., Francisco et al. 1973). It was not until bacteria were recognized as being not only very abundant, but also active, that the notion of microbes as important partners in the marine food web gained widespread recognition (Pomeroy 1974). The early studies using radiotracer incorporation showed surprisingly high rates of bacterial