2015 Elsevier Inc. All rights reserved. Environmental microbiologists are not only interested in "who" is in the community, but also "what activities" the community carries out. Such activities can be identified and quantified via "physiological methods." The goal of this chapter is to examine different types of microbial activity measurements in both pure culture and environmental samples. In pure culture, activity measurements include: measurement of substrate disappearance; terminal electron acceptor (TEA) utilization; cell mass increase; and carbon dioxide evolution. Environmental activity measurements are discussed in terms of: carbon respiration; incorporation of radiolabeled tracers; adenylate energy determination; enzymatic assays; and stable isotope probing.
