The private life of environmental bacteria: pollutant biodegradation at the single cell level

Bacteria display considerable cell-to-cell heterogeneity in a number of genetic and physiological traits. Stochastic differences in regulatory patterns (e.g. at the transcriptional level) propagate into the metabolic and physiological status of otherwise isogenic cells, which ultimately results in appearance of sub-populations within the community. As new technologies emerge and because novel single cell strategies are constantly being refined, our knowledge on microbial individuality is in burgeoning and constant expansion. These approaches encompass not only molecular biology tools (e.g. fluorescent-protein based reporters) but also a suite of sophisticated, non-invasive technologies to gain insight into the metabolic state of individual cells. Defining the role of individual heterogeneities is thus instrumental for the population-level understanding of macroscopic processes in both environmental and industrial set-ups. The present article reviews the state-of-the-art methodologies for the investigation of single bacteria at both the genetic and metabolic level, and places the application of currently available tools in the context of microbial ecology and environmental microbiology. As a case example, we examine the stochastic and multi-stable behaviour of the TOL-encoded pathway of Pseudomonas putida mt-2 for the biodegradation of aromatic compounds. Bet-hedging strategies and division of labour are considered as factors pushing forward the evolution of environmental microorganisms.