Heterogeneity in GFP expression in isogenic populations of P. putida KT2440 investigated using flow cytometry and bacterial microarrays
Individual bacteria, even bacteria belonging to an isogenic population under uniform environmental conditions, display phenotypic diversity and variability in gene expression. The increased focus that is lately given to this topic within microbiology and quantitative biology has motivated a quest for new experimental approaches providing insight into phenotypic traits at the single-cell level. In the present paper we investigate the applicability of bacterial microarrays for studies of bacterial populations including their inherent heterogeneity. The results obtained from the microscopy of bacterial microarrays are compared to the results obtained using flow cytometry. Two different positive-regulated promoter systems were utilized in isogenic cultures of Pseudomonas putida, both systems leading to green fluorescent protein production upon induction. Using both experimental approaches, a shift to higher fluorescence intensities with increasing time and increasing inducer concentration was observed, as well as a broadening of the distributions. Additionally, the micrographs of the bacterial microarrays revealed heritable inter-cell variation in green fluorescent protein levels. These observations indicate that for the bacteria studied here the cell to cell heterogeneity in green fluorescent protein expression, as also detected in the flow cytometer, are due to relatively static inter-cell differences.