ABSTRACT: We report detailed characterization of physiological changes encoded by 63% of all genes within the archaeon Halobacterium salinarum subsp. NRC-1 during routine laboratory growth. While the majority of these changes occur during the transition from rapid exponential growth to the stationary phase, we were also able to detect transient changes in gene expression. This demonstrated the presence of several additional albeit subtle physiological states that exist beyond what might be anticipated from a direct interpretation of the growth profile. Changes in the abundance of several key intracellular metabolites over the growth curve corroborated observations of changes in gene expression of enzymes that catalyze their synthesis. Next, we investigated the roles of general transcription factors (GTFs) in mediating these global growth-associated gene expression changes. This revealed numerous phenotypic perturbations including slowed growth, gas vesicle biogenesis deficiency and morphologic abnormalities upon the overexpression of a single GTF - TBPd. These phenotypes were quantified and were attributed to a perturbation in the regulation of aconitase. Importantly, our results demonstrate why an experiment design as simple as a simple batch culture can be enormously informative of activities and interrelationships of a large fraction of all genes in a microbe. Halobacterium NRC-1 was grown in shaken (220RPM) complete medium liquid culture at 37°C in duplicate flasks. 20µg/ml uracil was added to the media. Samples were selected at 7 timepoints during the growth of this organism representing different phases of growth (e.g. early exponential, logrithmic, stationary etc.). RNA extractions were performed using the Stratagene Absolutely RNA Miniprep Kit and RNA quality checked with the Agilent Bioanalyzer and with Oligo Microarrays were fabricated at the Institute for Systems Biology Microarray Facility. The arrays contain 4 spots per unique 70-mer oligonucleotides for each of 2400 non-redundant genes in Halobacterium NRC-1 Labeling, hybridization and washing have been previously described (Baliga et al. 2002) with 10 μg of RNA from the sample and reference. RNA from the final time point of a replicate experiment was used as the reference. Bias in dye incorporation was accounted for by reversing the labeling dyes (dye-flip). Raw data was processed and converted into log10 ratios with lambda (λ) values determined by a maximum likelihood method.Baliga, N. S., Pan, M., Goo, Y. A., Yi, E. C., Goodlett, D. R., Dimitrov, K., Shannon, P., Aebersold, R., Ng, W. V. & Hood, L. (2002) Proc Natl Acad Sci U S A 99:14913-84. Keywords: growth curve, archaea, halobacterium
