Acinetobacter baylyi Starvation-Induced Genes Identified through Incubation in Long-Term Stationary Phase

Acinetobacter species encounter cycles of feast and famine in nature. We show that populations of Acinetobacter baylyi strain ADP1 remain dynamic for 6 weeks in batch culture. We created a library of lacZ reporters inserted into SalI sites in the genome and then isolated 30 genes with lacZ insertions whose expression was induced by starvation during long-term stationary phase compared with their expression during exponential growth. The genes encode metabolic, gene expression, DNA maintenance, envelope, and conserved hypothetical proteins.Acinetobacter species are ubiquitous soil organisms. Starvation during long-term stationary phase (LTSP) can serve as a laboratory model for natural competitive conditions such as those found in soils (4). This model has been used to study Escherichia coli, and here, we have applied it to Acinetobacter baylyi strain ADP1 (8).During long-term batch culture, an initially clonal population of Escherichia coli experiences five growth stages: lag, exponential, and stationary phases and then death phase and LTSP (4). Prior to LTSP, most of the cells die and serve as nutrition for starving survivors (6, 13). In LTSP, the cell population remains almost steady, declining slowly over years (reviewed in reference 4): for each newly dead cell, slightly less than one new cell is “born.”Much of what is known about starvation physiology during LTSP has been determined through study of the growth advantage in stationary phase (GASP) phenotype. The phenotype arises from genetic changes that occur when cells experience LTSP. During LTSP, the population may have a mutation frequency approaching 1 in 600 base pairs per genome (5).Some physiological changes that take place during LTSP have been described, as have some genes necessary for the development of GASP (13, reviewed in reference 12). Some mutant strains that exhibit GASP have mutations that enhance catabolic efficiency for processing amino acids (14-16). Another nutrient consumed is DNA, which requires genes homologous to strain ADP1''s competence genes (6). Additionally, mutations that knock out SOS polymerases interfere with the formation of GASP mutants (11).