Antibiotics, including tetracycline, could exert selective pressure on these plasmids and facilitate the spread of antibiotic resistance genes in the environment. TC prevents bacterial growth by binding to a single site on the 30S ribosomal subunit, and preventing attachment of aminoacyl tRNA molecules to the ribosome. TC-related antibiotics have been applied in clinics, and in agricultural and aquatic settings for disease control and animal growth promotion, and are frequently detected in the effluent from WWTPs. TC resistance could be acquired by three known mechanisms: energy-driven efflux pumps, ribosomal protection proteins, and TC-modifying enzymes. Efflux pumps encoded by several genes, such as tetA, tetC, tetE, tetG, and tetH, have been reported to be a major mechanism of TC resistance; these genes are frequently located in plasmids and transposons. Antibiotic resistance is known to exert a metabolic cost on bacteria, and antibiotic-resistant cells often show a reduced growth rate. The correlation between fitness cost and antibiotic resistance has been extensively reviewed. Previously, we demonstrated that not only bacterial growth, but also many cellular processes including quorum sensing, motility, and stress response could be affected by acquiring antibiotic resistance. A newly described tetracycline resistance plasmid, pAST2, was isolated from an activated sludge, and its entire plasmid genome was characterized. The pAST2 plasmid encodes the TC efflux pump, tetH, and tetR genes that BIBW2992 distributor confer tetracycline resistance to the host. Expression of the tetH gene is known to be regulated by a repressor, TetR. Based on our bioinformatics study, this tetH-tetR module originated in bovine and swine pathogens such as Pasteurella multocida, Mannheimia haemolytica, and Actinobacillus pleuropneumoniae. Recently, we demonstrated that the acquisition of this plasmid alters the phenotypic characteristics of the oil-degrading microbe Acinetobacter oleivorans DR1. Presence of the plasmid incurred high ecological costs for phenotypic and physiological functions in A. oleivorans DR1. This observation is consistent with the fact that antibiotic resistance plasmids alter the expression of host chromosomal genes and ecological adaptation in Salmonella. The aims of this study were to gain insight into the link between changes in host chromosomal expression and phenotypic changes in the presence of the pAST2 plasmid, and to distinguish the metabolic costs incurred by the plasmid replication burden and by changes in membrane integrity caused by addition of the plasmid-encoded tetracycline efflux pump. We compared four RNA-Seq transcriptomes of the wild-type and plasmidharboring cells in the presence and absence of TC. To understand the fitness costs of the efflux pump, a tetH-tetR knockout plasmid was generated and tested under different environmental conditions.