Feroz Ahmed

ORCID Identifier(s)


Graduation Semester and Year




Document Type


Degree Name

Doctor of Philosophy in Quantitative Biology



First Advisor

Joseph Boll


Acinetobacter baumannii is particularly problematic in hospital settings, where infections can occur in a range of tissues. This bacterium can endure extreme stress from various antimicrobial agents, biocides, host immune response etc. Not much is known about how these bacteria react to such high stress. A. baumannii also possesses a unique ability to inactivate lipooligosaccharide (LOS) biosynthesis, which is an essential molecule in most Gram-negative bacteria. LOS is enriched in the outer membrane and is the targeted by the last-resort antibiotic, colistin. LOS-deficient A. baumannii is highly resistant to the list-line antimicrobial. Previously, our lab discovered that a two-component system, called BaeSR, showed increased transcription in LOS-deficient cells relative to wild type. Furthermore, baeSR was required for LOS-deficient A. baumannii viability, suggesting that it regulated expression of some essential product. To determine BaeSR-dependent regulatory products we performed transcriptomics analysis on wild type and baeR mutants. Several pathways were downregulated in the mutant, including putative lipoproteins, lipoprotein transport genes, efflux pump genes, genes that regulate biofilm formation and phenylacetic acid catabolism. The paa operon acts on phenylacetic acid (PAA), an intermediary in the breakdown of phenylalanine, and is differently regulated in stress-induced conditions. Previous work showed that the GacSA two-component system also regulates the paa operon, but it was unknown if this regulation was direct or indirect. Notably, the sensor kinase, GacS, and response regulator, GacA, are not co-transcribed, which raises the possibility that the sensor kinase, GacS, may signal through other response regulators. We found that BaeR complementation not only restored wild type paa expression levels in ΔbaeR and ΔgacS, but IPTG-dependent overexpression further induced paa overexpression. Electrophoretic mobility shift assay showed that the paa promoter bound recombinant BaeR6X-his, suggesting a direct interaction. We also found that BaeR regulates expression of csu operon genes that controls biofilm formation. Biofilm formation is considered a stress response which relies on production of extracellular polymeric substances (EPS) to provide structural support so bacterial pathogens can withstand adverse conditions. This data presented here in suggest the BaeSR TCS contributes to A. baumannii survival in stress.


Stress Response, Lipopolysaccharides, Two-component System, Lipoproteins, Photosensitizers


Biology | Life Sciences


Degree granted by The University of Texas at Arlington

Available for download on Friday, August 01, 2025

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