Intra-strain Inhibition Between Bacterial Colonies is a Common Phenomenon Mediated by a Diffusible Compound Exhibiting Broad-spectrum Antibiotic Activity

Author

Ertan Kastrat, The Graduate Center, City University of New YorkFollow

Date of Degree

6-2024

Document Type

Dissertation

Degree Name

Ph.D.

Program

Biology

Advisor

Haiping Cheng

Committee Members

Edward Kennelly

Stephen Redenti

Anuradha Janakiraman

Akira Kawamura

David H Bechhofer

Subject Categories

Amino Acids, Peptides, and Proteins | Bacterial Infections and Mycoses | Bacteriology | Biochemistry | Microbial Physiology | Other Chemicals and Drugs

Keywords

Bacteriology, Drug discovery, Microbial physiology, Biochemistry

Abstract

Bacteria possess a repertoire of tools which function to aid in the competition for nutrients and space in their environment. One strategy employed in this competitive behavior involves the production and secretion of secondary metabolites which exhibit antibiotic activity, leading to the inhibition of growth or killing of competing bacteria. Antibiotic secondary metabolites can be peptidic in nature and may or may not be ribosomally synthesized and post-translationally modified. Some known peptidic antibiotics are bacteriocins, microcins, thiopeptides, and lasso peptides. The spectrum of activity for antibiotic peptides is generally narrow; activity can be observed across a small number of select species, across strains, and in the rarest of cases, peptidic antibiotics can exhibit clonal inhibition. The use of antibiotic peptides in a clinical setting is hampered by their narrow spectrum of activity. Clinically significant antibiotics are generally non-proteinaceous/peptidic in nature. Examples of these compounds are aminoglycosides, polymyxins, and tetracyclines, amongst others. A lesser employed strategy of bacterial competition is more altruistic in nature, involving the suicide of a cell, in a mechanism known as bacterial programmed cell death, which bears hallmarks analogous to eukaryotic programmed cell death. Considering the dire need for novel antibiotics to combat the growing trend of drug-resistant bacterial infections, we can look to these natural phenomena to gain greater insight into new methods for natural product screening and discovery. Our work focuses on a self-inhibition phenotype we discovered in Gram-negative and Gram-positive bacteria resulting in the formation of inhibitory boundaries between expanding neighboring bacterial colonies. We hypothesize this boundary contains an inhibitory compound that is secreted, functioning to disrupt the encroachment of a competing colony. We postulate that the inhibitory compound is produced through sensing of crowded or high cell density conditions and show that it functions as an antibiotic agent active against the producer strain and other bacterial species. We developed methods to upregulate the production of the compound functioning in self-inhibition and obtained broad-spectrum antibiotic supernatants derived from Escherichia coli and other bacteria. Treatment with the E. coli supernatant results in bactericidal activity against the producer strain along with all Gram-negative and Gram-positive bacteria we tested, including multi-drug resistant clinical isolates and Mycobacterium tuberculosis. Our data suggest the E. coli antibiotic supernatant contains a novel compound displaying a treatment phenotype not previously described in the literature. Biochemical analysis revealed the active compound is hydrophilic in nature and is likely to be a few hundred Daltons in size, falling in line with the expected size and chemistry of compounds capable of traversing the bacterial membrane. The active compound exhibits pH-dependent activity, making it an optimal candidate for treatment of infections, where dysregulation of physiological pH typically occurs. We also show that the active compound is non-toxic to eukaryotic cells and does not lyse human red blood cells, suggesting the mechanism of action is unique towards bacteria. Together, this work unveils a possibly novel antibiotic compound effective against drug resistant bacteria and introduces methods for eliciting the production of bioactive compounds from bacteria.

Recommended Citation

Kastrat, Ertan, "Intra-strain Inhibition Between Bacterial Colonies is a Common Phenomenon Mediated by a Diffusible Compound Exhibiting Broad-spectrum Antibiotic Activity" (2024). CUNY Academic Works.
https://academicworks.cuny.edu/gc_etds/5846