Siderophores are small, iron chelating molecules produced by many bacteria to help meet the iron requirements of the cell. Multiple metabolic functions require iron as it serves as a cofactor in many enzymes and cellular processes. However, in the presence of oxygen and at physiologic pH, iron forms insoluble ferric complexes that cause the nutrient to be unavailable to bacterial cells. Siderophores alleviate this limitation by chelating the ferric iron, rendering it soluble and available for uptake. One group of microorganisms known for their ability to produce siderophores is the rhizobia. These bacteria are characterized both by their formation of symbiotic relationships with leguminous plants and their ability to fix atmospheric nitrogen. Rhizobium leguminosarum ATCC 14479, which infects the red clover Trifolium pratense, was found to produce a trihydroxamate siderophore. Purification and chemical characterization identified this siderophore as Vicibactin that has been found to be produced by other rhizobial strains.

Iron is necessary for many cellular processes such as the electron transport chain and gene regulation. However, most iron on earth is found in insoluble iron-hydroxide complexes. In addition, iron is tightly sequestered in the human body by proteins such as transferrin, making it unavailable for pathogens. In order to overcome these limitations bacteria have evolved siderophores. Siderophores are low molecular weight compounds that bind ferric iron with a high affinity. Staphylococcus aureus is an important human pathogen that is known to produce at least four siderophores, and these siderophores contribute to its virulence. S. aureus strain H372 was found to produce a siderophore that was a carboxylate type, hydrophilic, and contained ornithine. These properties were similar to the known siderophore staphyloferrin A. However, the probable molecular weight was 658, which is different from known staphylococcal siderophores.

Many important antibiotics have become nearly obsolete due to the rise of antibiotic resistant pathogens. Rhodococcus, an actinomycete related to the prolific antibiotic producing genus Streptomyces, harbors over 30 genes for secondary metabolism that could be involved in antibiotic production. Several antibiotics have already been reported for Rhodococcus, suggesting the genus may be a good source for new inhibitory compounds. Fifty four soil bacteria were isolated using enrichment culture techniques (including 37 Rhodococcus) and screened for antibiotic producers. BTHX2, a species of Bacillus was found to have activity against Micrococcus luteus and Rhodococcus erythropolis. BTHX2 has a 16S rDNA sequence 97% homologous to Bacillus licheniformis, and may be a new strain of B. licheniformis. The inhibitory substance produced by BTHX2 was and found to have a spectrum of activity against a broad Gram-positive bacteria and some fungus, and may have cytolytic activity.

Iron is essential for life and growth in most organisms. Although it is abundant, iron exists mostly as insoluble iron-oxyhydroxide. Bacteria secrete siderophores to chelate iron and transport it into the cell via specific outer membrane receptors. The FhuA receptor protein transports ferrichrome, a siderophore produced by Ustilago sphaerogena. We determined the binding affinity of variants from the conserved 'lock region' of FhuA and also created and characterized variants of the highly conserved R452 to determine its role in ferrichrome transport. We hypothesize that during transport the plug domain of FhuA does not leave the barrel; rather it undergoes a conformational change to form a channel. We mutated selected amino acids to cysteine to form disulfide bonds to tether the plug, preventing its displacement or unfolding during transport. The tetra-cysteine mutant 72/615/109/356C was able to bind and transport radiolabeled ferrichrome. One double-cysteine mutant, 104/149C, was purified for crystallization.

Iron is an essential nutrient for most bacteria because enzymes like nitrate reductase and cytochromes use it as a cofactor. However, in most aerobic, neutral pH environments, iron is essentially insoluble and not easily available for bacteria to use. Many bacteria respond to this problem by releasing small organic compounds called siderophores that bind and effectively solubilize iron so that it can be transported into the cell for growth. The focus of this study was to learn more about the iron acquisition and especially the transport of iron by the soil bacterium Rhodococcus erythropolis. To fulfill this aim, mutant strains of the bacteria were screened for those that overproduce siderophore. Often, a bacterium will over produce siderophore to compensate for a defect in transport. One such mutant, R187-12, was further analyzed by cloning the region of the chromosome containing the defective gene responsible for over production of siderophore into a plasmid vector. The DNA sequence of this region was determined and analyzed for the presence of similar genes encoding transport proteins.

Control of antibiotic resistance in bacteria is based on the concept that resistance incurs a fitness cost in non-selective conditions. Fitness costs were assessed for low- and high-level mupirocin resistance in locally-derived Staphylococcus aureus and S. epidermidis. Costs of resistance were assessed in pure cultures by comparing growth curve characteristics and in mixed culture as the proportion of resistant cells surviving. Costs were not present in comparisons of growth rates among groups of naturally-occurring isolates from the different resistance categories. However, in S. aureus, growth rates within resistance categories differed by approximately 30 – 90%. Among near-isogenic pairs of strains, fitness costs ≥10% were present in three of eleven pairs under pure culture and in six of eleven pairs under competition in mixed culture. Differences in intrinsic growth rates could easily mask fitness costs of the magnitudes observed. Thus, clinical outcomes also depend on whether there is a mixed infection and if so, on the growth rates of strains present.

Many drugs used in the treatment of various cancers are derived from or influenced by compounds from nature. The soil bacterium Rhodococcus is of interest because of its identified secondary metabolic pathways and the production of novel natural antibiotics from several strains. In this study, a solid agar extraction method was used to collect compounds from strains of Rhodococcus. These bacterial compound extracts were then tested using a MTT assay in order to evaluate their effectiveness in augmenting MCF7 breast cancer cell death. The results of two way ANOVA analyses revealed 18 compound extracts from 15 strains of Rhodococcus that showed significant p-values when assayed with MCF7 breast cancer cells but nonsignificant interaction p-values when assayed with the healthy cell control. These results prompt further identification of specific compounds present in the bacterial extract that caused cell death as well as a mechanism of interaction with the breast cancer cells.

Pseudomonas aeruginosa is an infectious Gram-negative bacillus that is found in environments ranging from aerobic to anaerobic, soil to water, plant tissues to human tissues, and even found thriving on plastics and medical implant devices. P. aeruginosa is a major concern for individuals who have cystic fibrosis, chronic obstructive pulmonary disorder, diabetes, have recently undergone surgery, have recently experienced severe burns, or have experienced other ailments that resulted in a compromised immune system, such as Human Immunodeficiency Virus (HIV). P. aeruginosa evades the host immune response by expressing a myriad of virulence factors, and it is through stringent gene regulation of virulence factors that allow P. aeruginosa to initiate acute infections and persist as a chronic infection of its host. The expression of virulence factors is controlled by a complex regulatory system comprised of Two-Component Systems (TCS), post-transcriptional regulators, small non-coding RNAs (sRNA), and others. A significant post-transcriptional regulator involved in this regulatory network is the Regulator of Secondary Metabolites (RsmA). RsmA belongs to the CsrA family of mRNA binding proteins found in many Gram-negative bacteria. Much is known about the targets of RsmA and its functions; however, little is known about how RsmA itself is regulated. Leader sequences, 5’ and 3’, have been demonstrated to have regulatory roles. Using bioinformatics, we have observed potential for the formation of a stem-loop secondary structure in the 5’ leader sequence of rsmA. We propose that this stem-loop plays an important role in the expression of RsmA in P. aeruginosa. In this study, we constructed rsmA leader fusions using the lacUV5 promoter and lacZ reporter to measure translation with and without the secondary structure present. Secondly, we introduced point mutations in the stem of the stem-loop of the leader fusions to disrupt the formation of the stem-loop. Finally, we performed Site-Directed Mutagenesis on the rsmA leader to examine protein levels in vivo via western blot analysis using an HA-tagged rsmA. Our data shows that when the stem-loop formation is disrupted or deleted, translation of RsmA increases. This data suggests that the stem-loop provides a regulatory function in the expression of RsmA.

We present research investigating how, with in depth knowledge of the community, microbial communities may be harnessed for bioremediation of hazardous water contaminants. We focused on the bacterial reduction of perchlorate, a common water contaminant. For this we studied the structure and capabilities of a novel sulfur-utilizing, perchlorate-reducing bacterial (SUPeRB) consortium. Initially, we characterized the minimal consortium that retained functional capabilities, using 16S rRNA and functional gene analysis. A diverse functional consortium dominated by Beta-Proteobacteria of the family Rhodocyclaceae and sulfur-oxidizing Epsilon-Proteobacteria was found. We also examined the optimal growth conditions under which perchlorate degradation occurred and uncovered the upper limits of this function. Bacterial isolates were screened for function and the presence of functional genes. We expanded to bioreactor studies at bench- and pilot-scale, and first used a perchlorate-reducing, bench-scale bioreactor to probe the stability of the microbial ecosystem. During stable reactor function, a core consortium of Beta- and Epsilon-Proteobacteria reduced perchlorate and the co-contaminant nitrate. A disturbance of the vi consortium led to a failure in function and to higher system diversity. This suggests that the SUPeRB consortium was not metabolically flexible and high population diversity was necessary for a return to stable function. In a pilot-scale bioreactor we determined that the SUPeRB consortium could stably degrade low levels of perchlorate to below the EPA maximum recommended limit. Field conditions, such as temperature extremes and intermittent perchlorate feed, did not negatively impact overall function. When all reactor consortia were compared we observed that the volume of the reactor and the initial inoculum were not as important to stable reactor function as the acclimatization of the consortium to the system and maintenance of favorable conditions within the reactor. In summary we found that the SUPeRB consortium successfully degraded perchlorate in multiple systems. The study of this novel consortium expands our knowledge of the metabolic capabilities of perchlorate-reducing bacteria and suggests potential evolutionary pathways for perchlorate-reduction by microorganisms. The SUPeRB consortium may be used to establish bioremediation systems for perchlorate and other environmental contaminants.

Infections caused by the organism Staphylococcus aureus are one of the most common causes for community-associated and healthcare-acquired infections (HAI). Isolates of this bacterium found within the healthcare setting often demonstrate a higher prevalence of antibiotic resistance making these infections difficult to treat. Historically, considerable focus has been placed on methicillin-resistant S. aureus (MRSA), which are strains resistant to β-lactam antibiotics like penicillin, oxacillin and cephalosporins; however, methicillin-sensitive (MSSA) strains may also possess resistance to several first-line antibiotics. Resistance to antibiotics can be acquired through horizontal gene transfer (HGT) by means of mobile genetic elements or by random DNA mutations as product of DNA replication. Bacteria have elucidated these mechanisms to defend themselves from antibiotics and one cause that promotes resistance is the inappropriate use or prescription of antibiotics to treat infections, i.e., using antibiotics to treat COVID-19. Through the SARS-CoV-2 pandemic, the CDC reported an increased prescription for antibiotics, similarly, other previous studies reported that antibiotics were part of treatment plant in some patients with COVID-19. The aim of this thesis is to study the differences in antibiotic resistance profiles of Staphylococcus aureus strains collected from carriage and disease samples at Nemours Children's Hospital in Orlando, FL from 2019-2022. The focus will be on comparing the susceptibility of methicillin-sensitive and methicillin-resistant strains to various antibiotics. The results will provide clinicians with valuable information that will allow for better treatments and consideration for antibiotic use when creating a treatment plan for patients.