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Title: Novel pleiotropic regulators of gas vesicle biogenesis in Serratia
Author: Quintero Yanes, Alex Armando
ISNI:       0000 0004 7660 8856
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2019
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Serratia sp. ATCC 39006 (S39006) is known for producing carbapenem and prodiginine antibiotics; 1-carbapen-2-em-3-carboxylic acid (car) and prodigiosin. It displays different motility mechanisms, such as swimming and swarming aided by flagellar rotation and biosurfactant production. In addition, S39006 produces gas vesicles to float in aqueous environments and enable colonization of air-liquid interfaces. Gas vesicles are thought to be constructed solely from proteins expressed from a gene cluster composed of two contiguous operons, gvpA1-gvpY and gvrA-gvrC. Prior to this study, three cognate regulators, GvrA, GvrB, and GvrC, encoded by the right hand operon were known to be essential for gas vesicle synthesis. Post-transcriptional regulators such as RsmA-rsmB were also known to be involved in the inverse regulation of gas vesicles and flagella based motility. Furthermore, gas vesicle formation, antibiotic production, and motility in S39006 were affected by cell population densities and de-repressed at high cellular densities through a quorum sensing (QS) system. The aim of this research study was to identify novel regulatory inputs to gas vesicle production. Mutants were generated by random transposon mutagenesis followed by extensive screening, then sequencing and bioinformatic identification of the corresponding mutant genes. After screening, 31 mutants and seven novel regulatory genes impacting on cell buoyancy were identified. Phenotypic and genetic analysis revealed that the mutations were pleiotropic and involved in cell morphology, ion transport and central metabolism. Two new pleiotropic regulators were characterized in detail. Mutations in an ion transporter gene (trkH) and a putative transcriptional regulator gene (floR) showed opposite phenotypic impacts on flotation, flagella-based motility and prodigiosin, whereas production of the carbapenem antibiotic was affected in the transcription regulator mutant. Gene expression assays with reporter fusions, phenotypic assays in single and double mutants, and proteomics suggested that these regulatory genes couple different physiological inputs to QS and RsmA-dependent and RsmA-independent pathways.
Supervisor: Salmond, George Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: Serratia sp. ATCC 39006 ; Gas vesicles ; Carbapenem ; Prodigiosin ; Flagella ; Cell buoyancy ; Swimming motility ; Swarming motility ; Quorum sensing ; RsmA ; rsmB ; Potassium transport ; TrkH ; DeoR ; TMT 10plex ; Proteomics