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Bioprospecting and characterisation of heavy metal stress-induced antimicrobials from rhizospheric Bacillus sp. against multidrug-resistant Pseudomonas Aeruginosa (strain ATCC 27853) and Acinetobacter baumannii (strain ATCC-BAA-1605)
Dissertation (Meng (Chemical Engineering))--University of Pretoria, 2026.
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| Format: | Thesis |
| Language: | English |
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University of Pretoria
2026
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| _version_ | 1869483958264135680 |
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| access_status_str | Open Access |
| author2 | Iwarere, Samuel Ayodele |
| author_browse | Iwarere, Samuel Ayodele |
| author_facet | Iwarere, Samuel Ayodele |
| collection | Thesis |
| dc_rights_str_mv | © 2024 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. |
| description | Dissertation (Meng (Chemical Engineering))--University of Pretoria, 2026. |
| format | Thesis |
| id | oai:repository.up.ac.za:2263/107926 |
| institution | University of Pretoria (South Africa) |
| language | English |
| last_indexed | 2026-07-01T04:07:15.930Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UPSpace — University of Pretoria Institutional Repository |
| publishDate | 2026 |
| publishDateRange | 2026 |
| publishDateSort | 2026 |
| publisher | University of Pretoria |
| publisherStr | University of Pretoria |
| record_format | dspace |
| source_str | UPSpace — University of Pretoria Institutional Repository |
| spelling | oai:repository.up.ac.za:2263/107926 Bioprospecting and characterisation of heavy metal stress-induced antimicrobials from rhizospheric Bacillus sp. against multidrug-resistant Pseudomonas Aeruginosa (strain ATCC 27853) and Acinetobacter baumannii (strain ATCC-BAA-1605) Iwarere, Samuel Ayodele u20426888@tuks.co.za Unuofin, John Invernizzi, Luke Millard, Kylah UTCD Sustainable Development Goals (SDGs) Secondary metabolites Antimicrobial activity Multidrug resistance Bioassay-guided fractionation Dissertation (Meng (Chemical Engineering))--University of Pretoria, 2026. This thesis explores the potential of heavy-metal-contaminated rhizospheres as a source of antimicrobial secondary metabolites capable of inhibiting multidrug-resistant pathogens. X-Ray Fluorescence (XRF) analysis confirmed substantial contamination of soils from Salvage and Recycling in Silverton, creating an extreme environment that selected for stress-resilient rhizospheric microorganisms. Several bacterial isolates were derived from these soils, particularly Bacillus subtilis Steel 7, which, among other isolates, that displayed strong inhibitory activity against Pseudomonas aeruginosa ATCC 27853 and Acinetobacter baumannii ATCC BAA-1605, This demonstrates that heavy-metal stress enhances antimicrobial metabolite production. Chemical profiling of the most active bacterial extract using ultra-high-performance liquid chromatography coupled to photodiode array detection and high-resolution mass spectrometry (UPLC-PDA-HRMS) revealed a complex metabolite mixture, with ions at mass-to-charge ratio (m/z) 132 and 166 recurring across active chromatographic fractions. Through sequential bioassay-guided fractionation and multi-platform structural elucidation, including mass spectroscopy (MS), proton nuclear magnetic resonance (¹H NMR) and carbon-13 nuclear magnetic resonance (¹³C NMR), heteronuclear single quantum correlation (HSQC), and heteronuclear multiple bond correlation (HMBC), the main compound of 132 m/z was identified as leucine in the bacterial extract. The antimicrobial testing of the crude bacterial extract exhibited strong activity whereas the identified leucine compound was inactive against the test pathogens, indicating that the potent antimicrobial activity observed in crude extract is attributable to one or more of the low-abundance metabolites. However, leucine is not individually active against the pathogens tested, it may contribute synergistically (as an adjuvant or otherwise) to the sensitivity or susceptibility of the pathogens to the active antimicrobial compound in the crude extract. Thus, while a major constituent (leucine) in the bacterial secretions was conclusively characterised, the true active compound(s) remain undiscovered in the crude extract. This work demonstrates that extreme environments stimulate antimicrobial secretion and bio-assay guided isolation of the active metabolite(s) clarifies the chemical complexity underlying this activity, and provides a methodological foundation for future high-resolution, bioassay-guided isolation of the active metabolite(s). Based on the findings in this work, stressed rhizospheric microbiomes could serve as a potentially valuable reservoir for novel antibiotic discovery. A1G264 UP Postgraduate Bursary Chemical Engineering Meng (Chemical Engineering) Unrestricted Faculty of Engineering, Built Environment and Information Technology SDG-03: Good health and well-being 2026-02-06T09:02:58Z 2026-02-06T09:02:58Z 2026-05 2026 Dissertation * A2026 http://hdl.handle.net/2263/107926 10.25403/UPresearchdata.31274095 en © 2024 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. application/pdf University of Pretoria |
| spellingShingle | UTCD Sustainable Development Goals (SDGs) Secondary metabolites Antimicrobial activity Multidrug resistance Bioassay-guided fractionation Bioprospecting and characterisation of heavy metal stress-induced antimicrobials from rhizospheric Bacillus sp. against multidrug-resistant Pseudomonas Aeruginosa (strain ATCC 27853) and Acinetobacter baumannii (strain ATCC-BAA-1605) |
| title | Bioprospecting and characterisation of heavy metal stress-induced antimicrobials from rhizospheric Bacillus sp. against multidrug-resistant Pseudomonas Aeruginosa (strain ATCC 27853) and Acinetobacter baumannii (strain ATCC-BAA-1605) |
| title_full | Bioprospecting and characterisation of heavy metal stress-induced antimicrobials from rhizospheric Bacillus sp. against multidrug-resistant Pseudomonas Aeruginosa (strain ATCC 27853) and Acinetobacter baumannii (strain ATCC-BAA-1605) |
| title_fullStr | Bioprospecting and characterisation of heavy metal stress-induced antimicrobials from rhizospheric Bacillus sp. against multidrug-resistant Pseudomonas Aeruginosa (strain ATCC 27853) and Acinetobacter baumannii (strain ATCC-BAA-1605) |
| title_full_unstemmed | Bioprospecting and characterisation of heavy metal stress-induced antimicrobials from rhizospheric Bacillus sp. against multidrug-resistant Pseudomonas Aeruginosa (strain ATCC 27853) and Acinetobacter baumannii (strain ATCC-BAA-1605) |
| title_short | Bioprospecting and characterisation of heavy metal stress-induced antimicrobials from rhizospheric Bacillus sp. against multidrug-resistant Pseudomonas Aeruginosa (strain ATCC 27853) and Acinetobacter baumannii (strain ATCC-BAA-1605) |
| title_sort | bioprospecting and characterisation of heavy metal stress induced antimicrobials from rhizospheric bacillus sp against multidrug resistant pseudomonas aeruginosa strain atcc 27853 and acinetobacter baumannii strain atcc baa 1605 |
| topic | UTCD Sustainable Development Goals (SDGs) Secondary metabolites Antimicrobial activity Multidrug resistance Bioassay-guided fractionation |
| url | http://hdl.handle.net/2263/107926 |