Optical O2 Sensors Also Respond to Redox Active Molecules Commonly Secreted by Bacteria
ABSTRACT From a metabolic perspective, molecular oxygen (O2) is arguably the most significant constituent of Earth’s atmosphere. Nearly every facet of microbial physiology is sensitive to the presence and concentration of O2, which is the most favorable terminal electron acceptor used by organisms a...
| Main Authors: | , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
American Society for Microbiology
2022-12-01
|
| Series: | mBio |
| Subjects: | |
| Online Access: | https://journals.asm.org/doi/10.1128/mbio.02076-22 |
| _version_ | 1811196263202291712 |
|---|---|
| author | Avi I. Flamholz Samuel Saccomano Kevin Cash Dianne K. Newman |
| author_facet | Avi I. Flamholz Samuel Saccomano Kevin Cash Dianne K. Newman |
| author_sort | Avi I. Flamholz |
| collection | DOAJ |
| description | ABSTRACT From a metabolic perspective, molecular oxygen (O2) is arguably the most significant constituent of Earth’s atmosphere. Nearly every facet of microbial physiology is sensitive to the presence and concentration of O2, which is the most favorable terminal electron acceptor used by organisms and also a dangerously reactive oxidant. As O2 has such sweeping implications for physiology, researchers have developed diverse approaches to measure O2 concentrations in natural and laboratory settings. Recent improvements to phosphorescent O2 sensors piqued our interest due to the promise of optical measurement of spatiotemporal O2 dynamics. However, we found that our preferred bacterial model, Pseudomonas aeruginosa PA14, secretes more than one molecule that quenches such sensors, complicating O2 measurements in PA14 cultures and biofilms. Assaying supernatants from cultures of 9 bacterial species demonstrated that this phenotype is common: all supernatants quenched a soluble O2 probe substantially. Phosphorescent O2 probes are often embedded in solid support for protection, but an embedded probe called O2NS was quenched by most supernatants as well. Measurements using pure compounds indicated that quenching is due to interactions with redox-active small molecules, including phenazines and flavins. Uncharged and weakly polar molecules like pyocyanin were especially potent quenchers of O2NS. These findings underscore that optical O2 measurements made in the presence of bacteria should be carefully controlled to ensure that O2, and not bacterial secretions, is measured, and motivate the design of custom O2 probes for specific organisms to circumvent sensitivity to redox-active metabolites. IMPORTANCE When they are closely packed, as in biofilms, colonies, and soils, microbes can consume O2 faster than it diffuses. As such, O2 concentrations in natural environments can vary greatly over time and space, even on the micrometer scale. Wetting soil, for example, slows O2 diffusion higher in the soil column, which, in concert with microbial respiration, greatly diminishes [O2] at depth. Given that variation in [O2] has outsized implications for microbial physiology, there is great interest in measuring the dynamics of [O2] in microbial cultures and biofilms. We demonstrate that certain classes of bacterial metabolites frustrate optical measurement of [O2] with phosphorescent sensors, but also that some species (e.g., E. coli) do not produce problematic secretions under the conditions tested. Our work therefore offers a strategy for identifying organisms and culture conditions in which optical quantification of spatiotemporal [O2] dynamics with current sensors is feasible. |
| first_indexed | 2024-04-12T00:55:42Z |
| format | Article |
| id | doaj.art-4dff9602900c445c8df3f26a994358e2 |
| institution | Directory Open Access Journal |
| issn | 2150-7511 |
| language | English |
| last_indexed | 2024-04-12T00:55:42Z |
| publishDate | 2022-12-01 |
| publisher | American Society for Microbiology |
| record_format | Article |
| series | mBio |
| spelling | doaj.art-4dff9602900c445c8df3f26a994358e22022-12-22T03:54:37ZengAmerican Society for MicrobiologymBio2150-75112022-12-0113610.1128/mbio.02076-22Optical O2 Sensors Also Respond to Redox Active Molecules Commonly Secreted by BacteriaAvi I. Flamholz0Samuel Saccomano1Kevin Cash2Dianne K. Newman3Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, California, USAChemical and Biological Engineering, Colorado School of Mines, Golden, Colorado, USAChemical and Biological Engineering, Colorado School of Mines, Golden, Colorado, USADivision of Biology and Biological Engineering, California Institute of Technology, Pasadena, California, USAABSTRACT From a metabolic perspective, molecular oxygen (O2) is arguably the most significant constituent of Earth’s atmosphere. Nearly every facet of microbial physiology is sensitive to the presence and concentration of O2, which is the most favorable terminal electron acceptor used by organisms and also a dangerously reactive oxidant. As O2 has such sweeping implications for physiology, researchers have developed diverse approaches to measure O2 concentrations in natural and laboratory settings. Recent improvements to phosphorescent O2 sensors piqued our interest due to the promise of optical measurement of spatiotemporal O2 dynamics. However, we found that our preferred bacterial model, Pseudomonas aeruginosa PA14, secretes more than one molecule that quenches such sensors, complicating O2 measurements in PA14 cultures and biofilms. Assaying supernatants from cultures of 9 bacterial species demonstrated that this phenotype is common: all supernatants quenched a soluble O2 probe substantially. Phosphorescent O2 probes are often embedded in solid support for protection, but an embedded probe called O2NS was quenched by most supernatants as well. Measurements using pure compounds indicated that quenching is due to interactions with redox-active small molecules, including phenazines and flavins. Uncharged and weakly polar molecules like pyocyanin were especially potent quenchers of O2NS. These findings underscore that optical O2 measurements made in the presence of bacteria should be carefully controlled to ensure that O2, and not bacterial secretions, is measured, and motivate the design of custom O2 probes for specific organisms to circumvent sensitivity to redox-active metabolites. IMPORTANCE When they are closely packed, as in biofilms, colonies, and soils, microbes can consume O2 faster than it diffuses. As such, O2 concentrations in natural environments can vary greatly over time and space, even on the micrometer scale. Wetting soil, for example, slows O2 diffusion higher in the soil column, which, in concert with microbial respiration, greatly diminishes [O2] at depth. Given that variation in [O2] has outsized implications for microbial physiology, there is great interest in measuring the dynamics of [O2] in microbial cultures and biofilms. We demonstrate that certain classes of bacterial metabolites frustrate optical measurement of [O2] with phosphorescent sensors, but also that some species (e.g., E. coli) do not produce problematic secretions under the conditions tested. Our work therefore offers a strategy for identifying organisms and culture conditions in which optical quantification of spatiotemporal [O2] dynamics with current sensors is feasible.https://journals.asm.org/doi/10.1128/mbio.02076-22Pseudomonas aeruginosaoxygenpyocyaninredox-active metabolitessensors |
| spellingShingle | Avi I. Flamholz Samuel Saccomano Kevin Cash Dianne K. Newman Optical O2 Sensors Also Respond to Redox Active Molecules Commonly Secreted by Bacteria mBio Pseudomonas aeruginosa oxygen pyocyanin redox-active metabolites sensors |
| title | Optical O2 Sensors Also Respond to Redox Active Molecules Commonly Secreted by Bacteria |
| title_full | Optical O2 Sensors Also Respond to Redox Active Molecules Commonly Secreted by Bacteria |
| title_fullStr | Optical O2 Sensors Also Respond to Redox Active Molecules Commonly Secreted by Bacteria |
| title_full_unstemmed | Optical O2 Sensors Also Respond to Redox Active Molecules Commonly Secreted by Bacteria |
| title_short | Optical O2 Sensors Also Respond to Redox Active Molecules Commonly Secreted by Bacteria |
| title_sort | optical o2 sensors also respond to redox active molecules commonly secreted by bacteria |
| topic | Pseudomonas aeruginosa oxygen pyocyanin redox-active metabolites sensors |
| url | https://journals.asm.org/doi/10.1128/mbio.02076-22 |
| work_keys_str_mv | AT aviiflamholz opticalo2sensorsalsorespondtoredoxactivemoleculescommonlysecretedbybacteria AT samuelsaccomano opticalo2sensorsalsorespondtoredoxactivemoleculescommonlysecretedbybacteria AT kevincash opticalo2sensorsalsorespondtoredoxactivemoleculescommonlysecretedbybacteria AT dianneknewman opticalo2sensorsalsorespondtoredoxactivemoleculescommonlysecretedbybacteria |