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Baker IR, Matzen SL, Schuler CJ, Toner BM, Girguis PR. Aerobic iron-oxidizing bacteria secrete metabolites that markedly impede abiotic iron oxidation. PNAS NEXUS 2023; 2:pgad421. [PMID: 38111821 PMCID: PMC10727123 DOI: 10.1093/pnasnexus/pgad421] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/24/2023] [Accepted: 11/29/2023] [Indexed: 12/20/2023]
Abstract
Iron is one of the Earth's most abundant elements and is required for essentially all forms of life. Yet, iron's reactivity with oxygen and poor solubility in its oxidized form (Fe3+) mean that it is often a limiting nutrient in oxic, near-neutral pH environments like Earth's ocean. In addition to being a vital nutrient, there is a diversity of aerobic organisms that oxidize ferrous iron (Fe2+) to harness energy for growth and biosynthesis. Accordingly, these organisms rely on access to co-existing Fe2+ and O2 to survive. It is generally presumed that such aerobic iron-oxidizing bacteria (FeOB) are relegated to low-oxygen regimes where abiotic iron oxidation rates are slower, yet some FeOB live in higher oxygen environments where they cannot rely on lower oxygen concentrations to overcome abiotic competition. We hypothesized that FeOB chemically alter their environment to limit abiotic interactions between Fe2+ and O2. To test this, we incubated the secreted metabolites (collectively known as the exometabolome) of the deep-sea iron- and hydrogen-oxidizing bacterium Ghiorsea bivora TAG-1 with ferrous iron and oxygen. We found that this FeOB's iron-oxidizing exometabolome markedly impedes the abiotic oxidation of ferrous iron, increasing the half-life of Fe2+ 100-fold from ∼3 to ∼335 days in the presence of O2, while the exometabolome of TAG-1 grown on hydrogen had no effect. Moreover, the few precipitates that formed in the presence of TAG-1's iron-oxidizing exometabolome were poorly crystalline, compared with the abundant iron particles that mineralized in the absence of abiotic controls. We offer an initial exploration of TAG-1's iron-oxidizing exometabolome and discuss potential key contributors to this process. Overall, our findings demonstrate that the exometabolome as a whole leads to a sustained accumulation of ferrous iron in the presence of oxygen, consequently altering the redox equilibrium. This previously unknown adaptation likely enables these microorganisms to persist in an iron-oxidizing and iron-precipitating world and could have impacts on the bioavailability of iron to FeOB and other life in iron-limiting environments.
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Affiliation(s)
- Isabel R Baker
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA
| | - Sarick L Matzen
- Department of Soil, Water, and Climate, University of Minnesota Twin Cities, Saint Paul, MN 55108, USA
| | - Christopher J Schuler
- Department of Earth and Environmental Sciences, University of Minnesota Twin Cities, Saint Paul, MN 55108, USA
| | - Brandy M Toner
- Department of Soil, Water, and Climate, University of Minnesota Twin Cities, Saint Paul, MN 55108, USA
- Department of Earth and Environmental Sciences, University of Minnesota Twin Cities, Saint Paul, MN 55108, USA
| | - Peter R Girguis
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA
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Rosenheim JA, Schreiber SJ. Pathways to the density-dependent expression of cannibalism, and consequences for regulated population dynamics. Ecology 2022; 103:e3785. [PMID: 35818739 DOI: 10.1002/ecy.3785] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/08/2021] [Revised: 04/13/2022] [Accepted: 04/21/2022] [Indexed: 12/13/2022]
Abstract
Cannibalism, once viewed as a rare or aberrant behavior, is now recognized to be widespread and to contribute broadly to the self-regulation of many populations. Cannibalism can produce endogenous negative feedback on population growth because it is expressed as a conditional behavior, responding to the deteriorating ecological conditions that flow, directly or indirectly, from increasing densities of conspecifics. Thus, cannibalism emerges as a strongly density-dependent source of mortality. In this synthesis, we review recent research that has revealed a rich diversity of pathways through which rising density elicits increased cannibalism, including both factors that (a) elevate the rate of dangerous encounters between conspecifics and (b) enhance the likelihood that such encounters will lead to successful cannibalistic attacks. These pathways include both features of the autecology of cannibal populations and features of interactions with other species, including food resources and pathogens. Using mathematical models, we explore the consequences of including density-dependent cannibal attack rates on population dynamics. The conditional expression of cannibalism generally enhances stability and population regulation in single-species models but also may increase opportunities for alternative states and prey population escape from control by cannibalistic predators.
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Affiliation(s)
- Jay A Rosenheim
- Department of Entomology and Nematology, University of California, Davis, California, USA
| | - Sebastian J Schreiber
- Department of Evolution and Ecology, University of California, Davis, California, USA
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Behavioral Effects of a Chemorepellent Receptor Knockout Mutation in Tetrahymena thermophila. mSphere 2017; 2:mSphere00182-17. [PMID: 28685161 PMCID: PMC5497023 DOI: 10.1128/msphere.00182-17] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2017] [Accepted: 05/25/2017] [Indexed: 12/19/2022] Open
Abstract
Although many single-cell eukaryotes have served as classical model systems for chemosensory studies for decades, the major emphasis has been on chemoattraction and no chemorepellent receptor gene has been identified in any unicellular eukaryote. This is the first description of a gene that codes for a chemorepellent receptor in any protozoan. Integration of both depolarizing chemorepellent pathways and hyperpolarizing chemoattractant pathways is as important to chemoresponses of motile unicells as excitatory and inhibitory neurotransmitter pathways are to neurons. Therefore, both chemoattractant and chemorepellent pathways should be represented in a useful unicellular model system. Tetrahymena cells provide such a model system because simple behavioral bioassays, gene knockouts, biochemical analysis, and other approaches can be used with these eukaryotic model cells. This work can contribute to the basic understanding of unicellular sensory responses and provide insights into the evolution of chemoreceptors and possible chemorepellent approaches for preventing infections by some pathogenic protozoa. A conditioned supernatant from Tetrahymena thermophila contains a powerful chemorepellent for wild-type cells, and a gene called G37 is required for this response. This is the first genomic identification of a chemorepellent receptor in any eukaryotic unicellular organism. This conditioned supernatant factor (CSF) is small (<1 kDa), and its repellent effect is resistant to boiling, protease treatment, and nuclease digestion. External BAPTA eliminated the CSF response, suggesting that Ca2+ entry is required for the classical avoiding reactions (AR) used for chemorepulsion. A macronuclear G37 gene knockout (G37-KO) mutant is both nonresponsive to the CSF and overresponsive to other repellents such as quinine, lysozyme, GTP, and high potassium concentrations. All of these mutant phenotypes were reversed by overexpression of the wild-type G37 gene in a G37 overexpression mutant. Overexpression of G37 in the wild type caused increased responsiveness to the CSF and underresponsiveness to high K+ concentrations. Behavioral adaptation (by prolonged exposure to the CSF) caused decreases in responsiveness to all of the stimuli used in the wild type and the overexpression mutant but not in the G37-KO mutant. We propose that the constant presence of the CSF causes a decreased basal excitability of the wild type due to chemosensory adaptation through G37 and that all of the G37-KO phenotypes are due to an inability to detect the CSF. Therefore, the G37 protein may be the CSF receptor. The physiological role of these G37-mediated responses may be to both moderate basal excitability and detect the CSF as an indicator of high cell density growth. IMPORTANCE Although many single-cell eukaryotes have served as classical model systems for chemosensory studies for decades, the major emphasis has been on chemoattraction and no chemorepellent receptor gene has been identified in any unicellular eukaryote. This is the first description of a gene that codes for a chemorepellent receptor in any protozoan. Integration of both depolarizing chemorepellent pathways and hyperpolarizing chemoattractant pathways is as important to chemoresponses of motile unicells as excitatory and inhibitory neurotransmitter pathways are to neurons. Therefore, both chemoattractant and chemorepellent pathways should be represented in a useful unicellular model system. Tetrahymena cells provide such a model system because simple behavioral bioassays, gene knockouts, biochemical analysis, and other approaches can be used with these eukaryotic model cells. This work can contribute to the basic understanding of unicellular sensory responses and provide insights into the evolution of chemoreceptors and possible chemorepellent approaches for preventing infections by some pathogenic protozoa.
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Frankel J, Buhse HE. In Memoriam: Norman E. Williams (1928-2016): Pioneer of Ciliate Architecture. J Eukaryot Microbiol 2017. [DOI: 10.1111/jeu.12395] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Affiliation(s)
- Joseph Frankel
- Department of Biology; The University of Iowa; Iowa City Iowa 52242
| | - Howard E. Buhse
- Department of Biological Sciences; University of Illinois at Chicago; Chicago Illinois 60607
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Plattner H. Signalling in ciliates: long- and short-range signals and molecular determinants for cellular dynamics. Biol Rev Camb Philos Soc 2015; 92:60-107. [PMID: 26487631 DOI: 10.1111/brv.12218] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2015] [Revised: 07/28/2015] [Accepted: 08/21/2015] [Indexed: 12/30/2022]
Abstract
In ciliates, unicellular representatives of the bikont branch of evolution, inter- and intracellular signalling pathways have been analysed mainly in Paramecium tetraurelia, Paramecium multimicronucleatum and Tetrahymena thermophila and in part also in Euplotes raikovi. Electrophysiology of ciliary activity in Paramecium spp. is a most successful example. Established signalling mechanisms include plasmalemmal ion channels, recently established intracellular Ca2+ -release channels, as well as signalling by cyclic nucleotides and Ca2+ . Ca2+ -binding proteins (calmodulin, centrin) and Ca2+ -activated enzymes (kinases, phosphatases) are involved. Many organelles are endowed with specific molecules cooperating in signalling for intracellular transport and targeted delivery. Among them are recently specified soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs), monomeric GTPases, H+ -ATPase/pump, actin, etc. Little specification is available for some key signal transducers including mechanosensitive Ca2+ -channels, exocyst complexes and Ca2+ -sensor proteins for vesicle-vesicle/membrane interactions. The existence of heterotrimeric G-proteins and of G-protein-coupled receptors is still under considerable debate. Serine/threonine kinases dominate by far over tyrosine kinases (some predicted by phosphoproteomic analyses). Besides short-range signalling, long-range signalling also exists, e.g. as firmly installed microtubular transport rails within epigenetically determined patterns, thus facilitating targeted vesicle delivery. By envisaging widely different phenomena of signalling and subcellular dynamics, it will be shown (i) that important pathways of signalling and cellular dynamics are established already in ciliates, (ii) that some mechanisms diverge from higher eukaryotes and (iii) that considerable uncertainties still exist about some essential aspects of signalling.
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Affiliation(s)
- Helmut Plattner
- Department of Biology, University of Konstanz, PO Box M625, 78457, Konstanz, Germany
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Grønlien HK, Bruskeland GE, Jansen AK, Sand O. Electrophysiological Properties of the Microstome and Macrostome Morph of the Polymorphic Ciliate Tetrahymena vorax. J Eukaryot Microbiol 2012. [DOI: 10.1111/jeu.12006] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Heidi K. Grønlien
- Department of Molecular Biosciences; University of Oslo; Blindern N-0316 Oslo Norway
- Faculty of Health and Social Studies; Østfold University College; N-1757 Halden Norway
| | - Guttorm E. Bruskeland
- Department of Molecular Biosciences; University of Oslo; Blindern N-0316 Oslo Norway
| | - Anne K. Jansen
- Department of Molecular Biosciences; University of Oslo; Blindern N-0316 Oslo Norway
| | - Olav Sand
- Department of Molecular Biosciences; University of Oslo; Blindern N-0316 Oslo Norway
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Grønlien HK, Hagen B, Sand O. Microstome--macrostome transformation in the polymorphic ciliate Tetrahymena vorax leads to mechanosensitivity associated with prey-capture behaviour. ACTA ACUST UNITED AC 2012; 214:2258-66. [PMID: 22799008 DOI: 10.1242/jeb.055897] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Ciliates feed by phagocytosis. Some ciliate species, such as Tetrahymena vorax, are polymorphic, a strategy that provides more flexible food utilization. Cells of the microstomal morph of T. vorax feed on bacteria, organic particles and organic solutes in a non-selective manner, whereas macrostome cells are predators that consume specific prey ciliates. In the present study, we investigated a possible correlation between phagocytosis and mechanosensitivity in macrostome T. vorax. Microstome cells seem to be insensitive to mechanical stimulation whereas macrostome cells depolarise in response to mechanical stimulation of the anterior part of the cell. The amplitude of the receptor potential induced by either a prey ciliate or a 5 μm push by a glass needle was sufficient to elicit a regenerative Ca²⁺ spike. The difference in mechanosensitivity of the two forms correlates with the swimming behaviour when hitting an obstacle; microstome cells swim alongside the obstacle whereas macrostome cells swim backwards, turn and resume forward swimming. Macrostome cells prevented from backward swimming and the subsequent turn failed to capture prey cells in their pouch. Macrostome cells consumed heterospecific prey ciliates preferentially over conspecific microstome cells. This selectivity is not due to electrical membrane responses elicited by physical contact. Both microstome and macrostome cells accumulated in an area containing putative substances released from heterospecific prey ciliates, but the substances did not elicit any electrophysiological membrane responses. We conclude that the mechanosensitivity of macrostome cells is associated with the prey-capture behaviour, whereas the selective phagocytosis is probably due to chemo-attraction to heterospecific prey ciliates.
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Affiliation(s)
- Heidi K Grønlien
- Department of Molecular Biosciences, University of Oslo, Blindern, N-0316 Oslo, Norway.
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Banerji A, Morin PJ. Phenotypic plasticity, intraguild predation and anti-cannibal defences in an enigmatic polymorphic ciliate. Funct Ecol 2009. [DOI: 10.1111/j.1365-2435.2008.01499.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Burdette AJ, Maki AB, Sanstead JK, Riggs BM, Ryals PE. Phospholipids of the Differentiating Species of Tetrahymena. J Eukaryot Microbiol 2006; 53:12-5. [PMID: 16441574 DOI: 10.1111/j.1550-7408.2005.00069.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
The whole-cell phospholipid composition of the six known polymorphic species of Tetrahymena has been examined by [(3)H]acetate and [(3)H]myristic acid radiolabeling, and by gas-liquid chromatography of total phospholipid-bound fatty acids. Five of the polymorphic species contained similar phospholipid profiles following radiolabeling in that phosphatidylethanolamine (PE) was the predominant phospholipid; however, in cells of Tetrahymena patula LFF, aminoethylphosphonolipid was present in amounts nearly equal to PE. Tetrahymena patula LFF contained an unusually large percentage of sphingolipid (16.2% by [(3)H]acetate radiolabeling). Substantial differences were found in the fatty acid profiles of the polymorphic species, which included the degree of fatty acid unsaturation and relative weight percentages of odd-chain fatty acids. Tetrahymena vorax contained a low ratio of unsaturated C(18) fatty acids to saturated C(18) fatty acids as compared with all other species examined. The differentiating species generally contained a lesser percentage of monoenoic fatty acids and a lower ratio of unsaturated C(16) fatty acids to saturated C(16) fatty acids as compared with the two monomorphic species examined.
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Shemarova IV, Korotkov SM, Nosova IY. Study of the mechanism of the cytostatic effect of picolinic acid on proliferating Tetrahymena pyriformis cells. DOKLADY BIOLOGICAL SCIENCES : PROCEEDINGS OF THE ACADEMY OF SCIENCES OF THE USSR, BIOLOGICAL SCIENCES SECTIONS 2004; 391:299-302. [PMID: 14556515 DOI: 10.1023/a:1025182013170] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Affiliation(s)
- I V Shemarova
- Sechenov Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, pr. Morisa Toreza 44, St. Petersburg, 194223 Russia
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Rothschild LJ. Introductory remarks: protozoology (protistology) at the dawn of the 21st century. J Eukaryot Microbiol 2004; 51:3-7. [PMID: 15068260 DOI: 10.1111/j.1550-7408.2004.tb00155.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Affiliation(s)
- Lynn J Rothschild
- Ecosystem Science and Technology Branch, Mail Stop 239-20, NASA Ames Research Center, Moffett Field, CA 94035-1000, USA.
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Ryals PE, Smith-Somerville HE, Buhse HE. Phenotype switching in polymorphic Tetrahymena: a single-cell Jekyll and Hyde. INTERNATIONAL REVIEW OF CYTOLOGY 2002; 212:209-38. [PMID: 11804037 DOI: 10.1016/s0074-7696(01)12006-1] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
For nearly half a century, phenotype switching in the group of polymorphic species of the ciliate genus Tetrahymena has been the subject of investigations of the underlying mechanisms, the accompanying biochemical and structural changes, and the evolution of polymorphic survival strategy. Beginning with the pioneering systematic studies by Furgason in 1940 of hymenostome ciliates, the experimental approach rapidly expanded to include investigations of growth, nutrition, physiology, morphology, and morphogenesis in the polymorphic species. Recently, with progress in elucidation of the novel signaling ligand and identification of elements of the subsequent signal transduction cascade, in addition to the growing catalog of intracellular events associated with differentiation in these unicellular eukaryotes, we have begun to address the mechanistic basis of polymorphism. This review summarizes and integrates the history and recent discoveries concerning Tetrahymena polymorphic cells. We are now poised to answer fundamental questions about this interesting pathway of cell differentiation.
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Affiliation(s)
- Phillip E Ryals
- Department of Biochemistry and Molecular Biology, Mississippi State University, Mississippi State 39762, USA
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