A moderately thermophilic three-species bioleaching consortium used to study the effects of quorum sensing (QS) signaling on pyrite and chalcopyrite dissolution. This acidophilic community consists of Leptospirillum ferriphilum DSM 14647, Acidithiobacillus caldus DSM 8584, and Sulfobacillus thermosulfidooxidans DSM 9293, operating at pH 2.0-2.5 and 40°C. The consortium demonstrates coordinated microbial behavior mediated by diffusible signal factor (DSF) and N-acyl-homoserine lactone (AHL) quorum sensing systems. Treatment with DSF-family compounds (DSF and BDSF at 2 μM each) reduced pyrite and chalcopyrite dissolution via inhibitory effects on iron oxidation and mineral colonization. DSF compounds induced A. caldus motility and dispersion from pyrite with concomitant expansion of L. ferriphilum on mineral surfaces, while AHL-mediated signaling (C12-AHL, C14-AHL, 3-OH-C12-AHL, 3-OH-C14-AHL at 5 μM each) repressed L. ferriphilum motility. The consortium was subjected to RNA-seq transcriptomics (12 samples, 271 Gbases) to elucidate gene expression changes in response to QS molecules (NCBI BioProject PRJNA1259591). This system represents the first comprehensive study of quorum sensing regulation in moderately thermophilic biomining bacteria, revealing that QS molecules change planktonic/mineral subpopulation distributions and modulate leaching efficiency through control of cell attachment and iron oxidation rates.
Taxonomy
| Taxon | Ontology ID | Functional Roles | Abundance |
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| Leptospirillum ferriphilum | NCBITaxon:178606 · TaxonMech · TraitMech |
PRIMARY_PRODUCER
PRIMARY_DEGRADER
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DOMINANT |
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| Acidithiobacillus caldus | NCBITaxon:33059 · TaxonMech · TraitMech |
PRIMARY_DEGRADER
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ABUNDANT |
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| Sulfobacillus thermosulfidooxidans | NCBITaxon:28034 · TaxonMech · TraitMech |
PRIMARY_PRODUCER
PRIMARY_DEGRADER
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ABUNDANT |
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Ecological Interactions
The graph shows only explicitly linked interaction participants. Community members without an asserted participant link are omitted; membership alone does not imply an interaction.
Ferrous Iron Oxidation by Leptospirillum
L. ferriphilum DSM 14647 oxidizes ferrous iron to ferric iron for chemolithoautotrophic growth. Ferric iron is a chemical oxidant of sulfide minerals, not evidence of a measured nutrient transfer to a named microbial recipient. Carbon fixation is retained without assigning the Calvin-Benson-Bassham pathway. The 2025 study measured growth, redox potential and mineral-colonization responses to added signal compounds at 40 C. Relative enrichment on pyrite in the mixed culture is not an absolute increase in every condition or proof of natural density-dependent control of iron oxidation.
Participating Taxa: Leptospirillum ferriphilum
Metabolites: Fe(II) (CHEBI:29033 · MediaIngredientMech · CMMMech), Fe(III) (CHEBI:29034 · MediaIngredientMech · CMMMech)
Biological oxidation regenerates ferric iron, the chemical oxidant that attacks sulfide minerals and enables their dissolution. This is the iron-recycling mechanism described in the cited studies, not a pairwise cross-feeding assay or proof that increasing oxidation always improves chalcopyrite recovery; its redox-potential window matters.
Evidence
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doi:10.1038/s41598-021-95324-9 - PARTIAL (IN_VITRO)"iron(II)-ion oxidation regenerates iron(III) ions, the chemical oxidant of the metal sulfide bond"
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doi:10.3389/fmicb.2025.1592588 - PARTIAL (IN_VITRO)"L. ferriphilum is the single moderately thermophilic Leptospirillum species and uses iron(II) as sole energy source and fixes carbon dioxide"
Sulfur Oxidation by Acidithiobacillus caldus
A. caldus DSM 8584 supplies inorganic sulfur-oxidizing capacity in the three-species culture. Sulfur oxidation contributes to acid generation, but the cited mixed-culture study does not isolate a passivation-removal benefit to another named species or selective DSF control of sulfur-oxidation flux. Under added DSF/BDSF, pyrite-attached relative abundance decreased while the planktonic fraction increased; flagellar transcript changes support a dispersal interpretation. Axenic and mixed-culture responses differ.
Participating Taxa: Acidithiobacillus caldus
Metabolites: sulfuric acid (CHEBI:26836 · MediaIngredientMech · CMMMech)
Evidence
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doi:10.3389/fmicb.2025.1592588 - PARTIAL (IN_VITRO)"A. caldus is an aerobic, ISC oxidizing obligate chemolithoautotroph"
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doi:10.3389/fmicb.2025.1592588 - PARTIAL (IN_VITRO)"DSF compounds induced Acidithiobacillus caldus motility and dispersion from pyrite"
Dual Iron and Sulfur Oxidation by Sulfobacillus
S. thermosulfidooxidans DSM 9293 has both ferrous-iron and inorganic sulfur-oxidizing capacity and can grow mixotrophically. The 2025 consortium assays used 40 C, not the species growth optimum. Its biofilm relative distribution at 7 and 14 days was not significantly changed by DSF/BDSF, although other assay designs and time points showed inhibition. The separate 2020 two-species study found that co-inoculation improved leaching relative to S. thermosulfidooxidans alone but not relative to L. ferriphilum biofilms; precolonization could impair leaching. These condition-dependent findings do not establish universal mutualism or measured consumption of partner lysate or EPS.
Participating Taxa: Sulfobacillus thermosulfidooxidans
Metabolites: Fe(II) (CHEBI:29033 · MediaIngredientMech · CMMMech), Fe(III) (CHEBI:29034 · MediaIngredientMech · CMMMech), sulfuric acid (CHEBI:26836 · MediaIngredientMech · CMMMech)
Evidence
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doi:10.3389/fmicb.2020.00044 - PARTIAL (IN_VITRO)"Since L. ferriphilum can oxidize only ferrous ion for energy but S. thermosulfidooxidans can use both, ferrous ion and RISCs, as energy source"
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doi:10.3389/fmicb.2020.00044 - SUPPORT (IN_VITRO)"the bioleaching efficiency was better than that of a pure culture of S. thermosulfidooxidans"
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doi:10.3389/fmicb.2025.1592588 - SUPPORT (IN_VITRO)"the presence of DSF/BDSF molecules did not affect its biofilm distribution at 7 and 14 days"
Pyrite and Chalcopyrite Dissolution
The three-species culture catalyzes sulfide-mineral dissolution through iron and sulfur oxidation. Ferric attack releases ferrous iron that can be reoxidized; copper release reports chalcopyrite dissolution. Added DSF/BDSF decreased bioleaching under the tested conditions, with effects on growth, redox potential and colonization. The contributions of signaling, fatty-acid stress and cell damage were not selectively separated. Pyrite and chalcopyrite responses differ; the outcome is not evidence of Leptospirillum-to-Sulfobacillus mutualism or uniformly beneficial biofilm stabilization by AHLs.
Participating Taxa: Leptospirillum ferriphilum, Acidithiobacillus caldus, Sulfobacillus thermosulfidooxidans
Metabolites: pyrite (CHEBI:86471 · MediaIngredientMech · CMMMech), chalcopyrite (CHEBI:86202 · MediaIngredientMech · CMMMech), Fe(III) (CHEBI:29034 · MediaIngredientMech · CMMMech), Fe(II) (CHEBI:29033 · MediaIngredientMech · CMMMech), copper(2+) (CHEBI:29036 · MediaIngredientMech · CMMMech), sulfuric acid (CHEBI:26836 · MediaIngredientMech · CMMMech)
Chemical attack on sulfide minerals releases ferrous iron, providing substrate for L. ferriphilum to regenerate ferric oxidant. This closes the mineral iron-recycling loop without asserting a measured interspecies nutrient-transfer event.
Evidence
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doi:10.3389/fmicb.2025.1592588 - SUPPORT (IN_VITRO)"reduced pyrite and chalcopyrite dissolution via an inhibitory effect on iron oxidation and mineral colonization by the mixed culture"
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doi:10.3389/fmicb.2020.00044 - PARTIAL (IN_VITRO)"Ferrous ion is then re-oxidized to ferric ion by the iron-oxidizing microorganisms"
Responses to Added DSF and BDSF
The 2025 mixed-culture experiments added DSF and BDSF at 2 uM each. Pyrite relative abundances and planktonic transcripts support A. caldus dispersal and relative L. ferriphilum enrichment on mineral surfaces, with context-dependent inhibition of growth and leaching. The separate 2021 study confirmed biogenic DSF in L. ferriphilum and L. ferrooxidans pyrite cultures by GC-MS at nanomolar concentrations. That production result is retained, but it does not prove the micromolar treatment phenotype arises from endogenous transfer within this three-species consortium. HYPOTHESIZED: natural niche defense and receptor-mediated regulation; fatty-acid stress can also contribute. Neither mutual benefit nor density-dependent protection against mineral overexploitation was demonstrated.
Participating Taxa: Leptospirillum ferriphilum, Acidithiobacillus caldus, Sulfobacillus thermosulfidooxidans
Metabolites: cis-11-methyl-2-dodecenoic acid (CHEBI:81585 · MediaIngredientMech · CMMMech), (2Z)-2-dodecenoic acid (CHEBI:38372 · MediaIngredientMech · CMMMech)
Evidence
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doi:10.3389/fmicb.2025.1592588 - SUPPORT (IN_VITRO)"The DSF/BDSF addition resulted in a decreased cell density"
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doi:10.1038/s41598-021-95324-9 - SUPPORT (IN_VITRO)"unambiguously identified the presence of biogenic DSF in cultures of both Leptospirillum species"
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doi:10.1038/s41598-021-95324-9 - PARTIAL (IN_VITRO)"Micromolar DSF/BDSF concentrations are unlikely to occur in leptospirilli containing habitats"
Responses to Added AHL Mixture
External addition of C12-AHL, C14-AHL, 3-OH-C12-AHL and 3-OH-C14-AHL at 5 uM each changed the mixed-culture relative abundances and planktonic transcript profiles. The methods specify DL-homoserine-lactone reagents; specific L-enantiomer or generic class CURIEs must not stand in for the exact supplied molecules. Decreased L. ferriphilum flagellar transcripts support a motility interpretation, not a direct motility-rate measurement. These experiments do not demonstrate A. caldus production of AHLs, a LuxI-dependent donor-recipient exchange, natural density sensing, or necessary AHL-DSF cross-talk. Proposed biofilm and c-di-GMP mechanisms remain PARTIAL.
Participating Taxa: Leptospirillum ferriphilum, Acidithiobacillus caldus, Sulfobacillus thermosulfidooxidans
Evidence
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doi:10.3389/fmicb.2025.1592588 - PARTIAL (IN_VITRO)"AHLs induced changes in transcript counts of some L. ferriphilum flagellar genes"
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doi:10.3389/fmicb.2025.1592588 - SUPPORT (IN_VITRO)"N-acyl-DL-homoserine lactones (AHLs) were used as a mixture"
Knowledge gaps & discussions (1)
KNOWLEDGE_GAP OPEN Which endogenous signals and receptors mediate mineral redistribution at natural concentrations?
Biogenic DSF production has experimental support, but micromolar additions combine signaling and stress. Density-matched and receptor/production perturbations are needed to assign the three-species phenotype to endogenous signaling. AHL-producing partners and exact compound groundings remain unresolved. Non-graph assay and signaling metadata remain issue #1896.
Attaches to: ecological_interactions#Responses to Added DSF and BDSF, ecological_interactions#Responses to Added AHL Mixture
2 evidence item(s)
unambiguously identified the presence of biogenic DSF in cultures of both Leptospirillum species
GC-MS supports actual DSF production in separate pyrite-grown cultures; it is not erased by qualification of the consortium inference.
Micromolar DSF/BDSF concentrations are unlikely to occur in leptospirilli containing habitats
Authors distinguish treatment concentrations from measured natural culture levels; local accumulation/niche defense remains a hypothesis.
Environmental Factors
| Factor | Value | Unit |
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| Temperature | 40 | °C |
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| pH | 2.0-2.5 | pH units |
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| DSF Quorum Sensing Signals | 2 | μM |
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| AHL Quorum Sensing Signals | 5 | μM |
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| Mineral Substrates | Pyrite and Chalcopyrite | qualitative |
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| RNA-Seq Transcriptomics | 12 samples, 271 Gbases | sequencing data |
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| Oxygen Availability | Aerobic | qualitative |
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Growth Media
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