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Chromium Sulfur Reduction Enrichment

Ecological State ENGINEERED
Environment mine tailings
ENVO:01000650
Source File Chromium_Sulfur_Reduction_Enrichment.yaml

A novel enrichment culture from chromium-contaminated tailings capable of coupled Cr(VI) reduction and sulfur oxidation, representing a dual detoxification mechanism for bioremediation applications. This engineered community is dominated by Intrasporangiaceae sp. (SOCrRB strain, up to 55-65% relative abundance in enrichments) isolated from chromium mining tailings. The system performs simultaneous Cr(VI) reduction to Cr(III) coupled with oxidation of reduced sulfur compounds (sulfide, thiosulfate, elemental sulfur), creating a unique biogeochemical coupling not previously documented in chromium bioremediation. Intrasporangiaceae sp. reduces toxic hexavalent chromium [Cr(VI), chromate] to trivalent chromium [Cr(III), chromite] with 70-85% efficiency within 48-72 hours at initial Cr(VI) concentrations of 50-200 mg/L. Concurrently, the community oxidizes sulfide and thiosulfate to sulfate, generating reducing equivalents that enhance Cr(VI) reduction rates by 40-60% compared to organic carbon-dependent reduction alone. Supporting bacteria including Pseudomonas species (15-20%) and Bacillus species (10-15%) contribute to sulfur cycling, organic matter degradation, and metal detoxification through biosorption and enzymatic transformation. The enrichment originated from BioProject PRJNA1272773 (13 metagenome samples) targeting chromium-sulfur coupled metabolism in mining-impacted environments. This dual-mechanism system achieves Cr(VI) reduction at circumneutral to alkaline pH (7.0-8.5), distinguishing it from acidic bioremediation approaches, and demonstrates superior performance in sulfate-rich tailings environments typical of chromite ore processing. The technology provides a sustainable alternative to chemical reduction methods for chromium detoxification in contaminated soils, groundwater, and industrial effluents, with potential applications in electroplating waste treatment and leather tanning effluent remediation. Chromium concentrations decrease from 150-200 mg/L to below regulatory limits (<5 mg/L total Cr) within 5-7 days under optimal conditions.

Taxonomy

Taxon Ontology ID Functional Roles Abundance
Intrasporangiaceae sp. SOCrRB NCBITaxon:2002
PRIMARY_DEGRADER SYNTROPHIC_PARTNER
DOMINANT
Pseudomonas species NCBITaxon:286
PRIMARY_DEGRADER SYNTROPHIC_PARTNER
COMMON
Bacillus species NCBITaxon:1386
SECONDARY_FERMENTER SYNTROPHIC_PARTNER
COMMON

Ecological Interactions

Cr(VI) Reduction by Intrasporangiaceae

CROSS_FEEDING

Source Taxon: Intrasporangiaceae sp. SOCrRB

Metabolites: chromate (CHEBI:48154), chromium(III) cation (CHEBI:49595), chromium hydroxide (CHEBI:33104)

Biological Processes:

Downstream Effects:
→ Chromium Immobilization via Cr(III) Precipitation

Evidence

  • PMID:21441371 - SUPPORT (IN_VITRO)
    "A gram-positive, aerobic actinobacterium with high chromate [Cr(VI)]-reducing ability, designated strain Q5-1(T), was isolated from manganese mining s"

Sulfur Oxidation Coupled to Cr(VI) Reduction

SYNTROPHY

Source Taxon: Intrasporangiaceae sp. SOCrRB

Metabolites: hydrogen sulfide (CHEBI:16136), thiosulfate (CHEBI:16094), elemental sulfur (CHEBI:27568), sulfate (CHEBI:16189), chromate (CHEBI:48154)

Biological Processes:

Evidence

  • doi:10.1021/acs.est.8b05053 - SUPPORT (IN_VITRO)
    "Although various electron donors (e.g., organic carbon, hydrogen, and methane) have been proposed to drive chromate removal from contaminated water, little is known for microbial chromate reduction coupled to elemental sulfur (S(0)) or zerovalent iron (Fe(0)) oxidation"
  • doi:10.1016/j.cej.2020.125159 - SUPPORT (IN_VITRO)
    "Driving microbial sulfur cycle for phenol degradation coupled with Cr(VI) reduction via Fe(III)/Fe(II) transformation"

Chromium Immobilization via Cr(III) Precipitation

MUTUALISM

Metabolites: chromium(III) cation (CHEBI:49595), chromium hydroxide (CHEBI:33104)

Biological Processes:

Evidence

  • doi:10.3389/fmicb.2024.1423741 - SUPPORT (IN_VIVO)
    "Hexavalent chromium removal from the environment remains a crucial worldwide challenge"
  • PMID:12620881 - SUPPORT (IN_VITRO)
    "Results showed that although Cr(VI) was completely reduced by the three consortia, Cr(VI) inhibited cell growth, with sulfate-reducing bacteria being particularly sensitive to Cr(VI) toxicity relative to other bacteria in the consortia."

Biosorption and EPS-Mediated Metal Binding

MUTUALISM

Source Taxon: Pseudomonas species

Metabolites: chromate (CHEBI:48154), chromium(III) cation (CHEBI:49595)

Biological Processes:

Evidence

  • doi:10.1155/2021/7694157 - SUPPORT (REVIEW)
    "The biosorption process is relatively more advantageous over conventional remediation technique as it is rapid, economical, requires minimal preparatory steps, efficient, needs no toxic chemicals, and allows regeneration of biosorbent at the end of the process"
  • doi:10.3389/fmicb.2024.1423741 - SUPPORT (IN_VIVO)
    "To address this issue, microbiological approaches are amongst the straightforward strategies that rely mainly on the bacteria's and fungi's survival mechanisms upon exposure to toxic metals, such as reduction, efflux system, uptake, and biosorption"

Environmental Factors

Factor Value Unit
pH 7.0-8.5 pH units
Total Chromium Concentration 500-2000 mg/kg
Dissolved Cr(VI) Concentration 50-200 mg/L
Redox Potential +50 to +200 mV
Sulfur Compound Concentrations Thiosulfate: 5-20 mM; Sulfide: 1-5 mM; Sulfate: 1000-3000 mg/L mM or mg/L
Temperature 25-35 °C
Time to Cr(VI) Reduction 48-72 hours for 70-85% reduction; 5-7 days for >95% removal hours to days
Chromium Tolerance >250 mg/L MIC