AMD Acidophile Heterotroph Network

Community ID CommunityMech:000001

Ecological State STABLE

Environment acid mine drainage
ENVO:00002186

A heterotrophic microbial network in acid mine drainage (AMD) systems dominated by Acidiphilium species and related acidophilic heterotrophs. This community plays a crucial role in coupling carbon and iron cycles in extremely acidic environments, supporting autotrophic iron oxidizers through organic matter processing and nutrient remineralization. The network thrives at pH 2-4 in AMD sites globally, where heterotrophs metabolize organic compounds produced by autotrophs or released from lysed cells, preventing organic carbon accumulation that would inhibit autotrophic iron oxidizers. Key members include Acidiphilium multivorum (facultative Fe(III) reducer and organic carbon degrader), Ferrimicrobium acidiphilum (iron-oxidizing heterotroph and dissolved organic carbon remover), Acidocella facilis (obligate aerobic heterotroph), Acidisphaera rubrifaciens (photoheterotrophic bacteriochlorophyll producer), and Acidobacterium capsulatum (chemoorganotrophic acidophile). These organisms collectively perform organic matter degradation, ferric iron reduction, biofilm formation, and nutrient cycling. The heterotroph-autotroph coupling maintains community stability by removing inhibitory organic carbon, recycling nutrients (nitrogen, phosphorus), generating ferrous iron for autotrophic energy generation, and facilitating metal tolerance through extracellular polymeric substances (EPS) production. This network represents a critical functional guild in AMD ecosystems, enabling the persistence of autotrophic iron-oxidizing communities through metabolic cooperation and resource partitioning.

Taxonomy

Taxon	Ontology ID	Functional Roles	Abundance
Acidiphilium multivorum	NCBITaxon:62140	CROSS_FEEDER SYNTROPHIC_PARTNER	DOMINANT
doi:10.1099/00207713-36-2-197 - PARTIAL (IN_VIVO) "Acidophilic heterotrophic bacteria recovered from samples of water and sediment collected from acidic mine drainage streams" PMID:10427060 - SUPPORT (IN_VITRO) "Analysis of the 16S rRNA gene sequence of JF-5 demonstrated that it was closely related to an Australian isolate of Acidiphilium cryptum (99.6% sequence similarity), an organism not previously shown to couple the complete oxidation of sugars to the reduction of Fe(III)"
Ferrimicrobium acidiphilum	NCBITaxon:121039	CROSS_FEEDER PRIMARY_PRODUCER	COMMON
doi:10.1099/ijs.0.65409-0 - SUPPORT (IN_VITRO) "Two novel extremely acidophilic, iron-oxidizing actinobacteria were isolated, one from a mine site in North Wales, UK (isolate T23(T)), and the other from a geothermal site in Yellowstone National Park, Wyoming, USA (Y005(T))" doi:10.3389/fmicb.2015.00475 - SUPPORT (IN_VIVO) "Low-pH conditions appear to be the main factor underlying the limited diversity of the microbial populations thriving in these environments, although temperature, ionic composition, total organic carbon, and dissolved oxygen are also considered to significantly influence their microbial life"
Acidiphilium cryptum	NCBITaxon:524	CROSS_FEEDER SYNTROPHIC_PARTNER	COMMON
PMID:10427060 - SUPPORT (IN_VITRO) "Analysis of the 16S rRNA gene sequence of JF-5 demonstrated that it was closely related to an Australian isolate of Acidiphilium cryptum (99.6% sequence similarity), an organism not previously shown to couple the complete oxidation of sugars to the reduction of Fe(III)" doi:10.3389/fmicb.2024.1374800 - SUPPORT (IN_VITRO) "Similarly, as these microorganisms grow in highly acidic media and the chances of contamination are reduced by the low pH, they may be employed to implement robust fermentation processes"
Acidocella facilis	NCBITaxon:525	CROSS_FEEDER	COMMON
doi:10.3389/fmicb.2024.1374800 - SUPPORT (REVIEW) "Despite acidophiles are usually associated with an autotrophic metabolism, more than 80 microorganisms capable of utilizing organic matter have been isolated from natural and man-made environments" doi:10.1007/s11356-014-3789-4 - SUPPORT (IN_VIVO) "Numbers of cultivatable heterotrophic acidophilic bacteria were over an order of magnitude greater than those of chemolithotrophic acidophiles in both AMD ponds examined"
Acidisphaera rubrifaciens	NCBITaxon:50715	CROSS_FEEDER	RARE
PMID:10939661 - SUPPORT (IN_VITRO) "On the basis of these results, it was concluded that the four isolates should be classified into a new genus and a new species, for which the name Acidisphaera rubrifaciens is proposed" doi:10.1099/00207713-50-4-1539 - SUPPORT (IN_VITRO) "On the basis of these results, it was concluded that the four isolates should be classified into a new genus and a new species, for which the name Acidisphaera rubrifaciens is proposed"
Acidobacterium capsulatum	NCBITaxon:33075	CROSS_FEEDER	RARE
doi:10.1007/BF02106205 - SUPPORT (IN_VITRO) "Acidobacterium is proposed as a new genus for the acidophilic, chemoorganotrophic bacteria containing menaquinone isolated from acidic mineral environments" doi:10.3389/fmicb.2016.00744 - SUPPORT (COMPUTATIONAL) "Genomic and metagenomic data predict a number of ecologically relevant capabilities for some acidobacteria, including the ability to: use of nitrite as N source, respond to soil macro-, micro nutrients and soil acidity, express multiple active transporters, degrade gellan gum and produce exopolysaccharide (EPS)"

Ecological Interactions

Taxon

Cross-feeding

Mutualism

Syntrophy

Competition

Commensalism

Niche partitioning

Colonization facilitation

Strain competition

Predation

Organic Carbon Scavenging and Remineralization

CROSS_FEEDING

Source Taxon: Acidiphilium multivorum

Target Taxon: Ferrimicrobium acidiphilum

Metabolites: organic molecular entity (CHEBI:50860), carbon dioxide (CHEBI:16526), ammonium (CHEBI:28938), phosphate (CHEBI:18367)

Biological Processes:

organic substance catabolic process (GO:1901575)
aerobic respiration (GO:0009060)
nitrogen compound metabolic process (GO:0006807)

Evidence

doi:10.3389/fmicb.2015.00475 - SUPPORT (IN_VIVO)

"Low-pH conditions appear to be the main factor underlying the limited diversity of the microbial populations thriving in these environments, although temperature, ionic composition, total organic carbon, and dissolved oxygen are also considered to significantly influence their microbial life"
doi:10.1128/msystems.00867-20 - SUPPORT (REVIEW)

"We found in the genomes of Acidiphilium an abundant repertoire of horizontally transferred genes (HTGs) contributing to environmental adaption and metabolic ability expansion, as indicated by phylogenetic reconstruction and gene context comparison"

Ferric Iron Reduction and Ferrous Iron Regeneration

MUTUALISM

Source Taxon: Acidiphilium multivorum

Target Taxon: Acidiphilium cryptum

Metabolites: iron(3+) (CHEBI:29034), iron(2+) (CHEBI:29033), glucose (CHEBI:17234), organic acid (CHEBI:64709)

Biological Processes:

oxidation-reduction process (GO:0055114)
iron ion transport (GO:0006826)
anaerobic respiration (GO:0009061)

Downstream Effects:

→ Organic Carbon Scavenging and Remineralization

Evidence

PMID:10427060 - SUPPORT (IN_VITRO)

"These collective results indicate that the in situ reduction of Fe(III) in acidic sediments can be mediated by heterotrophic Acidiphilium species that are capable of coupling the reduction of Fe(III) to the complete oxidation of a large variety of substrates including glucose and H(2)."
doi:10.1093/femsec/49.1.137 - SUPPORT (IN_VITRO)

"Iron respiration by Acidiphilium cryptum at pH 5"

Heterotrophic Iron Oxidation by Ferrimicrobium

CROSS_FEEDING

Source Taxon: Ferrimicrobium acidiphilum

Target Taxon: Acidiphilium multivorum

Metabolites: iron(2+) (CHEBI:29033), iron(3+) (CHEBI:29034), organic molecular entity (CHEBI:50860)

Biological Processes:

oxidation-reduction process (GO:0055114)
iron ion transport (GO:0006826)
heterotrophy (GO:0019752)

Evidence

doi:10.1099/ijs.0.65409-0 - SUPPORT (IN_VITRO)

"Two novel extremely acidophilic, iron-oxidizing actinobacteria were isolated, one from a mine site in North Wales, UK (isolate T23(T)), and the other from a geothermal site in Yellowstone National Park, Wyoming, USA (Y005(T))"
doi:10.1128/aem.01906-20 - SUPPORT (IN_VITRO)

"acidiphilum as it respired on extracellular iron using an integrating cavity absorption meter that permitted accurate optical measurements in turbid suspensions of the intact bacterium under physiological conditions"

Biofilm Formation and Metal Sequestration

MUTUALISM

Source Taxon: Acidocella facilis

Target Taxon: Acidiphilium multivorum

Metabolites: polysaccharide (CHEBI:18154), protein (CHEBI:36080), copper(2+) (CHEBI:29036), zinc(2+) (CHEBI:29105)

Biological Processes:

biofilm formation (GO:0042710)
extracellular matrix organization (GO:0030198)
metal ion transport (GO:0030001)

Evidence

doi:10.1128/aem.02301-09 - SUPPORT (IN_VIVO)

"Characterization of Extracellular Polymeric Substances from Acidophilic Microbial Biofilms"
PMID:18330567 - SUPPORT (IN_VITRO)

"The efficiency of five extraction methods for extracellular polymeric substances (EPS) was compared on three benthic eukaryotic biofilms isolated from an extreme acidic river, Río Tinto (SW, Spain)"

Photoheterotrophic Carbon Cycling

CROSS_FEEDING

Source Taxon: Acidisphaera rubrifaciens

Target Taxon: Acidocella facilis

Metabolites: organic molecular entity (CHEBI:50860)

Biological Processes:

photosynthesis (GO:0015979)
organic substance catabolic process (GO:1901575)

Evidence

PMID:10939661 - SUPPORT (IN_VITRO)

"On the basis of these results, it was concluded that the four isolates should be classified into a new genus and a new species, for which the name Acidisphaera rubrifaciens is proposed"

Complex Polysaccharide Degradation

CROSS_FEEDING

Source Taxon: Acidobacterium capsulatum

Target Taxon: Acidiphilium cryptum

Metabolites: polysaccharide (CHEBI:18154), glucose (CHEBI:17234), organic acid (CHEBI:64709)

Biological Processes:

polysaccharide catabolic process (GO:0000272)
organic substance catabolic process (GO:1901575)

Evidence

doi:10.1007/BF02106205 - SUPPORT (IN_VITRO)

"Acidobacterium is proposed as a new genus for the acidophilic, chemoorganotrophic bacteria containing menaquinone isolated from acidic mineral environments"
doi:10.3389/fmicb.2016.00744 - SUPPORT (COMPUTATIONAL)

"Genomic and metagenomic data predict a number of ecologically relevant capabilities for some acidobacteria, including the ability to: use of nitrite as N source, respond to soil macro-, micro nutrients and soil acidity, express multiple active transporters, degrade gellan gum and produce exopolysaccharide (EPS)"

Environmental Factors

Factor	Value	Unit
pH Range	2.0-4.0	pH
doi:10.3389/fmicb.2024.1374800 - SUPPORT (REVIEW) "Despite acidophiles are usually associated with an autotrophic metabolism, more than 80 microorganisms capable of utilizing organic matter have been isolated from natural and man-made environments" doi:10.1099/00207713-36-2-197 - PARTIAL (IN_VITRO) "unable to grow at or above pH 6.0"
Dissolved Organic Carbon	Variable, 10-500 mg/L	mg/L DOC
doi:10.3389/fmicb.2015.00475 - SUPPORT (IN_VIVO) "Low-pH conditions appear to be the main factor underlying the limited diversity of the microbial populations thriving in these environments, although temperature, ionic composition, total organic carbon, and dissolved oxygen are also considered to significantly influence their microbial life" doi:10.1128/msystems.00867-20 - SUPPORT (REVIEW) "We found in the genomes of Acidiphilium an abundant repertoire of horizontally transferred genes (HTGs) contributing to environmental adaption and metabolic ability expansion, as indicated by phylogenetic reconstruction and gene context comparison"
Oxygen Availability	Aerobic to anaerobic	qualitative
doi:10.3389/fmicb.2024.1374800 - SUPPORT (REVIEW) "Despite acidophiles are usually associated with an autotrophic metabolism, more than 80 microorganisms capable of utilizing organic matter have been isolated from natural and man-made environments" PMID:10427060 - SUPPORT (IN_VITRO) "Analysis of the 16S rRNA gene sequence of JF-5 demonstrated that it was closely related to an Australian isolate of Acidiphilium cryptum (99.6% sequence similarity), an organism not previously shown to couple the complete oxidation of sugars to the reduction of Fe(III)"
Temperature	15-40	°C
doi:10.1099/00207713-36-2-197 - WRONG_STATEMENT (IN_VITRO) "All 37 bacterial strains examined were rod shaped, motile, gram negative, and strictly aerobic"
Metal Concentrations	Fe: 0.5-5 g/L; Zn: 100-1000 mg/L; Cu: 50-500 mg/L	g/L or mg/L
doi:10.3389/fmicb.2024.1374800 - SUPPORT (REVIEW) "Despite acidophiles are usually associated with an autotrophic metabolism, more than 80 microorganisms capable of utilizing organic matter have been isolated from natural and man-made environments"