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Legume-Rhizobia Mars Simulant Symbiosis

Community ID CommunityMech:000311
Ecological State ENGINEERED
Environment Mars soil-simulant legume growth assay (laboratory culture) — ontology label: laboratory environment
ENVO:01001405 · HabitatMech ↗
Modeled Environment regolith
ENVO:01000747 · HabitatMech ↗

A model legume-rhizobia nitrogen-fixing symbiosis tested for its ability to establish on Mars soil simulants. The community pairs the model legume Medicago truncatula with two of its symbiotic rhizobial partners, Sinorhizobium meliloti and Sinorhizobium medicae. Plants were grown on different grades of the Mojave Mars Simulant (MMS-1: Coarse, Fine, Unsorted, Superfine) and the MMS-2 simulant. Root nodules developed on M. truncatula roots grown on the Mars simulants comparably to plants grown on sand, and nifH (a reporter gene for nitrogen fixation) expression was detected inside the nodules, demonstrating that the simulants can support the legume-rhizobia symbiosis. Total plant mass was higher on MMS-2 than on MMS-1 and its grain-size variants, indicating that simulant chemical composition matters more than grain size; MMS-2 Superfine was recommended for future studies. The system is a model for beneficial plant-microbe associations enabling sustainable, nitrogen-fixing agriculture on Mars, exploiting the nitrogen present in the martian atmosphere.

Taxonomy

Taxon Ontology ID Functional Roles Abundance
Sinorhizobium meliloti NCBITaxon:382 · TaxonMech · TraitMech
NITROGEN_FIXING_SYMBIONT
N/A
  • PMID:34879082 - SUPPORT (IN_VITRO)
    "symbiotic partners, Sinorhizobium meliloti and Sinorhizobium medicae"
Sinorhizobium medicae NCBITaxon:110321 · TaxonMech · TraitMech
NITROGEN_FIXING_SYMBIONT
N/A
  • PMID:34879082 - SUPPORT (IN_VITRO)
    "Sinorhizobium meliloti and Sinorhizobium medicae"

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.

Ecological interaction network for Legume-Rhizobia Mars Simulant Symbiosis Bipartite graph where circles represent taxa and non-circular symbols represent interactions. Rare or untyped interactions share the Other symbol; exact curated types remain in the interaction details.
Taxon
Other

Mars Simulant Root Nodulation

In separate Medicago truncatula A17 inoculations with S. meliloti 2011 or S. medicae WSM419, nodules formed on every tested MMS simulant after 14 days. Counts were mostly comparable to sand, with significant decreases for S. meliloti on MMS-1 Unsorted and S. medicae on MMS-1 Fine. These living-host greenhouse results do not establish fixed-nitrogen delivery or reciprocal benefit; the two bacterial species were alternative inoculants, not a coculture.

Participating Taxa: Sinorhizobium meliloti, Sinorhizobium medicae

Biological Processes:

Evidence

  • PMID:34879082 - SUPPORT (IN_VIVO)
    "root nodules could develop on M. truncatula roots when grown on these Mars soil simulants"

Mars Simulant Nodule nifH Promoter Activity

S. meliloti 1021 carrying PnifH::uidA showed nodule-localized promoter activity by GUS staining at 14 days on all tested substrates. This reporter assay used S. meliloti only, not S. medicae. PARTIAL - promoter activity is evidence of nitrogenase-associated gene regulation, not direct N2-fixation flux, ammonia delivery to the host or a selective test that nodulation itself induces nifH.

Participating Taxa: Sinorhizobium meliloti

Biological Processes:

Evidence

  • PMID:34879082 - PARTIAL (IN_VIVO)
    "M. truncatula plants were inoculated with S. meliloti 1021 carrying the PnifH::uidA fusion"
  • PMID:34879082 - PARTIAL (IN_VIVO)
    "Our results show that the nifH promoter was active in the nodules"

Mars Simulant Dependent Plant Phenotypes

At 14 days after separate rhizobial inoculations, Medicago plant mass was lower on MMS-1 variants than sand and comparable between MMS-2 Superfine and sand. Lateral-root numbers were reduced on every simulant relative to sand. HYPOTHESIZED - chemical composition may explain substrate differences, but individual chemical mediation was not selectively tested. These Earth-greenhouse, living-host endpoints do not show that nifH activity caused plant mass, prove mutual benefit or demonstrate growth under a Martian atmosphere or perchlorate exposure.

Participating Taxa: Sinorhizobium meliloti, Sinorhizobium medicae

Biological Processes:

Evidence

  • PMID:34879082 - SUPPORT (IN_VIVO)
    "total mass of plants grown on MMS-2 Superfine soil was comparable to the total mass of plants grown on sand"
  • PMID:34879082 - SUPPORT (IN_VIVO)
    "average lateral root number was significantly reduced on plants grown on these soils if compared to plants grown on sand"

Knowledge gaps & discussions (1)

KNOWLEDGE_GAP OPEN Does the observed nodule promoter activity yield fixed nitrogen and host benefit on each simulant?

Retain nodules, nifH promoter activity and substrate-dependent plant phenotypes; drop the anatomical-context and conclusion arrows rather than asserting causal mediation. No direct N2-fixation rate, ammonia delivery, plant nitrogen measurement or uninoculated host-benefit comparison establishes the proposed chain. The reporter used S. meliloti 1021 only; phenotype inoculations used S. meliloti 2011 or S. medicae WSM419 separately. The host is absent from the canonical roster (#1553), so listed bacteria are a partial participant set, not a complete microbial coculture. Earth greenhouse conditions and simulants without perchlorates are not Mars conditions. Chemistry is a proposed explanation, not an isolated additive perturbation. Main body and captions read, not original image pixels, separate supplements or raw measurements.

Attaches to: ecological_interactions#Mars Simulant Root Nodulation, ecological_interactions#Mars Simulant Nodule nifH Promoter Activity, ecological_interactions#Mars Simulant Dependent Plant Phenotypes

Environmental Factors

Factor Value Unit
Mojave Mars Simulant grades (MMS-1) and MMS-2 substrate MMS-1 (Coarse/Fine/Unsorted/Superfine) and MMS-2 N/A
  • PMID:34879082 - SUPPORT (IN_VITRO)
    "different grades of the Mojave Mars Simulant (MMS)-1: Coarse, Fine, Unsorted, Superfine, and the MMS-2 simulant"
Atmospheric nitrogen as fixation substrate Nitrogen present in the Mars atmosphere N/A
  • PMID:34879082 - SUPPORT (IN_VITRO)
    "The presence of nitrogen in the Mars atmosphere offers the possibility to take advantage of this important plant-microbe association"

Growth Media

Tryptone-Yeast extract (TY) medium, for the rhizobial inoculum

Temperature 30 °C
Atmosphere AEROBIC

Preparation notes: Sinorhizobium meliloti 2011, S. medicae WSM419 and S. meliloti 1021 (PnifH::uidA) were grown to OD600 0.8 with appropriate antibiotics, then applied at 1e8 cells/mL. This is the medium for the bacterial partner only; the plant substrate is recorded separately.

Evidence

PMID:34879082

"The bacterial strains were grown in Tryptone-Yeast extract medium and supplemented with appropriate antibiotics at 30°C to an optical density (600 nm) of 0.8. Each plant was inoculated with the appropriate bacterium at a concentration of 1x108 cells/ml."

Mojave Mars Simulant substrate (MMS-1 Coarse/Fine/Unsorted/Superfine, MMS-2) with sand control

Temperature 22 °C
Atmosphere AEROBIC

Preparation notes: The substrate is a sterile mineral simulant, not a microbial source: the community here is the deliberately introduced legume-rhizobium pair, so the simulant supplies physical and chemical context rather than an inoculum. Grain-size grades were the variable.

Evidence

PMID:34879082

"we used different Mars soil simulants (different grades of the Mojave Mars Simulant (MMS)-1: Coarse, Fine, Unsorted, Superfine, and the MMS-2 simulant) available through The Martian Garden (Austin, TX) along with sand. We used sand (Quikrete all-purpose sand) as our control substrate in this study."

PMID:34879082

"The germinated seedlings were planted on trays with inserts (2.35” X 1.94” X 2.23”; CN-IKN, Greenhouse Megastore, USA) filled with the different Mars soil simulants. These plants were allowed to grow in a temperature-controlled (22°C—25°C) greenhouse with a 16-hour photoperiod."

PMID:34879082

"The plants were watered every 24–48 hours with each plant receiving 1ml of water. The plants were grown for seven days before inoculation with bacteria."

PMID:34879082

"The different plant phenotypes (total plant mass, lateral root number, average nodule number) were recorded 14 days post-inoculation."

1% plant agar with 1 mM gibberellic acid (GA3), for germination

Temperature 25 °C
Atmosphere AEROBIC

Preparation notes: Seeds were surface-sterilised in 1 M sulfuric acid for 8 min, washed, rinsed in 5.6% sodium hypochlorite and imbibed in sterile water before plating; plates were stratified at 4 C for at least 48 h then held at 25 C for 48-96 h to germinate.

Evidence

PMID:34879082

"The seeds were surface-sterilized in concentrated sulfuric acid (1M) for 8 minutes, then washed four times with sterile diH2O followed by one rinse with 5.6% (v/v) sodium hypochlorite solution. The seeds were rinsed an additional three times with sterile diH2O and allowed to imbibe in sterile diH2O for a minimum of 2 h in a sterile environment."

PMID:34879082

"sterilized seeds were transferred to 9-cm Petri plates (#633185, Greiner Bio-one, Monroe, NC, USA) containing 1% (w/v) plant agar (#A038-2.5KG, Caisson Laboratories Inc., Smithfield, UT, USA) supplemented with 1 mM Gibberellic acid (GA3) medium under sterile conditions."

PMID:34879082

"The plates were sealed with parafilm, wrapped completely in aluminum foil, and placed at 4°C for a minimum of 48 h, removed from the refrigerator, and then placed at room temperature (25°C) for an additional 48–96 h to allow the seeds to germinate."

Cross-Mech Suite Links

Explore related entities across the CultureBotAI X-Mech knowledge bases:

HabitatMech: Mars soil-simulant legume growth assay (laboratory culture) ↗ TaxonMech: Sinorhizobium meliloti ↗ TraitMech: Sinorhizobium meliloti ↗ TaxonMech: Sinorhizobium medicae ↗ TraitMech: Sinorhizobium medicae ↗ CultureMech Growth Media ↗ PathwayMech Pathways ↗