Legume-Rhizobia Mars Simulant Symbiosis

Community ID CommunityMech:000311

Ecological State ENGINEERED

Environment Mars soil-simulant legume growth assay (laboratory culture)
ENVO:01001405

Modeled Environment regolith
ENVO:01000747

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	NITROGEN_FIXING_SYMBIONT	N/A
PMID:34879082 - SUPPORT (IN_VITRO) "symbiotic partners, Sinorhizobium meliloti and Sinorhizobium medicae"
Sinorhizobium medicae	NCBITaxon:110321	NITROGEN_FIXING_SYMBIONT	N/A
PMID:34879082 - SUPPORT (IN_VITRO) "Sinorhizobium meliloti and Sinorhizobium medicae"

Ecological Interactions

Taxon

Mutualism

Legume-rhizobia nitrogen-fixing symbiosis on Mars simulants

MUTUALISM

Source Taxon: Sinorhizobium spp. (rhizobial symbionts)

Target Taxon: Medicago truncatula (host legume)

Biological Processes:

nodulation (GO:0009877)
nitrogen fixation (GO:0009399)

Evidence

PMID:34879082 - SUPPORT (IN_VITRO)

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

"detected nifH (a reporter gene for nitrogen fixation) expression inside these nodules"

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."