Fig 1.
Concept of host mediated microbiome engineering (HMME).
1) An initial microbiome is inoculated. 2) Seeds are planted into well-watered conditions. 3) Emerging seedlings are then exposed to a drought stress by withholding watering. 4) When 90% of the plants display symptoms of water stress (wilting, leaf curling, etc.), the 5 best-performing plants are selected. Their rhizospheres (roots and planting medium) are amalgamated with autoclaved Metro-Mix 900 in a 1:10 ratio. The next round of selection is then initiated by planting seeds into the engineered planting medium.
Fig 2.
Effect of host-mediated microbiome engineering (HMME) rounds of selection on seedling drought tolerance.
The number of days without water was determined as the day on which 90% of the seedlings displayed severe water stress symptoms.
Fig 3.
Effect of host-mediated microbiome engineering (HMME) on seedling phenotypes under drought stress.
Wheat seedlings growing in planting medium combined with either autoclaved (left) or non-autoclaved (right) rhizosphere inoculum from the final HMME round of selection after 10 days of withholding water.
Fig 4.
Transferability of the host-mediated microbiome engineering (HMME) effect on plant water stress tolerance.
Dilution of rhizosphere inoculum from HMME Round 6 demonstrates no loss of effectiveness in mediating the onset drought stress symptoms at day 10 for the 1x10-1 (HMME) and 1x10-2 dilution, but loss of efficacy at the 1x10-3 dilution, which displayed a similar phenotype to the treatment having no HMME inoculum (control).
Fig 5.
Transferability of the host-mediated microbiome engineering (HMME) effect on water loss.
Percentage of water loss calculated from the difference in pot weight every 48 hrs. relative to the starting pot weight. Treatments include pots growing seedlings inoculated with either a dilution series of rhizosphere inoculum from HMME Round 6: 1x10-1 (HMME), 1x10-2, 1x10-3, or no HMME inoculum (control). Standard error bars are shown, and significant differences are indicated.
Table 1.
Analysis of variance (ANOVA) for testing the effect of the host-mediated microbiome engineering (HMME) on plant phenotype under drought stress.
Table 2.
Comparison of root system traits for plants grown with either non-autoclaved (HMME) or autoclaved HMME inoculum (control).
Fig 6.
Stacked bar charts presenting relative abundance of each taxa at the phylum level (top) and class level (bottom). This comparison demonstrates host-mediated microbiome engineering (HMME) resulted in taxonomic increases in Proteobacteria and Betaproteobacteria in the community rhizosphere when comparing Round 0, 3 and 6 of HMME. Taxa were referenced to the 99% OTU Greengenes 13–8 database with a 1% abundance cutoff.
Table 3.
Phylum level analysis of variance (ANOVA) comparing Rounds 0, 3, and 6 of host-mediated microbiome engineering (HMME).
Table 4.
Class level analysis of variance (ANOVA) comparing Rounds 0, 3, and 6 of host-mediated microbiome engineering (HMME).
Fig 7.
When comparing both a Bray Curtis dissimilarity index (A) and a Weighted UNIFRAC PCoA plot (B), successive generations show increasing divergence or dissimilarity from the original community extracted from Round 0 (red), with Round 3 (blue) transitioning between Round 0 and Round 6 (orange) of host-mediated microbiome engineering (HMME).
Table 5.
Comparative analysis of Rounds 0, 3, and 6 of host-mediated microbiome engineering (HMME) using a PERMANOVA pseudo-F association analysis (permutations = 999).