Abstract
Plant specialized metabolites (PSMs) are secreted into the rhizosphere, i.e., the soil zone surrounding the roots of plants. They are often involved in root-associated microbiome assembly, but the association between PSMs and microbiota is not well characterized. Saponins are a group of PSMs widely distributed in angiosperms. In this study, we compared the bacterial communities in field soils treated with the pure compounds of four different saponins. All saponin treatments decreased bacterial α-diversity and caused significant differences in β-diversity when compared with the control. The bacterial taxa depleted by saponin treatments were higher than the ones enriched; two families, Burkholderiaceae and Methylophilaceae, were enriched, while eighteen families were depleted with all saponin treatments. Sphingomonadaceae, which is abundant in the rhizosphere of saponin-producing plants (tomato and soybean), was enriched in soil treated with α-solanine, dioscin, and soyasaponins. α-Solanine and dioscin had a steroid-type aglycone that was found to specifically enrich Geobacteraceae, Lachnospiraceae, and Moraxellaceae, while soyasaponins and glycyrrhizin with an oleanane-type aglycone did not specifically enrich any of the bacterial families. At the bacterial genus level, the steroidal-type and oleanane-type saponins differentially influenced the soil bacterial taxa. Together, these results indicate that there is a relationship between the identities of saponins and their effects on soil bacterial communities.
Highlights
At least one million diverse plant specialized metabolites (PSMs) [1] exist that have a wide range of bioactivities and contribute to a plant’s ability to adapt to its environment and protect against pathogens and herbivores [2]
We propose that the correlation of rhizosphere microbiome formation with the chemical structure of PSMs may be a factor for microbiome variation among plant species
We treated field soil with α-solanine, dioscin, soyasaponins, and glycyrrhizin compounds at doses of 10, 50, and 250 nmol g soil−1. α-Diversity in untreated soils was slightly higher than 8, and the high concentration of each saponin treatment (250 nmol g soil−1) significantly reduced the α-diversity compared with control (p < 0.05; Figure 2)
Summary
At least one million diverse plant specialized metabolites (PSMs) [1] exist that have a wide range of bioactivities and contribute to a plant’s ability to adapt to its environment and protect against pathogens and herbivores [2]. Multiple studies have revealed that PSMs are involved in the formation of the rhizosphere and root microbiome [10,11]. Saponins are a group of PSMs widely distributed in angiosperm plants They exhibit biological and pharmacological activities, including antibacterial, antifungal, hemolytic, and cytotoxic properties [23]. They exhibit pbeionloogiidcalsaanpdopnhainrmtahcoaltogiiscaul sacetdiviatiess,ainnclautduinrgaalnstwibaecetetreianl,earntaifnundgails, hfeomuonlydtico, nly in licorice (Glycyrrhiza sapnpd.c)yt[o2to4x]i.c Sprooypearstiaesp[2o3n].iTnhseyacroensoislteoaf ntwaonpea-rttsy: pa heytdrriotpehropbiecnskoeiledtosna, wphoicnhiinss found in several legume patlhgaelynactgoslny,eciosnntrceulcuutnudirte,i,nasngadpobanahinrysrdearrolepmchliaeliscdsisfiiacecdc(hMinartoeiddteri,ictwearghpioecnhtoriisdutnshaecpagotlnuyicnloass,)isdtaeicnroudindiastl.osBayapbsoeendainonsn, (Glycine max). We compared bacterial communities in field soils treated with steroidal-type and oleanane-type saponins. We propose that the correlation of rhizosphere microbiome formation with the chemical structure of PSMs may be a factor for microbiome variation among plant species
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