Earthworm gut bacteria increase silicon bioavailability and acquisition by maize

Silicon improves plant resistance to a wide range of biotic and abiotic stresses. However, available silicon as a plant nutrient in soil is scarce. A continuous supply of available silicon is vital for plants. Earthworms are important detritivores in many terrestrial ecosystems. Therefore, we hypothesized that earthworms harbor silicate solubilizing bacteria in their guts and play a key role in silicon weathering and dynamics. Silicate solubilizing bacteria were isolated from the gut of geophagous endogeic earthworm (Pheretima guillelmi) and their effects on silicon weathering and availability to maize (Zea mays) were examined. Significantly more silicate solubilizing bacteria were observed in the earthworms gut than those in the surrounding soil in all sampling locations. The 16S rRNA analysis showed a higher silicate solubilizing bacteria diversity with 20 bacterial strains isolated from the gut walls, belonging to the genera of Aeromonas, Bacillus, Cellvibrio, Ensifer, Flavobacterium, Microbacterium, Paracoccus, Pseudomonas, Rhizobium, and Streptomyces. Of these bacteria, only three species were found in the surrounding soil. Inoculation with the three fastest-growing strains in liquid culture increased soluble silicon released from the feldspar and quartz powder in the media. Inoculation with the 3C1 strain in the potting soil significantly increased soluble silicon content in the soil, enhanced silicon uptake and accumulation in maize plants and promoted seedling growth. Taken together, these results not only highlight the importance of earthworm gut microbes in soil silicon weathering but also indicate a new approach in searching for silicate solubilizing bacteria to increase soil silicon availability in agriculture.