Silicate-Solubilizing Bacteria in Louisiana Soils: Identification, Profiling, and Functions in Crop Production

Abstract

Studies were conducted to determine the potential of silicate-solubilizing bacteria (SSB) as biostimulant in Louisiana rice (Oryza sativa L.) production systems. Isolation and profiling of SSB in Louisiana soils; evaluation on its effects on the silicon (Si) uptake and productivity of rice using various carriers derived from slag, rice hull, and sugarcane (Officinarum spp.) bagasse; and development of a feasible approach of incorporating SSB to the rice production system were conducted. Results showed that numerous bacteria isolated from Louisiana soils can solubilize silicate and produce multiple plant growth-promoting compounds. These potential SSBs were identified into four genera: Aeromonas, Bacillus, Enterobacter, and Pseudomonas. In the greenhouse, the differences in agronomic variables and Si nutrition of rice were evident between Commerce silt loam and Gigger silt loam soil. While Si addition did not result in a significant grain yield increase, there was a significant improvement observed on rice Si uptake. The survival test confirmed the presence of SSB in the different carriers, thus the observed improvement on straw Si content of rice can be associated with the use of SSB-inoculated carriers. Even so, this did not significantly increase rice biomass and grain yield. The lack of rice yield response to Si addition and SSB inoculation was partly explained by the high initial Si availability in both soil types. The semi-quantitative evaluation of silica bodies distribution on the leaf surface of rice (treated with wollastonite and SSB using different carriers) via SEM-EDX further confirmed that the soil type had greater influence than Si addition and SSB inoculation on rice Si nutrition. More silica bodies were observed on the leaf surface of rice planted in Commerce silt loam than in Gigger silt loam. In the laboratory, the highest population of SSB was 5.0 x 106 CFU g-1 (log number of cells, 6.70) obtained in bagasse + soil carrier at 150 days after inoculation with a final population of 4.6 x 106 CFU g-1 at 180 days after inoculation (log number of cells, 6.66). The fluorescent microscopy analysis showed that the green fluorescence protein tagged-SSB can colonize the root tissues of the two-week-old rice seedlings indicating its ability to survive when used as a seed treatment, which is a very practical and efficient application method of potential bioinoculant to the field in the future. Future research will focus on (1) determining the optimum concentration of SSB to be inoculated in different carriers, and (2) evaluating