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. 2022 Nov 17;8(11):e11674.
doi: 10.1016/j.heliyon.2022.e11674. eCollection 2022 Nov.

Effects of Bacillus subtilis and Pseudomonas fluorescens as the soil amendment

Charles Wang Wai Ng  1 , Wen Hui Yan  1 , Karl Wah Keung Tsim  2 , Pui San So  1 , Yi Teng Xia  2 , Chun Ting To  1
Affiliations

Effects of Bacillus subtilis and Pseudomonas fluorescens as the soil amendment

Charles Wang Wai Ng et al. Heliyon. .

Abstract

The application of soil beneficial bacteria (SBB) in agriculture is steadily increasing as it provides a promising way to replace chemical fertilisers and other supplements. Although the role of SBB as a biofertiliser is well understood, little is known about the response of soil physiochemical properties via the change in soil enzymatic activities with SBB growth. In this study, sterilised bulk soil was inoculated with Bacillus subtilis (BS) and Pseudomonas fluorescens (PF), which exhibit excellent characteristics in vitro for potentially improving soil quality. It is found that the contents of bioavailable nitrogen and ammonium in soil inoculated with SBB increased significantly, up to 34% and 57% relative to a control. This resulted from the enhancement of soil urease activity with BS and PF treatments by approximately 90% and 70%, respectively. The increased soil urease activity can be explained by the increased microorganism activity evident from the larger population size of BS (0.78-0.97 CFU mL-1/CFU mL-1) than PF (0.55-0.79 CFU mL-1/CFU mL-1) (p < 0.05). Results of principal component analysis also reinforce the interaction apparent in the significant relationship between soil urease activity and microbial biomass carbon (p < 0.05). Therefore, it can be concluded that the enhancement of soil enzymatic activities induced bulk soil fertility upregulation because of bacterial growth. These results demonstrate the application of SBB to be a promising strategy for bulk soil amendment, particularly nutrient restoration.

Keywords: Bacillus subtilis; Pseudomonas fluorescens; Soil beneficial bacteria; Soil fertility; Soil urease.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Characterisation of bacterial traits in vitro (A) bacterial indole-3-acetic acid (IAA) production capability (B) bacterial inorganic phosphorus (P) solubilisation capability. L-Trp: L-tryptophan. CK: control. BS: Bacillus subtilis. PF: Pseudomonas fluorescens. Each result is presented as the mean ± S.D., calculated from three independent samples. ∗ represents a significant difference (p < 0.05), and ns represents no significant difference within the group. Letters in each column mean a significant difference (p < 0.05) among treatments.
Figure 2
Figure 2
Effects of beneficial bacteria on soil physicochemical properties (A) indole-3-acetic acid (IAA) content (B) soil bioavailable phosphate (AP) content (C) carbon content (D) nitrogen content. TOC: total organic carbon. MBC: microbial biomass carbon. SUVA254: specific ultraviolet absorbance at 254 nm. AN: soil bioavailable nitrogen. AM: soil ammonium. CK: control. BS: Bacillus subtilis treatment. PF: Pseudomonas fluorescens treatment. Each result is presented as the mean ± S.D., calculated from three independent samples. Letters in each column mean a significant difference (p < 0.05) among treatments.
Figure 3
Figure 3
Effects of beneficial bacteria on soil enzymatic activities (A) soil acid phosphatase (SACP) activity (B) soil catalase (SCAT) activity (C) soil urease (SURE) activity. CK: control. BS: Bacillus subtilis treatment. PF: Pseudomonas fluorescens treatment. Each result is presented as the mean ± S.D., calculated from three independent samples. Letters in each column mean a significant difference (p < 0.05) among treatments.
Figure 4
Figure 4
Log relative growth of two bacteria strains (as a colony-forming unit at each time point/colony-forming unit at the beginning) during cultivation in soil. The parameters in the table represent the linear fitting for the exponential growth phase (EGP) (BS) Bacillus subtilis (PF) Pseudomonas fluorescens. Each result is presented as the mean ± S.D., calculated from three independent samples. ∗ represents a significant difference between BS and FP treatments at each time point (p < 0.05).
Figure 5
Figure 5
Principal component analysis describing the relationship between soil quality and beneficial bacterial growth. Yellow, blue, and orange shadows are 95% confidence ellipses for CK, BS, and PF treatments, respectively. EC: electrical conductivity. IAA: indole-3-acetic acid. AP: soil bioavailable phosphate. TOC: total organic carbon. MBC: microbial biomass carbon. SUVA: specific ultraviolet absorbance. AN: soil bioavailable nitrogen. AM: soil ammonium. SACP: soil acid phosphatase. SCAT: soil catalase. SURE: soil urease. SBB: soil beneficial bacteria. CK: control. BS: Bacillus subtilis treatment. PF: Pseudomonas fluorescens treatment.
Figure 6
Figure 6
Pearson correlation coefficient analysis plot describing the relationship between soil quality and soil beneficial bacteria. The colour bar shows that the correlation ranges from -1 to 1. Values closer to zero mean a less linear trend between the two variables. EC: electrical conductivity. IAA: indole-3-acetic acid. AP: soil bioavailable phosphate. TOC: total organic carbon. MBC: microbial biomass carbon. SUVA: specific ultraviolet absorbance. AN: soil bioavailable nitrogen. AM: soil ammonium. SACP: soil acid phosphatase. SCAT: soil catalase. SURE: soil urease. SBB: soil beneficial bacteria.
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