Recruitment of beneficial cucumber rhizosphere microbes mediated by amino acid secretion induced by biocontrol Bacillus subtilis isolate 1JN2

Abstract

Introduction: At present, the use of beneficial microorganisms to control cucumber Fusarium wilt is a widely used method, and the rhizosphere microecological reset is one of the mechanisms involved. However, how biocontrol strains reshape cucumber rhizosphere microecology remains to be further studied.

Methods: The composition changes of cucumber root exudates induced by biocontrol strain 1JN2, the microbial ecology of cucumber rhizosphere and the colonization ability of biocontrol strain 1JN2 in cucumber rhizosphere were analyzed through UHPLC-MS/MS analysis, Illumina high-throughput sequencing and SEM, respectively.

Results: First, cucumber plants treated with biocontrol Bacillus 1JN2 reduced the disease severity of Fusarium wilt by 60%. Significant changes in cucumber root exudates were found after 1JN2 inoculation and the contents of four amino acids including glutamine, tryptophan, glycine and glutamic acid were significantly increased. Second, It was found that the bacterial diversity in the rhizosphere of cucumber was significantly increased in both the strain treatment group and the amino acid mixture treatment group, The number of Bacillus was the largest in all dominant populations, exceeded 20% in all treatment groups. The bacteria of Hydrogenispora and Vicinamibacteria were significantly increased after treatment.

Discussion: Overall, the results demonstrated that amino acid substances in cucumber root exudates induced by biocontrol strain 1JN2 can shift the cucumber root microenvironment and prevent the occurrence of Fusarium wilt disease.

Keywords: Fusarium wilt; amino acids; biocontrol; recruitment; rhizosphere microbiome.

Figure 1

Plate antagonistic activity (A) and greenhouse control effect (B) of biocontrol strain 1JN2 against cucumber Fusarium wilt.

Figure 2

Colonization of the biocontrol strain 1JN2 on cucumber roots. (A1,A2) Were root tip and taproot of cucumber treated with 1JN2 suspension, (A3,A4) were root tip and taproot of cucumber treated with water. (B) Shows the survival of 1JN2 in the soil with (T) or without cucumber (C).

Figure 3

Analysis on the differences of amino acids between the strain treatment group and strain induction group. (A1–A3) Mean the differences of amino acids between the strain treatment group to CK, strain induction group to CK, and strain treatment group and strain induction group. (B1–B3) mean the score scatter plot of the OPLS-DA model for the strain treatment group to CK, strain induction group to CK, and strain treatment group and strain induction group.

Figure 4

Community analysis of rhizosphere bacteria of cucumber (sunburst plot on the genus level). (A1–A5) Means soil samples collected 1 day before treated with 1JN2 suspension and 1 day, 3 days, 7 days, and 14 days after treatment. (B1–B5) Means soil samples collected 1 day before treated with amino acid solution and 1 day, 3 days, 7 days, and 14 days after treatment.

Figure 5

Analysis of single species difference test (Kruskal–Wallis H test on the genus level). 1JN2_1 to 1JN2_5 means soil samples collected 1 day before treated with 1JN2 suspension and 1 day, 3 days, 7 days, and 14 days after treatment. H3_11L_1 to H3_11L_5 means soil samples collected 1 day before treated with amino acid solution and 1 day, 3 days, 7 days, and 14 days after treatment.