The genetic diversity of antagonistic bacteria from the tobacco rhizosphere was examined by BOXAIR-PCR, 16S-RFLP, 16S rRNA sequence homology and phylogenetic analysis methods. These studies revealed that 4.01% of the 6652 tested had some inhibitory activity against Phytophthora nicotianae. BOXAIR-PCR analysis revealed 35 distinct amplimers aligning at a 91% similarity level, reflecting a high degree of genotypic diversity among the antagonistic bacteria. A total of 25 16S-RFLP patterns were identified representing over 33 species from 17 different genera. Our results also found a significant amount of bacterial diversity among the antagonistic bacteria compared to other published reports. For the first time; Delftia tsuruhatensis, Stenotrophomonas maltophilia, Advenella incenata, Bacillus altitudinis, Kocuria palustris, Bacillus licheniformis, Agrobacterium tumefaciens and Myroides odoratimimus are reported to display antagonistic activity towards Phytophthora nicotianae. Furthermore, the majority (75%) of the isolates assayed for antagonistic activity were Gram-positives compared to only 25% that were Gram-negative bacteria.

Background: Paenibacillus polymyxais a typical plant growth-promoting rhizobacterium (PGPR), and synthesis of indole-3-acetic acid (IAA) is one of the reasons for its growth-promoting capacity. The synthetic pathways of IAA inP. polymyxamust be identified and modified.Results: P. polymyxaSC2 and its spontaneous mutant SC2-M1 could promote plant growth by directly secreting IAA. Through metabonomic and genomic analysis, the genespatA,ilvB3, andfusEin the native IPyA pathway of IAA synthesis in strain SC2-M1 were predicted. A novel strong promoterP₀₄₄₂₀was rationally selected, synthetically analyzed, and then evaluated on its ability to express IAA synthetic genes.Co-expression of three genes,patA,ilvB3, andfusE, increased IAA yield by 60% in strain SC2-M1. Furthermore, the heterogeneous geneiaamof the IAM pathway and two heterogeneous IPyA pathways of IAA synthesis were selected to improve the IAA yield of strain SC2-M1.The genesELJP6_14505,ipdC,andELJP6_00725of the entire IPyA pathway fromEnterobacter ludwigiiJP6 were expressed well by promoterP₀₄₄₂₀in strain SC2-M1 and increased IAA yield in the engineered strain SC2-M1 from 13 to 31 μg/mL, which was an increase of 138%.Conclusions: The results of our study help reveal and enhance the IAA synthesis pathways ofP. polymyxaand its future application.

Bacillus atrophaeusGQJK17 was isolated from the rhizosphere ofLycium barbarumL. in China, which was shown to be a plant growth-promoting rhizobacterium as a new biological agent against pathogenic fungi and gram-positive bacteria. We present its biological characteristics and complete genome sequence, which contains a 4,325,818 bp circular chromosome with 4,181 coding DNA sequences and a G+C content of 43.3%. A genome analysis revealed a total of 8 candidate gene clusters for producing antimicrobial secondary metabolites, including surfactin, bacillaene, fengycin, and bacillibactin. Some other antimicrobial and plant growth-promoting genes were also discovered. Our results provide insights into the genetic and biological basis ofB. atrophaeusstrains as a biocontrol agent for application in agriculture.

Delftia tsuruhatensis MTQ3 is a plant growth-promoting rhizobacterium (PGPR) isolated from tobacco rhizosphere. Here, we report the draft genome sequence of D. tsuruhatensis MTQ3. Several functional genes related to antimicrobial activity and environment adaption have been found in the genome. This is the first genome sequence of D. tsuruhatensis related to PGPR.

Two bacteria,Streptomyces albireticuliMDJK11 andS. alboflavusMDJK44, which are potential plant growth-promoting rhizobacteria against pathogenic fungi were isolated from the rhizosphere soil of peony in Shandong, China. Their biological characteristics and complete genome sequences were reported in this study. The total genome size of MDJK11 was only 8.14 Mb with 6,550 protein-coding genes and a high GC content of 72.8 mol%. The MDJK44 genome comprises a 9.62 Mb chromosome with 72.1 mol% GC content, 7,285 protein-coding genes, and two plasmids. Some gene sequences in these two genomes were analyzed to be heterologously obtained by horizontal transfer. Gene or gene cluster candidates responding to secondary metabolites production, antimicrobial activities, and plant growth-promoting capacities were also analyzed in this paper. The genomic information and biological characteristics will facilitate the understanding and application ofS. albireticuliandS. alboflavusspecies as biocontrol agents in future agriculture.