Junqing Qiao

Novel Routes for Improving Biocontrol Activity of Bacillus Based Bioinoculants

Biocontrol (BC) formulations prepared from plant-growth-promoting bacteria are increasingly applied in sustainable agriculture. Especially inoculants prepared from endospore-forming Bacillus strains have been proven as efficient and environmental-friendly alternative to chemical pesticides due to their long shelf life, which is comparable with that of agrochemicals. However, these formulations of the first generation are sometimes hampered in their action and do not fulfill in each case the expectations of the appliers. In this review we use the well-known plant-associated Bacillus amyloliquefaciens type strain FZB42 as example for the successful application of different techniques offered today by comparative, evolutionary and functional genomics, site-directed mutagenesis and strain construction including marker removal, for paving the way for preparing a novel generation of BC agents.

Stimulation of plant growth and biocontrol by Bacillus amyloliquefaciens subsp. plantarum FZB42 engineered for improved action

During the last decade, the use of plant-root colonizing bacteria with plant growth-promoting activity has been proven as an efficient and environmental-friendly alternative to chemical pesticides and fertilizers. Biofertilizer and biocontrol formulations prepared from endospore-forming Bacillus strains are increasingly applied due to their long shelf life, which is comparable with that of agrochemicals. Today, spore suspensions from natural representatives of mainly Bacillus amyloliquefaciens, Bacillus subtilis, and Bacillus pumilus are available. However, these biofertilizers, directly prepared from environmental strains, are sometimes hampered in their action and do not fulfill in each case the expectations of the appliers (Borriss R, Bacteria in agrobiology: plant growth responses, Springer, 2011, pp. 41-76). This review will focus on several ways to improve the action of B. amyloliquefaciens subsp. plantarum FZB42T, the type strain for the group of plant-associated B. amyloliquefaciens strains. We are focusing here on genomics and genetic engineering techniques as helpful tools for developing more powerful biofertilizer and biocontrol agents.

Depressed biofilm production in Bacillus amyloliquefaciens C06 causes γ-polyglutamic acid (γ-PGA) overproduction.

Bacillusamyloliquefaciens C06, a potential agent in biological preservation of post-harvest fruit, was found to secrete extra-cellular γ-polyglutamic acid (γ-PGA) in liquid culture. In this work, M306, a transposon mutant of B. amyloliquefaciens C06, defective in forming structured colony and displaying enhanced ability of producing γ-PGA, was obtained. Inverse PCR and quantitative reverse transcription PCR (qRT-PCR) analysis demonstrated that the defective phenotype in M306 was associated with an ORF showing high similarity to RBAM_034550 from B. amyloliquefaciens FZB42. In this paper, the ORF was designated pbrA, standing for γ-PGA production and biofilm formation regulatory factor. qRT-PCR analysis also indicated that pbrA down-regulated mRNA expression of epsD and yqxM, the crucial genes involved in biofilm formation, but affected little on expression of ywtB, the gene directing γ-PGA synthesis. Evaluations in γ-PGA productivity of wild-type C06 and its mutants C06ΔepsA and C06ΔtasA, respectively, deficient in producing exopolysaccharides (EPS) and TasA, revealed that γ-PGA overproduction in M306 was probably due to the redistributed metabolic flux caused by defective production of EPS.

Cloning, expression and characterization of a new aspartate aminotransferase from Bacillus subtilis B3.

In the present study, we report the identification of a new gene from the Bacillus subtilis B3 strain (aatB3), which comprises 1308 bp encoding a 436 amino acid protein with a monomer molecular weight of 49.1 kDa. Phylogenetic analyses suggested that this enzyme is a member of the Ib subgroup of aspartate aminotransferases (AATs; EC 2.6.1.1), although it also has conserved active residues and thermostability characteristic of Ia‐type AATs. The Asp232, Lys270 and Arg403 residues of AATB3 play a key role in transamination. The enzyme showed maximal activity at pH 8.0 and 45 °C, had relatively high activity over an alkaline pH range (pH 7.0–9.0) and was stable up to 50 °C. AATB3 catalyzed the transamination of five amino acids, with l‐aspartate being the optimal substrate. The Km values were determined to be 6.7 mm for l‐aspartate, 0.3 mm for α‐ketoglutarate, 8.0 mm for l‐glutamate and 0.6 mm for oxaloacetate. A 32‐residue N‐terminal amino acid sequence of this enzyme has 53% identity with that of Bacillus circulans AAT, although it is absent in all other AATs from different organisms. Further studies on AATB3 may confirm that it is potentially beneficial in basic research as well as various industrial applications.

The Rhizobacterium Bacillus amyloliquefaciens subsp. plantarum NAU-B3 Contains a Large Inversion within the Central Portion of the Genome

ABSTRACT The genome of rhizobacterium Bacillus amyloliquefaciens subsp. plantarum strain NAU-B3 is 4,196,170 bp in size and harbors 4,001 genes. Nine giant gene clusters are dedicated to the nonribosomal synthesis of antimicrobial lipopeptides and polyketides. Remarkably, NAU_B3 contains a large inversion within the central portion of the genome.