Specific detection ofLysobacter enzymogenes(Christensen and Cook 1978) strain 3.1T8 with TaqMan®PCR

Specific detection of Lysobacter antibioticus strains in agricultural soil using PCR and real-time PCR

Lysobacter antibioticus is an important biocontrol bacteria against phytopathogens in soil, and with the ability to produce nonvolatile antimicrobial metabolites has been extensively characterised. It is important to establish applicable techniques to detect and monitor L. antibioticus directly and accurately in soil samples. We developed and tested 13 primer sets according to phenazine gene (phzA, phzB, phzD, phzF, phzS) and the cyclohexanone monooxygenase gene (phzNO1); a pair of primer phzNO1 F1/phzNO1 R1 based on the cyclohexanone monooxygenase (phzNO1) gene of L. antibioticus strain OH13 was selected and optimized polymerase chain reaction (PCR) amplification conditions for rapid and accurate detection. After screening eight strains of L. antibioticus, two strains of Lysobacter enzymogenes, one strain of Lysobacter capsici, Arthrobacterium, Bacillus, Microbacterium, Burkholderia, Pseudomonas and other bacterial strains isolated from different agricultural soils, the phzNO1 F1/phzNO1 R1 primers amplified a single PCR band of about 229 bp from L. antibioticus. The detection sensitivity with primers phzNO1 F1/phzNO1 R1 was 5.14 × 104 fg/25μL of genomic DNA and 2.254 × 1010 to 2.254 × 1011 colony-forming units/mL for the soil samples. Quantitative PCR assays were to develope as a specific method to monitor the L. antibioticus population in soil as well as guide soil micro-ecological management.

Monitoring Lysobacter capsici AZ78 using strain specific qPCR reveals the importance of the formulation for its survival in vineyards

Survival in the phyllosphere is a critical feature for biofungicides based on non-spore forming bacteria. Moreover, knowledge of their persistence on plants is important to design effective formulations and application techniques. With this scope, the aim of this work was to develop a specific method to monitor the fate in the environment of Lysobacter capsici AZ78, a biocontrol agent of Plasmopara viticola, and to evaluate the contribution of formulation in its persistence on grapevine leaves. A strain-specific primer pair derived from REP-PCR fingerprinting was used in quantitative PCR experiments to track the evolution of L. capsici AZ78 population in vineyards. The population reached between 5 and 6 log10 cells gram of leaf(-1) after application and decreased by more than 100 times in one week. Multiple regression analysis showed that unfavourable temperature was the main environmental factor correlating with the decrease of L. capsici AZ78 persistence on grapevine leaves. Importantly, the use of formulation additives protected L. capsici AZ78 against environmental factors and improved its persistence on the leaves by more than 10 times compared to nude cells. Formulation and the knowledge about the persistence of L. capsici AZ78 in vineyards will be useful to develop commercial biofungicides for foliar application.

Diversity and Activity of Lysobacter Species from Disease Suppressive Soils

The genus Lysobacter includes several species that produce a range of extracellular enzymes and other metabolites with activity against bacteria, fungi, oomycetes, and nematodes. Lysobacter species were found to be more abundant in soil suppressive against the fungal root pathogen Rhizoctonia solani, but their actual role in disease suppression is still unclear. Here, the antifungal and plant growth-promoting activities of 18 Lysobacter strains, including 11 strains from Rhizoctonia-suppressive soils, were studied both in vitro and in vivo. Based on 16S rRNA sequencing, the Lysobacter strains from the Rhizoctonia-suppressive soil belonged to the four species Lysobacter antibioticus, Lysobacter capsici, Lysobacter enzymogenes, and Lysobacter gummosus. Most strains showed strong in vitro activity against R. solani and several other pathogens, including Pythium ultimum, Aspergillus niger, Fusarium oxysporum, and Xanthomonas campestris. When the Lysobacter strains were introduced into soil, however, no significant and consistent suppression of R. solani damping-off disease of sugar beet and cauliflower was observed. Subsequent bioassays further revealed that none of the Lysobacter strains was able to promote growth of sugar beet, cauliflower, onion, and Arabidopsis thaliana, either directly or via volatile compounds. The lack of in vivo activity is most likely attributed to poor colonization of the rhizosphere by the introduced Lysobacter strains. In conclusion, our results demonstrated that Lysobacter species have strong antagonistic activities against a range of pathogens, making them an important source for putative new enzymes and antimicrobial compounds. However, their potential role in R. solani disease suppressive soil could not be confirmed. In-depth omics'-based analyses will be needed to shed more light on the potential contribution of Lysobacter species to the collective activities of microbial consortia in disease suppressive soils.

Indigenous populations of three closely related Lysobacter spp. in agricultural soils using real-time PCR

Previous research had shown that three closely related species of Lysobacter, i.e., Lysobacter antibioticus, Lysobacter capsici, and Lysobacter gummosus, were present in different Rhizoctonia-suppressive soils. However, the population dynamics of these three Lysobacter spp. in different habitats remains unknown. Therefore, a specific primer-probe combination was designed for the combined quantification of these three Lysobacter spp. using TaqMan. Strains of the three target species were efficiently detected with TaqMan, whereas related non-target strains of Lysobacter enzymogenes and Xanthomonas campestris were not or only weakly amplified. Indigenous Lysobacter populations were analyzed in soils of 10 organic farms in the Netherlands during three subsequent years with TaqMan. These soils differed in soil characteristics and crop rotation. Additionally, Lysobacter populations in rhizosphere and bulk soil of different crops on one of these farms were studied. In acid sandy soils low Lysobacter populations were present, whereas pH neutral clay soils contained high populations (respectively, <4.0-5.87 and 6.22-6.95 log gene copy numbers g(-1) soil). Clay content, pH and C/N ratio, but not organic matter content in soil, correlated with higher Lysobacter populations. Unexpectedly, different crops did not significantly influence population size of the three Lysobacter spp. and their populations were barely higher in rhizosphere than in bulk soil.