Dewen Liu

Comparative Genomic and Regulatory Analyses of Natamycin Production of Streptomyces lydicus A02

Streptomyces lydicus A02 is used by industry because it has a higher natamycin-producing capacity than the reference strain S. natalensis ATCC 27448. We sequenced the complete genome of A02 using next-generation sequencing platforms, and to achieve better sequence coverage and genome assembly, we utilized single-molecule real-time (SMRT) sequencing. The assembled genome comprises a 9,307,519-bp linear chromosome with a GC content of 70.67%, and contained 8,888 predicted genes. Comparative genomics and natamycin biosynthetic gene cluster (BGC) analysis showed that BGC are highly conserved among evolutionarily diverse strains, and they also shared closer genome evolution compared with other Streptomyces species. Forty gene clusters were predicted to involve in the secondary metabolism of A02, and it was richly displayed in two-component signal transduction systems (TCS) in the genome, indicating a complex regulatory systems and high diversity of metabolites. Disruption of the phoP gene of the phoR-phoP TCS and nsdA gene confirmed phosphate sensitivity and global negative regulation of natamycin production. The genome sequence and analyses presented in this study provide an important molecular basis for research on natamycin production in Streptomyces, which could facilitate rational genome modification to improve the industrial use of A02.

Identification and characterization of ZL261, a novel Collimonas pratensis strain with antagonistic activity toward Monilinia fructicola

Soil bacteria from the genus Collimonas were isolated for the first time by De Boer et al., and they have been shown to display antifungal activity toward many different fungi (De Boer et al., 1998). These affected fungi include pathogens of economically important plants, such as spruce, potato, flax, and lettuce, suggesting the potential for the broad application of Collimonas as a biocontrol agent. Brown rot caused by Monilinia fructicola is among the most important postharvest diseases of commercially grown stone fruits in production areas worldwide (Pellegrino et al., 2009). Application of chemical fungicides is currently the most common method to control brown rot. However, chemical controls can leave fungicide residue on the fruits and induce fungicide resistance in the pathogen. The biological control of plant diseases by using antagonistic microorganisms is a promising strategy for sustainable agriculture. Strain ZL261 isolated from alpine meadow soil on Sejila Mountain in Tibet, China, exhibited a specific inhibitory effect against the brown rot pathogen M. fructicola. The sequence of the 16S rDNA gene in ZL261 showed 99% similarity with those in Collimonas pratensis, C. fungivorans, and C. arenae. The DNA-DNA hybridization value between strain ZL261 and C. pratensis strain CCUG 54728T was 83.88%, suggesting

Identification and evaluation of Aspergillus tubingensis as a potential biocontrol agent against grey mould on tomato

Grey mould of tomato caused by Botrytis cinerea is a highly damaging disease worldwide. This study was aimed at identifying fungal strain QF05, which was isolated from the sandy soil collected in the Qinghai-Tibet Plateau in China and to evaluate its biocontrol potential on grey mould and growth promotion effect on tomato plants. On the basis of morphological observation and a multigene phylogeny based on the ITS, β-tubulin and calmodulin genes, QF05 was identified as Aspergillus tubingensis. An in vitro dual culture test indicated obvious antagonistic activity by strain QF05 against B. cinerea. Strain QF05 distinctly reduced grey mould in assays on tomato fruits and plants. Treatments with the culture filtrate of strain QF05 and a tenfold dilution of the filtrate gave disease biocontrol efficacy of 34.5 and 31.0% on tomato plants, respectively. QF05 also promoted seed germination and plant growth of tomato. Length and total fresh and dry mass of tomato plants were all significantly increased by 17.8, 25.7 and 56.8%, respectively, after treatment with the tenfold dilution of the culture filtrate. QF05 also had positive biocontrol attributes such as indoleacetic acid and siderophore production, phosphate solubilization, and rhizosphere colonization. All these results indicated the good performance of A. tubingensis QF05 for the biocontrol of tomato grey mould and growth promotion of tomato plants.