We tested the ability of 14 strains of Trichoderma to emit volatile compounds that decreased or stopped the growth of Phytophthora infestans. Volatile organic compounds (VOCs) emitted from Trichoderma strains designated T41 and T45 inhibited the mycelial growth of P. infestans grown on a laboratory medium by 80 and 81.4%, respectively, and on potato tubers by 93.1 and 94.1%, respectively. Using the DNA sequence analysis of the translation elongation factor region, both Trichoderma strains were identified as Trichoderma atroviride. VOCs emitted by the strains were analyzed, and 39 compounds were identified. The most abundant compounds were 3-methyl-1-butanol, 6-pentyl-2-pyrone, 2-methyl-1-propanol, and acetoin. Electron microscopy of the hyphae treated with T. atroviride VOCs revealed serious morphological and ultrastructural damages, including cell deformation, collapse, and degradation of cytoplasmic organelles. To our knowledge, this is the first report describing the ability of Trichoderma VOCs to suppress the growth of the late blight potato pathogen.

BackgroundAlpha-amylases hydrolyze 1,4 α-glycosidic bonds of starch and produce malto-oligosaccharides. It is an important enzyme generally applied in textile, food and brewing industries. Enhancement in thermal stability and productivity of enzymes are the two most sought after properties for industrial use. The Aspergillus oryzae (Koji) has Generally Recognized as Safe (GRAS) status and safe for use in food industry. Hence, Koji strain’s development for the screening of potent mutants, hyper producer of thermostable α-amylases, with desired attributes is the need of the time.ResultsA process has been developed to improve super Koji (A. oryzae cmc1) strain through γ-rays treatment. The doses i.e. 0.60, 0.80, 1.00, 1.20 & 1.40 KGy gave more than 3.0 log kill. Initially, 52 Koji mutants resistant to 1% (w/v) Triton X-100 were selected. 2nd screening was based on α-amylases hyper production and 23 mutants were sorted out by measuring clearing zones index (CI). Afterwards nine potent mutants, resistant to 2-deoxy D-glucose, were screened based on CI. These were further analyzed for thermal stability and productivity of α-amylase under submerged conditions. The mutants’ M-80(10), M-100(6) & M-120(5) gave about four fold increases in α-amylases productivity. The half life of M-100(6) α-amylase at 55 °C was 52 min and was highest among the mutants. Liquid Chromatography-Mass Spectrometry (LC-MS) analysis confirmed that mutants did not produce aflatoxins. Field Emission Scanning Electron Microscopy (FESEM) of Koji mycelia depicted that exposure to gamma rays increased rigidity of the mycelium. The potent Koji mutant M-100(6) was grown on soluble starch in 10L fermenter and produced 40.0 IU ml-1 of α-amylases with specific activity of 2461 IU mg-1 protein. Growth kinetic parameters were: μ = Specific growth rate= 0.069 h-1, td = Biomass doubling time= 10.0 h, Yp/x = Product yield coefficient with respect to cell mass = 482 U g-1; qp= Specific rate of product formation= 33.29 U g-1 h-1.ConclusionIt was concluded that the developed five step screening process has great potential to generate potent mutants for the hyper production of thermostable enzymes through γ-rays mediated physical mutagenesis. The developed thermostable α-amylases of super Koji mutantM-100(6) has immense potential for application in saccharification process for maltose syrup production. Moreover, the developed five step strain’s development process may be used for the simultaneous improvement in productivity and thermal stability of other microbial enzymes.Electronic supplementary materialThe online version of this article (10.1186/s12866-018-1345-y) contains supplementary material, which is available to authorized users.

No abstract