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This study has been proved that statistical experimental designs offer efficient and feasible approaches for determination of culture medium and fermentation conditions of Streptomyces lavendulae Xjy. Nutrition and cultural conditions have high influence on the antibiotic production of S. lavendulae Xjy. Soya bean meal, NaCl and (NH4)2SO4 were identified as the best ingredients for high antifungal activity of Xjy based on single variable experiments. Using response surface methodology, the best concentrations of medium ingredients were 1.46% soya bean meal, 2.25% NaCl and 1.26% (NH4)2SO4. The potential components were reduced from seven to three, and the antibiotic activity was increased by 10%. The optimized conditions for Xjy in a 250‐ml Erlenmeyer flask were initial pH 5, medium volume 25 ml/250 ml and inoculation volume 10% at 30°C with 200 rpm by response surface methodology. Validation experiments carried out to check the accuracy of the models indicated that the predicted values agreed with the experimental values. The extension of necrosis lesion of Botryosphaeria dothidea was impeded by the application of Xjy in apple fruit. In tomato plants, Xjy showed the 43.7–51.7% curative and protective effects against Fulvia fulva. The optimal medium not only gave a 20% increase in antifungal activity, but it provided a simpler formulation. The results will set a basis for further study on large‐scale fermentation volumes using S. lavendulae Xjy and be useful for the development of more advanced control strategies on plant diseases.

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Since bacterial quorum sensing system has been verified to regulate many microbial physiological activities, such as virulence factor production and biofilm formation in pathogens, blocking quorum sensing has being recognized as a viable approach for the development of novel therapeutics in treating bacterial infections. In this study, quorum quenching activities of marine actinomycetes isolated from seawater sample were investigated. Out of 56 morphological different strains, 5 strains had been found exhibiting anti-quorum sensing activity against the violacein production of Chromobacterium violaceum 12472. One highly active strain HY026 was identified as Streptomyces parvulus based on the 16S rDNA sequence analysis and morphological features. Spent culture medium of HY026 could also significantly inhibit the biofilm formation of four bacteria. One major active compound named F1-4, accounting for 26.3% of crude extracts, was obtained from HY026 cultures and identified as actinomycin D based on the analysis of the NMR and MS. F1-4 could significantly inhibit the violacein production of C. violaceum with the inhibition rate of 64.9% but not affect the bacterial growth at the concentration of 12.5 mg/mL. F1-4 could also inhibit the prodigiosin production of Serratia proteamaculans 657 with the pigment inhibition zone of 13.5 mm at concentration of 25 mg/disc without affecting the bacterial growth. Another pure compound, cyclic (4-hydroxy-Pro-Phe) was also isolated and identified from this actinomycetes strain. The higher production and easier isolation of actinomycin D from S. parvulus HY026 indicated that this strain could be a potential source of quorum sensing inhibitors.

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