AUTHOR=Qi Dengfeng , Zou Liangping , Zhou Dengbo , Chen Yufeng , Gao Zhufen , Feng Renjun , Zhang Miaoyi , Li Kan , Xie Jianghui , Wang Wei 

TITLE=Taxonomy and Broad-Spectrum Antifungal Activity of Streptomyces sp. SCA3-4 Isolated From Rhizosphere Soil of Opuntia stricta

JOURNAL=Frontiers in Microbiology

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2019.01390

DOI=10.3389/fmicb.2019.01390

ISSN=1664-302X

ABSTRACT=<p>Actinobacteria are important producers of bioactive compounds. Extreme ecosystems cause evolution of novel secondary metabolic pathways of Actinobacteria and increase the possible discovery of new biological functions of bioactive compounds. Here, we isolated 65 Actinobacteria from rhizosphere soil samples of <italic>Opuntia stricta</italic>. An Actinobacteria strain (named SCA3-4) was screened against <italic>Fusarium oxysporum</italic> f. sp. <italic>cubense</italic> Tropical Race 4 (<italic>Foc</italic> TR4, ATCC 76255). The strain produced pink–white aerial mycelia and brown substrate mycelium on Gause No. 1 agar. Biverticillate chains of cylindrical spores were observed by scanning electron microscopy (SEM). Based on alignment of 16<italic>S</italic> rRNA sequences, a constructed phylogenetic tree showed that strain SCA3-4 shared a 99.54% similarity with <italic>Streptomyces lilacinus</italic> NRRL B-1968T. The morphological, biochemical, physiological, and molecular characteristics further indicated that strain SCA3-4 belongs to the <italic>Streptomyces</italic> sp. It can grow well on medium with the following antibiotics chloramphenicol, streptomycin, penicillin-G, gentamicin, erythromycin, nystatin or neomycin sulfate. The polymerase chain reaction (PCR) amplification of types I and II polyketide synthase genes (<italic>PKS-I</italic> and <italic>PKS-II</italic>) suggested its bioactive potential. Under treatment with 100 μg/ml of ethyl acetate extracts isolated from <italic>Streptomyces</italic> sp. SCA3-4, growth of <italic>Foc</italic> TR4 was inhibited and cell membrane was destroyed. Crude extracts also showed a broad-spectrum antifungal activity against 13 phytopathogenic fungi including <italic>Foc</italic> TR4 and displayed the lowest minimum inhibitory concentration (MIC) (0.781 μg/ml) against <italic>Colletotrichum fragariae</italic> (ATCC 58718). A total of 21 different compounds identified by gas chromatography–mass spectrometry (GC-MS) were composed of phenolic compound, pyrrolizidine, hydrocarbons, esters, and acids. Besides the known active compounds, <italic>Streptomyces</italic> sp. SCA3-4 possesses antimicrobial or other biological activities. Further attention will be paid on other compounds with no functional annotation, aiming at the discovery of new bioactive substances.</p>