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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  Opuntia stricta . An Actinobacteria strain (named SCA3-4) was screened against  Fusarium oxysporum  f. sp.  cubense  Tropical Race 4 ( Foc  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 S  rRNA sequences, a constructed phylogenetic tree showed that strain SCA3-4 shared a 99.54% similarity with  Streptomyces lilacinus  NRRL B-1968T. The morphological, biochemical, physiological, and molecular characteristics further indicated that strain SCA3-4 belongs to the  Streptomyces  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 ( PKS-I  and  PKS-II ) suggested its bioactive potential. Under treatment with 100 μg/ml of ethyl acetate extracts isolated from  Streptomyces  sp. SCA3-4, growth of  Foc  TR4 was inhibited and cell membrane was destroyed. Crude extracts also showed a broad-spectrum antifungal activity against 13 phytopathogenic fungi including  Foc  TR4 and displayed the lowest minimum inhibitory concentration (MIC) (0.781 μg/ml) against  Colletotrichum fragariae  (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,  Streptomyces  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.

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