**New Antimicrobial Phenyl Alkenoic Acids Isolated from an Oil Palm Rhizosphere-Associated Actinomycete,** *Streptomyces palmae* **CMU-AB204<sup>T</sup>**

**Kanaporn Sujarit 1,2, Mihoko Mori 2,3,\*, Kazuyuki Dobashi 2, Kazuro Shiomi 2,3, Wasu Pathom-aree 1,4 and Saisamorn Lumyong 1,4,5,\***


Received: 15 January 2020; Accepted: 28 February 2020; Published: 1 March 2020

**Abstract:** Basal stem rot (BSR), or *Ganoderma* rot disease, is the most serious disease associated with the oil palm plant of Southeast Asian countries. A basidiomycetous fungus, *Ganoderma boninense*, is the causative microbe of this disease. To control BSR in oil palm plantations, biological control agents are gaining attention as a major alternative to chemical fungicides. In the course of searching for effective actinomycetes as potential biological control agents for BSR, *Streptomyces palmae* CMU-AB204T was isolated from oil palm rhizosphere soil collected on the campus of Chiang Mai University. The culture broth of this strain showed significant antimicrobial activities against several bacteria and phytopathogenic fungi including *G. boninense*. Antifungal and antibacterial compounds were isolated by antimicrobial activity-guided purification using chromatographic methods. Their structures were elucidated by spectroscopic techniques, including Nuclear Magnetic Resonance (NMR), Mass Spectrometry (MS), Ultraviolet (UV), and Infrared (IR) analyses. The current study isolated new phenyl alkenoic acids **1**–**6** and three known compounds, anguinomycin A (**7**), leptomycin A (**8**), and actinopyrone A (**9**) as antimicrobial agents. Compounds **1** and **2** displayed broad antifungal activity, though they did not show antibacterial activity. Compounds **3** and **4** revealed a strong antibacterial activity against both Gram-positive and Gram-negative bacteria including the phytopathogenic strain *Xanthomonas campestris* pv. *oryzae*. Compounds **7**–**9** displayed antifungal activity against *Ganoderma*. Thus, the antifungal compounds obtained in this study may play a role in protecting oil palm plants from *Ganoderma* infection with the strain *S. palmae* CMU-AB204T.

**Keywords:** actinomycetes; antimicrobial; phenyl alkenoic acid; rhizosphere; *Streptomyces palmae*
