Research Paper Antifungal properties of rhamnolipid produced by Pseudomonas aeruginosa DS9 against Colletotrichum falcatum Debahuti Goswami 1 , Siddhartha Narayan Borah 1 , Jiumoni Lahkar 1 , Pratap Jyoti Handique 2 and Suresh Deka 1 1 Environmental Biotechnology Laboratory, Life Sciences Division, Institute of Advanced Study in Science and Technology (IASST), Paschim Boragaon, Guwahati, Assam, India 2 Department of Biotechnology, Gauhati University, Guwahati, Assam, India The rhamnolipid biosurfactant (RL-DS9) extracted from the bacterial strain Pseudomonas aeruginosa DS9 was evaluated for its antifungal activity against Colletotrichum falcatum that causes red rot in sugarcane. The surface tension (ST) reduction, biosurfactant production, and antifungal activity of biosurfactant against C. falcatum were investigated by using the medium with different carbon sources and it was found to be maximum in glucose. Moreover, highest reduction of ST and production of biosurfactant was achieved at 4.5% (w/v) concentration of glucose. The efficacy of RL- DS9 was compared with a commercially available rhamnolipid (RL-R95) using microtitre plate assay. Results showed that at 100 mg ml 1 concentration RL-DS9 exhibited 86.6% inhibition against C. falcatum spore germination, and in the same concentration RL-R95 showed 83.3% inhibition. From liquid chromatography-mass spectrometry (LC-MS) analysis, it was revealed that only two similar congeners Rha-(C 10 ) and Rha-Rha-(C 10:1 ) were found to be in common among both the rhamnolipids. In the plant bioassay test, it was noted that red rot incidence was reduced on the sugarcane plants treated with RL-DS9. This is the first report that rhamnolipid biosurfactant produced by Pseudomonas aeruginosa DS9 could be able to control red rot disease of sugarcane caused due to the infection with the fungus Colletotrichum falcatum. : Additional supporting information may be found in the online version of this article at the publisher’s web-site. Keywords: Antifungal property / Colletotrichum falcatum / Pseudomonas aeruginosa DS9 / Red rot / Rhamnolipid biosurfactant Received: April 10, 2015; accepted: June 23, 2015 DOI 10.1002/jobm.201500220 Introduction Red rot disease of sugarcane (causal agent: Colletotrichum falcatum Went; perfect stage: Glomerella tucumanensis) is a chronic and widely distributed fungal disease that is known to cause devastating reduction in crop yield [1]. It is considered as the major constraint for sugarcane production in India [2]. The disease caused by C. falcatum was first reported from Java (Indonesia) by Went [3]. It produces spores both by asexual (conidia) as well as sexual (perithecium) means [4]. Like other pathogens, it infects by appressoria and haustaria by penetrating inside the epidermis of the host plant [5, 6] through any sort of injury injected by insects or borers or natural growth cracks [7]. The pathogen can attack any part of the sugarcane plant; be it stalk, leaf, buds, or roots. C. falcatum completes its lifecycle on the sugarcane leaf and usually the damage to leaf does not pose a serious threat to cane or cause much harm to the plant. The most damaging phase of red rot occurs when the pathogen attacks the stalk [8]. Symptoms of red rot are highly variable depending upon the susceptibility of the sugarcane cultivar, pathogen virulency, and environ- ment [9]. The disease has been blamed for worldwide loss Correspondence: Prof. Suresh Deka, Environmental Biotechnology Laboratory, Life Sciences Division, Institute of Advanced Study in Science and Technology (IASST), Paschim Boragaon, Guwahati 781035, Assam, India E-mail: sureshdeka@yahoo.com Phone: þ91 9508464445 Fax: þ91 3612279909 Environment  Health  Techniques Rhamnolipid against Colletotrichum falcatum 1265 ß 2015 WILEY-VCH Verlag GmbH & Co. KGaA,Weinheim www.jbm-journal.com J. Basic Microbiol. 2015, 55, 1265–1274