ORIGINAL PAPER Endophytic actinomycetes isolated from Aquilaria crassna Pierre ex Lec and screening of plant growth promoters production Pongrawee Nimnoi Æ Neelawan Pongsilp Æ Saisamorn Lumyong Received: 27 May 2009 / Accepted: 12 August 2009 / Published online: 9 September 2009 Ó Springer Science+Business Media B.V. 2009 Abstract A total of 10 endophytic actinomycete strains were successfully isolated from healthy shoots and roots of Aquilaria crassna Pierre ex Lec (eaglewood). Analysis of 16S rDNA sequencing of those isolates showed that they belong to members of the genera Streptomyces (2 isolates), Nonomuraea (1 isolate), Actinomadura (1 isolate), Pseud- onocardia (1 isolate) and Nocardia (3 isolates). The remaining 2 isolates were unidentified. All of isolates produced the amount of indole-3-acetic acid (IAA) and ammonia ranging between 9.85 ± 0.31 to 15.14 ± 0.22 lg ml -1 and 2 to 60 mg ml -1 , respectively. Among 10 isolates tested, the amount of hydroxamate-type sidero- phore produced by 2 isolates was undetectable. While the remaining 8 isolates produced the amount of hydroxamate- type ranging between 3.21 ± 0.12 and 39.30 ± 0.40 lg ml -1 . Also, catechols-type siderophore produced by 9 isolates was undetectable. Actinomadura glauciflava is only one isolate that produced catechols-type 4.12 ± 0.90 lg ml -1 . In addition, 10 endophytic actinomycetes showed protease activity ranging from undetectable to 8.16 ± 0.15 unit ml -1 . Genetic relatedness amongst these isolates was determined base on Random amplified polymorphic DNA (RAPD) and Enterobacterial repetitive intergenic consensus polymerase chain reaction (ERIC PCR). Both methodologies generated specific patterns corresponding to particular genotypes. RAPD fingerprinting proved to be slightly more discriminatory than ERIC PCR. This study is the first published report that actinomycetes can be isolated as endophytes within this plant. It is also the first published report that endophytic actinomycetes are capable of pro- ducing IAA and siderophores. Keywords Endophytic actinomycetes Á Idole-3-acetic acid Á Siderophores Á Enterobacterial repetitive intergenic consensus polymerase chain reaction (ERIC PCR) Á Random amplified polymorphic DNA (RAPD) Introduction The definition of endophytes are described as micro- organisms that establish an endosymbiotic relationship with plants, whereby plants receive ecological benefits from the presence of the symbionts, such as the ability to increase tolerance to stresses or plant growth promotion (Hasegawa et al. 2006). On the other hand, endophytes are defined as any micro-organisms that do not visibly harm plants and can be isolated from the surface of the disin- fected plant tissues or extracted from the inside of the plants. However, most endophytes have been demonstrated to improve and promote the growth of the host plants as well as reduce disease symptoms caused by plant patho- gens or various environmental stresses. The association of actinomycetes with plants is found to confer many advantages to host plants such as the production of phy- tohormones and siderophores, the nitrogen fixation and the protection against plant pathogens by producing antibiotics P. Nimnoi Á S. Lumyong (&) Microbiology Division, Department of Biology, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand e-mail: scboi009@chiangmai.ac.th P. Nimnoi e-mail: umco_perra@hotmail.com N. Pongsilp Department of Microbiology, Faculty of Science, Silpakorn University, Nakhon Pathom 73000, Thailand e-mail: neelawan@su.ac.th 123 World J Microbiol Biotechnol (2010) 26:193–203 DOI 10.1007/s11274-009-0159-3