99 INTRODUCTION Metroxylon sagu Rottb. (sago) palms commonly abundant in the Agusan Marsh of Mindanao exhibit interestingly luxuriant growth. Three bacterial isolates from the rhizosphere of M. sagu in 2005 were initially screened and observed to have growth-promoting properties. The ability of these sago palms to adapt to acidic peat soil and oxygen-deficient environments in the marsh may be attributed to the presence in the rhizosphere of these beneficial bacteria. Vernaiz (2006) determined the growth responses of acclimatized sago palm suckers cultivated in garden soil inoculated singularly with three isolates Rh1-MS-CO, Rh2-MS-CO and Rh3-MS-CO. The isolates were found to colonize the root-soil environment in the transplanted acclimatized M. sagu suckers. This soil inoculation study demonstrated that the isolates promoted the growth and contributed to the survival of the acclimatized sago suckers. The suckers inoculated with these isolates exhibited high rate of girth increase, promoted leaf emergence and improved the health status of the suckers. The growth-promoting properties were observed as evidenced by an increase in radicle length in corn varieties NK 5447 Bt and NK 5447 conventional (Roda 2007), and increase in shoot length in tomato varieties Characterization of Potential Plant Growth -Promoting Rhizobacterial Isolates from Sago ( Metroxylon sagu Rottb.) Palms Phoebe S. Nemenzo 1,* , Gilda C. Rivero 1,2 and Windell L. Rivera 2,3 1 Department of Biological Sciences and Environmental Studies, College of Science and Mathematics, University of the Philippines Mindanao, Davao City, Philippines 2 Institute of Biology, College of Science, University of the Philippines Diliman, Quezon City, Philippines 3 Natural Sciences Research Institute, University of the Philippines Diliman, Quezon City, Philippines * Author for correspondence: e-mail: navy_phoebe@yahoo.com; Tel./Fax: (082) 293-0302 Three bacterial isolates from the rhizosphere of sago (Metroxylon sagu Rottb.) palms in the Agusan Marsh of Mindanao were previously observed to have potential plant growth-promoting properties in corn and tomato. This study aimed to taxonomically identify the rhizobacterial isolates, viz., Rh1-MS- CO, Rh2-MS-CO and Rh3-MS-CO. The isolates were characterized by examining their cell and colony morphology, as well as by biochemical and molecular analyses. The three isolates were found to be rod-shaped with rounded ends, irregularly occurring in singles, pairs, or clusters. The circular colonies of Rh1-MS-CO and Rh3-MS-CO were cream in color, mucoidal with low convex elevation and entire margin; while Rh2-MS-CO colonies were white, circular, transparent, and mucilaginous with high convex elevation and entire margin. The Rh2-MS-CO and Rh3-MS-CO isolates were Gram-negative while Rh1-MS-CO isolate was Gram-positive, although at some phases of its growth, exhibited Gram-negative reaction. Biochemical tests further revealed that the isolates developed colonies when cultured in Dobereiner N-free culture medium, were strictly aerobic, positive for amylase, catalase and casein tests, and negative for indole test. Vitek 2 profile test results revealed that Rh1-MS-CO isolate is Bacillus subtilis, which showed positive results in Vogues-Proskauer, mannitol, xylose and citrate tests; Rh2- MS-CO strain is Agrobacterium tumefaciens which showed positive results in urea and esculin hydrolysis tests; while Rh3-MS-CO isolate is Pseudomonas veronii which showed positive results in nitrate reduction, arginine dihydrolase, urea, glucose, mannitol and xylose tests. Sequencing of purified polymerase chain reaction (PCR) products of 16S rDNA and phylogenetic analyses confirmed that the Rh1-MS-CO isolate is Bacillus subtilis, the Rh2-MS-CO isolate is Agrobacterium tumefaciens, and the Rh3-MS-CO isolate is Pseudomonas veronii. These rhizobacterial species produced exopolysaccharides and fixed nitrogen, enabling them to be efficient plant growth-promoting rhizobacteria in the rhizosphere of Metroxylon sagu Rottb. Key Words: 16S rDNA, Agrobacterium tumefaciens, Bacillus subtilis, plant growth-promoting rhizobacteria, Pseudomonas veronii ISSN 0031-7454 PHILIPP AGRIC SCIENTIST Vol. 95 No. 1, 99-105 March 2012 The Philippine Agricultural Scientist Vol. 95 No.1 (March 2012)