Research note: characterization of potential plant growth-promoting rhizobacterial isolates from sago (Metroxylon sagu Rottb.) palms.

摘要

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-MSCO, 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.