Potential PGPR properties of cellulolytic, nitrogen-fixing, and phosphate-solubilizing bacteria of a rehabilitated tropical forest soil

In the midst of major soil degradation and erosion faced by tropical ecosystems, rehabilitated forests are established to avoid further deterioration of forest land. In this context, cellulolytic, nitrogen-fixing (N-fixing), and phosphate-solubilizing bacteria are very important functional groups in regulating the elemental cycle and plant nutrition, hence replenishing the nutrient content in forest soil. As other potential plant growth-promoting (PGP) rhizobacteria, these functional bacteria could have cross-functional abilities or beneficial traits that are essential for plants and improve their growths. This study was conducted to isolate, identify, and characterize selected PGP properties of these 3 functional groups of bacteria from tropical rehabilitated forest soils at Universiti Putra Malaysia Bintulu Sarawak Campus, Malaysia. Isolated cellulolytic, N-fixing and phosphate-solubilizing bacteria were characterized for respective functional activities, biochemical properties, molecularly identified, and assessed for PGP assays based on seed germination and indole-3-acetic acid (IAA) production. Out of 15 identified bacterial isolates exhibiting beneficial phenotypic traits, a third belong to genus Burkholderia and a fifth to Stenotrophomonas sp. with both genera consisting of members from two different functional groups. Among the tested bacterial strains, isolate Serratia nematodiphila C46d, Burkholderia nodosa NB1, and Burkholderia cepacia PC8 showed outstanding cellulase, N-fixing, and phosphate-solubilizing activities, respectively. The results of the experiments confirmed the multiple PGP traits of selected bacterial isolates based on respective high functional activities, root, shoot lengths, and seedling vigour improvements when bacterized on mung bean seeds, as well as presented some significant IAA productions. The results of this study indicated that these functional bacterial strains could potentially be included in future biotechnological screenings to produce beneficial synergistic effects via their versatile properties on improving soil fertility and possible crop growth stimulation.