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Oil palm plantations are the most invasive land use changes in Southeast Asia. It must have affected unique natural biodiversity. This study aimed to investigate the diversity of soil bacteria based on 16S rRNA gene profiles from tropical forest and oil palm plantation in Jambi Province, Indonesia. Soil sample was taken from tropical forest and oil palm plantation from Jambi province, Indonesia. The forest site is in Bukit Duabelas National Park, and the nearby oil palm plantation is in Sarolangun District, Jambi Province, Indonesia. The diversity of bacterial communities from topsoil was studied using Denaturing gradient gel electrophoresis (DGGE) of 16S rRNA gene and common biodiversity indices. PCR amplification of 16S rRNA gene was successfully conducted primers-using 33F/ 518R primers. Phylogenetic approach was used for revealing the community shift of bacterial phyla and genera in both areas. Phylogenetic analysis showed there were 4 phyla of bacteria i.e., Firmicutes, Alphaproteobacteria, Gammaproteobacteria, and Actinobacteria, respectively. Actinobacteria was the most dominant group in both areas. The composition of soil bacterial community in the oil palm plantation, based on total number of bands 16S rRNA generated from DGGE was richer than that in the Bukit Dua Belas National Park. It was probably caused by plantation year circle more than 10 years and routine activities during the plantation management, such as applications of agricultural lime, herbicide and fertilizer.

Several bacteria were isolated from straw mushroom (Volvariella volvacea) cultivation medium. There are three potential isolates previously characterized and has growth inhibition effect against V. volvacea. This screening result lead to the further study about the inhibition activity against phytopathogenic fungi. The aim of this research is to investigate the antifungal activity of three bacterial isolates against three phytopathogenic fungi and identification of the bacteria. The method used in this study are antifungal assay using co-culture method and disk difussion assay using the filtrate of each bacteria. The profile of antifungal compound was identified using ethyl acetate extract followed by evaporation and gas chromatography (GC-MS) analysis. Identification of each isolates was performed using 16S rDNA amplification and sequencing. Three phytopathogenic fungi i.e Cercospora lactucae (InaCC F168), Colletotrichum gloeosporides (InaCC F304) and Fusarium oxysporum f.sp. cubense (F817) were co-cultured with bacterial isolates C2.2, C3.8, and D3.3. The C3.8 isolate has highest average inhibition activity either using isolate and filtrate. The result relatively consistent against three phytopathogenic fungi. The metabolite profile of C3.8 isolate showed the Bis(2-ethylhexyl) phthalate as the main compound with 97% similarity. Bis(2-ethylhexyl) phthalate has potential effect as antibacterial and antifungal compound. According to EzBioCloud and GeneBank databases, the C2.2 isolate identified as Bacillus tequilensis, C3.8 as Bacillus siamensis and D3.3 as Bacillus subtilis subsp. Subtilis. This study also shows the potential of Bacillus siamensis C3.8 as biocontrol against phytopathogenic fungi.