Judul: Screening of Significant Medium Components for Biosurfactant Production by Potential Bacteria of DSW17 using Plackett- Burman Experimental Design and Its Application as Food Preservative Agent
Abstrak: Biosurfactant or microbial surfactants produced by variety of microbes are capable of reducing surface and interfacial tension and have a wide range of industrial and environmental applications. Potential biosurfactant-producing microbe was successfully isolated from the Laboratory of Bioenergy and Bioprocess, Research Center for Biotechnology, LIPI. Based on the analysis of 16S rRNA sequence and phylogenetic tree, microorganisms DSW17 was 97% identical to Bacillus altitudinis TAZ1-5 HQ236061. In the present research, statistical screening of media components for biosurfactant production by microorganism DSW17 was carried out using Plackett-Burman experimental design. Nine out of eleven factors of the production medium were found to be significantly affecting the production process of biosurfactant. FeSO4.7H2O, NaNO3, waste vegetable oil, CaCl2.2H2O, K2HPO4 and sucrose were directly proportional to the biosurfactant production while ZnSO4.7H2O, KH2PO4 and MgSO4.7H2 showed inversely proportional correlation with the biosurfactant production in the selected experimental range. Several modified mediums were formulated based on the statistical Plackett-Burman screening result in order to validate the optimum media composition in producing biosurfactant. Modified medium combination 1 (MM1) as an optimized medium (2.13 g/L) showed 124% increase in biosurfactant production over the unoptimized medium or MM6 (0.95 g/L). From the validation result obtained, it was known that the optimized medium was proven to show better performance in the biosurfactant production, while it was also economically applicable compared to the other modification media. The biosurfactant produced by Bacillus sp. DSW17 in optimized medium showed antimicrobial activity against spoilage microorganisms. Based on the antimicrobial properties of the biosurfactant, it was then applied as a preservative agent in foods (tofu, beef and chicken meat) and also beverages (strawberry and tomato juice). Biosurfactant from Bacillus sp. DSW17showed the ability to extend the shelf life of tofu, strawberry juice and tomato juice for 4 hours, 2 hours and 1 hour, respectively. While in beef and chicken meat, biosurfactant were not able to extend its shelf-life.
Keyword: biosurfactant, biosurfactant production, statistical optimization, Plackett-Burman, preservative agent

Judul: Biosurfactant Activity of Bacillus sp. strain LP04 Isolate and Its Antifungal Potency against Ganoderma boninense
Abstrak: Biosurfaktan adalah salah satu kelas dari molekul amfipatik yang dapat diproduksi oleh berbagai mikroorganisme. Biosurfaktan dimanfaatkan sebagai biopestisida dan agens biokontrol, karena memiliki aktivitas antimikrob khususnya sebagai agens anticendawan pada beberapa spesies cendawan patogen seperti Ganoderma boninense yang menyerang tanaman kelapa sawit. Penelitian ini bertujuan mendeteksi aktivitas biosurfaktan dari isolat Bacillus sp. galur LP04 dan potensinya sebagai agens anticendawan terhadap cendawan Ganoderma boninense. Biosurfaktan diproduksi pada media mineral salt medium (MSM) dengan cara memanen supernatan bebas sel. Penapisan isolat penghasil biosurfaktan dilakukan dengan uji oil spreading assay, hemolysis assay, dan indeks emulsifikasi. Aktivitas anticendawan isolat kemudian diuji dengan metode agar diffusion. Isolat Bacillus sp. galur LP04 merupakan bakteri Gram positif yang berpotensi memiliki aktivitas biosurfaktan yang dicirikan dengan hasil positif pada uji oil spreading assay, dan memiliki indeks emulsifikasi 48.33 ± 2.87%. Isolat bakteri ini dapat menghambat pertumbuhan cendawan Ganoderma boninense dengan persentase penghambatan sebesar 51.11%., Biosurfactants are a class of amphipathic molecules that can be produced by various microorganisms. Biosurfactants are used as biopesticides and biocontrol agents, because they have antimicrobial activity, especially as antifungal agents in several species of fungal pathogens such as Ganoderma boninense that attack the palm oil trees. This study aims to detect the biosurfactant activity of Bacillus sp. strain LP04 and its potential as antifungal agent against the fungi Ganoderma boninense. Biosurfactants were produced in mineral salt medium (MSM) by harvesting cell-free supernatants. Screening of biosurfactant-producing isolates was carried out by oil spreading assay, hemolysis assay, and emulsification index. The antifungal activity of the isolates was then tested by the agar diffusion method. Bacillus sp. strain LP04 is a Gram-positive bacterium that has the potential to have biosurfactant activity which is characterized by a positive result on the oil spreading assay test, and has an emulsification index of 48.33 ± 2.87%. This bacterial isolate was able to inhibit the growth of Ganoderma boninense with the growth inhibition rate of 51.11%.
Keyword: Emulsification index, inhibition percentages, lipopeptide, oil spreading

Judul: Cycle Hamilton pada Graf Lengkap, Graf Regular, dan Graf 2-Connected 4-Regular Berorder Kurang dari Sepuluh.
Abstrak: Suatu graf disebut graf Hamilton apabila graf tersebut memuat cycle Hamilton, yaitu cycle yang melewati setiap vertex tepat satu kali. Menentukan keberadaan cycle Hamilton pada suatu graf dapat menggunakan syarat cukup yang berupa teorema-teorema yang telah diperkenalkan sejak tahun 1950-an. Beberapa syarat cukup yang dibahas dalam karya ilmiah ini adalah syarat cukup yang berhubungan dengan graf lengkap dan graf regular. ,,,
Keyword: graf Hamilton, graf regular, graf lengkap, graf 2-connected 4-regular.