Judul: Physiological Characterization and Molecular Identification of Bacteriocin Producer Bacillus spp Isolated from Cangkuang Forest.
Abstrak: Bacillus spp from Cangkuang’s forest (A21, F13, and G3 isolates) were able to inhibit the growth of Xanthomonas oryzae pv. oryzae, Escherichia coli, and Staphylococcus aureus. Determination of inhibition activity, physiologycal, and sequences of 16S rRNA gene were conducted in this research. A21 isolate had the biggest inhibition index against S. Aureus and E. coli. G3 isolate had the biggest inhibition index against X. oryzae pv. oryzae. All Bacillus isolates showed a positive reaction for nitrates (exept F13), starch, gelatine, glucose, and O-nitrophenyl-β- D-galactopyranoside. 16S rRNA sequences of A21 and G3 isolates showed 94-95% similarity to Bacillus cereus, while F13 isolate had 96% similarity to Bacillus subtilis. Phylogenetic tree showed that all isolates were placed in the same group.
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Judul: Activity of Bacillus cereus INT1c and Bacillus thuringiensis SGT3g AHL-Lactonase on Xanthomonas oryzae pv. oryzae and Pseudomonas syringae pv. glycinea Patogenicity Inhibition
Abstrak: Quorum sensing (QS) is a mechanism of communication between bacterial cells mediated by autoinducer (AI) signal molecules and depend on density of bacterial cells. AI is a signal molecules that secreted, accumulated, reabsorbed, and recognized by bacteria to regulate the expressions of target genes. QS on Gram-negative bacteria use N-acyl homoserine lactone (AHL) AI types as signal molecules. The high level of AHL in the cell will be responded by activating cell regulatory protein. Regulatory proteins help the expression of pathogens genes. Xanthomonas oryzae pv. oryzae and Pseudomonas syringae pv. glycinea are phytopatogenic Gram-negative bacteria that perform quorum sensing using Nacyl homoserine lactone (AHL) signal to regulate expression of their patogenicity genes. X. oryzae pv. oryzae causes pustule disease on paddy (Oryzae sativa) and P. syringae pv. glycinea cause leaf blight disease on soybean (Glycine max). One of natural approaches to inactivate their quorum sensing mechanisms was by degrading the signal molecules using AHL-lactonase from Bacillus cereus INT1c and Bacillus thuringiensis SGT3g. This study was conducted to test the ability of B. cereus INT1c and B. thuringiensis SGT3g AHL lactonase activity in degrading AHL to inhibit X. oryzae pv. oryzae and P. syringae pv. glycinea patogenicity. AHL degradation activity had been confirmed in B. cereus INT1c and B. thuringiensis SGT3g using Chromobacterium violaceum as bioindicator with inhibition index 0.23 and 0.12, respectively. Inhibition test by using tobacco plants was used to determine which is the most effective to inhibit phytopatogen in vivo. B. cereus INT1c was more effective to inhibit X. oryzae pv. oryzae patogenicity (85.62%) whereas B. thuringiensis SGT3g was more effective to inhibit P. syringae pv. glycinea pathogenicity, it was up to 90.51%. The highest inhibition activity of B. cereus INT1c was showed in IRBB7 varieties (93.69%) and the lowest was in Kencana Bali varieties (65.65%) on the in vivo test on paddy. Whereas in vivo on soybean test showed that B. thuringiensis SGT3g inhibition activity in Anjasmara and Wilis varieties were not much different, it was 96% and 95,35%, respectively.
Keyword: AHL-lactonase, Bacillus cereus, Bacillus thuringiensis, phytopatogen inhibition activity, quorum sensing

Judul: Hamiltonian formulation for linear waves motion in two layers fluid
Abstrak: The surface wave could be considered as a wave that separates two fluids, namely water and air. Based on this assumption, it is introduced the interfacial wave, a wave between two layers of fluid with different density. The formulation of interfacial waves motion begins with deriving the base equation of irrotational ideal fluid. Furthermore, according to irrotational fluid assumption, the base equation can be stated in velocity potential. In this derivation, the fluids domain is assumed to be restricted by rigid lid boundary conditions, both at the upper and lower limit. Therefore, the interfacial waves motion can be explained in a hamiltonian formulation. In the hamiltonian formulation, total energy is defined as the sum of kinetic and potential energy. The hamiltonian system is obtained from reduction of kinetic energy by using the Dirichlet Neumann Operator. The resulted kinetic energy equation is nonlinear. Therefore, this form is linearized by first part of the Taylor expansion. This linearization gives a dispersion relation of linear wave. Based on this dispersion relation, the phase speed of the linear wave depends on the density ratio of the two layers fluid.
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