Judul: Detection of Biosynthetic Genes for Secondary Metabolites and Evaluation of Antibacterial Activity from Endophytic Bacteria Isolated from Syzygium cumini
Abstrak: Eksplorasi aktivitas antibakteri dari bakteri endofit yang berasosiasi dengan duwet (Syzygium cumini) perlu dilakukan untuk mengatasi kasus resistensi bakteri patogen terhadap antibiotik. Penelitian ini bertujuan mendeteksi keberadaan gen-gen biosintetik metabolit sekunder dan mengevaluasi aktivitas antibakteri dari bakteri endofit duwet. Berdasarkan teknik PCR, 9 dari 15 isolat bakteri endofit duwet (60%) membawa minimal satu gen biosintetik metabolit sekunder. Dual-culture assay menunjukkan bahwa empat dari 15 isolat bakteri endofit tanaman ini memiliki aktivitas antibakteri terhadap 2 atau 1 bakteri target Staphylococcus aureus ATCC 6538 dan Bacillus subtilis ATCC 19659. Isolat B2 dan D1 merupakan 2 isolat dengan aktivitas antibakteri terbaik. Secara konsisten, ekstrak kasar kedua isolat tersebut juga dapat menghambat S. aureus ATCC 6538 dan B. subtilis ATCC 19659 dengan zona hambat berkisar antara 8–12,33 mm. Nilai minimum inhibitory concentration (MIC) dan minimum bactericidal concentration (MBC) telah ditentukan menggunakan teknik microbroth-dilution. Nilai MIC ekstrak kasar kedua isolat lebih aktif terhadap B. subtilis ATCC 19659, dibandingkan dengan S. aureus ATCC 6538. Kedua ekstrak tersebut memiliki nilai MBC yang lebih tinggi dibanding nilai MIC-nya. Analisis Liquid Chromatography Quadrupole-tandem Mass Spectrometry (LC-MS/MS) menunjukkan bahwa ekstrak bakteri endofit duwet mengandung beberapa senyawa antibakteri, seperti cyclo(tyrosyl-propyl) dan cyclo(prolylvalyl)., Exploration of antibacterial activity from endophytic bacteria associated with Syzygium cumini is necessary to provide new sources of antibiotics to overcome resistance in pathogenic bacteria. This study aimed to detect the presence of antibiotic-biosynthetic genes and evaluate the antibacterial activity of endophytic bacteria isolated from S. cumini. Based on PCR screening, 9 out of 15 isolates (60%) carried at least one antibiotic-biosynthetic gene. Furthermore, the dual-culture assay showed that four out of 15 isolates showed remarkable antibacterial activity against either one or both target bacteria, including Staphylococcus aureus ATCC6538 and Bacillus subtilis ATCC19659. Endophytic bacteria coded as B2 and D1 exhibited the most promising antibacterial activity against both strains. Consistently, crude extracts of these isolates could inhibit the growth of B. subtilis ATCC19659 and S. aureus ATCC6538, with inhibition zone diameters ranging from 8 to 12.33 mm. According to microbroth-dilution assay, the minimum inhibitory concentration (MIC) values of these isolates were more active against B. subtilis ATCC19659 compared to S. aureus ATCC6538. Both extracts had minimum bactericidal concentration (MBC) higher than their MIC values. Liquid chromatography quadrupole-tandem mass spectrometry (LC-MS/MS) analysis showed the crude extracts derived from these isolates contained several antimicrobial compounds, such as cyclo (tyrosyl-propyl) and cyclo (prolylvalyl).
Keyword: antibacterial, Bacillus subtilis, biosynthetic genes, Staphylococcus aureus, Syzygium cumini

Judul: Antibacterial Activity of Endophytic Bacteria Isolates from Clove Leaf (Syzygium aromaticum) and Identification Based on Morphological and Physiological Characteristics
Abstrak: Infeksi bakteri patogen masih menjadi masalah utama dalam kesehatan yang banyak menimbulkan kematian. Bakteri endofit pada tanaman obat berpotensi sebagai agen penghasil antibakteri. Keberadaan bakteri endofit pada tanaman cengkeh (Syzygium aromaticum) memungkinkannya memproduksi senyawa bioaktif yang sama seperti yang terkandung dalam inangnya. Penelitian ini bertujuan menganalisis aktivitas antibakteri isolat bakteri endofit asal daun cengkeh dan karakterisasi isolat yang potensial. Metode penelitian dilakukan dengan peremajaan isolat dan bakteri uji, skrining potensi aktivitas antibakteri secara disc diffusion, karakterisasi morfologi dan fisiologi isolat paling potensial, penentuan kurva pertumbuhan, serta uji aktivitas antibakteri isolat potensial pada waktu inkubasi optimum. Hasil penelitian menunjukan bahwa isolat bakteri endofit dari daun tanaman cengkeh (Syzygium aromaticum) mempunyai aktivitas antibakteri terhadap bakteri patogen. Isolat DCL1 bersifat bakterisidal kuat terhadap Escherichia coli, sedangkan isolat DCL3 bersifat bakterisidal intermediet terhadap Pseudomonas aeruginosa. Dua isolat bakteri endofit asal daun cengkeh tersebut memiliki kesamaan karakteriskik dengan genera Bacillus berdasarkan karakter morfologi koloni, morfologi sel, dan aktivitas biokimia yang menghasilkan enzim katalase. Aktivitas antibakteri isolat bakteri endofit daun cengkeh DCL1 dan DCL3 paling baik pada jam ke-40 waktu inkubasi optimum berdasarkan kurva pertumbuhan., Pathogenic bacterial infection is still a major health problem that causes many deaths. Endophytic bacteria in medicinal plants have the potential as antibacterial agents. The presence of endophytic bacteria in the clove plant (Syzygium aromaticum) allows it to produce the same bioactive compounds as those contained in its host. This study aims to analyze the antibacterial activity of endophytic bacteria from clove leaves and characterize the potential isolates. The research method was carried out by rejuvenating isolates and testing bacteria, screening for potential antibacterial activity by disc diffusion, morphological and physiological characterizations of the most potential isolates, determining growth curves, and testing the antibacterial activity at optimum incubation times. Based on the results, endophytic bacteria from clove leaf (Syzygium aromaticum) have antibacterial activity against pathogenic bacteria. DCL1 isolate is strong bactericidal against Escherichia coli, while DCL3 isolate is intermediate bactericidal against Pseudomonas aeruginosa. The two isolates of endophytic bacteria from clove leaf have similar characteristics to the Bacillus genera based on colony morphology, cell morphology, and biochemical activity that produce catalase enzymes. The best antibacterial is shown by isolating DCL1 and DCL3 at 40 hours of optimum incubation time based on the growth curve.
Keyword: antibacterial, bioactive compound, disc diffusion, endophytic bacteria, pathogenic bacteria

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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