Judul: Algoritma penentuan lintasan terpendek untuk semua pasangan simpul
Abstrak: Graf merupakan pasangan terurut (V,E), dimana V adalah himpunan tak kosong dan terbatas yang anggotanya disebut simpul (vertex) dan E adalah himpunan sisi (edge). Hubungan antara simpul dan sisi tersebut membentuk suatu jaringan (network). Selanjutnya, dari jaringan tersebut dapat ditentukan lintasan(path) yang dilalui untuk suatu pasangan simpul, tetapi masalah yang penting dalam hal ini adalah menentukan Iintasan terpendek (shortest path) di antara Iintasan-Iintasan yang mungkin dari pasangan simpuI tersebut. Hal ini menarik, karena berkaitan dengan masalah pengoptimuman, antara lain meminimumkan biaya dan efisiensi waktu yang digunakan.
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Judul: Penentuan Path Terpendek Dengan Algoritme Dekomposisi Jarvis-Tufekci
Abstrak: Salah satu masalah arus dalam suatu network adalah penentuan path terpendek. Masalah path terpendek ini merupakan masalah pengoptimuman, karena dengan diperolehnya path terpendek diharapkan dapat mengoptimumkan faktor yang lain (misalkan: waktu dan biaya). Secara umum, masalah path terpendek dalam suatu network ini terbagi menjadi 3 tipe, yakni menentukan (1) path terpendek antara suatu simpul dan simpul lainnya, (2) path terpendek antara suatu simpul dengan semua simpul lainnya, dan (3) path terpendek antara semua pasang simpul yang terdapat pada network tersebut. Salah satu algoritme yang dapat digunakan untuk menentukan path terpendek tipe (1) yakni path terpendek antara suatu simpul dan simpul lainnya adalah algoritme dekomposisi Jarvis- Tufekci. Dalam karya ilmiah ini kedua simpul tersebut masing-masing adalah simpul source (sumber) dan sink (tujuan). Tahapan yang dilakukan dalam algoritme ini adalah mendekomposisi suatu network yang diberikan menjadi beberapa buah subnetwork yang bertindih secara linear (linearly overlapping). Lima tahap utama akan dilakukan dalam menyelesaikan masalah path terpendek dengan algoritme dekomposisi Jarvis-Tufekci ini. Berdasarkan seluruh tahapan algoritme dekomposisi Jarvis-Tufekci ini juga akan dilakukan penghitungan kompleksitasnya.
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Judul: Extracellular Expression of thermostable Geobacillus stearothermophilus T1.2RQ Lipase for Biodiesel Production
Abstrak: The extracellular expression of enzymes in an excellent secretion host such as Bacillus subtilis is a useful strategy for making enzymes of industrial significance more affordable by lowering the cost of its downstream processing. Lipases are a category of hydrolases that catalyze the hydrolysis of triglycerides to glycerol and free fatty acids. Also, lipases catalyze the hydrolysis and transesterification of other esters as well as the synthesis of esters. They can perform very specific biotransformation reactions and are widely used in food, organic synthesis, detergents, cosmetic, and pharmaceutical industries. Geobacillus stearothermophilus T1.2RQ lipase is an industrially-desired thermostable lipolytic enzyme with an excellent hydrolytic and transesterification activity. This study aimed to express T1.2RQ lipase, in B. subtilis WB800 and ensure its secretion into the extracellular medium. Three signal peptides (AmyQ, Epr, LipA) and two promoters (Pgrac01 and Pgrac100) were used in the secretory-expression of T1.2RQ lipase, based on five constructed expression vectors constructed by restriction cloning and PCR mutagenesis. Sangers sequencing was used to verify constructs to ensure they are in the correct reading frame. Recombinants vectors, pHT43 (plasmid control), pHT43-T1.2RQ, pHT43- T1.2RQ_AmyQ, pHT43-T1.2RQ_Epr, and pHT43-T1.2RQ_LipA, were transformed by electroporation into Bacillus subtilis WB800. The electroporation was successful with the optimum condition of 2500V, 200 ohms, 25µF, and 5milliseconds. Recombinant B. subtilis pHT43 (negative control) and pHT43-T1.2RQlip + signal peptides were streaked on the lipidic agar, LA+TBN. All four recombinants, including the negative control (B. subtilis WB800-pHT43), produced clear zones on the TBN agar plate after overnight incubation (fig 2), indicating the presence of a lipolytic enzyme in all of the recombinant B. subtilis cells. pHT43-T1.2RQlip + signal peptides (AmyQ, Epr, and LipA) have clear zones with significantly higher diameters than B. subtilis WB800-pHT43 (negative control). This phenomenon suggests that the recombinant thermostable lipase T1.2RQ introduced into these cells was successfully expressed, thereby increasing the lipolytic capability of its host cells T1.2RQ lipase was expressed in 50ml terrific broth medium (TB) and the expression induced with 1mM IPTG. Lipase activity assay using p-nitrophenyl esters showed that all three signal peptides directed the secretion of T1.2RQ lipase into the extracellular medium. Signal peptide, LipA, resulted in the highest extracellular activity of 5.6 U/mL, which corresponds to a 6-fold increase over the parent B. subtilis WB800 strain. Meanwhile, signal peptides, AmyQ and Epr produced 4.2 U/mL and 3.4 U/mL activity respectively. SDS-Zymogram analysis confirmed that T1.2RQ lipase was correctly processed and secreted in its original size of 44 kDa. An attempt to further increase lipase expression level by promoter optimization showed that, contrary to expectation, promoter Pgrac100 exhibited similar expression levels as the original Pgrac01. Nevertheless, the demonstration of the successful secretion of T1.2RQ lipase in this work confirms the latter as a promising approach for the industrial production of the enzyme
Keyword: Bacillus subtilis, Expression, Extracellular, Heterologous, Lipase, Thermostable