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: Kemampuan Bacillus sp. penghasil AHL-Laktonase dalam menghambat proses quorum sensing patogenisitas bakteri fitopatogen
Abstrak: Quorum Sensing (QS) is a process that bacteria are be able to communicate using a secreted signal molecule called autoinducer (AI). AI molecule of Gram negative bacteria is N-acylhomoserine lactone (AHL). The AHL can be degraded by an enzyme called Acyl Homoserine Lactonase (AHL-Lactonase). AHL-laktonase is an anti-QS compound can be used as to control bacterial pathogen virulence. This study aimed to test the ability of Bacillus sp. producing AHL lactonase in inhibiting QS processes of phytopatogenic bacteria. The highest inhibition index of violacein production by Chromobacterium violaceum was achieved by Bacillus sp. SGT3g with a value of 0.33. Inhibition test of QS process in Erwinia chrysanthemi showed that Bacillus sp. INT1c could inhibit its virulence in potatoes. Test in tobacco plants also showed that Bacillus sp. NTT3a, NTT3e, SGT3g and INT1c was able to inhibit the emergence of necrotic leaf tissue symptoms of Ralstonia solanacearum, Pseudomonas syringae pv. glycines, Pseudomonas fluorescens, dan Xanthomonas oryzae. Inhibition percentage inhibition of necrotic symptoms by the four Bacillus isolates was up to 99%.
Keyword: AHL-lactonase, autoinducer, bioluminescens, quorum sensing, virulence

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. Suatu graf lengkap berorder 𝑛������ ≥ 3 dan graf r-regular berorder 𝑛������ ≤ 2𝑟������ + 1 merupakan graf Hamilton, Karena kedua graf tersebut memuat cycle Hamilton. Selanjutnya, syarat cukup tersebut digunakan untuk menentukan keberadaan cycle Hamilton pada graf 2-connected 4- regular berorder kurang dari 10.
Keyword: graf Hamilton, graf regular, graf lengkap, graf 2-connected 4-regular