Judul: The Occurrence of Genes for Folate Production in Local Isolates of Lactic Acid Bacteria and Distribution of Extracellular and Intracellular Folates
Abstrak: Folate-producing lactic acid bacteria (LAB) can act as folate-efficient producers or overproducers. Folate-efficient bacteria will only produce folate as their needs and only if folate is not available in the medium, whereas folate-overproducing bacteria can produce folate beyond their needs, even though there is early folate in the medium. However, a microorganism must have an efficient metabolic system; hence, finding folate-overproducing bacteria might be challenging. This work aimed to determine key genes for folate production and obtain folate-producing LAB. In particular, the objectives of this research were: (1) mapping the folate biosynthesis genes in diverse LAB species and identifying their role in the ability of LAB to produce folate; (2) finding potential folate biosynthesis marker genes in the genotypic screening for folate producers; (3) identifying the types of folate and the distribution of intra- and extracellular folate; and (4) applying stress exposure to methotrexate (a folate analogue) and the addition of enhancer compounds (PABA, glutamate, PABA-glutamate, CaCl2, and ascorbic acid) for effectively increasing extracellular folate production in LAB. Of 13 LAB isolates from Indonesian fermented foods (tempeh, tapai, fermented mustard, kefir granules) and breast milk, eleven isolates had all of the eight genes involved in folate biosynthesis (folE, folQ, folB, folK, folP, folC1, folA, and folC2) and could produce extracellular folate (ranging from 10.37 to 31.10 µg/mL). In contrast, two LAB isolates lacked several folate biosynthesis genes (folQ, folP, and folA) and could not produce extracellular folate. The folQ gene, which was not found in non-folate-producing isolates, could potentially be used as a marker for folate biosynthesis. Phylogenetic tree analysis showed that the folate biosynthesis genes (except folK and folP) of the LAB isolates in this study were on the same branch as the folate biosynthesis genes of the various LAB isolates from the database, supported by a higher percentage of conserved sites than the variable sites. The folK and folP genes may be non-essential genes in the folate biosynthesis pathway, and further research is needed to study their contribution level to de novo folate biosynthesis. Production of extracellular folate by selected LAB isolates was further evaluated in folate-free media and analyzed using the HPLC-DAD method with three individual-form folate standards, i.e., tetrahydrofolate (THF), 5-methyl-tetrahydrofolate (5-MTHF), and folic acid. Although the three folate standards could be detected with good peak separation, only the 5-MTHF peak was detected in extracellular folate samples of LAB isolates. Another peak that was only found in samples of folate-producing isolates was also suspected to be a folate peak and had a much higher area than the 5-MTHF peak, and further quantified as other folates, although further analysis is needed to confirm the form of folate. Five LAB isolates (R23, JK13, BK27, S2SR08, and NG64) produced 10% of 5-MTHF, while the other 7 LAB isolates (4C261, R12, R15, BD2, JK16, BG7), which included the reference strain (WCFS1), produced a 5-MTHF content of only 6%, and the rest are other folates. The highest extracellular folate producer isolates, namely Lacticaseibacillus rhamnosus R23 from ASI and Limosilactobacillus fermentum JK13 from kefir granules produced a much higher proportion of extracellular folate (95%)
Keyword: lactic acid bacteria, biosynthesis, distribution, folate, production, strategy

Judul: Seleksi dan Optimasi Bakteri Asam Laktat Penghasil Senyawa Antikapang
Abstrak: Silage is the forage preservation product through anaerobic fermentation by using lactic acid bacteria (LAB). The presence of oxygen may activate the other microbe that could be contaminate and interrupt the silage processing. Fungi is a microbe that often contaminate silage processing. In Indonesia, prevention of silage contamination by fungi is necessary in order to support livestock business. By using the inoculum that able to produce antifungal compounds, the fungi contamination could be prevented. This research was dedicated to screen LAB having antifungal properties, taxonomic study and optimization of antifungal production. Screening of antifungal producing LAB was initiated by growing LAB on de Man Rogosa Sharpe Agar (MRSA) against Aspergillus fumigatus, A. flavus, and Penicillium by plate assay method (aerobic condition) and verified by deep tube technique (anerobic condition). The results showed that strain DR 1-6-2 could inhibit A. fumigatus and A. flavus in aerobic condition with percentage of inhibition was 41% and 32 %, respectively. In anaerobic condition, strain DR 1-6-2 could inhibit not only A. fumigatus, A. flavus, but also Penicillium. Identification of selected LAB was carried out using 16S rRNA gene sequencing with 27F and 1492R primer. Based on molecular analysis, strain DR 1-6-2 is belong to Lactobacillus plantarum with the degree of homology of 98%. Optimization of antifungal production by selected LAB was carried out using Response Surface Method (RSM) with Central Composite Design (CCD) on five variables (glucose, yeast extract, CH3COONa, K2HPO4, Tween 80) and five level combinations. From statistical analysis, the production of antifungal which is represented by the total lactic acid production of selected LAB is significantly influenced by glucose, combination of glucose and K2HPO4, combination of yeast extract and K2HPO4 and Tween 80. The optimum concentration of glucose is 2.91%, yeast extract 0.58%, K2HPO4 0.29% and Tween 80 0.19% with a maximum predicted lactic acid yield of 2.61%, which is increased by 59%. This result is confirmed when the optimum concentration of nutritions used. The production of lactic acid increased by 58%. Benefit of this research is utilization of indegenous LAB isolates as the silage inoculum and antifungi to prevention of contamination and to obtain a good silage quality. This LAB utilization is capable to trigger the silage production, which in turn could increase the silage utilization as animal feed, increasing the production of meat, and could support the government's efforts to achieve the national demand of meat product. In silage fermentation using L. plantarum DR 1-6-2, anaerobic condition is a requirement to be considered. Identification of other antifungal compounds produced by L. plantarum DR1-6-2 is need to be studied.
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Judul: Closed Knight’s Tour pada Papan Catur Berbentuk Persegi Panjang dengan Ukuran Maksimal 8 × 8
Abstrak: Closed Knight’s Tour merupakan langkah kuda yang mengunjungi setiap kotak pada papan catur tepat satu kali dengan langkah kuda berawal dan berakhir pada kotak yang sama. Graf yang terbentuk dari closed knight’s tour dinotasikan sebagai graf G(m,n), dengan m adalah banyaknya baris dan n adalah banyaknya kolom. Graf tersebut memuat Hamiltonian cycle. Sebuah graf terhubung G adalah graf bipartite jika dan hanya jika graf tersebut tidak memiliki cycle dengan panjang ganjil. Papan catur yang memenuhi syarat cukup untuk memiliki closed knight’s tour adalah papan catur berukuran 5 × 6, 5 × 8, 6 × 6, 6 × 7, 6 × 8, 7 × 8, dan 8 × 8.
Keyword: bipartite, closed knight’s tour, hamiltonian cycle, knight’s tour, teori graf