ケブカシバンムシのリグノセルロース分解と腸内微生物叢に関する研究

京都大学新制・課程博士博士(農学)甲第24906号農博第2569号京都大学大学院農学研究科森林科学専攻(主査)教授 大村 和香子, 教授 髙野 俊幸, 教授 飛松 裕基学位規則第4条第1項該当Doctor of Agricultural ScienceKyoto UniversityDGA

Antimicrobial Potential of an Actinomycete Gordonia terrae JSN1.9-Derived Orange Pigment Extract

Actinomycetes are known to be a source of natural products and drugs. Gordonia terrae, an actinomycete pigment producer, shows potential in producing pigment with antimicrobial activity. This study aims to determine the antimicrobial activity of the active pigment fraction produced by the actinomycete G. terrae, assess the effects of the active pigment fraction on microbial cells, and identify the types of compounds present in the fraction. The pigment extract exhibited antimicrobial activity against Gram-positive bacteria and fungi. Specifically, it showed activity against Bacillus subtilis ATCC 6633, Staphylococcus aureus ATCC 25293, and Candida albicans ATCC 10231. Furthermore, the study evaluated the antimicrobial activities of the active fractions, revealed the active fraction had better antimicrobial activity than the crude extract. Scanning electron microscopy (SEM) confirmed that the active fraction of the pigment causes damage to B. subtilis ATCC 6633 cells, inhibits the formation of filaments in C. albicans ATCC 10231, and alters the normal shape of the cells. LC-MS/MS results showed that the active fraction contained several compounds known for their antimicrobial activity. Among the dominant compounds identified were cholestyramine, aminopregnane, and sphinganine. Thus, this study demonstrated that the orange pigment extract derived from G. terrae JSN1.9 exhibits promising antimicrobial activity

Penapisan Bakteri Filosfer Penghasil Senyawa Bioaktif Anti Xanthomonas oryzae pv. oryzae Penyebab Penyakit Hawar Daun Bakteri pada Padi

Bacterial leaf blight caused by Xanthomonas oryzae pv. oryzae (Xoo) is one of the important diseases in rice crops in Indonesia. The disease is difficult to be controlled since it attacks the rice plant at different growth stages such as tillering, flowering and ripening. One of the alternatives that could be used to control the disease is by using phyllosphere bacteria as the biocontrol agents. This study aims to isolate, characterize and screen the rice phyllosphere bacteria producing bioactive compounds against Xoo. Phyllosphere bacteria isolated from healthy leaves of rice var. Ciherang by using 4 different media obtained 285 bacterial isolates which were consisted of the 65 isolates of King’s B agar, 86 isolates of Nutrient agar, 81 isolates of Luria-Bertani agar, and 53 isolates of Trypticase Soy agar media. Antagonist test using double layer method showed 58 isolates of phyllosphere bacteria produced bioactive compounds that inhibited the growth of Xoo. Pathogenicity test agaist rice leaf revealed 18 bacterial isolates did not perform their potencies as pathogenic bacteria. Among the 18 non-phytopathogenic bacterial isolates, 14 isolates belong to Gram-positive bacteria and 4 isolates belong to Gram-negative bacteria. Five isolates among Gram positive bacteria were predicted as Bacillus genera.

Structural basis of lignocellulose deconstruction by the wood-feeding anobiid beetle Nicobium hirtum

The details of the lignocellulose deconstruction processes in the digestive systems of wood-feeding insects remain elusive. This study aimed to examine the biochemical conversion of lignocellulose in the digestive system of a wood-feeding anobiid beetle, Nicobium hirtum, one of the most important pests of wooden products in Japan. To this end, N. hirtum larvae were fed with Japanese red pine (softwood) and Japanese beech (hardwood) sapwood diets, as well as an artificial diet containing Shorea wood (hardwood) sapwood sawdust. The structural differences between the original and digested (feces) lignocellulose samples were examined using wet-chemical and two-dimensional (2D) nuclear magnetic resonance (NMR) methods. Cellulose and hemicelluloses, especially mannan in the softwood diet, were preferentially degraded over lignin in the larval digestive system. As a result, lignin was enriched in the digested lignocellulose residues. Lignin compositional analyses based on thioacidolysis and 2D NMR determined that the proportions of oxidized lignin aromatic units were notably increased after digestion. Further, the 2D NMR analyses revealed the accumulation of aldehyde and hydroxypropiovanillone/syringone end-unit structures in lignin, indicating that oxidative and/or reductive modifications of lignin polymers occur in the larval digestive system. Such structural alterations of lignin may facilitate the dissociation of the lignin barrier, thereby liberating polysaccharides for subsequent enzymatic conversion for assimilation and energy

Effects of dietary variation on lignocellulose degradation and physiological properties of Nicobium hirtum larvae

We investigated the feeding behavior of larvae of the wood-destroying beetle Nicobium hirtum (Coleoptera: Anobiidae), an important wood pest in Japan, to determine the effects of dietary variation on lignocellulose degradation and larval growth and survival. Cultured colonies of N. hirtum larvae were fed artificial diets containing various amounts of starch (20, 50, and 80 wt%) mixed with hardwood (Shorea) lignocellulose. The polysaccharide degradation by N. hirtum was determined by chemical analyses of the initial artificial diets and fecal residues collected during the feeding experiment. Starch was preferentially decomposed when the larvae were fed the high-starch diet, whereas the decompositions of cellulose and hemicelluloses were more prominent when the larvae were fed medium- or low-starch diets. The larvae’s size and survival were recorded periodically to determine the diets’ effects on larval development. The survival rates ranged from 60 to 87% and were highest for the larvae fed the medium-starch diet and lowest for those fed the high-starch diet. Body size was highest in the larvae fed the high-starch diet. Fecal size increased along with the larval size increase. Overall, these results suggest that although starch is an essential carbon source for N. hirtum larval growth, lignocellulose also plays a key role as a nutrient that maintains the physiological activities of N. hirtum larvae and enhances their survival

BAKTERI ENTOMOPATOGEN SEBAGAI AGEN BIOKONTROL TERHADAP LARVA Spodoptera litura (F.)

Spodoptera litura (F.) (Lepidoptera: Noctuidae) is one of the agricultural pests that attacking almost all kinds of herbaceous plants, especiallyvegetables. Insect control using entomopathogenic bacteria is an alternative strategy that is effective and has a lower environmental impact than the use of synthetic insecticides. The purpose of this research was to explore entomopathogenic bacteria that have insecticidal activity against S. litura larvae at various stages of instars. The result showed that 25% of total number of isolated bacteria have potency as entomopathogenic bacteria. Isolate Staphylococcus sciuri strain BLSP-3 and isolate Serratia sp. strain BLSP-4 showed the highest larvicidal activity against the first and second instar larvae of S. litura 83% and 86%, respectively. The activity against on the third instar larvae however was only by 40%. However, the mortality caused by both isolates was lower than that of Bacillus thuringiensis (more than 90% mortality to the first and second instars and 80 % of the third instar larvae). It is suggested that both of isolates are potential to be developed further as a biocontrol agent to control S. litura population