Aureobasidium pullulans における機能性β-グルカン生産と細胞形態の関係  [in Japanese] Relationship between the functional β-glucan polysaccharide-production and the cell morphologies of Aureobasidium pullulans  [in Japanese]

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Aureobasidium pullulansは多様な細胞形態を示し,菌の保存と培養の制御が難しい.また,本菌株の細胞形態とβ-グルカン生産の関連性が解明されていない.本研究では,A.pullulans AFO202の生活環の解明と,細胞形態とβ-グルカン生産の関連性について検討した.対数増殖期に本菌株は,分生子から伸長途中菌糸を経て菌糸形細胞になり,内生分生子が観察された.一方,酵母形細胞では分生子が出芽や分裂を繰り返すことによって増殖した.定常期の菌糸や酵母形細胞は,膨張細胞へと移行し,菌糸形膨張細胞は,分節することによって酵母形膨張細胞に変化した.定常期初期には膨張細胞が増加し,次いで厚膜胞子へと変化したが,その後,生育環境の変化に応じて発芽し,再増殖を開始した.顕微鏡下の膨張細胞において,β-グルカンが形成する多糖層の観察には,墨汁染色法が有効であった.米糠培地では,本菌株はプルランを生産せずにβ-グルカンを生産し,菌糸形と酵母形の両膨張細胞が関与していることが明らかになった.本菌株を用いて効率よくβ-グルカンを生産するためには,分生子や菌糸といった栄養細胞から膨張細胞への分化に要する時間の短縮と,膨張細胞の維持が重要であることが示唆された.

Aureobasidium pullulans is a fungus that has multiple cellular forms, and preservation and growth of this fungus has proven to be challenging. A. pullulans produces the extracellular polysaccharide β-glucan, but the relationship between cell morphology and β-glucan production in this organism remained to be elucidated. In this study, we investigated the complex life cycle of A. pullulans strain AFO202 and studied the relationship between cell morphology and production of β-glucan. In logarithmic growth phase, the cell morphology of the strain changed from a conidia to a mycelial form through the germ-tube, and the formation of an endoconidium inside the mycelial form was observed. Yeast-like cells proliferated by budding and division of the conidia. In the stationary phase, both the mycelial form and the yeast-like form became swollen. Swollen mycelial cells then became segmented and changed into yeast-like cells. In the early stationary phase, the number of swollen cells increased and these cells changed into chlamydospores. The chlamydospores then germinated and resumed proliferation in response to environmental changes. Microscopy of the swollen cells, stained with Indian ink, revealed a polysaccharide layer formed by β-glucan. When this strain was cultivated in rice bran medium, it produced β-glucan but no pullulan. Our results revealed that the swollen cells of both the mycelial form and the yeast-like form are involved in the production of β-glucan. These results suggested that shortening the time of differentiation of the vegetative cells, i.e., differentiation of conidia and mycelium into swollen cells, and increasing the duration of the swollen cell morphology, are important factors in the highly efficient production of β-glucan by this strain.


  • 生物工学会誌 : seibutsu-kogaku kaishi

    生物工学会誌 : seibutsu-kogaku kaishi 88(12), 634-641, 2010-12-25


References:  31


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