title: Effects of melanin on the accumulation of exopolysaccharides by Aureobasidium pullulans grown on nitrate.
abstract: Aureobasidium pullulans produced pullulan and melanin when grown in medium containing low nitrate levels. With high nitrate concentrations, however, this fungus produced a mixture of exopolysaccharides (EPS) without melanin synthesis. At 0.78 g l(-1) N as nitrate, where no melanin synthesis occurred, maximum EPS yields reached 6.92 g l(-1) and then decreased to the final yield of 2.36 g l(-1). Following melanin addition (0.1 g l(-1)), yields reached 7.02 g l(-1) at 48 h and fell to a final yield of 5.21 g l(-1). The EPS produced in high nitrate medium contained both pullulan and (1-->3)-beta-glucan, but only pullulan was produced with melanin-supplementation. With melanin addition a doubling of (1-->3)-beta-glucanase activity was observed in high nitrate medium compared to that without supplementation. On the other hand amylolytic activities disappeared in medium with melanin production or addition. Culture filtrates sustained a higher reducing capacity (RC) when melanin was present. Low RC appeared to reduce (1-->3)-beta-glucanase activity and increase amylolytic activities. Thus, higher RC appears to inhibit production/activity of amylose-degrading enzymes capable of degrading pullulan, and stimulates (1-->3)-beta-glucanase synthesis/activity, leading to a preferential accumulation of pullulan.
authors: Key Laboratory for Biotechnology on Medicinal Plants, Xuzhou Normal University, Xuzhou 221116, China. yyzw@xznu.edu.cn
authors: Weifa
authors: W
authors: Zheng
authors: Bradley S
authors: BS
authors: Campbell
authors: Barbara M
authors: BM
authors: McDougall
authors: Robert J
authors: RJ
authors: Seviour
mesh_terms: D001203:Ascomycota / Q000378:metabolism*; D019149:Bioreactors / Q000382:microbiology; D003470:Culture Media; D005285:Fermentation; D005936:Glucans / Q000096:biosynthesis*; D006863:Hydrogen-Ion Concentration; D008543:Melanins / Q000378:metabolism*; D009566:Nitrates / Q000378:metabolism*; D011134:Polysaccharides / Q000096:biosynthesis*; D013696:Temperature; D013997:Time Factors
chemical_list: D003470:Culture Media; D005936:Glucans; D008543:Melanins; D009566:Nitrates; D011134:Polysaccharides; C009109:pullulan