Cyanothece sp. 113, a unicellular, aerobic, diazotrophic and photosynthetic marine cyanobacterium, produced 22.34 g/l of exopolysaccharidein 11 days at 29℃, aeration rate of 7.0 l/min and continuous illumination with 4300 lux. After purification, the spectra of UV, IR, 1H NMR, 13C NMR and GC–MS analysis showed that the purified exopolysaccharide was a-D-1,6-homoglucan. This is first report describing linear a-D-1,6-homoglucan exopolysaccharide produced by marine cyanobacteria.

The extracellular alkaline protease in the supernatant of cell culture of the marine yeast Aureobasidium pullulans 10 was purified to homogeneity with a 2.1-fold increase in specific protease activity as compared to that in the supernatant by ammonium sulfate fractionation, gel filtration chromatography (Sephadexi G-75), and anion-exchange chromatography (DEAE Sepharose Fast Flow). According to the sodium dodecyl sulfate-polyacrylamide gel electrophoresis data, the molecular mass of the purified enzyme was estimated to be 32.0 kDa. The optimal pH and temperature of the purified enzyme were 9.0 and 45℃, respectively. The enzyme was activated by Cu2+ (at a concentration of 1.0 mM) and Mn2+ and inhibited by Hg2+, Fe2+, Fe3+, Zn2+, and Co2+. The enzyme was strongly inhibited by phenylmethylsulfonyl fluoride, but weakly inhibited by EDTA, 17–10-phenanthroline, and iodoacetic acid. The Km and Vmax values of the purified enzyme for casein were 0.25 mg/ml and 0.0286 mmol/min/mg of protein, respectively. After digestion of shrimp protein, spirulina (Arthospira platensis) protein, proteins of marine yeast strains N3C (Yarrowia lipolytica) and YA03a (Hanseniaspora uvarum), milk protein, and casein with the purified alkaline protease, angiotensin I converting enzyme (ACE) inhibitory activities of the resulting peptides reached 85.3%, 12.1%, 29.8%, 22.8%, 14.1%, and 15.5%, respectively, while the antioxidant activities of these were 52.1%. 54.6%, 25.1%, 35%, 12.5%, and 24.2%, respectively, indicating that ACE inhibitory activity of the resulting peptides from the shrimp protein and antioxidant activity of those produced from the spirulina protein were the highest, respectively. These results suggestthat the bioactive peptides produced by digestion of the shrimp protein with the purified alkaline protease have potential applications in the food and pharmaceutical industries.

Yeast strain Y68, producing a large amount of pullulan, was isolated from the leaves collected in the south of China. This strain was identified to be Rhodotorula bacarum by BIOLOG analysis and routine yeast identification. This is the first time to report that pullulan was produced by R. bacarum. The optimal medium for pullulan production by this strain was 8.0% (w/v) glucose, 2.0% (w/v) soybean cake hydrolysate, 0.5% (w/v) K2HPO4, 0.1% (w/v) NaCl, 0.02% (w/v) MgSO4·7H2O, 0.06% (w/v) (NH4)2SO4, pH 7.0. The optimal cultivation conditions for pullulan production by this strain in 300-ml shake flask containing 50 ml of medium were observed at 28℃ and with 180 rpm. Under these conditions, 5.9% (w/v) pullulan was produced within 60 h. This was the highest pullulan yield produced by yeasts obtained so far. No pigment in the medium was observed during the fermentation, suggesting that strain Y68 was a non-pigmented yeast strain.

Under the optimal conditions, 10 U/ml of glucoamylase was produced by the marine yeast Aureobasidium pullulans N13d. It was noticed that the crude glucoamylase actively hydrolyzed potato starch granules, but poorly digested raw corn starch and sweet potato starch, resulting in conversion of 68.5, 19 and 22% of them into glucose within 6 h of incubation in the presence of 40 g/l of potato starch granules and 20 U/ml of the crude enzyme. When potato starch granules concentration was increased from 10 to 80 g/l, hydrolysis extent was decreased from 85.6 to 60%, while potato starch granules concentration was increased from 80 to 360 g/l, hydrolysis extent was decreased from 60 to 56%. Ratio of hydrolysis extent of potato starch granules to hydrolysis extent of gelatinized potato starch was 86.0% and the hydrolysis extent of potato starch granules by action of the crude glucoamylase (1.0 U/ml) was 18.5% within 30 min at 60 8C. Only glucose was detected during the hydrolysis, indicating that the crude enzyme could hydrolyze both a-1,4 and a-1,6 linkages of starch molecule in the potato starch.