Acetobacter acidum-mucosum Tosic & Walker, n.sp., an Organism Forming a Starch-like Polysaccharide

This paper describes Acetobacter acidum-mucosum, a new bacterial species isolated from brewery yeast. The organism exhibits distinctive morphological and physiological characteristics that differentiate it from eighteen known Acetobacter species. Cells are predominantly coccoid or short rod-shaped, non-motile, and Gram-negative. A defining feature is the formation of large capsules in malt extract medium, particularly at pH 4.5 or below, where capsules can reach 8 micrometers in length. Notably, this species produces a starch-like polysaccharide, giving an intense blue-black reaction with iodine—a characteristic not previously observed in Acetobacter species. Growth characteristics vary depending on medium pH; at lower pH values (below 4.5), the organism produces voluminous viscid sediments, while at higher pH values, deposits are powdery. The organism is strictly aerobic, grows optimally at 25-30°C, and produces acetic acid from ethanol oxidation. It cannot utilize ammonium salts as sole nitrogen source and shows negative Voges-Proskauer and gelatin liquefaction reactions. The organism tolerates moderate ethanol concentrations but is sensitive to higher levels.

Key findings

• Acetobacter acidum-mucosum is a new species producing starch-like polysaccharide, unique among Acetobacter species
• Large pH-dependent capsule formation occurs at pH 4.5 or below, contrasting with smaller capsules at higher pH
• The organism produces voluminous viscid sediments in low-pH media and powdery deposits in neutral media
• Optimal growth temperature is 25-30°C; the organism is strictly aerobic and produces acetic acid from ethanol
• Cannot utilize ammonium salts as sole nitrogen source and shows negative Voges-Proskauer reaction