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Attempts were made to clarify the precise location and possible site of production of the K-glucan pullulan in different morphological forms of the fungus Aureobasidium pullulans. Gold-conjugated pullulanase was used as the specific probe for this purpose. No cell wall pullulan-like material was detected by transmission electron microscopy (TEM) in any morphological form of this fungus, although intracellular electron transparent material bound this probe. When silver enhancement of this gold-conjugated pullulanase probe was used, the data strongly suggested that only swollen cells and chlamydospores, and neither hyphae nor unicellular blastospores, often held responsible for pullulan formation, appeared to produce pullulan-like material. ß

Aims:  To identify if culture conditions affect the chemical composition of exopolysaccharide (EPS) produced by Aureobasidium pullulans. Methods and Results:  In batch airlift and continuously stirred tank (CSTR) reactors the EPS produced with low (0·13 g l−1 N) initial NaNO3 or (NH4)2SO4 levels contained pullulan, with maltotriose as its major component, similar to that synthesized in the airlift reactor with high (0·78 g l−1 N) initial NaNO3 levels. EPS produced by CSTR grown cultures with high (NH4)2SO4 levels contained little pullulan, possibly because of a population shift from unicells to mycelium. This chemical difference may explain why total EPS yields did not fall as they did with cultures grown under identical conditions with high NaNO3 levels, where the pullulan component of the EPS disappeared. EPS synthesized in N‐limiting chemostat cultures of A. pullulans changed little with growth rate or N source, being predominantly pullulan consisting of maltotriose units. Conclusions:  While the EPS chemical composition changed little under N‐limiting conditions, high initial medium N levels determined maltotriose content and/or pullulan content possibly by dictating culture morphology. Significance and Impact of the Study:  These results emphasize the requirement of all studies to determine EPS chemical composition when examining the influence of culture conditions on EPS yields.

The transesterification of trimethyl phosphite with meso-hydrobenzoin has been found to lead to the single isomeric product, trans-methyl meso-hydrobenzoin phosphite. The phosphite has been converted by ozonolysis to the analogous trans-methyl meso-hydrobenzoin phosphate. Single-crystal X-ray diffraction studies have been completed for both compounds. The phosphite, CisHisPCh, crystallizes in space group P2|2i2i with cell dimensions a = 9.924 (3), b = 5.969 (1), c = 23.225 (5) A, and Z = 4. The phosphate, C15H15PO4, crystallizes in space group Pna2\ with a = 18.559 (4), b = 6.609 (1), c = 23.614 (5) A, and Z = 8. A comparison of the structural features of the phosphite and phosphate is reported. The results show that P-O bond lengths are longer and the O-P-O angles smaller in the phosphite than in the corresponding phosphate.