Thomas P. West

Exopolysaccharide production by entrapped cells of the fungus Aureobasidium pullulans ATCC 201253

The production of the exopolysaccharide pullulan using entrapped cells of the fungus Aureobasidium pullulans ATCC 201253 was investigated. Fungal cells entrapped in agarose or carrageenan were capable of elaborating pullulan for 2 production cycles. Those fungal cells entrapped in carrageenan were more productive than the agarose‐immobilized cells during the initial cycle while the reverse was true during the second production cycle. The agarose‐entrapped cells synthesized polysaccharide with a higher pullulan content than did the carrageenan‐immobilized cells. Fungal cells entrapped in carrageenan demonstrated a lower degree of leakage than did those entrapped in agarose.

Polysaccharide production by sponge‐immobilized cells of the fungus Aureobasidium pullulans

T.P. WEST AND B.R.‐H. STROHFUS. 1996. Cells of the fungus Aureobasidium pullulans ATCC 42023 were immobilized in sponge cubes and examined for their ability to elaborate the polysaccharide pullulan in relation to carbon source. It was found that fungal cells grown on corn syrup, sucrose or glucose as a carbon source could be immobilized in sponge cubes and that comparable cell weights and viable cell concentrations were immobilized. Independent of the carbon source tested, the immobilized fungal cells could be used at least three times for the production of polysaccharide. The immobilized A. pullulans cells elaborated the highest polysaccharide levels in the culture medium after 5–7 d of growth at 30°C.

Control of the pyrimidine biosynthetic pathway in Pseudomonas pseudoalcaligenes

The five de novo enzyme activities unique to the pyrimidine biosynthetic pathway were found to be present in Pseudomonas pseudoalcaligenes ATCC 17440. A mutant strain with 31-fold reduced orotate phosphoribosyltransferase (encoded by pyrE) activity was isolated that exhibited a pyrimidine requirement for uracil or cytosine. Uptake of the nucleosides uridine or cytidine by wild-type or mutant cells was not detectable; explaining the inability of the mutant strain to utilize either nucleoside to satisfy its pyrimidine requirement. When the wildtype strain was grown in the presence of uracil, the activities of the five de novo enzymes were depressed. Pyrimidine limitation of the mutant strain led to the increase in aspartate transcarbamoylase and dihydroorotate dehydrogenase activities by more than 3-fold, and dihydroorotase and orotidine 5′-monophosphate decarboxylase activities about 1.5-fold, as compared to growth with excess uracil. It appeared that the syntheses of the de novo enzymes were regulated by pyrimidines. In vitro regulation of aspartate transcarbamoylase activity in P. pseudoalcaligenes ATCC 17440 was investigated using saturating substrate concentrations; transcarbamoylase activity was inhibited by Pi, PPi, uridine ribonucleotides, ADP, ATP, GDP, GTP, CDP, and CTP.

Reductive catabolism of pyrimidine bases by Pseudomonas stutzeri

Pyrimidine base catabolism in Pseudomonas stutzeri ATCC 17588 was investigated and was found to occur by means of the reductive pathway. Pyrimidine bases and their respective reductive pathway catabolic products could serve as nitrogen sources for growth of P. stutzeri. Activities of the three enzymes associated with the reductive pathway of pyrimidine catabolism were detected in cells of P. stutzeri. The initial enzyme of the reductive pathway, dihydropyrimidine dehydrogenase, utilized NADH as its nicotinamide cofactor. Cells grown on pyrimidine bases as nitrogen sources contained elevated dehydrogenase activity relative to those grown on ammonium sulphate as nitrogen source. Activities of the second and third reductive pathway enzymes, dihydropyrimidinase and N-carbamoyl-β-alanine amidohydrolase, respectively, were also affected by growth conditions. If pyrimidine or dihydropyrimidine bases served as nitrogen sources, increases in the levels of these enzymes were observed compared to their activities determined when the nitrogen source was ammonium sulphate.

Pyrimidine base and ribonucleoside utilization by thePseudomonas alcaligenes group

Pyrimidine base and ribonucleoside utilization was investigated in the two type strains of thePseudomonas alcaligenes group. As sole sources of nitrogen, the pyrimidine bases uracil, thymine and cytosine as well as the dihydropyrimidine bases dihydrouracil and dihydrothymine supported the growth ofPseudomonas pseudoalcaligenes ATCC 17440 but neither these bases nor pyrimidine nucleosides supportedPseudomonas alcaligenes ATCC 14909 growth. Ribose, deoxyribose, pyrimidine and dihydropyrimidine bases as well as pyrimidine nucleosides failed to be utilized by eitherP. pseudoalcaligenes orP. alcaligenes as sole carbon sources. The activities of the pyrimidine salvage enzymes nucleoside hydrolase, cytosine deaminase, dihydropyrimidine dehydrogenase and dihydropyrimidinase were detected in cell-free extracts ofP. pseudoalcaligenes andP. alcaligenes. InP. pseudoalcaligenes, the levels of cytosine deaminase, dihydropyrimidine dehydrogenase and dihydropyrimidinase could be affected by the nitrogen source present in the culture medium.

Citric acid production by Aspergillus niger on wet corn distillers grains

Aims:  To determine which citric acid‐producing strain of Aspergillus niger utilized wet corn distillers grains most effectively to produce citric acid.

Polysaccharide production by a reduced pigmentation mutant of Aureobasidium pullulans NYS-1

Aims: To isolate a reduced pigmentation mutant of Aureobasidium pullulans NYS‐1 and characterize its cellular pigmentation plus its polysaccharide and biomass production relative to carbon source.

Isolation and characterization of a dihydropyrimidine dehydrogenase mutant of Pseudomonas chlororaphis

A dihydropyrimidine dehydrogenase mutant of Pseudomonas chlororaphis ATCC 17414 was isolated and characterized in this study. Initially, reductive catabolism of uracil was confirmed to be active in ATCC 17414 cells. Following chemical mutagenesis and d-cycloserine counterselection, a mutant strain unable to utilize uracil as a nitrogen source was identified. It was also unable to utilize thymine as a nitrogen source but could use either dihydrouracil or dihydrothymine as a sole source of nitrogen. Subsequently, it was determined that the mutant strain was deficient for the initial enzyme in the reductive pathway dihydropyrimidine dehydrogenase. The lack of dehydrogenase activity did not seem to have an adverse effect upon the activity of the second reductive pathway enzyme dihydropyrimidinase activity. It was shown that both dihydropyrimidine dehydrogenase and dihydropyrimidinase levels were affected by the nitrogen source present in the growth medium. Dihydropyrimidine dehydrogenase and dihydropyrimidinase activities were elevated after growth on uracil, thymine, dihydrouracil or dihydrothymine as a source of nitrogen.

Curdlan production by Agrobacterium sp. ATCC 31749 on an ethanol fermentation coproduct

The production of the polysaccharide curdlan from the ethanol processing coproduct condensed corn distillers solubles by the bacterium Agrobacterium sp. ATCC 31749 was investigated. It was found that curdlan could be produced by the bacterium using condensed corn distillers solubles as a source of carbon and nitrogen. As the concentration of condensed corn distillers solubles was increased from 50 g l–1 to 400 g l–1, the concentration of curdlan increased but not proportionally. The highest curdlan concentration was produced by the strain on 400 g l–1 condensed corn distillers solubles after 120 h and its level was higher than was observed for glucose‐based curdlan production. Biomass production by ATCC 31749 was also highest after 120 h of growth on 400 g l–1 condensed corn distillers solubles and was higher than found for glucose‐based biomass production. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Polysaccharide production by immobilized Aureobasidium pullulans cells in batch bioreactors

Cells of the fungus Aureobasidium pullulans ATCC 201253 were entrapped within 4% agar cubes or 5% calcium alginate beads and were examined for their production of the polysaccharide pullulan in batch bioreactors. The batch bioreactors were utilized twice for 168 hours of polysaccharide production in medium containing corn syrup as a carbon source. The agar-entrapped cells produced nearly equivalent pullulan concentrations during both production cycles. The alginate-entrapped cells produced higher polysaccharide levels during the second cycle compared to the levels observed during the initial cycle. The agar-entrapped cells elaborated a polysaccharide with a higher pullulan content than did the alginate-entrapped cells during both production cycles.