P. S. Meyer

Effect of culture conditions on astaxanthin production by a mutant of Phaffia rhodozyma in batch and chemostat culture

Temperature and pH had only a slight effect on the astaxanthin content of a Phaffia rhodozyma mutant, but influenced the maximum specific growth rate and cell yield profoundly. The optimum conditions for astaxanthin production were 22°C at pH 5.0 with a low concentration of carbon source. Astaxanthin production was growth-associated, and the volumetric astaxanthin concentration gradually decreased after depletion of the carbon source. The biomass concentration decreased rapidly during the stationary growth phase with a concomitant increase in the cellular content of astaxanthin. Sucrose hydrolysis exceeded the assimilation rates of D-glucose and D-fructose and these sugars accumulated during batch cultivation. D-Glucose initially delayed D-fructose uptake, but D-fructose utilization commenced before glucose depletion. In continuous culture, the highest astaxanthin content was obtained at the lowest dilution rate of 0.043 h−1. The cell yield reached a maximum of 0.48 g cells·g−1 glucose utilized between dilution rates of 0.05 h−1 and 0.07 h−1 and decreased markedly at higher dilution rates.

Astaxanthin production by a Phaffia rhodozyma mutant on grape juice

During fermenter cultivation of Phaffia rhodozyma on a grape juice medium, the presence of glucose initially delayed fructose utilization, although fructose was consumed before glucose depletion. Total pigment and astaxanthin production were growth associated and reached maximum values of 15.9 μg/ml and 9.8 μg/ml, respectively, after depletion of the carbon source. The total cellular pigment and astaxanthin content increased during the stationary growth phase due to a decrease in biomass, reaching final values of 2120 μg/g and 1350 μg/g, respectively, without the volumetric concentration in the culture changing. The final cell yield was 0.33 g/g sugar utilized. High sugar concentrations in shake-flasks as well as O2 limitation decreased the astaxanthin content of the cells. Addition of yeast extract to a grape juice minimal medium markedly increased the maximum specific growth rate, total pigment and astaxanthin content of the cells. An excess of ammonia decreased the intracellular astaxanthin content, which reached a maximal value in cultures with no residual glucose or ammonia.

Selection and evaluation of astaxanthin-overproducing mutants of Phaffia rhodozyma.

Mutagenesis of Phaffia rhodozyma with NTG yielded a mutant with an astaxanthin content of 1688 μg (g dry biomass)-1, a cell yield coefficient of 0.47 on glucose and a maximum specific growth rate of 0.12 h-1. Re-mutation of the mutant decreased the cell yield and maximum specific growth rate but increased the astaxanthin content. The use of mannitol or succinate as carbon sources enhanced pigmentation, yielding astaxanthin contents of 1973 μg g-1 and 1926 μg g-1, respectively. The use of valine as sole nitrogen source also increased astaxanthin production, but severely decreased the maximum specific growth rate and cell yield coefficient. The optimum pH for growth of P. rhodozyma was between pH 4.5 and 5.5, whereas the astaxanthin content remained constant above pH 3.

Photo-Regulated Astaxanthin Production by Phaffia rhodozyma Mutants

Summary Astaxanthin production by Phaffia rhodozyma mutants was photo-inducible. The intracellular astaxanthin concentration during cultivation in the dark was almost constant in the different mutants and did not reflect the concentrations reached in cells grown in the light, which differed considerably among these mutants. The final astaxanthin concentration obtained was determined by the total time of illumination, the growth phase subjected to illumination and the light intensity. Higher astaxanthin levels were obtained when cells were illuminated during the exponential growth phase. Subjecting cells to a 15 min light pulse greatly enhanced pigment production, but the stimulation was of a transient nature and a reduction in total pigment content was observed when the cultures were returned to the dark. The maximum astaxanthin production was obtained when cultures were continuously illuminated at moderate light intensities (5 to 100 µE.m -2 · -1 ). Blue light was primarily responsible for photo-induced astaxanthin production in P. rhodozyma .

Effect of acetic acid on astaxanthin production by Phaffia rhodozyma

SummaryLow concentrations of acetic acid decreased the growth rate of and astaxanthin production by Phaffia rhodozyma on glucose, with growth completely inhibited by 2 g acetic acid/l. Using H2SO4 for pH control after sugar depletion caused a decline in the biomass concentration, whereas using acetic acid as titrant resulted in an increase in the biomass with a high astaxanthin content of 1430 μg/g cells. An extended culture with a continuous glucose feed failed to maintain a high astaxanthin content.

Isolation and evaluation of yeasts for biomass production from bagasse hemicellulose hydrolysate

Summary A total of 26 yeast cultures, capable of utilising D-xylose or both D-xylose and L-arabinose in vitamin-free medium at 36 °C, were isolated from 250 samples originating from various localities. Six of these isolates, all identified as Candida blankii strains, were selected on the basis of their potential for biomass production from hemicellulose sugars. These isolates also utilised sucrose and acetic acid and grew well at 44 °C and at pH 3. These isolates were superior to C. utilis for biomass production from hemicellulose hydrolysates in that they utilised L-arabinose and were capable of growth at higher temperatures.

The effect of monoterpenes on astaxanthin production by a mutant ofPhaffia rhodozyma

SummaryThe total pigment and astaxanthin content ofPhaffia rhodozyma increased with increasing concentrations α-pinene up to 500 μl α-pinene/l. Above this concentration the total pigment and astaxanthin content as well as the biomass production decreased. The addition of 500 μl α-pinene/l increased the total pigment content from 1652 μg/g to 2201 μg/g and the astaxanthin content from 1554 μg/g to 1883 μg/g. A sharp decrease in maximum specific growth rate occurred above 150 μl α-pinene/l.

Transport-limited sucrose utilization and neokestose production by Phaffia rhodozyma

SummaryGrowth of an astaxanthin hyper-producing strain of Phaffia rhodozyma on sucrose is accompanied by the accumulation of glucose and fructose in the medium due to the limited capacity of the corresponding monosaccharide transport system or systems. This is accompanied by the production of the trisaccharide neokestose by transglycosylation reactions.

Cultivation of Candida blankii in simulated bagasse hemicellulose hydrolysate

SummaryAll fourCandida blankii isolates evaluated for growth in simulated bagasse hemicellulose hydrolysate utilized the sugars and acetic acid completely. The utilization ofd-xylose,l-arabinose and acetic acid were delayed by the presence ofd-glucose, but after glucose depletion the other carbon sources were utilized simultaneously. The maximum specific growth rate of 0.36 h−1 and cell yield of 0.47 g cells/g carbon source assimilate compared with published results obtained withC. utilis. C. blankii appeared superior toC. utilis for biomass production from hemicellulose hydrolysate in that it utilizedl-arabinose and was capable of growth at higher temperatures.

The effect of mixtures of acetic acid and D-xylose on the growth rate of Candida blankii

SummaryThe growth rate of the yeastCandida blankii in carbon-limited chemostat culture on a mixture of D-xylose and acetic acid as carbon sources was determined not only by the acetic acid concentration in the feed, but also by the ratio of xylose to acetic acid. The hypothesis is put forward that the inhibitory effect of acetic acid on the growth rate is determined, in part, by the specific rate of acetic acid metabolism.