Lena Hansson

Effect of culture conditions on mycelial growth and production of γ-linolenic acid by the fungus Mortierella ramanniana

SummaryEffect of culture conditions on cell growth, lipid accumulation and γ-linolenic acid production is reported for four Mortierella species. The highest concentration as well as the highest productivity of γ-linolenic acid in lipid was determined in strains of M. ramanniana. M. ramanniana CBS 112.08 was used in the studies of the influence of medium composition, concentration of carbon- and nitrogen sources and growth temperature. Several carbon sources provided good growth and a high lipid content in biomass. The highest dry weights (11–12g/l) and lipid contents (∼24%, w/w), were observed if glucose or fructose was used as carbon source, whereas the highest amount of γ-linolenic acid (∼26%) was determined in starch-grown cells. The fatty acid composition in the lipid was influenced by the cultivation time, growth temperature and, to a minor extent, by the carbon source used. In fermentor cultures, both strains of Mortierella ramanniana showed relatively poor growth and incomplete consumption of glucose. M. vinacea, on the other hand, grew well in tower reactors. M. vinacea, which has a different morphology than M. ramanniana strains, also showed higher yields of biomass and lipid and higher yield coefficients than the latter.

Production of γ-linolenic acid by the fungus Mucor rouxii in fed-batch and continuous culture

SummaryThe production of γ-linolenic acid (GLA) and lipid was studied in Mucor rouxii CBS 416.77. In a fed-batch culture productivities of 39.4 mg/l per hour for GLA and 99 mg/l per hour for the total amount of lipid were determined at 18 h of cultivation. At this point the highest value of GLA in lipid (39.7%, w/w) was also reached. Production of GLA was also studied in a series of continuous cultures. It was observed that, in addition to growth rate, the nitrogen concentration of the input medium was of great importance for high productivities. The highest productivity values for GLA (37 mg/l per hour) and for lipid (95 mg/l per hour) were reached at a dilution rate of 0.10 h-1 with a concentration of 4.5g/l NH4Cl in the input medium.

Influence of cultivation conditions on lipid production by Cryptococcus albidus

SummaryCryptococcus albidus var. albidus CBS 4517 was able to accumulate lipid under nitrogen-limited as well as excess-nitrogen conditions. The highest lipid-producting capacity was, however, observed in nitrogen-limited cultivations. In nitrogen-limited batch cultures, a lipid content of 34% (w/w) in biomass and a maximum specific lipid productivity of 37 mg lipid/g lipid-free biomass·h, was determined. The yield of lipid from glucose was about 0.15 g/g in nitrogen-limited and 0.11 g/g in excess-nitrogen cultures.In a nitrogen-limited fed-batch culture, 12.4 g/l lipid was produced at 90 h of cultivation and the cells contained 46.3% (w/w) lipid.Higher lipid yield and cellular lipid content were observed when inorganic nitrogen sources were used compared with organic. The choice of carbon source was seen to influence growth as well as lipid production and the highest yields of lipid were obtained when glucose, maltose or mannitol was used.A cultivation temperature of 20°C provided the highest lipid productivity compared to 25°C and 30°C. Addition of citrate to the growth medium was seen to have a stimulating effect on the specific lipid productivity.

Continuous culture with complete cell recycle to obtain high cell densities in product inhibited cultures; cultivation ofStreptococcus lactis for production of superoxide dismutase

SummaryA cultivation system is described for cultivatingStreptococcus lactis in continuous culture with complete cell recycle. The aim was to obtain high cell densities for the production of su-peroxide dismutase (SOD) while avoiding the growth inhibiting effects of the lactic acid produced. This type of cultivation was performed both at constant and at increasing dilution rates. Comparisons made include those between cell mass productivity and SOD productivity in recycling cultivations and batch cultivations. In the recycling cultivation at increasing dilution rates a cell mass of 19 g/1 was obtained after 22 h of cultivation and the SOD productivity was 43.103 U/1.h which is four times higher than for batch cultivations. The effect of recyclingS. lactis was also considered and no damage of the microorganisms was observed.

Production of ψ-linolenic acid by the fungus Mucor rouxii on cheap nitrogen and carbon sources

SummaryThe production of ψ-linolenic acid (GLA) by the fungus Mucor rouxii CBS 416.77 was studied on low budget nitrogen and carbon sources, i.e. rape meal, cocos expeller and two types of yeast extract (nitrogen sources), and starch, starch hydrolysate, beet molasses and cocos expeller (carbon sources). As references, Difco yeast extract and glucose were used. In flask cultivations the three yeast extracts were fully interchangeable, while the Difco yeast extract (the most expensive of those tested) gave a higher productivity of GLA in fermentor cultures (14 mg·l−1·h−1). The yield of lipids and GLA were increased in the order yeast extract < rape meal < cocos expeller. Thus the amount of lipid increased from 0.56 to 2.8 g·l−1, and that of GLA from 0.15 to 0.33 g·l−1. Use of beet molasses or cocos expeller as carbon sources gave poor growth. Starch and starch hydrolysate resulted in better productivity of GLA than glucose (4.7 and 4.9 compared to 3.4 mg·l−1·h−1).

Effect of culture conditions on fatty acid composition in lipids produced by the yeastcryptococcus albidus var. albidus

The influence of culture conditions on the fatty acid composition in lipids produced by Cryptococcus albidus var. albidus CBS 4517 was studied.The major fatty acids in C. albidus var. albidus were oleic (18:1), linoleic (18:2) and palmitic (16:0) acid. The relative amounts of fatty acids produced varied considerably during growth and lipid accumulation phases in nitrogen-limited as well as excess-nitrogen cultures. The degree of unsaturation correlated to the lipid content in the biomass and decreased with increasing amounts of cellular lipid. After glucose exhaustion, no further changes in the fatty acid composition nor in the lipid content of the cells were observed. A number of carbon and nitrogen sources could be utilized for lipid synthesis, but they influenced the fatty acid composition only to a minor extent.

Lipid formation by Cryptococcus albidus in nitrogen-limited and in carbon-limited chemostat cultures

SummaryCryptococcus albidus var. Albidus CBS 4517 was grown in nitrogen-limited and in carbon-limited chemostat cultures. The effect of growth rate and limiting nutrient on lipid accumulation and fatty acid composition was investigated.The maximum lipid content in the biomass was, in both cultivation systems, observed at the lowest dilution rate (growth rate) tested. At this dilution rate, D=0.31 h-1, cells from the nitrogen-limited culture contained 41% (w/w) lipid and cells from the carbon-limited culture 37%. These results indicate the ability of C. albidus, unlike other oleaginous yeasts, to accumulate lipid also in carbon-limited chemostats.The yield of lipid from carbon source was about the same at D=0.031 h-1 in nitrogen-limited (YL/S=0.16 g/g) as in carbon-limited (YL/S=0.17 g/g) cultures and decreased with increasing growth rates. In the nitrogen-limited culture, the lipid productivity was about constant at low growth rates (0.031–0.056 h-1) and a slight decrease was observed at D=0.08 h-1, while the specific lipid productivity, qL, increased to 27.5 mg/g per hour. In the carbon-limited culture, however, lipid productivity increased with increasing growth rates and reached its maximum value near μmax, whereas qL was about constant at 20 mg/g per hour.The fatty acid composition was influenced by the specific growth rate in nitrogen-limited as well as in carbon-limited cultures, although the changes were more pronounced during carbonlimitation. A decrease in the degree of unsaturation (Δ/mole) was also observed with increasing lipid content in the cells.

The Equivalence Principle Comes to School--Falling Objects and Other Middle School Investigations.

Comparing two objects falling together is a small-scale version of Galileo’s classical experiment, demonstrating the equivalence between gravitational and inertial mass. We present here investigations by a group of ten-year-olds, who used iPads to record the drops. The movie recordings were essential in the follow-up discussions, enabling the students to compare the different situations and to discern situations where air resistance was essential and where it could be neglected. By considering a number of familiar situations and simple investigations that can be performed, e.g., on a playground, students may come closer to an appreciation of the deep significance of the non-influence of mass on motion under gravity.

Working with the nature of science in physics class: Turning 'ordinary' classroom situations into nature of science learning situations

In the science education research field there is a large body of literature on the nature of science (NOS). NOS captures issues about what characterizes the research process as well as the scientific knowledge. Here we, in line with a broad body of literature, use a wide definition of NOS including also e.g. socio-cultural aspects. It is argued that NOS issues, for a number of reasons, should be included in the teaching of science/physics. Research shows that NOS should be taught explicitly. There are plenty of suggestions on specific and separate NOS activities, but the necessity of discussing NOS issues in connection to specific science/physics content and to laboratory work, is also highlighted. In this article we draw on this body of literature on NOS and science teaching, and discuss how classroom situations in secondary physics classes could be turned into NOS-learning situations. The discussed situations have been suggested by secondary teachers, during in-service teacher training, as situations from every-day physics teaching, from which NOS could be highlighted.

Motion on an Inclined Plane and the Nature of Science.

Friction is an important phenomenon in everyday life. All children are familiar with playground slides, which may thus be a good starting point for investigating friction. Motion on an inclined plane is a standard physics example. This paper presents an investigation of friction by a group of 11-year olds. How did they plan their investigations? What aspects of friction could they discern? What understanding of the nature of science was revealed—and developed—during their investigation and subsequent discussion with the teacher?