Kjell Magne Fagerbakke

The elemental composition of bacteria: A signature of growth conditions?

Abstract X-ray microanalysis combined with Transmission Electron Microscopy (TEM) has been employed to measure cell quotas of P:C, N:C and O:C of individual cells from cultures and natural microbial communities. The relevance of such data for evaluation of nutrient availability and growth is discussed according to the Droop model. Using minimum subsistent quotas of 0.031 (P:C) and 0.17 (N:C) and μmax of 1 h−1 we have been able to identify some of the criteria for nutrient limited growth, but energy/carbon limitation will interfere with interpretation of these data. An additional signature for growth limitation may be the O:C ratio for which preliminary data indicate values of >0.40 for growing cells and

Emiliania huxleyi. Chemical composition and size of coccoliths from enclosure experiments and a Norwegian fjord

Abstract Single Emiliania huxleyi (Lohmann) Hay et Mohler, type A, coccoliths harvested from mesocosm enclosures (June 1991) with different nutrient regimes, and the Norwegian fjord, Samnangerfjorden (October 1992), were analyzed with- X-ray microanalysis in a Transmission Electron Microscope (TEM). The average molar Ca : C ratios of the free coccoliths varied within a range of 0.65–1.0, dependent on growth condition of E. huxleyi. Free coccoliths sampled from enclosures with high production or density of E. huxleyi, had Ca : C ratios near 1. Coccoliths sampled from Samnangerfjorden, and enclosures with low production or cell density the Ca : C ratios were close to 0.7. The excess of carbon in the coccoliths compared to CaC03 is probably due to organic matter, mainly carbohydrates. It is concluded that the amount of organic matter associated with coccoliths of E. huxleyi, is dependent on the growth conditions, and carbohydrate may protect the coccoliths from dissolution. A higher Ca : C ratio (0.8 versus ...

Effects of unbalanced nutrient regime on coccolith morphology and size in Emiliania huxleyi (Prymnesiophyceae)

Single coccoliths of Emiliania huxleyi grown in mesocosm enclosures (60°16′N, 05°14′E, May–June 1991) under different N:P regimes were analysed in a scanning electron microscope. The results indicate that only E. huxleyi with Type A coccoliths was present in the enclosures. Approximately 80–90% of the total coccolith assemblages had developed normally, whilst the remainder were malformed, incompletely grown or dissolved. Severely under-calcified specimens were rare and dissolution and breakage less than 5%. The coccoliths were of larger size than normal, as has been found previously in fjords of southwestern Norway, supporting the conclusion that a local population of E. huxleyi has developed, specific to these waters. Both phosphorus and nitrogen stress caused significant changes in coccolith size and evidence of malformation was clear, particularly in the low-phosphate enclosure. Although the observations presented here concern only Type A coccoliths and it is not known how nutrient stress may affect th...

Elemental composition of individual pico- and nano-sized marine detrital particles in the northwestern Mediterranean Sea

The elemental composition of individual < 10 μm detrital particles from Mediterranean surface waters was analysed using a Transmission Electron Microscope (TEM) equipped with an energy dispersive X-Ray microanalyser. Results show that carbon and phosphorus content per detritus volume are much higher in pico-detrital particles < 2 μm (42 kg C m−3 and 1 kg P m−3) than in 5–10 μm detrital particles (20 kg C m−3 and 0.1 kg P m−3). The C:N:P atomic ratios for different sized fractions of the detrital particles were found to be 82:10:1 for < 2 μm particles, 120:29:1 for 2–5 μm particles and 308:37:1 for 5–10 μm particles. The average ratio for all size classes of detrital particles (< 10 μm) was 132:23:1. The differences in elementary compositions of the detrital particles studied here suggest that the different size fractions probably have different origins. The role and origins of < 10 μm detrital particles within the biogeochemical cycles are discussed.