Tineke Burger-Wiersma

Prochlorthrix hollandica gen. nov. sp. nov., a Filamentous Oxygenic Photoautotrophic Procaryote Containing Chlorophylls a and b: Assignment to Prochlorotrichaceae fam. nov. and Order Prochlorales Florenzano, Balloni, and Materassi 1986, with Emendation of the Ordinal Description

The genus Prochlorothrix gen., with one species, Prochlorothrix hollandica sp. nov., is proposed for filamentous oxygenic photoautotrophic procaryotes containing chlorophylls a and b. The cylindrical cells are arranged in trichomes which lack sheaths, are not motile, and do not possess differentiated cells. P. hollandica grows in liquid media or on solid mineral media and is incapable of dinitrogen fixation. Optimum growth occurs between 20 and 30°C and at pH 8.4. The deoxyribonucleic acid base composition of this organism is 53 mol% guanine plus cytosine. Emendation of the description of the order Prochlorales Florenzano, Balloni, and Materassi 1986 is proposed since the original definition of this taxon would exclude the genus Prochlorothrix. To accommodate the filamentous genera in the order Prochlorales. we propose the family Prochlorotrichaceae fam. nov.

Coupling of phytoplankton and detritus in a shallow, eutrophic lake (Lake Loosdrecht, The Netherlands)

An oscillating steady state is described of phytoplankton, dominated by Prochlorothrix hollandica and Oscillatoria limnetica, and sestonic detritus in shallow, eutrophic Lake Loosdrecht (The Netherlands). A steady-state model for the coupling of the phytoplankton and detritus is discussed in relation to field and experimental data on phytoplankton growth and decomposition. According to model predictions, the phytoplankton to detritus ratio decreases hyperbolically at increasing phytoplankton growth rate and is independent of a lakes trophic state. The seston in L. Loosdrecht contains more detritus than phytoplankton as will apply to many other lakes. The model provides a basis for estimating the loss rate of the detritus, including decomposition, sedimentation and hydraulic loss. In a shallow lake like L. Loosdrecht detritus will continue to influence the water quality for years.

Influence of medium frequency light/dark cycles of equal duration on the photosynthesis and respiration of Chlorella pyrenoidosa

Chlorella pyrenoidosa was grown in three continuous cultures each receiving a different light regime during the light period of a diurnal cycle. Hourly samples taken during the light period were subjected to medium frequency light/dark oscillations of equal duration, ranging from 3 to 240 seconds. The oxygen consumption and production of each sample were measured with an oxygen electrode in a small oxygen chamber. Although the light/dark cycles had little overall influence on photo synthetic activity, the microalgae appeared to adapt to the light regime to which they were subjected. Large differences were found between the maximum chlorophyll-specific production rates (P max B ), the chlorophyll-specific production rates (PB) and the respiration rates between the cultures and treated subsamples. Respiration rates increased during the light period, whilst PB either increased, or had a mid light period minimum or maximum. The culture which received an hourly light oscillation during the light period had the highest P max B and lowest respiration rates, and it is suggested that these algae react as in nature, whereas either a sinusoidal or a block light pattern is ‘unnatural’. The latter light regime is commonly used in laboratory studies.

LIPIDS AND CHEMOTAXONOMY OF PROCHLOROTHRIX HOLLANDICA, A PLANKTONIC PROKARYOTE CONTAINING CHLOROPHYLLS a AND b'

The lipid composition of a planktonic prokaryote, Prochlorothrix hollandica Burger‐Wiersma, isolated from Lake Loosdrecht (The Netherlands) has been determined. This species is only the second prokaryote that has been found to contain chlorophylls a and b. Its lipid composition is similar to that of another prochlorophyte, Prochloron didemni Lewin, as well as to some cyanobacteria and bacteria, but there are also some unique features. Major fatty acids were 14:0, 14: 1ω5, 16:0, 16: 1ω7 and two novel fatty acids 16: 1ω12 (hexadec‐4‐enoic acid) and a new 16:2 isomer. Double bond positions in monounsaturated fatty acids and alkenes were determined by derivatization with dimethyl disulfide followed by analysis of the products by gas chromatography‐mass spectrometry. Hydrocarbons consisted mainly of the pentacyclic triterpene hop‐22(29)‐ene and straight‐chain n‐heptadecane and n‐heptadec‐5‐ene. The presence of hopanoids, low abundance of triacylglycerols and absence of sterols clearly show that the lipid biochemistry of this organism is more closely related to that of prokaryotes than to eukaryotes even though it contains chlorophyll b which is more typical of green algae. Implications of these data to chemotaxonomic studies of this unusual group of prokaryotes are discussed.

The effect of dynamic light regimes on Chlorella. II: Minimum quantum requirement and photosynthesis-irradiance parameters

Comparisons were made of photosynthesis in three light limited cyclostat cultures (LD = 8:16, dilution rate 0.7 d−1) of Chlorella pyrenoidosa, differing only in the dynamics of irradiance supply: as a constant rate, i.e. a block culture; as a sine function of the light period, i.e. a sinusoidal culture; as an 8 h sine function superimposed by an 1 h sine function, i.e. an oscillating culture. The sinusoidal culture had a constant minimum quantum requirement for oxygen evolution (QR) of 10.8 over the photoperiod. The OR of the oscillating culture increased from 24 to 37 during the photoperiod. From changes in α and Pmax we suggest that: (1) photosynthetic units (PSU) of the block and sinusoidal sulture increased in number; (2) increasingly fewer chlorophyll molecules participated in oxygenic photosynthesis with a decreasing turnover time of the PSUs during an oscillating photoperiod. Values of Ik decreased slightly in the block culture, increased slightly in the sinusoidal culture and showed a twofold increase in the oscillating culture. From the ratio of in situ oxygen production (qO2) and Pmax we infer a balanced equilibrium between photosystem activity and electron transport capacity for the block and sinusoidal culture. We hypothesize that the qO2 values of the oscillating culture underestimated true oxygen production rates due to a nonlinear response at peak light intensities. The results show that a dynamical photoperiod provoked significantly different photosynthetic responses, even though the overall growth rate was unaffected.

Status Report on Prochlorothrix hollandica, a Free-Living Prochlorophyte

Ever since the description of Prochloron sp. (Lewin and Withers, 1975; Lewin, 1976, 1977), the search for a nonsymbiotic species with analogous properties became obvious. Such an organism was discovered in the Loosdrecht Lakes (The Netherlands) (Burger-Wiersma et al., 1986), a shallow freshwater lake system that originated from peat excavation.

Carbohydrate dynamics and growth rate of natural phytoplankton populations

Diurnal changes in carbohydrate content of natural phytoplankton populations differed from those found for cyanobacteria grown in continuous cultures. The carbohydrate accumulation rate was not constant during the light period. Also in contrast to results obtained using continuous cultures the photosynthetic characteristics changed during the light period. A close correlation was observed between changes in carbohydrate accumulation rate and the efficiency of photosynthesis over 24 hours. Seasonal changes in carbohydrate consumption rate over the dark period were proportional to changes in growth rate.