Rhena Schumann

The genus Laminaria sensu lato : recent insights and developments

This review about the genus Laminaria sensu lato summarizes the extensive literature that has been published since the overview of the genus given by Kain in 1979. The recent proposal to divide the genus into the two genera Laminaria and Saccharina is acknowledged, but the published data are discussed under a ‘sensu lato’ concept, introduced here. This includes all species which have been considered to be ‘Laminaria’ before the division of the genus. In detail, after an introduction the review covers recent insights into phylogeny and taxonomy, and discusses morphotypes, ecotypes, population genetics and demography. It describes growth and photosynthetic performance of sporophytes with special paragraphs on the regulation of sporogenesis, regulation by endogenous rhythms, nutrient metabolism, storage products, and salinity tolerance. The biology of microstages is discussed separately. The ecology of these kelps is described with a focus on stress defence against abiotic and biotic factors and the role of Laminaria as habitat, its trophic interactions and its competition is discussed. Finally, recent developments in aquaculture are summarized. In conclusion to each section, as a perspective and guide to future research, we draw attention to the remaining gaps in the knowledge about the genus and kelps in general.

Mycosporine-like amino acids and phylogenies in green algae : Prasiola and its relatives from the trebouxiophyceae (Chlorophyta)

A UV‐absorbing mycosporine‐like amino acid (324 nm‐MAA), so far only known from the green macroalgal genus Prasiola (Trebouxiophyceae), was also identified in other morphologically diverse green algae closely related to Prasiola spp. in 18S rDNA phylogenies. Using HPLC, a second UV‐absorbing compound was found only in Myrmecia incisa Reisigal among all studied strains. This substance showed an absorption maximum at 322 nm and hence was designated as putative 322 nm‐MAA. Preliminary UV‐exposure experiments indicated that all species containing one or the other MAA showed a strong accumulation of the respective compound, thus supporting their function as putative UV sunscreen. Both UV‐absorbing substances were only identified in the studied members of the Trebouxiophyceae but were absent in members of the Ulvophyceae and Chlorophyceae. When mapped on an 18S rDNA phylogeny, the distribution of 324 nm‐MAA was found to be scattered within the Trebouxiophyceae but was consistent with a distribution that follows phylogenetic patterns rather than ecological adaptations. The 324 nm‐MAA was also detected in two phylogenetically related species from freshwater as well as from subaerial habitats, Watanabea reniformis Hanagata et al. and isolate UR7/5, which were phylogenetically independent of Prasiola and its closer allies. MAAs were absent in another Trebouxiophyceae clade comprising lichen photobionts (Coccomyxa pringsheimii Jaag) as well as freshwater picoplanktonic algae (Choricystis minor (Skuja) Fott). The data presented suggest a chemotaxonomic value of the 324 nm‐MAA in green algal taxonomy. To address the paraphyly of the genus Myrmecia Printz as presently circumscribed, we propose the new combination Lobosphaera incisa.

Chloroidium, a common terrestrial coccoid green alga previously assigned to Chlorella (Trebouxiophyceae, Chlorophyta)

Ellipsoidal Chlorella-like species are very common in all kinds of aquatic and terrestrial habitats, and often identified as Chlorella saccharophila or C. ellipsoidea. However, the taxonomic status of these species remains unclear, because they are not related to the type species of the genus, Chlorella vulgaris. In this study, 23 strains isolated from different habitats, were investigated using a polyphasic approach, i.e. morphology and reproduction, ecophysiology, and combined SSU and ITS rDNA sequences. Phylogenetic analyses clearly demonstrated that these isolates formed a monophyletic lineage within the green algal class Trebouxiophyceae. All strains were characterized by ellipsoidal cell shape, unequal autospores during reproduction, and parietal chloroplasts, as well as by the biochemical capability to synthesize and accumulate the rather unusual polyol, ribitol. Although ribitol is a typical stress metabolite involved in osmotic acclimation, it can also be used as a chemotaxonomic marker. Comparative growth measurements under different temperature regimes indicated similar optimum growth temperatures and maximum growth rates in all studied Chlorella-like species. However, these were different from those of C. vulgaris. We therefore propose to transfer all Chlorella-like strains related to Chlorella saccharophila and C. ellipsoidea to the genus Chloroidium Nadson and to emend its diagnosis. We propose four new combinations: Chloroidium saccharophilum comb. nov., Chloroidium ellipsoideum comb. nov., Chloroidium angusto-ellipsoideum comb. nov. and Chloroidium engadinensis comb. nov. In contrast, Chlorella ellipsoidea sensu Punčochárová, which has other morphological and ecophysiological characters, should be assigned to the genus Pseudochlorella (P. pringsheimii comb. nov.).

New and fast method to quantify respiration rates of bacterial and plankton communities in freshwater ecosystems by using optical oxygen sensor spots.

ABSTRACT A new method of respiration rate measurement based on oxygen luminescence quenching in sensor spots was evaluated for the first time for aquatic bacterial communities. The commonly used Winkler and Clark electrode methods to quantify oxygen concentration both require long incubation times, and the latter additionally causes signal drift due to oxygen consumption at the cathode. The sensor spots proved to be advantageous over those methods in terms of precise and quick oxygen measurements in natural bacterial communities, guaranteeing a respiration rate estimate during a time interval short enough to neglect variations in organism composition, abundance, and activity. Furthermore, no signal drift occurs during measurements, and respiration rate measurements are reliable even at low temperatures and low oxygen consumption rates. Both a natural bacterioplankton sample and a bacterial isolate from a eutrophic river were evaluated in order to optimize the new method for aquatic microorganisms. A minimum abundance of 2.2 × 106 respiring cells ml−1 of a bacterial isolate was sufficient to obtain a distinct oxygen depletion signal within 20 min at 20°C with the new oxygen sensor spot method. Thus, a culture of a bacterial isolate from a eutrophic river (OW 144; 20 × 106 respiring bacteria ml−1) decreased the oxygen saturation about 8% within 20 min. The natural bacterioplankton sample respired 2.8% from initially 94% oxygen-saturated water in 30 min. During the growth season in 2005, the planktonic community of a eutrophic river consumed between 0.7 and 15.6 μmol O2 liter−1 h−1. The contribution of bacterial respiration to the total plankton community oxygen consumption varied seasonally between 11 and 100%.

Aeroterrestrial Microalgae Growing in Biofilms on Facades—Response to Temperature and Water Stress

The photosynthetic performance of a microalgal biofilm colonizing a building facade was investigated between February and July 2004, with an emphasis on changing water availability and air humidity. The fluorimetric measurements of the quantum efficiency (Fv/Fm) indicated diurnal activity patterns. At most sampling dates the algal biofilm photosynthesized particularly in the morning and substantially less in the afternoon. As long as liquid water was present, the microalgae exhibited at least some degree of photosynthesis. However, Fv/Fm values never exceeded 0.4, pointing to slight photoinhibition or damage of the cells. Dried cells without photosynthesis could recover within minutes after artificial moistening.Three microalgal strains were isolated from aeroterrestrial biofilms and established as unialgal cultures. Their photosynthesis and growth were characterized under different air humidities and temperatures. Photosynthesis and growth of strain ROS 55/3 (Stichococcus sp.) showed similar patterns with decreasing relative air humidity. Positive growth and optimum photosynthesis were recorded at 100% relative air humidity. At air humidities below 93%, both processes were strongly inhibited. All studied strains grew between 1 and 30°C with optimum rates at 20–23°C, indicating eurythermal features.The data indicate that liquid water or 100% air humidity are the prerequisite for optimum photosynthesis and growth of aeroterrestrial microalgae. However, when dried and consequently inactive, these microorganisms can recover quickly if water is suddenly available, e.g., after rain events. These physiological capabilities explain well the ecological success of aeroterrestrial microalgae in occupying many man-made substrata such as building facades and roof tiles in urban areas.

Quality analysis of commercial Chlorella products used as dietary supplement in human nutrition

Chlorella vulgaris is one of the best-studied phototrophic eukaryotes. From the 1950s on, C. vulgaris and some other algal species were cultivated in huge quantities to meet the growing demand for alternative protein sources. After drying, algal biomass can be merchandised as tablets, capsules, extract or powder with specific biochemical qualities. However, the products quality, e.g. the containing species, microbial contamination or content and quality of pigments varies enormously. In this study, commercial Chlorella products, unprocessed Chlorella powders and several production strains were investigated. Molecular analysis of the 18S rDNA confirmed either the existence of more than one species per product or only other green algae species in about half of the samples tested. Many of the examined samples contained critical amounts of bacterial contaminations. Furthermore, cyanobacteria were detected in some of the samples. The content of chlorophyll a varied greatly between the samples and pheophytin, a degradation product of chlorophyll, was detected in some samples in large concentrations. These data indicate that quality control of microalgal products is an important issue that should be addressed by the manufactures.

Prevention of biofilm growth on man-made surfaces: evaluation of antialgal activity of two biocides and photocatalytic nanoparticles.

As algal growth on man-made surfaces impacts their appearance, biocides and surfaces with self-cleaning properties are widely used in the building and paint industries. The objective of this study was to evaluate the antialgal activity of two biocides (triazine and isothiazoline) and photocatalytic nanoparticles of zinc oxide (20–60 nm). An aeroterrestrial green, microalgal strain of the genus Stichococcus was chosen as the test organism. By comparing a set of different structural and physiological performance parameters, lethal and also sublethal (chronic) effects were determined. Even though the herbicide triazine effectively inhibited growth (EC50 = 1.6 μmol l−1) and photosynthetic performance, structural properties (eg membrane integrity) were unaffected at the EC100 (250 μmol l−1), hence this herbicide did not kill the algal cells. In contrast, and due to their multiple modes of action, isothiazoline and the photocatalytic nanoparticles (the latter activated with low UV radiation) severely impacted all performance and structural parameters.

Quantification of algal biofilms colonising building materials: chlorophyll a measured by PAM-fluorometry as a biomass parameter

Abstract The aim of this study was to quantify algal colonisation on anthropogenic surfaces (viz. building facades and roof tiles) using chlorophyll a (chl a) as a specific biomarker. Chl a was estimated as the initial fluorescence F0 of ‘dark adapted’ algae using a pulse-modulated fluorometer (PAM-2000). Four isolates of aeroterrestrial green algae and one aquatic isolate were included in this study. The chl a concentration and F0 showed an exponential relationship in the tested range between 0 and 400 mg chl a m−2. The relationship was linear at chl a concentrations <20 mg m−2. Exponential and linear models are presented for the single isolates with large coefficients of determination (exponential: r2 > 0.94, linear: r2 > 0.92). The specific power of this fluorometric method is the detection of initial algal colonisation on surfaces in thin or young biofilms down to 3.5 mg chl a m−2, which corresponds to an abundances of the investigated isolates between 0.2 and 1.5 million cells cm−2.

Characterisation of Amyloid Nanostructures in the Natural Adhesive of Unicellular Subaerial Algae

The composition and nanoscale mechanical characteristics of the adhesive from two species of subaerial green unicellular microalgae (Chlorophyta), Coccomyxa sp. and Glaphyrella trebouxiodes, have been studied using Raman spectroscopy, chemical staining, and atomic force microscopy (AFM). Raman spectroscopy confirmed the adhesive proteins of both species to be predominantly in ß-sheet conformations and composed of a number of hydrophobic amino acid residues. Chemical staining with Congo red and thioflavin-T dyes further confirmed the presence of amyloid-like structures. Probing the adhesives with AFM revealed highly ordered and repetitive mechanical responses indicative of highly ordered structures within the adhesive. The repetitive nature of the sawtooth response is typical of a “sacrificial bond” and “hidden length” mechanism, and what we -propose is the result of mechanical manipulation of individual molecules within an intermolecular ß-sheet that makes up the generic amyloid structure. The mechanical data show how amyloid provides cohesive strength to the adhesives, and this intrinsic mechanical property of an amyloid-based adhesive explains the ecological success of attachment of these subaerial microalgae on various surfaces in urban environments. It is unknown to what extent amyloid fibrils occur in algal adhesives, but we postulate that the amyloid structure could provide a widespread mechanism for mechanical strength.

The Effect of Electrostatic Charge of Food Particles on Capture Efficiency by Oxyrrhis marina Dujardin (Dinoflagellate)

Laboratory experiments were carried out to investigate the effect of food quality, measured as surface charge of the particles, on capture efficiency and ingestion rate by the heterotrophic dinoflagellate Oxyrrhis marina. Fluorescent particles in two size classes of around 1 and 4 microm and of 7 different qualities were offered to the flagellate: carbohydrate and albumin particles, the algae Synechocystis spec. and Chlorella spec., carboxylated microspheres, silicate particles and bacteria. Rates of particle uptake showed significant differences depending on particle size and quality, and ranged from 0 to 4 particles cell(-1) h(-1). Ingestion rates were up to 4 times higher for 4 pm particles than for 1 microm particles, which indicates strong size-selective feeding. Our main result is that the surface charge or zeta potential, of artificial particles, i.e. carboxylated microspheres (> or = -107 mV) and silicate particles, strongly differ from more natural and natural food (< or = -17 mV). For both size classes Oxyrrhis had ingestion rates up to 4 times higher for particles with less negative charge, such as albumin particles or algae. Thus, the zeta potential of the model food should be considered in experimental design. Particles with a zeta potential similar to that of natural food, e.g. albumin, seem to be the preferred model food.