Glycine betaine is the main organic osmotic solute in a stratified microbial community in a hypersaline evaporitic gypsum crust

We have examined the organic osmotic solutes content within the stratified microbial communities in an evaporitic gypsum crust found in an evaporation pond (~194 g/l total dissolved salts) of the salterns of the Israel Salt Company, Eilat. We extracted intracellular solutes from the upper three pigmented layers of the crust: a yellow-orange layer dominated by unicellular cyanobacteria, a green layer with filamentous cyanobacteria, and a layer colored red-purple by purple sulfur bacteria; dense communities of heterotrophic bacteria were present in all layers. The solutes were analyzed by Raman spectroscopy, ¹H and ¹³C nuclear magnetic resonance, and HPLC. All layers contained glycine betaine as the only detectable osmotic solute; ectoine and other solutes known to be produced by many halophilic and halotolerant prokaryotes were not found. In this first attempt to assess the osmotic solute content within complex natural communities of halophilic microorganisms, the predominant role of glycine betaine as an osmolyte was established. Most heterotrophic bacteria cannot produce glycine betaine but preferentially use it when it is supplied. Presence of glycine betaine produced by the photoautotrophic members of the community, therefore, may relieve the heterotrophs from the need to synthesize other compounds at a high-energy cost.     

BIOCHEMICAL COMPOSITION AND FATTY ACID CONTENT OF FILAMENTOUS NITROGEN-FIXING CYANOBACTERIA

The biochemical composition and fatty acid content of twelve strains of filamentous, heterocystous, nitrogen-fixing cyanobacteria have been determined. When grown under diazotrophic conditions, protein, carbohydrate, lipid, and nucleic acids comprised 37–52%, 16–38%, 8–13%, and 8–11% of the dry weight, respectively. The presence of a combined nitrogen source resulted in an increase in the protein content of the cells and a decrease in the levels of lipids and carbohydrates, although biomass productivity was not affected significantly. Biochemical composition also changed during culture growth, with the highest levels of proteins and lipids occurring as the culture entered stationary phase, whereas the highest levels of carbohydrate and nucleic acids were found during the exponential phase. Total fatty acid levels in the strains assayed ranged between 3 and 5.7% of the dry weight. With regard to fatty acid composition, all strains showed high levels of polyunsaturated fatty acids (PUFAs) and saturated fatty acids (SAFAs), with values of 24–45% and 31–52% of total fatty acids, respectively, whereas the levels of monounsaturated fatty acids (MUFAs) were in general lower (11– 32%). Palmitic acid (16:0) was the most prevalent SAFA, whereas palmitoleic (16:1n- 7) and oleic acid (18:1n-9) were the most abundant MUFAs in all the strains. Among PUFAs, γ-linolenic acid (GLA, 18:3n-6) was present at high levels (18% of total fatty acids) in Nostoc sp. (Chile) and at lower levels (3.6% of total fatty acids) in Anabaenopsis sp. The presence of GLA has not been previously reported in these genera of cyanobacteria. The rest of the strains exhibited high levels (12–35% of total fatty acids) of α-linolenic acid (ALA, 18:3n-3). Linoleic acid (18:2n-6) was also present at a substantial level in most of the strains. Eicosapentaenoic acid (EPA, 20:5n-3) was also detected in Nostoc sp. (Albufera). Some filamentous nitrogen-fixing cyanobacteria therefore represent potential sources of commercially interesting fatty acids.     

Lipid Fatty Acid Composition and Thermophilicity of Cyanobacteria

An analysis of lipid fatty acid composition in several unicellular and filamentous forms of mesophilic and thermophilic cyanobacteria was performed. At 47°C (the temperature of thermophilic cyanobacteria maintenance in the collection), the unicellular thermophilic Synechococcus strains were devoid of polyenoic acids as distinct from the mesophilic forms of this genus at the temperature of 20°C (the temperature of this cyanobacterial maintenance in the collection). In the thermophilic Synechococcus elongatusIPPAS B-267 strain, a decrease in temperature did not result in the occurrence of C18 polyenoic acids, but the quantitative relationship between the saturated and unsaturated fatty acids (S/U ratio) was decreased twofold. In contrast, the culturing of mesophilic strains at 25–32°C resulted in an increase in the S/U ratio due to an increase in the proportion of the 16:0 acid. In the Synechococcus IPPAS B-434 strain, this treatment resulted in a decrease in the relative content of monoenoic, mainly hexadecenoic, acids. The cyanobacterium Gloeobacter violaceus, which lacks thylakoids, and whose photosystems are formed in a cell membrane, contained polyenoic acids. The filamentous thermophilic cyanobacterium Phormidium laminosum, at the maintenance temperature of 47°C, did contain polyenoic acids, but their proportion was considerably lower than that in the filamentous mesophilic forms, such as Tolypothrix sp. and Spirulina platensis. A relative content of hexadecenoic acids in Ph. laminosum was higher than in the mesophilic forms. A possible role of hexadecenoic acids in the processes of adaptation of cyanobacteria to high temperatures is discussed. A relationship between the characteristics of fatty acid composition fixed by evolution and the changes caused by adaptation to a particular environment is considered.     

Phototrophic Biofilms on Ancient Mayan Buildings in Yucatan, Mexico

Buildings at the important archaeological sites of Uxmal and Kabah, Mexico, are being degraded by microbial biofilms. Phospholipid fatty acid (PLFA) and chlorophyll a analyses indicated that phototrophs were the major epilithic microorganisms and were more prevalent on interior walls than exterior walls. Culture and microscopical techniques showed that Xenococcus formed the major biomass on interior surfaces, but the stone-degrading genera Gloeocapsa and Synechocystis were also present in high numbers. Relatively few filamentous algae and cyanobacteria were detected. The fatty acid analysis also showed that complex biofilms colonize these buildings. Circular depressions observed by scanning electron microscopy (SEM) on stone and stucco surfaces beneath the biofilm corresponded in shape and size to coccoid cyanobacteria. SEM images also demonstrated the presence of calcareous deposits on some coccoid cells in the biofilm. Phototrophic biofilms may contribute to biodegradation by (1) providing nutrients that support growth of acid-producing fungi and bacteria and (2) active “boring” behavior, the solubilized calcium being reprecipitated as calcium carbonate. Received: 15 March 1999 / Accepted: 24 June 1999     

Fatty acids filamentous green algae

Fatty acid analyses of several filamentous green algae were conducted using gas-liquid chromatography. Two bryophytes were also examined. Qualitatively, the genera of algae studied were divided into two groups: (A) algae that have significant amounts of polyunsaturated C₂₀ fatty acids and (B) algae that lack or only have very small amounts of the C₂₀ acids. On the basis of fatty acid content, the algae of Group A more closely resemble the bryophytes than do the algae of Group B. Culture age was shown to cause quantitative but not qualitative variations in fatty acid content. It is evident from this study that extrapolation to land plants, from studies on the fatty acid content of the green algae, should include the filamentous forms.     

Microbial Biofilms on the Sandstone Monuments of the Angkor Wat Complex,Cambodia

Discoloring biofilms from Cambodian temples Angkor Wat, Preah Khan, and the Bayon and West Prasat in Angkor Thom contained a microbial community dominated by coccoid cyanobacteria. Molecular analysis identified Chroococcidiopsis as major colonizer, but low similarity values (<95%) suggested a similar genus or species not present in the databases. In only two of the six sites sampled were filamentous cyanobacteria, Microcoleus, Leptolyngbya, and Scytonema, found; the first two detected by sequencing of 16S rRNA gene library clones from samples of a moist green biofilm on internal walls in Preah Khan, where Lyngbya (possibly synonymous with Microcoleus) was seen by direct microscopy as major colonizer. Scytonema was detected also by microscopy on an internal wall in the Bayon. This suggests that filamentous cyanobacteria are more prevalent in internal (high moisture) areas. Heterotrophic bacteria were found in all samples. DNA sequencing of bands from DGGE gels identified Proteobacteria (Stenotrophomonas maltophilia and Methylobacterium radiotolerans) and Firmicutes (Bacillus sp., Bacillus niacini, Bacillus sporothermodurans, Lysinibacillus fusiformis, Paenibacillus sp., Paenibacillus panacisoli, and Paenibacillus zanthoxyli). Some of these bacteria produce organic acids, potentially degrading stone. Actinobacteria, mainly streptomycetes, were present in most samples; algae and fungi were rare. A dark-pigmented filamentous fungus was detected in internal and external Preah Khan samples, while the alga Trentepohlia was found only in samples taken from external, pink-stained stone at Preah Khan. Results show that these microbial biofilms are mature communities whose major constituents are resistant to dehydration and high levels of irradiation and can be involved in deterioration of sandstone. Such analyses are important prerequisites to the application of control strategies.     

Microbial communities and processes within a hypersaline gypsum crust in a saltern evaporation pond (Eilat,Israel)

Gypsum crusts containing multicolored, stratified microbial communities develop in the evaporation ponds of a commercial saltern in Eilat, Israel at salt concentrations between 190 and 240 g l⁻¹. The upper 0.5–2 cm of the crust is densely populated by orange-brown unicellular cyanobacteria. Below, a layer of green-colored filamentous cyanobacteria is found. Underneath, a bright purple layer of anoxygenic phototrophs is present, below which a reduced black layer is found. We have investigated the biological properties of this crust using a wide variety of techniques, and we here review the results of these interdisciplinary studies. The tests performed included microscopic examination of the biota, phylogenetic analyses based on 16S rRNA gene clone libraries and denaturing gradient gel electrophoresis, fatty acid analysis, light intensity and light quality measurements, microelectrode studies of oxygen profiles and oxygen evolution, determination of sulfate reduction using radioisotope methods, and measurement of methane evolution. The stable vertical stratification in the system enabled separate analyses of the different layers with a high spatial resolution. It was therefore possible to combine the different approaches and obtain information on the activities of the different types of oxygenic and anoxygenic phototrophs, dissimilatory sulfate reducers and methanogens in the different layers, as well as phylogenetic information on the nature of the microorganisms responsible for these processes. The gypsum crust thus becomes a paradigm for the study of a wide variety of microbial processes and their interrelationships in the presence of high salt concentrations. Guest Editors: J. John & B. Timms Salt Lake Research: Biodiversity and Conservation—Selected papers from the 9th Conference of the International Society for Salt Lake Research     

Seasonal distribution and fatty acid composition of littoral microalgae in the Yenisei River

We studied fatty acid (FA) composition of littoral microalgae in the fast-flowing oligotrophic river, the Yenisei, Siberia, monthly for 3 years. Seasonal dynamics of species composition had similar patterns in all the studied years. In springs, a pronounced dominance of filamentous green algae occurred, in summer and autumn diatoms were abundant, and in late autumn and winter epilithic biofilms consisted primarily of cyanobacteria and detritus. In general, FA composition of the algal periphytic community was dominated by 16:0, 16:1ω7, 20:5ω3, 14:0, and 18:3ω3 throughout the studied period. Several groups of FAs, which had peculiar seasonal dynamics, were differentiated by statistical analysis based on a method of correlation graphs. The seasonal changes in FA composition could be partly explained by the seasonal succession of species composition of the community. Besides, we found that populations of both diatom and green algae grown in summer at a higher water temperature were lower in polyunsaturated fatty acids than those in spring, at a lower temperature. Hence, we suppose that the regular seasonal dynamics of FA composition of the studied littoral microalgae was driven both by changes in species composition and by temperature adaptations of the algal populations. The highest content of essential polyunsaturated FAs, eicosapentaenoic and docosahexaenoic acids, in the spring “psychrophilic” populations of diatoms could make them of the higher nutritive value for zoobenthic primary consumers.     

Evaluation of extraction methods for recovery of fatty acids from Botryococcus braunii LB 572 and Synechocystis sp. PCC 6803

Microalgae are a very diverse group of organisms that consist in both prokaryotic and eukaryotic forms. Some species of microalgae can be induced to overproduce particular fatty acids through simple manipulations of the physical and chemical properties of the culture medium. In this paper, the effect of different extraction techniques on the recovery of fatty acids from the freeze-dried biomass from two lipid-producing microalgal strains: Botryococcus braunii LB 572 (green algae) and Synechocystis sp. PCC 6803 (cyanobacteria) was examined. Five procedures were used: after conversion of the lipid material into the corresponding fatty acid methyl esters (FAMEs) via suitable derivatization reactions (extraction-transesterification) and direct transesterification of biomass to produce FAMEs (without the initial extraction step) that used differential types of catalysts and processing conditions. This study has shown that procedure 3, a one step practical procedure for lipid extraction and in situ methyl ester derivation could be used successfully for the determination of the fatty acid compositions of microalgae and cyanobacteria.     

Screening of Red Algae Filaments As a Potential Alternative Source of Eicosapentaenoic Acid

Lipids were extracted by a supercritical fluid extraction method from 10 species of filamentous red algae obtained from culture collections and their fatty acid compositions were determined. The fatty acid profiles of the 10 species were similar. The major fatty acids were 16:0, 20:4ω6 and 20:5ω3 (eicosapentaenoic acid, EPA), which amounted to over 70% of the total fatty acids. The highest EPA content (29.8 mg/L), as a percentage of total fatty acids, was produced by Liagora boergesenii filaments, which has good potential for EPA mass production in pilot plants.     

Fatty acid activation and utilization by Alistipes finegoldii,a representative Bacteroidetes resident of the human gut microbiome

Members of the Bacteroidetes phylum, represented by Alistipes finegoldii, are prominent anerobic, Gram-negative inhabitants of the gut microbiome. The lipid biosynthetic pathways were analyzed using bioinformatic analyses, lipidomics, metabolic labeling and biochemistry to characterize exogenous fatty acid metabolism. A. finegoldii only produced the saturated fatty acids. The most abundant lipids were phosphatidylethanolamine (PE) and sulfonolipid (SL). Neither phosphatidylglycerol nor cardiolipin are present. PE synthesis is initiated by the PlsX/PlsY/PlsC pathway, whereas the SL pathway is related to sphingolipid biosynthesis. A. finegoldii incorporated medium-chain fatty acids (≤14 carbons) into PE and SL after their elongation, whereas long-chain fatty acids (≥16 carbons) were not elongated. Fatty acids >16 carbons were primarily incorporated into the 2-position of phosphatidylethanolamine at the PlsC step, the only biosynthetic enzyme that utilizes long-chain acyl-ACP. The ability to assimilate a broad-spectrum of fatty acid chain lengths present in the gut environment is due to the expression of two acyl-acyl carrier protein (ACP) synthetases. Acyl-ACP synthetase 1 had a substrate preference for medium-chain fatty acids and synthetase 2 had a substrate preference for long-chain fatty acids. This unique combination of synthetases allows A. finegoldii to utilize both the medium- and long-chain fatty acid nutrients available in the gut environment to assemble its membrane lipids.     

Characterization of Cyanobacterial Hydrocarbon Composition and Distribution of Biosynthetic Pathways

Cyanobacteria possess the unique capacity to naturally produce hydrocarbons from fatty acids. Hydrocarbon compositions of thirty-two strains of cyanobacteria were characterized to reveal novel structural features and insights into hydrocarbon biosynthesis in cyanobacteria. This investigation revealed new double bond (2- and 3-heptadecene) and methyl group positions (3-, 4- and 5-methylheptadecane) for a variety of strains. Additionally, results from this study and literature reports indicate that hydrocarbon production is a universal phenomenon in cyanobacteria. All cyanobacteria possess the capacity to produce hydrocarbons from fatty acids yet not all accomplish this through the same metabolic pathway. One pathway comprises a two-step conversion of fatty acids first to fatty aldehydes and then alkanes that involves a fatty acyl ACP reductase (FAAR) and aldehyde deformylating oxygenase (ADO). The second involves a polyketide synthase (PKS) pathway that first elongates the acyl chain followed by decarboxylation to produce a terminal alkene (olefin synthase, OLS). Sixty-one strains possessing the FAAR/ADO pathway and twelve strains possessing the OLS pathway were newly identified through bioinformatic analyses. Strains possessing the OLS pathway formed a cohesive phylogenetic clade with the exception of three Moorea strains and Leptolyngbya sp. PCC 6406 which may have acquired the OLS pathway via horizontal gene transfer. Hydrocarbon pathways were identified in one-hundred-forty-two strains of cyanobacteria over a broad phylogenetic range and there were no instances where both the FAAR/ADO and the OLS pathways were found together in the same genome, suggesting an unknown selective pressure maintains one or the other pathway, but not both.     

An Endolithic Microbial Community in Dolomite Rock in Central Switzerland: Characterization by Reflection Spectroscopy, Pigment Analyses, Scanning Electron Microscopy, and Laser Scanning Microscopy

A community of endolithic microorganisms dominated by phototrophs was found as a distinct band a few millimeters below the surface of bare exposed dolomite rocks in the Piora Valley in the Alps. Using in situ reflectance spectroscopy, we detected chlorophyll a (Chl a), phycobilins, carotenoids, and an unknown type of bacteriochlorophyll-like pigment absorbing in vivo at about 720 nm. In cross sections, the data indicated a defined distribution of different groups of organisms perpendicular to the rock surface. High-performance liquid chromatography analyses of pigments extracted with organic solvents confirmed the presence of two types of bacteriochlorophylls besides chlorophylls and various carotenoids. Spherical organisms of varying sizes and small filaments were observed in situ with scanning electron microscopy and confocal laser scanning microscopy (one- and two-photon technique). The latter allowed visualization of the distribution of phototrophic microorganisms by the autofluorescence of their pigments within the rock. Coccoid cyanobacteria of various sizes predominated over filamentous ones. Application of fluorescence-labeled lectins demonstrated that most cyanobacteria were embedded in an exopolymeric matrix. Nucleic acid stains revealed a wide distribution of small heterotrophs. Some biological structures emitting a green autofluorescence remain to be identified.     

Cyanobacteria and eukaryotic algae in sports turf and amenity grasslands: a review

A review is presented on the occurrence and role of cyanobacteria and eukaryotic algae in sports turf, especially golf curses, and on the problems arising when these organisms become abundant. The literature depends largely on observations in only a few countries, mainly Canada, New Zealand, U.K. and U.S.A., but problem growths are probably widespread. The genera reported to be conspicuous at times include Nostoc, Phormidium, Coccomyxa, Cosmarium, Cylindrocystis, Klebsormidium, Mesotaenium and Zygogonium. Conspicuous surface growths are probably most often related to unsatisfactory drainage or irrigation practices, but other factors such as fertilizer treatment (especially excess ammonium sulphate) have been implicated. These surface growths sometimes incorporate copious mucilaginous ‘slime’, which can be a serious hazard by causing people to slip. U.K. observations suggest that this is especially likely under acidic conditions, where Coccomyxa, Cylindrocystis and Mesotaenium are among the probable culprits. Some literature indicates that cyanobacteria are also associated with a subsurface black layer, which can cause serious problems for turf management where sandy soils are subject to unsatisfactory drainage. It seems likely, however, that cyanobacteria are largely, if not entirely, absent from the subsurface layer, but may form a dark layer at the turf surface overlying the position of the subsurface black layer. The dark surface layer is probably due largely to narrow filamentous cyanobacteria, whose growth may enhance the poor drainage and thus reinforce the conditions favouring the black subsurface layer associated with anoxic conditions. The soil algal vegetation of sports turf may also be expected to exhibit beneficial effects known to occur in soils of other types of community, such as nitrogen fixation by some cyanobacteria and the binding of particles. However, little study on such effects has been directed specifically to sports turf.     

Influence of Linoleate Hydroperoxide Minor Isomers on GLC Analysis of Oleate Hydroperoxides

The distribution of the methylcitric acid cycle and the modified ^-oxidation pathway for propionate catabolism was surveyed in yeasts and filamentous fungi, mainly by comparing the activities of the key enzymes. All the six tested species of filamentous fungi belonging to five genera and 21 species of yeasts belonging to eleven genera were found to catabolize propionate through the methylcitric acid cycle, with the exception of Candida rugosa and one group of strains of C. catenulata, which catabolize propionate through the ß-oxidation pathway. From the observed diversity of propionate catabolism among closely related strains or species, it was assumed that different minor pathways evolved from universal metabolic pathways, such as the citric acid cycle and the ^-oxidation pathway for fatty acids, in later stages of an evolutionary history.     

Characterization of Microbial Mats from a Desert Wadi Ecosystem in the Sultanate of Oman

Desert wadis are widespread in the Arabian Peninsula and play a vital role in the ecology of the region; nevertheless, these ecosystems are among the least studied. Various types of microbial mats are predominant in wadis, but information on their bacterial diversity and spatial distribution is very scarce. We investigated bacterial diversity, pigments and lipid composition of ten mats located at the down-, mid- and upstream of a desert wadi in Oman. Direct microscopy revealed the existence of different unicellular and filamentous cyanobacteria, with the dominance of the heterocystous genera Calothrix and Scytonema. The majority of MiSeq 16S rRNA sequences (44-76%) were affiliated to Cyanobacteria and Proteobacteria. While Alphaproteobacteria was the most dominant proteobacterial class (10 to 48% of total sequences), Gamma- and Deltaproteobacteria were subdominant. Cluster analysis showed that the mats’ bacterial communities at the different locations along the wadi were different and shared less than 60% of their operational taxonomic units (OTUs). Chlorophyll a and scytonemin were the most predominant pigments in all mats. Different saturated, branched and mono- and poly-unsaturated fatty acids were detected in all mats, with C₁₆ and C₁₈ compounds as most dominant. The detected pigments and fatty acids indicate a major role of cyanobacteria in the wadi mats and the adaptation of microorganisms therein to the harsh wadi environment. Detection of diadinoxanthin and fucoxanthin confirmed the presence of diatoms. We conclude that microbial mats are important elements in wadi ecosystems and exist in a great variety of structure and community composition.     

Fatty acid synthesis inTrichophyton rubrum

Analysis of the fatty acid content ofT. rubrum showed that the organism is capable of synthesizing a variety of saturated and unsaturated long-chain fatty acids (Kostiw, Vicher &Lyon, 1966). The present study was undertaken to determine the mechanism of synthesis of these fatty acids. Experimental data point to the presence of two mechanisms of fatty acid synthesis inT. rubrum:de novo synthesis and chain elongation. The presence of both mechanisms is suggested by the nature of the enzyme preparation, by the cofactor requirements for either pathway, and by the reaction products.University of Illinois at the Medical Center, and Chicago Medical School, Chicago, Illinois. Presented in part at the International Society of Mycology Meeting, New Orleans, Louisiana, August 1967.     

Characterization of a Synechocystis sp. from Egypt with the potential of bioactive compounds production

A polyphasic approach was employed to describe a unicellular coccoid cyanobacterium isolated from Terraat El Khashab, Helwan, Egypt. The cells were characterised by their small diameter (1.9–2.2 μm) and lack of buoyancy. The cultures grew best at a temperature range of 20–40°C and moderate light intensity (20–50 μmol photon m⁻² s⁻¹). To verify its cyanobacterial nature, sequencing of 16S rRNA gene using cyanobacterial specific primers was performed followed by a phylogenetic analysis. The sequence best-matched Synechocystis sp. PCC6803 with 90% similarity. The phylogenetic analysis placed the isolate within a major clade containing different Synechocystis isolates. The fatty acid composition was rich in saturated fatty acids while polyunsaturated fatty acids were scarce. The phytochemical screening revealed the presence of flavenoids, alkaloids and saponins and absence of tannins. Vitamin C was also present in a considerable quantity. Some of the lipophilic fractions showed antimicrobial bioactivity against several pathogens. The pure bioactive compound from highest bioactive fraction was identified as oleic acid amide (M.wt.281) using chemical analyses including FT/IR, UV, proton H-NMR and GC-mass. The study highlights the importance of investigating the biotechnological potential of microorganisms inhabiting unusual niches.     

Low temporal dynamics of mycosporine‐like amino acids in benthic cyanobacteria from an alpine lake

1. Cyanobacteria are one of the oldest organisms on Earth and they originated at a time when damaging ultraviolet (UV) C radiation still reached the surface. Their long evolution led to several adaptations to avoid deleterious effects caused by exposure to solar UV radiation. Synthesis of sunscreen substances, such as mycosporine‐like amino acids (MAAs), allows them to photosynthesise with reduced risk of cell damage. The interplay of solar UV radiation and MAAs is well documented for cyanobacteria in the plankton realm, but little is known for those in the benthic realm, particularly of clear alpine lakes.
2. Here, we assessed the temporal dynamics of MAAs in the benthic algal community of one clear alpine lake dominated by cyanobacteria during the ice‐free season and along a depth gradient using state‐of‐the‐art analytical methods (high‐performance liquid chromatography, nuclear magnetic resonance, liquid chromatography–mass spectrometry). We differentiated between the epilithic cyanobacterial community and the overlying loosely attached filamentous cyanobacteria, as we expected they will have an important shielding/shading effect on the former. We hypothesised that in contrast to the case of phytoplankton, benthic cyanobacteria will show less pronounced temporal changes in MAAs concentration in response to changes in solar UV exposure.
3. Three UV‐absorbing substances were present in both types of communities, whereby all were unknown. The chemical structure of the dominant unknown substance (maximum absorption at 334 nm) resulted in the identification of a novel MAA that we named aplysiapalythine‐D for its similarity to the previously described aplysiapalythine‐C.
4. Chlorophyll‐a‐specific MAA concentrations for epilithic and filamentous cyanobacteria showed a significant decrease with depth, although only traces were found in the former community. The temporal dynamics in MAA concentrations of filamentous cyanobacteria showed no significant variations during the ice‐free season.
5. Our result on the low temporal MAA dynamics agrees with the reduced growth rates of benthic cyanobacteria reported for cold ecosystems. The permanent presence of this community, which is adapted to the high UV levels characteristic of clear alpine lakes, probably represents the most important primary producers of these ecosystems.

     

Screening for strains of the genusMortierella,showing elevated production of highly unsaturated fatty acids

The content of oligousaturated fatty acids was investigated in 13 strains of filamentous fungi of the genusMortierella. M. isabellina producing up to 500 mg/L of γ-linolenic acid andM. verticillata containing up to 300 mg/L of arachidonic acid were found to be perspective producers of these acids. InM. parvispora dihomo-γ-linolenic acid (100 mg/L) could be detected.