Michael Lakatos

Photosynthetic field capacity of cyanobacteria of a tropical inselberg of the Guiana Highlands

Photosynthesis of cyanobacteria is well characterized under laboratory conditions. We present a detailed study of photosynthetic capacity of cyanobacterial communities measured under natural conditions using chlorophyll fluorescence techniques. Cyanobacteria of extensive and diverse communities grow epi- and endolithically on the bare rock of inselbergs in the tropics where they are exposed to extreme and rapid fluctuations in irradiance, temperature and water availability. Extreme and rapidly changing environmental conditions impose various stresses on cyanobacteria and lead to small-scale niches of different communities along the furrows of an inselberg in French Guiana. These different cyanobacterial communities can easily be separated from each other by their species composition. Moreover, cyanobacteria of these zonal areas show significantly different rates of apparent quantum yield of photosystem II (PSII), are differently adapted to utilize early morning light energy and have different strategies to face rapid cycles of desiccation. These different physiological strategies have led to the development of different cyanobacterial communities in distinct zones which are determined by different resistance to dehydration, water transport and storage capacity. In spite of the extreme environmental conditions with very high solar radiation, predawn measurements of potential quantum yield of PS II showed that they are not photoinhibited. We describe the manifold photosynthetic strategies that have developed in cyanobacteria under these extreme and highly fluctuating natural conditions.

Carotenoid composition of terrestrial Cyanobacteria: response to natural light conditions in open rock habitats in Venezuela

Carotenoid contents of terrestrial cyanobacteria sampled from rock surfaces with different exposure to sunlight were studied in the Guyana-shield region of Venezuela. At the collecting locations of two table mountains Roraima-tepui (2700 m), Auyan-tepui (2000 m) and an inselberg near Puerto Ayacucho (80 m), the most frequent species were Stigonema ocellatum , Stigonema hormoides and Scytonema crassum , respectively. Usually, these species were associated with the unicellular cyanobacterium Gloeocapsa sanguinea . Their carotenoid and chlorophyll a contents were determined by high-performance liquid chromatography. In general, carotenoids consisted almost equally of myxolglycosides and of β-carotene derivatives, such as β-carotene, echinenone and canthaxanthin. On a chlorophyll a basis, myxolglycoside content increased in full exposure to solar irradiation. The relative proportions of the different β-carotene derivatives appeared to be even more strongly influenced by irradiance. Whereas their total amount was increased at full exposure, the content of β-carotene decreased and that of canthaxanthin increased. Maximal ratios of canthaxanthin/β-carotene of around 5 were observed in the most sun-exposed samples. We conclude that acclimation of the carotenoid content to irradiance, especially the adjustment of the ratio canthaxanthin/β-carotene, is a response found in many different terrestrial cyanobacterial species. However, when a natural population was artificially shaded for 6 days, short-term acclimation in pigment content was not detected. The results support a photoprotective function of canthaxanthin in terrestrial cyanobacteria under natural environmental conditions.

Lichens and Bryophytes: Habitats and Species

Poikilohydric desiccation tolerance enables lichens and bryophytes to survive long periods of water limitation and to recover quickly by rehydration. The evolutionary success of this strategy is reflected by the fact that cryptogams inhabit almost all terrestrial habitats from the tropics to cold and hot deserts. As ecosystem components, lichens and bryophytes may considerably impact the surrounding environment through frequent desiccation–rewetting cycles. What are the differences in mechanism and functioning to successfully compete with vascular plants in many micro-sites and habitats? This chapter reviews key issues of cryptogamic desiccation tolerance with particular emphasis on the following aspects: (1) Comparison of mechanisms and processes of water exchange. (2) Function and impacts of micro-scale fluxes to illustrate the effects of desiccation–rewetting cycles on the environment. (3) Global patterns of lichens and bryophytes as an indication for their ecological relevance.

Midday dew – an overlooked factor enhancing photosynthetic activity of corticolous epiphytes in a wet tropical rain forest

• Additional water supplied by dew formation is an important resource for microbes, plants and animals in precipitation-limited habitats, but has received little attention in tropical forests until now. • We evaluated the micro-environmental conditions of tree stem surfaces and their epiphytic organisms in a neotropical forest, and present evidence for a novel mechanism of diurnal dew formation on these surfaces until midday that has physiological implications for corticolous epiphytes such as lichens. • In the understorey of a lowland forest in French Guiana, heat storage of stems during the day and delayed radiative loss during the night decreased stem surface temperatures by 6°C in comparison to the dew-point temperature of ambient air. This measured phenomenon induced modelled totals of diurnal dew formation between 0.29 and 0.69 mm d⁻¹ on the surface of the bark and the lichens until early afternoon. • Crustose lichens substantially benefit from this dew formation, because it prolongs photosynthetic activity. This previously unrecognized mechanism of midday dew formation contributes to the water supply of most corticolous organisms, and may be a general feature in forest habitats world-wide.

Morphological, photosynthetic and water relations traits underpin the contrasting success of two tropical lichen groups at the interior and edge of forest fragments

Microclimatic edge effects and morpho-physiological characteristics are shaping lichen functional group distribution. Thus, lichen functional groups may be used as indicator for forest disturbance

Application of Biofilm Bioreactors in White Biotechnology

The production of valuable compounds in industrial biotechnology is commonly done by cultivation of suspended cells or use of (immobilized) enzymes rather than using microorganisms in an immobilized state. Within the field of wastewater as well as odor treatment the application of immobilized cells is a proven technique. The cells are entrapped in a matrix of extracellular polymeric compounds produced by themselves. The surface-associated agglomerate of encapsulated cells is termed biofilm. In comparison to common immobilization techniques, toxic effects of compounds used for cell entrapment may be neglected. Although the economic impact of biofilm processes used for the production of valuable compounds is negligible, many prospective approaches were examined in the laboratory and on a pilot scale. This review gives an overview of biofilm reactors applied to the production of valuable compounds. Moreover, the characteristics of the utilized materials are discussed with respect to support of surface-attached microbial growth.

Functional diversity of epiphytes in two tropical lowland rainforests, French Guiana: using bryophyte life-forms to detect areas of high biodiversity

Recent studies have described a new tropical lowland forest type in the Guianas, the tropical lowland cloud forest. It is characterized by an enriched epiphytic species diversity particularly for bryophytes compared to common lowland rainforest, and is facilitated by frequent early morning fog events in valley locations. While the increase in epiphytic species diversity in lowland cloud forests has been documented, uncertainties remain as to (1) how this small scale variation in water supply is shaping the functional diversity of epiphytic components in lowland forests, and (2) whether information on functional group composition of epiphytes might aid in discerning these cloud forests from the common lowland rainforest. We compare the distribution of functional groups of epiphytes across height zones in lowland cloud forest and lowland rain forest of French Guiana in terms of biomass, cover as well as the composition of bryophyte life-forms. Both forests differed in functional composition of epiphytes in the canopy, in particular in the mid and outer canopy, with the cloud forest having a higher biomass and cover of bryophytes and vascular epiphytes as well as a richer bryophyte life-form composition. Bryophyte life-forms characteristic for cloud forests such as tail, weft and pendants were almost lacking in the canopies of common rain forest whereas they were frequent in lowland cloud forests. We suggest that ground-based evaluation of bryophyte life-form composition is a straightforward approach for identifying lowland cloud forest areas for conservation, which represent biodiversity hotspots in tropical lowland forests.

δ18O characteristics of lichens and their effects on evaporative processes of the subjacent soil

The study presents first data on the δ18O performance of poikilohydrous lichen ground cover, and its potential impact on the isotopic composition of water fluxes arising from subjacent soil layers. As a model organism, the globally distributed lichen Cladina arbuscula was studied under laboratory conditions as well as in the field. During a desiccation experiment, δ18O of the lichens thallus water and of its respired CO2 became enriched by ∼7‰ and followed a similar enrichment pattern to that expected from homoiohydrous, vascular plants. However, the observed degree of enrichment was lower in comparison to vascular plants due to (i) the lichens inherent lower evaporative resistances; and (ii) a stronger effect of the more depleted surrounding water vapour. In lichens growing in their natural habitat, this specific pattern may show substantial variations depending on prevailing microclimatic conditions. Within a field study, thallus water δ18O of lichens principally proved to become more depleted when close to equilibration with the surroundings. It thereby strongly depended on the absorption of surrounding water vapour. Moreover, the results indicate that lichen mats substantially reduce evaporation rates arising from subjacent soil layers, and may alter the isotopic signal of vapour diffusing away from these layers into more depleted values.

Characterization of terrestrial cyanobacteria to increase process efficiency in low energy consuming production processes

Terrestrial cyanobacteria have seldom been used for biotechnological processes, even though they offer great potential for new pharmaceutical products or other value-added substances. Particularly cyanobacteria of xeric habitats are of biotechnological interest, because they tolerate high temperatures, are desiccation-tolerant and feature low water consumption. In addition, the cyanobacteria collected in deserts are able to produce more photoprotective agents than their counterparts from other habitats, because of their genetical preadaptation. In this study, carotenoid and chlorophyll content of two representative terrestrial cyanobacteria strains, i.e. Nostoc muscorum and Leptolyngbya spec. sampled in Columbia (USA) and Soebatsfontein (RSA), were studied after exposure of the strains to different light conditions and cultivation temperatures. A temperature raise from 17°C to 30°C led to an increase of 46% in chlorophyll a content as well as an increase of 39% in carotenoid content of Nostoc muscorum. An irradiation raise from 19 μmol m-2s-1 to 125 μmol m-2s-1 resulted in an increase of a 10 to 20 times higher chlorophyll content. Additional results from light-curves support the potential future use of terrestrial cyanobacteria within low energy biotechnological processes using a novel type of photobioreactor to reduce the downstream process costs and nutrients needed during the cultivation. Results indicate that especially light intensity optimization currently holds unused potential.

A new photobioreactor concept enabling the production of desiccation induced biotechnological products using terrestrial cyanobacteria

Cyanobacteria offer great potential for the production of biotechnological products for pharmaceutical applications. However, these organisms can only be cultivated efficiently using photobioreactors (PBR). Under submerged conditions though, terrestrial cyanobacteria mostly grow in a suboptimal way, which makes this cultivation-technique uneconomic and thus terrestrial cyanobacteria unattractive. Therefore, a novel emersed photobioreactor (ePBR) has been developed, which can provide the natural conditions for these organisms. Proof of concept as well as first efficiency tests are conducted using the terrestrial cyanobacteria Trichocoleus sociatus as a model organism. The initial maximum growth rate of T. sociatus (0.014±0.001h(-1)) in submerged systems could be increased by 35%. Furthermore, it is now possible to control desiccation-correlated product formation and related metabolic processes. This is shown for the production of extracellular polymeric substances (EPS). In this case the yield of 0.068±0.006g of EPS/g DW could be increased by more than seven times.