Motile Microalgae Research Articles

A Spotlight on the Potential of Microscopic Motile Algae as Novel Sources for Modern Cosmetic Products

The recognition and use of algae in the very trend-driven cosmetic industry is progressively increasing. Up to now, the main focus was on large seaweeds and a limited number of microalgae. However, motile microalgae, flagellates, remain underscored in this aspect, although some of them are utilized commercially. Flagellates from different taxonomic groups occupy various habitats and contain bioactive high-value multifunctional compounds, some of which are novel. Moreover, they may simultaneously produce different substances, which together with the development of downstream processing technologies, makes them a promising source for modern biotechnology. The present review covers data on 411 strains, 251 species from 110 genera from 6 phyla, and is oriented generally towards less explored flagellates. It demonstrates their great potential as bearers of interesting novel compounds that can be beneficially applied in modern cosmetics. Safety aspects of both sources and products are also discussed. Considering the gaps in the knowledge, the necessity to expand the research on both well-known and yet unexplored microalgae is shown, encouraging the development of upstreaming processes, including phycoprospecting. Last but not least, this paper outlines the role of living culture collections and of using good taxonomic expertise before running the biochemical tests, cultivation, and bioengineering experiments.

Toxicities of three metal oxide nanoparticles to a marine microalga: Impacts on the motility and potential affecting mechanisms

With the fast growth of the production and application of engineered nanomaterials (ENMs), nanoparticles (NPs) that escape into the environment have drawn increasing attention due to their ecotoxicological impacts. Motile microalgae are a type of primary producer in most ecosystems; however, the impacts of NPs on the motility of microalgae have not been studied yet. So the toxic impacts of three common metal oxide NPs (nTiO2, nZnO, and nFe2O3) on swimming speed and locomotion mode of a marine microalgae, Platymonas subcordiformis, were investigated in this study. Our results demonstrated that both the velocity and linearity (LIN) of swimming were significantly decreased after the exposure of P. subcordiformis to the tested NPs. In addition, the obtained data indicate that NPs may suppress the motility of P. subcordiformis by constraining the energy available for swimming, as indicated by the significantly lower amounts of intracellular ATP and photosynthetic pigments and the lower activities of enzymes catalyzing glycolysis. Incubation of P. subcordiformis with the tested NPs generally resulted in the overproduction of reactive oxygen species (ROS), aggravation of lipid peroxidation, and induction of antioxidant enzyme activities, suggesting that imposing oxidative stress, which may impair the structural basis for swimming (i.e. the membrane of flagella), could be another reason for the observed motility suppression. Moreover, NP exposure led to significant reductions in the cell viability of P. subcordiformis, which may be due to the disruption of the energy supply (i.e., photosynthesis) and ROS-induced cellular damage. Our results indicate that waterborne NPs may pose a great threat to motile microalgae and subsequently to the health and stability of the marine ecosystem.

Light-switchable deposits from evaporating drops containing motile microalgae.

Deposits from evaporating drops have been shown to take a variety of shapes, depending on the physicochemical properties of both solute and solvent. Classically, the evaporation of drops of colloidal suspensions leads to the so-called coffee ring effect, caused by radially outward flows. Here we investigate deposits from evaporating drops containing living motile microalgae (Chlamydomonas reinhardtii), which are capable of resisting these flows. We show that utilizing their light-sensitivity allows control of the final pattern: adjusting the wavelength and incident angle of the light source enables forcing the formation, completely suppressing and even directing the spatial structure of algal coffee rings.

Is it feasible to cryopreserve motile microalgae with plant vitrification solutions?

Is it feasible to cryopreserve motile microalgae with plant vitrification solutions?

De novo transcriptome of the newly described phototrophic dinoflagellate Yihiella yeosuensis: comparison between vegetative cells and cysts

Dinoflagellates are often responsible for red tides or harmful algal blooms. Many dinoflagellates move quickly to capture prey cells, escape from predation, and conduct diurnal vertical migrations, but they form cysts (non-motile stage) when growth conditions are not favorable. To investigate differences in gene expression between vegetative cells and cysts of dinoflagellates, transcriptomes of the newly described dinoflagellate Yihiella yeosuensis, one of the fastest dinoflagellates, at the cysts and vegetative cells were de novo assembled. The gene expression profiles of Y. yeosuensis showed 5479 up-regulated and 4790 down-regulated significantly differentially expressed genes, when cells changed from the vegetative cells to cysts. In particular, ‘polyketide synthase’ and ‘cell-wall biogenesis’ genes, related to anti-predation, were highly up-regulated, whereas flagellum-related genes, related to motility, were generally down-regulated. Among the flagellum-related genes of Y. yeosuensis, the ‘central pair’ and ‘radial spoke’ genes, related to direct flagellar movement, were most down-regulated genes. When approximately a hundred flagellum-related genes of motile and non-motile microalgae and plants were analyzed, the number of the genes increased with increasing motility, and furthermore, there was a considerable difference in the presence of the ‘central pair’ and ‘radial spoke’ genes among the motile microalgae. Therefore, high down-regulation of the ‘central pair’ and ‘radial spoke’ genes when Y. yeosuensis cells change from the motile to non-motile stage is possibly related to the presence of these genes in microalgae and plants in their evolution. Conclusively, when Y. yeosuensis form cysts, motility might trade off with anti-predation.

Isolating Single Euglena gracilis Cells by Glass Microfluidics for Raman Analysis of Paramylon Biogenesis.

Time-course analysis of single cells is important to characterize heterogeneous activities of individual cells such as the metabolic response to their environment. Single-cell isolation is an essential step prior to time-course analysis of individual cells by collecting, culturing, and identifying multiple single-cell targets. Although single-cell isolation has been performed by various methods previously, a glass microfluidic device with semiclosed microchannels dramatically improved this process with its simple operation and easy transfer for time-course analysis of identified single cells. This study demonstrates isolating single cells of the highly motile microalgae, Euglena gracilis, by semiclosed microchannels with liquid flow only. The isolated single cells were identified in isolating channels and continuously cultured to track, by Raman microscopy, for the formation of subcellular granules composed of polysaccharide paramylon, a unique metabolite of E. gracilis, generated through photosynthesis. Through low-temperature glass bonding, a thin glass interface was incorporated to the microfluidic device. Thus, the device could perform the direct measurements of cultured single cells at high magnification by Raman microscopy with low background noise. In this study, the first demonstration of sequential monitoring of paramylon biogenesis in a single identified E. gracilis cell is shown.

Helical and oscillatory microswimmer motility statistics from differential dynamic microscopy

The experimental characterisation of the swimming statistics of populations of micro-organisms or artificially propelled particles is essential for understanding the physics of active systems and their exploitation. Here, we construct a theoretical framework to extract information on the three-dimensional motion of micro-swimmers from the intermediate scattering function (ISF) obtained from differential dynamic microscopy (DDM). We derive theoretical expressions for the ISF of helical and oscillatory breaststroke swimmers, and test the theoretical framework by applying it to video sequences generated from simulated swimmers with precisely-controlled dynamics. We then discuss how our theory can be applied to the experimental study of helical swimmers, such as active Janus colloids or suspensions of motile microalgae. In particular, we show how fitting DDM data to a simple, non-helical ISF model can be used to derive three-dimensional helical motility parameters, which can therefore be obtained without specialised 3D microscopy equipment. Finally, we discus how our results aid the study of active matter and describe applications of biological and ecological importance.

Toxicity of BDE-47, BDE-99 and BDE-153 on swimming behavior of the unicellular marine microalgae Platymonas subcordiformis and implications for seawater quality assessment

Polybrominated diphenyl ethers (PBDEs), a class of brominated flame retardants, have been extensively applied and eventually leached into the surrounding environment. Marine microalgae are not only the dominant primary producers of marine ecosystem, but also food source for aquaculture. PBDEs have been found to remarkably inhibit growth, photosynthesis and metabolism of marine microalgae. However, whether they also affect swimming behavior of marine motile microalgae remains unknown. We chose BDE-47, BDE-99 and BDE-153 as model PBDEs, and the unicellular marine green flagellate, Platymonas subcordiformis, as test organism to figure out this issue. After two-hour exposure, motile cells proportion (MOT), swimming velocity (VCL, VAP and VSL), and swimming pattern (LIN and STR) of P. subcordiformis were measured via computer assisted cell movement tracking. Results suggest that the three PBDEs not only reduced motile cells proportion and swimming velocity, but also altered swimming pattern. BDE-47 was more toxic than BDE-99, followed by BDE-153, indicating their toxicity decreased as bromination degree increases. Swimming ability of P. subcordiformis was even completely arrested when BDE-47 and BDE-99 at 32 μg/L. The impairment of swimming ability by PBDEs might thereby hinder growth and survival of marine microalgae, and subsequently threaten marine ecosystem and aquaculture industry. More importantly, this study implies that marine microalgae swimming behavior test is more efficiency and sensitive than traditional marine microalgal bioassays, like growth and photosynthesis tests. We suggest that although future work is needed, swimming behavior analysis of P. subcordiformis with MOT, VCL and VAP as endpoints can be developed as a low-cost, convenient, fast, reliable and sensitive method for seawater quality assessment.

Probing the metabolic heterogeneity of live Euglena gracilis with stimulated Raman scattering microscopy.

Understanding metabolism in live microalgae is crucial for efficient biomaterial engineering, but conventional methods fail to evaluate heterogeneous populations of motile microalgae due to the labelling requirements and limited imaging speeds. Here, we demonstrate label-free video-rate metabolite imaging of live Euglena gracilis and statistical analysis of intracellular metabolite distributions under different culture conditions. Our approach provides further insights into understanding microalgal heterogeneity, optimizing culture methods and screening mutant microalgae.

Comparison of the intrinsic disorder propensities of the RuBisCO activase enzyme from the motile and non-motile oceanic green microalgae.

Green oceanic microalgae are efficient converters of solar energy into the biomass via the photosynthesis process, with the first step of carbon fixation in the photosynthesis being controlled by the enzyme ribulose-1, 5-bisphosphate carboxylase/oxygenase (RuBisCO), which is a large proteinaceous machine composed of large (L, 52kDa) and small (S, 12kDa) subunits arranged as a L8S8 hexadecamer that catalyzes the formation of 2 phosphoglyceric acid molecules from one ribulose 1,5-bisphosphate (RuBP) molecule and one of carbon dioxide (CO2) and that is considered as the most abundant protein on Earth. The catalytic efficiency of this protein is controlled by the RuBisCO activase (RCA) that interacts with RuBisCO and promotes the CO2 entrance to the active site of RuBisCO by removing RuBP. One of the peculiar features of RCA is the presence of functional disordered tails that might play a role in RCA-RuBisCO interaction. Based on their ability to move, microalgae are grouped into 2 major class, motile and non-motile. Motile microalgae have an obvious advantage over their non-motile counterparts because of their ability to actively migrate within the water column to find the most optimal environmental conditions. We hypothesizes that the RCA could be functionally different in the non-motile and motile microalgae. To check this hypothesis, we conducted a comparative computational analysis of the RCAs from the representatives of the non-motile (Ostreococcus tauri) and motile (Tetraselmis sp. GSL018) green oceanic microalgae.

Toxic Effect Monitoring by Analyzing Swimming Motions of Microbial Cells Confined in Microfluidic Chip with Micro-Trench Flow Injection

We improved our previous micro-device containing motile micro-algae (Euglena gracilis) cells for toxicity monitoring, by introducing micro-trenches between a micro-aquarium and two surrounding channels. Target test solution was introduced from the bypass channel to the micro-aquarium through micro-trenches, with a pulse injection and continuous diffusion. Although the chemical gradient formed in the micro-aquarium was not permanently sustainable but only temporal for a couple of 10min, the device was simple, easy-to-use, and cost-effective to evaluate the toxicity of the test solution. The cells showed their chemotaxis to the temporal chemical gradients, resulting in the deviated distribution of the cells in the micro-aquarium, whereas metabolic disturbing effects of toxic substances induced the unusual motion of the cells.

Photoacclimation state determines the photobehaviour of motile microalgae: The case of a benthic diatom

High productivity in intertidal microphytobenthic communities is achieved despite exposure to extreme and dynamic conditions (e.g. light, salinity, temperature). As an adaptation to this hostile environment, most of the microalgae species inhabiting fine-sediment habitats are motile, being able to migrate vertically within the uppermost layers of the sediment and actively regulating their exposure to light. In this work we tested the hypothesis that the migratory photobehaviour of benthic diatoms, the dominant group in microphytobenthic assemblages, is conditioned by their photophysiological state (i.e. photoacclimation). Unialgal cultures of the motile diatom Navicula cf. recens were grown under contrasting light regimes (20 and 300μmolquantam−2s−1) to induce different photoacclimation states. The migratory response to light was characterized by studying the distribution of motile cells along a light gradient (photoaccumulation curve), using a custom-build photoaccumulation chamber. The photoaccumulation curves were constructed by measuring the accumulation of cells along the light gradient using a light transmission index. The variation of the photophysiological state of the cells along the light gradient was measured using Pulse Amplitude Modulation (PAM) fluorometry (maximum quantum yield and light response curves of the relative electron transport rate of photosystem II). The results showed clearly different photoaccumulation curves for low and high-light acclimated cells. Although in both cases, cells avoided extreme low and high light levels, maximum cell accumulation was reached at markedly different light intensities depending on growth light conditions and resulting photoacclimation state: 72 and 104μmolquantam−2s−1 for the low and high light-acclimated cells, respectively. Strong relationships were found between photophysiological parameters characterizing photoacclimation or susceptibility to photoinhibition and migratory light response, supporting that this diatom uses motility to select the optimal light exposure according to its photophysiological preferences.

Microalga propels along vorticity direction in a shear flow

Using high-speed digital holographic microscopy and microfluidics, we discover that, when encountering fluid flow shear above a threshold, unicellular green alga Dunaliella primolecta migrates unambiguously in the cross-stream direction that is normal to the plane of shear and coincides with the local fluid flow vorticity. The flow shear drives motile microalgae to collectively migrate in a thin two-dimensional horizontal plane and consequently alters the spatial distribution of microalgal cells within a given suspension. This shear-induced algal migration differs substantially from periodic rotational motion of passive ellipsoids, known as Jeffery orbits, as well as gyrotaxis by bottom-heavy swimming microalgae in a shear flow due to the subtle interplay between torques generated by gravity and viscous shear. Our findings could facilitate mechanistic solutions for modeling planktonic thin layers and sustainable cultivation of microalgae for human nutrition and bioenergy feedstock.

From channelrhodopsins to optogenetics

We did not expect that research on the molecular mechanism of algal phototaxis or archaeal light‐driven ion transport might interest readers of a medical journal when we conceived and performed our experiments a decade ago. On the other hand, it did not escape our attention that channelrhodopsin is helping an ever‐increasing number of researchers to address their specific questions. For example, the channelrhodopsin approach is used to study the molecular events during the induction of synaptic plasticity or to map long‐range connections from one side of the brain to the other, and to map the spatial location of inputs on the dendritic tree of individual neurons. The current applications have been summarized in a number of recent reviews (Fenno et al, 2011; Yizhar et al, 2011; Zhang et al, 2011). Here, we give personal insight into the history of the discovery of channelrhodopsin and a biophysical perspective on this remarkable class of proteins that has been the main topic of our research since the 1990s. The discovery of channelrhodopsin is based on two quite different research fields, studies on living algae and experiments on reconstituted microbial rhodopsins. A number of researchers have characterized the swimming behaviour and light responses of motile microalgae over at least 140 years (Fig 1A). Early studies on green microalgae root back to L.G. Treviranus (Treviranus, 1817) and behavioural responses were described by A. Famintzin from St. Petersburg University in 1878 (Famintzin, 1878). During helical swimming of the green alga Chlamydomonas , its orange eye signals to the flagella to alter the flagellar beating plane (Mast, 1916). Researchers at Stanford University implicated Mg2+ and Ca2+ in the behavioural responses and identified the role of Ca2+ influx in flagellar beat frequency changes (Halldal, 1957, Schmidt & Eckert, 1976). Then Oleg Sineshchekov …

Effective Viscosity of Microswimmer Suspensions

The measurement of a quantitative and macroscopic parameter to estimate the global motility of a large population of swimming biological cells is a challenge. Experiments on the rheology of active suspensions have been performed. Effective viscosity of sheared suspensions of live unicellular motile microalgae (Chlamydomonas Reinhardtii) is far greater than for suspensions containing the same volume fraction of dead cells. In addition, suspensions show shear thinning behavior. We relate these macroscopic measurements to the orientation of individual swimming cells under flow and discuss our results in the light of several existing models.

Effects of chlorophyll fluorescence on the estimation of microphytobenthos biomass using spectral reflectance indices

The communities of benthic microalgae that form dense biofilms at the surface of aquatic sediments, or microphytobenthos, are important primary producers in estuarine intertidal flats and shallow coastal waters. The microalgal biomass present in the photic zone of the sediment is a key parameter for ecological and photophysiological studies on microphytobenthos, and has been routinely estimated using hyperspectral reflectance indices based on the chlorophyll (Chl) a red absorption peak at 675 nm, usually the Normalised Difference Vegetation Index (NDVI). This study reports that red region-based biomass indices measured on microphytobenthos biofilms can be significantly affected by the enrichment of reflected light with solar-induced Chl fluorescence emitted by the microalgae. Chl fluorescence emission peaks at 683 nm, counterbalancing the decrease in reflectance centered at 675 nm, thus causing the underestimation of NDVI. The interference of Chl fluorescence was found to be easily identified by a conspicuous double-peak feature in the 670–700 nm region of the second-derivative reflectance spectra. The fluorescence-induced NDVI underestimation was shown to be most pronounced for high surface biomass levels and low incident solar irradiance. Particular aspects of microphytobenthos biofilms, such as the increase in surface Chl fluorescence due the contribution of emission by subsurface layers, and vertical migratory responses by motile microalgae to changes in ambient light, further complicate the effects on biomass estimation using NDVI-like indices. By comparing NDVI with a fluorescence-independent biomass index for a wide range of natural light conditions, it was found that Chl fluorescence interference may cause the underestimation of microalgal biomass to reach over 25%, with errors above 10% being expected for more than half of the measuring occasions. These results indicate that the use of NDVI may compromise the correct assessment of important aspects of microphytobenthos ecology, such as the characterisation of migratory behaviour or the determination of biomass-specific productivity rates, and call for the use of alternative biomass indices, not based on the Chl a red absorption peak.

Inhibiting diatom motility: a new tool for the study of the photophysiology of intertidal microphytobenthic biofilms

The study of the photophysiology of intertidal microphytobenthos biofilms has been hampered by the confounding effects of vertical migration by motile microalgae. The present work introduces a methodology to obtain undisturbed nonmigratory biofilms, based on the diatom motility inhibitor latrunculin A (Lat A). Application of Lat A to intact sediments prevented light‐induced vertical migration while not affecting the biofilm photosynthetic activity or disrupting the photic zone microenvironment. The inhibition of microalgal migration maintained the surface microalgae biomass despite exposure to stimuli that induced large migratory responses in noninhibited samples, including supersaturating irradiances or darkness. The characterization of the photophysiological responses of undisturbed biofilms without the interference of changes in surface biomass was illustrated by addressing two questions that are not possible to study on migratory biofilms with the existing methods: (i) the construction of light‐response curves of steady‐state photosynthetic activity, commonly used to characterize the photoacclimation status of photoautotrophs, and (ii) the characterization of the induction and relaxation kinetics of nonphotochemical quenching of in vivo fluorescence, required for the study of photoprotective processes or photoinhibition.

Bioconvection in a stratified environment: Experiments and theory

Bioconvection is a fascinating phenomenon of fluid mechanics that is driven by the swimming motion of micro-organisms. Typically the velocity and spatial scale of the fluid motions are much larger than those associated with the swimming speed and size of an individual cell, resulting in rapid transport of cells and the formation of complex spatial patterns in cell concentration. Motile microalgae are ubiquitous in aquatic systems, and understanding how they are spatially distributed at a wide range of length and time scales is an important ecological task. In the natural environment, bioconvection is a little studied but potentially important mechanism influencing the vertical distribution, and therefore the growth and productivity, of motile microalgae at centimeter to meter scales. However, in order to make predictions about when and where bioconvection might occur, we need to understand how other physical factors, such as salinity stratification, will affect swimming behavior, fluid flow, and the resultant spatial distribution of cells. In this paper, we present laboratory experiments that demonstrate the importance of swimming in generating large scale, persistent spatial structure in stratified water. In the first experiment, cells in a weakly stratified fluid environment first aggregate at the surface, and then form a bioconvective plume that descends to the bottom of the tank over a distance of 20cm, equivalent to 104 cell body lengths. In the second experiment, addition of a low-salinity surface layer enables cells, initially well mixed due to bioconvection, to form a dense surface aggregation. Motivated by these experiments, we present a linear stability analysis for the onset of bioconvection in a stable linear salinity gradient. The concentration of cells is modeled by a continuous distribution and swimming is modeled as a constant upwards component combined with a diffusive component. We consider a deep chamber, where at equilibrium cells are concentrated in a thin boundary region. The ratio of chamber depth to boundary region depth is d⪢1. Using matched asymptotic analysis, we obtain the critical value of the cell Rayleigh number, Rcrit, for which the forcing due to a perturbation in cell concentration in the upper region drives flow. The effect of the salinity stratification depends on the salt Rayleigh number, Rs. If Rs1∕6=o(d), the salinity gradient suppresses the vertical extent of the perturbation to the flow and salinity to a region of nondimensional depth O(Rs−1∕6). The critical cell Rayleigh number is unaffected by the salinity gradient and is given at leading order by Rcrit=2d3δ, where δ is the ratio of horizontal to vertical cell self-diffusion. If Rs1∕6=O(d), the salinity gradient confines perturbations in the flow and salinity to the thin boundary region, and Rcrit is specified as an algebraic function of Rs. The experiments are then discussed in light of the derived theory.

Modelling the primary productivity of intertidal microphytobenthos:time scales of variability and effects of migratory rhythms

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 192:13-30 (2000) - doi:10.3354/meps192013 Modelling the primary productivity of intertidal microphytobenthos: time scales of variability and effects of migratory rhythms João Serôdio*, Fernando Catarino Instituto de Oceanografia and Departamento de Biologia Vegetal, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal *E-mail: joao.serodio@fc.ul.pt ABSTRACT: A simulation model based on the short-term variability of in situ irradiance and productive biomass, defined as the fraction of total biomass contributing to measurable production, was developed to describe the primary productivity of intertidal microphytobenthos in the Tagus estuary, Portugal. Hourly primary production was modelled based on the assumption that short-term variations in the community-level photosynthetic light response were caused by changes in productive biomass associated with the vertical migratory rhythms of motile microalgae. The hourly variability in productive biomass was quantified by non-destructively measuring the dark-level chlorophyll a fluorescence, Fo, emitted from undisturbed microphytobenthos samples. Fo was found to be a good predictor of community-level photosynthesis versus irradiance curve parameters α (initial slope) and Pm (maximum photosynthesis) under the range of conditions found in situ, which allowed for the estimation of hourly production rates from hourly time series of in situ observations of Fo and irradiance. By modelling the hourly and fortnightly variability in Fo, the model was used to calculate hourly production throughout the annual cycle, which resulted in an annual pattern characterised by fortnightly oscillations in daily production comparable in amplitude with those occurring at the seasonal time scale. A comparison of the variability in production on hourly (intraday), fortnightly (within spring-neap tidal cycles) and seasonal (month-to-month) time scales confirmed that microphytobenthic production is dominated by variability on sub-seasonal (hourly and fortnightly) time scales. Significant variability in hourly primary production rates was detected on hourly and fortnightly time scales but not among seasons. A sensitivity analysis made on the model showed that the occurrence of migratory rhythms may be expected to increase the variability in primary production both on hourly and on fortnightly time scales, and also to contribute to the high levels of primary productivity of intertidal microphytobenthos. The mean annual areal primary production was found to reach 156 g C m-2 yr-1. By considering the variation of production with tidal height, the model was used to calculate the annual production of the entire intertidal area of the Tagus estuary, which resulted in a total of 4265 t C yr-1. KEY WORDS: Microphytobenthos · Primary production · Modelling · Migratory rhythms · Chlorophyll a fluorescence Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 192. Publication date: January 31, 2000 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 2000 Inter-Research.

The spatial distribution of microalgae on Antarctic fellfield soils

The horizontal and vertical distributions of cyanobacteria and algae on soil polygons on Signy Island were investigated. Soil chlorophyll concentrations increased from the centre to the edge of the polygons. Similar distributions of the non-motile genera, such as Pseudanabaena and Nostoc, were observed, whereas the motile taxa, Phormidium and Pinnularia, were evenly distributed across the polygon. Phormidium autumnale was the most widespread taxon, and other Oscillatoriaceae were also important, although large differences in community composition between polygons were observed. Most of the algal biomass was concentrated near the surface of the soil, although chlorophyll degradation products were found to depths of up to 8 cm. Examination of the soil profile by fluorescence microscopy indicated that a large proportion of the microflora occurred in the zone 0–1 mm below the surface, and scanning electron microscopy confirmed that few algae occurred on the soil surface. It is suggested that this may be a desiccation-avoidance strategy. Vertical migration of the motile microalgae to the soil surface was not observed in the field, but could be induced in the laboratory in the presence of excess water, although no diel cycle to this movement was observed.