Distribution and Diversity of Cyanobacteria and Eukaryotic Algae in Qinghai–Tibetan Lakes

Cyanobacteria and eukaryotic algae are important primary producers in a variety of environments, yet their distribution and response to environmental change in saline lakes are poorly understood. In this study, the community structure of cyanobacteria and eukaryotic algae in the water and surface sediments of six lakes and one river on the Qinghai–Tibetan Plateau were investigated with the 23S rRNA gene pyrosequencing approach. Our results showed that salinity was the major factor controlling the algal community composition in these aquatic water bodies and the community structures of water and surface sediment samples grouped according to salinity. In subsaline–mesosaline lakes (salinity: 0.5–50 g L^?1), Cyanobacteria (Cyanobium, Synechococcus) were highly abundant, while in hypersaline lakes (salinity: >50 g L^?1) eukaryotic algae including Chlorophyta (Chlorella, Dunaliella), Bacillariophyta (Fistulifera), Streptophyta (Chara), and Dinophyceae (Kryptoperidinium foliaceum) were the major members of the community. The relative abundance ratio of cyanobacteria to eukaryotic algae was significantly correlated with salinity. The algae detected in Qinghai–Tibetan lakes exhibited a broader salinity range than previously known, which may be a result of a gradual adaptation to the slow evolution of these lakes. In addition, the algal community structure was similar between water and surface sediment of the same lake, suggesting that sediment algal community was derived from water column.     

Nitrifying bacterial growth inhibition in the presence of algae and cyanobacteria

Nitrifying bacteria, cyanobacteria, and algae are important microorganisms in open pond wastewater treatment systems. Nitrification involving the sequential oxidation of ammonia to nitrite and nitrate, mainly due to autotrophic nitrifying bacteria, is essential to biological nitrogen removal in wastewater and global nitrogen cycling. A continuous flow autotrophic bioreactor was initially designed for nitrifying bacterial growth only. In the presence of cyanobacteria and algae, we monitored both the microbial activity by measuring specific oxygen production rate (SOPR) for microalgae and cyanobacteria and specific oxygen uptake rate (SOUR) for nitrifying bacteria. The growth of cyanobacteria and algae inhibited the maximum nitrification rate by a factor of 4 although the ammonium nitrogen fed to the reactor was almost completely removed. Terminal restriction fragment length polymorphism (T‐RFLP) analysis indicated that the community structures of nitrifying bacteria remained unchanged, containing the dominant Nitrosospira, Nitrospira, and Nitrobacter species. PCR amplification coupled with cloning and sequencing analysis resulted in identifying Chlorella emersonii and an uncultured cyanobacterium as the dominant species in the autotrophic bioreactor. Notwithstanding their fast growth rate and their toxicity to nitrifiers, microalgae and cyanobacteria were more easily lost in effluent than nitrifying bacteria because of their poor settling characteristics. The microorganisms were able to grow together in the bioreactor with constant individual biomass fractions because of the uncoupled solids retention times for algae/cyanobacteria and nitrifiers. The results indicate that compared to conventional wastewater treatment systems, longer solids retention times (e.g., by a factor of 4) should be considered in phototrophic bioreactors for complete nitrification and nitrogen removal. Biotechnol. Bioeng. 2010;107: 1004–1011. © 2010 Wiley Periodicals, Inc.     

Trophic cascades in a temperate seagrass community

We assessed the relative importance of bottom–up and top–down processes in structuring an eelgrass community in Sweden, a system impacted both by eutrophication and overfishing. Using artificial seagrass as substrate, we manipulated nutrient levels and predator abundance in a full‐factorial cage‐experiment. The results revealed a seagrass community dominated by strong top–down processes controlling the aggregate biomass of mesograzers and macroalgae. In the absence of predators the large amphipod Gammarus locusta became very abundant resulting in a leaf community with low biomass of algae and smaller mobile fauna. One enclosed gobid fish predator reduced the abundance of adult G. locusta by >90%, causing a three to six times increase in the biomass of algae, smaller mesograzers and meiofauna. Numerous small predators in uncaged habitats reduced the biomass of G. locusta and other mesograzers by >95% in comparison to the fish treatment, further increasing the biomass of epiphytic algae and meiofauna. Although water column nutrient enrichment caused a temporal bloom of the filamentous macroalgae Ulva spp., no significant nutrient‐effects were found on the algal community at the end of the experiment. The only lasting nutrient‐effect was a significant increase in the biomass of G. locusta, but only in the absence of ambient predators. These results demonstrate that mesograzers can respond to enhanced food supply, increase their biomass and control the algal growth when predation rates are low. However, in the assessed system, high predation rates appear to make mesograzers functionally extinct, causing a community‐wide trophic cascade that promotes the growth of ephemeral algae. This top–down effect could penetrate down, despite a complex food‐web because the interaction strength in the community was strongly skewed towards two functionally dominant algal and grazer species that were vulnerable to consumption. These results indicate that overexploitation of gadoid fish may be linked to increased macroalgal blooms and loss of eelgrass in the area through a trophic cascade affecting the abundance of mesograzers.     

Development of filamentous green algae in the benthic algal community in a littoral sand-beach zone of Lake Biwa

Temporal changes of biomass and dominant species in benthic algal communities were investigated in a littoral sand-beach zone in the north basin of Lake Biwa from December 1999 to September 2000. Chlorophyll-a amounts of benthic algal communities per unit area of the sandy sediments rapidly increased from late April to June. Increases in biomass of the benthic algal communities are considered to result from the propagation of filamentous green algae Oedogonium sp. and Spirogyra sp. The cell numbers of filamentous green algae and chlorophyll-a amounts of benthic algal communities at depths of 30 and 50cm at a station protected by a breakwater in May were significantly higher than those of a station exposed directly to wave activity. Thus, the biomass accumulation of the benthic algal communities seems to be regulated strongly by wave disturbance. The development of filamentous green algae may contribute to the increase in biomass of the benthic algal community and to the changes in seasonal patterns of biomass in the sand-beach zone of Lake Biwa. We consider that the development of the filamentous green algal community in the littoral zone of Lake Biwa is the result of eutrophication.     

Impacts of forestry planting on primary production in upland lakes from north‐west Ireland

Planted forests are increasing in many upland regions worldwide, but knowledge about their potential effects on algal communities of catchment lakes is relatively unknown. Here, the effects of afforestation were investigated using palaeolimnology at six upland lake sites in the north‐west of Ireland subject to different extents of forest plantation cover (4–64% of catchment area). ²¹⁰Pb‐dated sediment cores were analysed for carotenoid pigments from algae, stable isotopes of bulk carbon (δ¹³C) and nitrogen (δ¹⁵N), and C/N ratios. In lakes with >50% of their catchment area covered by plantations, there were two‐ to sixfold increases in pigments from cryptophytes (alloxanthin) and significant but lower increases (39–116%) in those from colonial cyanobacteria (canthaxanthin), but no response from biomarkers of total algal abundance (β‐carotene). In contrast, lakes in catchments with <20% afforestation exhibited no consistent response to forestry practices, although all lakes exhibited fluctuations in pigments and geochemical variables due to peat cutting and upland grazing prior to forest plantation. Taken together, patterns suggest that increases in cyanobacteria and cryptophyte abundance reflect a combination of mineral and nutrient enrichment associated with forest fertilization and organic matter influx which may have facilitated growth of mixotrophic taxa. This study demonstrates that planted forests can alter the abundance and community structure of algae in upland humic lakes of Ireland and Northern Ireland, despite long histories of prior catchment disturbance.     

STREAM PERIPHYTON PHOTOACCLIMATION RESPONSE IN FIELD CONDITIONS: EFFECT OF COMMUNITY DEVELOPMENT AND SEASONAL CHANGES1

The photochemical behavior of intact stream periphyton communities in France was evaluated in response to the time course of natural light. Intact biofilms grown on glass substrata were collected at three development stages in July and November, and structural parameters of the biofilms were investigated (diatom density and taxonomy). At each season, physiological parameters based on pigment analysis (HPLC) and pulse‐amplitude‐modulated (PAM) chl fluorescence technique were estimated periodically during a day from dawn to zenith. Regardless of the community studied, the optimal quantum yield of PSII (F_v/F_m), the effective PSII efficiency (Φ_PSII), the nonphotochemical quenching (NPQ), and the relative electron transport rate (rETR) exhibited clear dynamic patterns over the morning. Moreover, microalgae responded to the light increase by developing the photoprotective xanthophyll cycle. The analysis of P‐I parameters and pigment profiles suggests that July communities were adapted to higher light environments in comparison with November ones, which could be partly explained by a shift in the taxonomic composition. Finally, differences between development stages were significant only in July. In particular, photoinhibition was less pronounced in mature assemblages, indicating that self‐shading (in relation to algal biomass) could have influenced photosynthesis in older communities.     

Herbivores control effects of algal species richness on community biomass and stability in a laboratory microcosm experiment

Hundreds of studies that have explored how biodiversity affects the productivity and stability of ecosystems have produced a consensus that communities composed of more species tend to have higher biomass that is more stable through time. However, the majority of this work stems from studies performed using highly simplified food webs, often composed of just primary producers competing for inorganic resources in the absence of trophic interactions. When studies have incorporated trophic interactions, diversity‐function relationships have been more variable, leaving open the question of how biodiversity affects the functioning of ecosystems with more trophic levels. Here we report the results of a laboratory experiment that used freshwater microcosms to test for effects of algal diversity (one or four species) on community biomass and temporal variability in the presence and absence of two different herbivore species (cladocerans Ceriodaphnia dubia and Daphnia pulex). When no herbivores were present, we found the classic pattern observed in hundreds of other studies – as species richness of algae increased, algal biomass increased, and the temporal variation in biomass decreased. This pattern was retained when one of the herbivores (C. dubia) was present. Ceriodaphnia dubia exhibited weak and non‐selective grazing on the focal algae, leaving the effect of diversity on biomass and variability essentially intact. In contrast, D. pulex exhibited strong and selective grazing in algal polycultures that qualitatively altered both diversity–function relationships. As algal richness increased, total algal biomass decreased and variation through time increased. These changes were coupled with larger and less variable populations of D. pulex. Our results show that herbivory leads to a richer array of diversity–function relationships than often observed in studies focused on just one trophic level, and suggests trophic interactions should be given more attention in work that seeks to determine how biodiversity impacts the functioning of ecosystems.     

Inverse relationship of epilithic algae and pelagic phosphorus in unproductive lakes: Roles of N2 fixers and light

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Top-down control of natural phyto- and bacterioplankton prey communities by Daphnia magna and by the natural zooplankton community of the hypertrophic Lake Blankaart

Biomanipulation, through the reduction of fish abundance resulting in an increase of large filter feeders and a stronger top-down control on algae, is commonly used as a lake restoration tool in eutrophic lakes. However, cyanobacteria, often found in eutrophic ponds, can influence the grazing capacity of filter feeding zooplankton. We performed grazing experiments in hypertrophic Lake Blankaart during two consecutive summers (1998, with and 1999, without cyanobacteria) to elucidate the influence of cyanobacteria on the grazing pressure of zooplankton communities. We compared the grazing pressure of the natural macrozooplankton community (mainly small to medium-sized cladocerans and copepods) with that of large Daphnia magna on the natural bacterioplankton and phytoplankton prey communities. Our results showed that in the absence of cyanobacteria, Daphnia magna grazing pressure on bacteria was higher compared to the grazing pressure of the natural zooplankton community. However, Daphnia grazing rates on phytoplankton were not significantly different compared to the grazing rates of the natural zooplankton community. When cyanobacteria were abundant, grazing pressure of Daphnia magnaseemed to be inhibited, and the grazing pressure on bacteria and phytoplankton was similar to that of the natural macrozooplankton community. Our results suggest that biomanipulation may not always result in a more effective top-down control of the algal biomass.     

Responses of algal communities to gradients in herbivore biomass and water quality in Marovo Lagoon, Solomon Islands

Settlement tiles were used to characterise and quantify coral reef associated algal communities along water quality and herbivory gradients from terrestrial influenced near shore sites to oceanic passage sites in Marovo Lagoon, the Solomon Islands. After 6 months, settlement tile communities from inshore reefs were dominated by high biomass algal turfs (filamentous algae and cyanobacteria) whereas tiles located on offshore reefs were characterised by a mixed low biomass community of calcareous crustose algae, fleshy crustose algae and bare tile. The exclusion of macrograzers, via caging of tiles, on the outer reef sites resulted in the development of an algal turf community similar to that observed on inshore reefs. Caging on the inshore reef tiles had a limited impact on community composition or biomass. Water quality and herbivorous fish biomass were quantified at each site to elucidate factors that might influence algal community structure across the lagoon. Herbivore biomass was the dominant driver of algal community structure. Algal biomass on the other hand was controlled by both herbivory and water quality (particularly dissolved nutrients). This study demonstrates that algal communities on settlement tiles are an indicator capable of integrating the impacts of water quality and herbivory over a small spatial scale (kilometres) and short temporal scale (months), where other environmental drivers (current, light, regional variability) are constant.     

Copepods act as a switch between alternative trophic cascades in marine pelagic food webs

A recent meta‐analysis indicates that trophic cascades (indirect effects of predators on plants via herbivores) are weak in marine plankton in striking contrast to freshwater plankton ( Shurin et al. 2002 , Ecol. Lett., 5, 785–791). Here we show that in a marine plankton community consisting of jellyfish, calanoid copepods and algae, jellyfish predation consistently reduced copepods but produced two distinct, opposite responses of algal biomass. Calanoid copepods act as a switch between alternative trophic cascades along food chains of different length and with counteracting effects on algal biomass. Copepods reduced large algae but simultaneously promoted small algae by feeding on ciliates. The net effect of jellyfish on total algal biomass was positive when large algae were initially abundant in the phytoplankton, negative when small algae were dominant, but zero when experiments were analysed in combination. In contrast to marine systems, major pathways of energy flow in Daphnia‐dominated freshwater systems are of similar chain length. Thus, differences in the length of alternative, parallel food chains may explain the apparent discrepancy in trophic cascade strength between freshwater and marine planktonic systems.     

Mechanisms of microalgae selection during the assembly of a planktonic community

We attempt to ascertain the selection mechanisms that affect algal species’ abilities to thrive in a given environment, and how the variability of the response is reflected in the community structure (total biomass, diversity) and also in community function (photosynthesis and respiration). For that, we formed algal communities, assembling eight species of freshwater cosmopolite algae with distinct morphologies (Cosmarium contractum, Cryptomonas ovata, Euglena gracilis, Limnothrix redekei, Monoraphidium contortum, Pediastrum tetras, Planktothrix agardhii and Scenedesmus acutus) and performed four treatments combining low and high nutrient concentrations (N and P) in the culture media and a presence or absence of herbivores (a mixture of Daphnia magna, Keratella cochlearis and Brachionus calicyflorus). Competition between pairs of algae was also studied, and the viability of the species as inocula after a senescence period. The presence of herbivores (predation) and nutrient concentration (competition) are the mechanisms affecting (individually or synergistically) microalgae assemblages, originating different alternative states from the same pool of species. However, the effect of these mechanisms may vary, depending on algal properties such as size, growth rate and viability as an inoculum. The presence of herbivores and oligotrophic conditions reduce the primary producer biomass but increase diversity due to relaxation of competition and increase the uncertainty of final states. The variations in the community structure directly reflect on community function, affecting primary production and respiration.     

Responses of benthic algae to nutrient enrichment in a shallow lake: Linking community production,biomass, and composition

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Impact of light quality on a native Louisiana Chlorella vulgaris/Leptolyngbya sp. co‐culture

Light effect on cultures of microalgae has been studied mainly on single species cultures. Cyanobacteria have photosynthetic pigments that can capture photons of wavelengths not available to chlorophylls. A native Louisiana microalgae (Chlorella vulgaris ) and cyanobacteria (Leptolyngbya sp.) co‐culture was used to study the effects of light quality (blue–467 nm, green–522 nm, red–640 nm and white–narrow peak at 450 nm and a broad range with a peak at 550 nm) at two irradiance levels (80 and 400 μmol m^?2 s^?1) on the growth, species composition, biomass productivity, lipid content and chlorophyll‐a production. The co‐culture shifted from a microalgae dominant culture to a cyanobacteria culture at 80 μmol m^?2 s^?1. The highest growth for the cyanobacteria was observed at 80 μmol μmol m^?2 s^?1 and for the microalgae at 400 μmol m^?2 s^?1. Red light at 400 μmol m^?2 s^?1 had the highest growth rate (0.41 d^?1), biomass (913 mg L^?1) and biomass productivity (95 mg L^?1 d^?1). Lipid content was similar between all light colors. Green light had the highest chlorophyll‐a content (1649 μg/L). These results can be used to control the species composition of mixed cultures while maintaining their productivity.     

Effects of sequential depositional basins on lake response to urban and agricultural pollution: a palaeoecological analysis of the Qu'Appelle Valley, Saskatchewan, Canada

1. Palaeolimnological analyses of fossil diatoms and pigments were conducted in four lakes of the Qu'Appelle Valley, Saskatchewan, Canada, to quantify the effect of upstream depositional basins on lake response to urban and agricultural human activities. Pasqua, Echo, Mission and Katepwa lakes exhibit similar modern limnological characteristics, lie sequentially downstream from urban point sources of growth‐limiting nitrogen (N), yet drain similarly large areas of farmland (38–40 × 10³ km²). 2. Analyses indicated that all lakes were naturally productive, contained eutrophic diatoms (i.e. Stephanodiscus niagarae, S. hantzchii, S. parvus and Aulacoseira granulata), and supported blooms of colonial (as myxoxanthophyll) and potentially toxic N‐fixing cyanobacteria (aphanizophyll), even prior to the onset of European settlement (ca. 1890) and urban development (ca. 1930). 3. The onset of agricultural practices ca. 1890 had only modest effects on algal communities in the Qu'Appelle lakes, with subtle increases in eutrophic diatom species (Pasqua, Mission and Katepwa lakes) and 25–50% increases in pigment‐inferred algal abundance (Echo, Mission and Katepwa lakes). 4. Despite naturally high production, total algal abundance (β‐carotene) in upstream Pasqua Lake increased by more than 350% after intense urbanization beginning ca. 1930, while eutrophic diatoms became more common and cyanobacteria populations increased ten‐fold. Principal components analysis (PCA) explained 64% of diatom variance, and identified three eras corresponding to baseline, pre‐agricultural communities (1776–1890), an era of high production (ca. 1925–1960) and recent variable community composition following tertiary treatment of urban sewage (ca. 1977–1990). 5. Analyses of three downstream lakes demonstrated that urban impacts following 1930 remained evident in fossil profiles of β‐carotene and myxoxanthophyll, but that large blooms of N‐fixing cyanobacteria were restricted to the past 25 years at downstream Mission and Katepwa lakes. Similarly, PCA showed that fossil diatom assemblages exhibited little directional variation until the 1970s. 6. Together, these analyses support the hypothesis that upstream lakes were effective at reducing the impacts of point‐source urban nutrients on downstream lakes. In contrast, diffuse agricultural activities had only limited impacts on water quality and these were less well ameliorated by upstream basins.     

Microalgal system for treatment of effluent from poultry litter anaerobic digestion

The potential of mixotrophic microalgae to utilize poultry litter anaerobic digester (AD) effluent (PLDE) as nutritional growth medium was evaluated. Three algal strains viz. Chlorella minutissima, Chlorella sorokiniana and Scenedesmus bijuga and their consortium showed significant biomass productivity in 6% (v/v) concentration of PLDE in deionized water. Multiple booster dosage of PLDE supported better growth relative to a single dose PLDE. The maximum biomass productivity of 76 mg L⁻¹ d⁻¹ was recorded. The biomass was rich in protein (39% w/w) and carbohydrates (22%) while lipids (<10%) were low, making it most suitable as an animal feed supplement. The mixotrophic algae showed sustainable growth against variations in PLDE composition in different AD batches, thus proving to be a suitable candidate for large scale wastewater treatment with concomitant production of renewable biomass feedstock for animal feed and bioenergy applications.     

Two coexisting tank bromeliads host distinct algal communities on a tropical inselberg

The tank bromeliads Aechmea aquilega (Salisb.) and Catopsis berteroniana (Schultes f.) coexist on a sun‐exposed Neotropical inselberg in French Guiana, where they permit conspicuous freshwater pools to form that differ in size, complexity and detritus content. We sampled the algal communities (both eukaryotic and cyanobacterial taxa, including colourless forms) inhabiting either A. aquilega (n = 31) or C. berteroniana (n = 30) and examined differences in community composition and biomass patterns in relation to several biotic and abiotic variables. Chlorella sp. and Bumilleriopsis sp. were the most common taxa and dominated the algal biomass in A. aquilega and C. berteroniana, respectively. Using a redundancy analysis, we found that water volume, habitat complexity and the density of phagotrophic protozoa and collector‐gatherer invertebrates were the main factors explaining the distribution of the algal taxa among the samples. Hierarchical clustering procedures based on abundance and presence/absence data clearly segregated the samples according to bromeliad species, revealing that the algal communities in the smaller bromeliad species were not a subset of the communities found in the larger bromeliad species. We conclude that, even though two coexisting tank bromeliad populations create adjacent aquatic habitats, each population hosts a distinct algal community. Hence, bromeliad diversity is thought to promote the local diversity of freshwater algae in the Neotropics.     

EFFECTS OF INCREASING UV‐B RADIATION DUE TO OZONE DEPLETION ON PHOTOSYNTHESIS OF ANTARCTIC CYANOBACTERIA

Ground level ultraviolet‐B (UV‐B; 290–320 nm) fluxes in Antarctica have been increasing due to stratospheric ozone depletion. Although mat‐forming cyanobacteria are major component of freshwater algal biomass in Antarctica, little is known about their response to increasing ultraviolet radiation (UVR). The present study evaluated the sensitivity to UVR of two strains of mat‐forming cyanobacteria with different cell size, Phormidium murrayi (6.0 x 3.2 μm) and Schizothrix calcicola (2.2 x 2.3 μm). Cyanobacterial photosynthesis was measured under different UV spectral quality and quantity achieved by polychromatic filters with different cutoff wavelengths and neutral density screens. The productivity and irradiance data were used to generate biological weighting functions (BWF) for the assessment of UV inhibition on photosynthesis. The kinetics of UV inhibition, as determined by PAM fluorometry, differed between the two species so that inhibition of P. murrayi and S. calcicola were modeled based on UV‐irradiance and cumulative exposure, respectively. After a one hour exposure, BWF's did not differ between the two isolates of cyanobacteria despite their differences in cell size. To evaluate the negative impact of increased UV‐B exposure due to ozone depletion on cyanobacteria, the BWF's were applied to two solar spectra obtained from McMurdo Station, one on a day when the ozone hole was prominent (O₃ = 170 Dobson units; DU = 10‐3 cm O₃), and the other on a day with high ozone concentration (O₃ = 328 DU). The decrease in ozone level would reduce productivity by 3–8%. Seasonal variation of UVR has a bigger impact on cyanobacterial productivity than ozone depletion.     

Dependency of Antarctic zooplankton species on ice algae‐produced carbon suggests a sea ice‐driven pelagic ecosystem during winter

How the abundant pelagic life of the Southern Ocean survives winter darkness, when the sea is covered by pack ice and phytoplankton production is nearly zero, is poorly understood. Ice‐associated (“sympagic”) microalgae could serve as a high‐quality carbon source during winter, but their significance in the food web is so far unquantified. To better understand the importance of ice algae‐produced carbon for the overwintering of Antarctic organisms, we investigated fatty acid (FA) and stable isotope compositions of 10 zooplankton species, and their potential sympagic and pelagic carbon sources. FA‐specific carbon stable isotope compositions were used in stable isotope mixing models to quantify the contribution of ice algae‐produced carbon (α_Ice) to the body carbon of each species. Mean α_Ice estimates ranged from 4% to 67%, with large variations between species and depending on the FA used for the modelling. Integrating the α_Ice estimates from all models, the sympagic amphipod Eusirus laticarpus was the most dependent on ice algal carbon (α_Ice: 54%–67%), and the salp Salpa thompsoni showed the least dependency on ice algal carbon (α_Ice: 8%–40%). Differences in α_Ice estimates between FAs associated with short‐term vs. long‐term lipid pools suggested an increasing importance of ice algal carbon for many species as the winter season progressed. In the abundant winter‐active copepod Calanus propinquus, mean α_Ice reached more than 50% in late winter. The trophic carbon flux from ice algae into this copepod was between 3 and 5 mg C m^?2 day^?1. This indicates that copepods and other ice‐dependent zooplankton species transfer significant amounts of carbon from ice algae into the pelagic system, where it fuels the food web, the biological carbon pump and elemental cycling. Understanding the role of ice algae‐produced carbon in these processes will be the key to predictions of the impact of future sea ice decline on Antarctic ecosystem functioning.     

Growth promoting and inhibiting effects of extracellular substances of soil microalgae and cyanobacteria on Escherichia coll and Micrococcus luteus

Different taxa of chlorophycean, trebouxiophycean and xanthophycean soil microalgae and of cyanobacteria have been tested for the release of substances that inhibit the growth of either Echerichia coli (Migula) Castellani et Chalmersor Micrococcus luteus (Schroeter) Cohn. Experiments suggest two types of antibacterial effects: one type is constitutive; that is, the antibacterial activity is always present in the algal culture medium, as is the case with the Chroococcus turgidus (medium that inhibits the growth of Escherichia coli). The other type is induced; that is, the antibacterial activity occurs only when algae are in contact with bacteria. This is the case when growth of Micrococcus luteus is inhibited in co‐culture with Chroococcus turgidus (Kützing) Nägeli or with Xanthonema debile (Vischer) Silva and when growth of Escherichia coll is inhibited in co‐culture with Tetracystis sp. As well as inhibition, promotion of bacterial growth was observed. This was probably an unspecific effect resulting from soluble organic and inorganic substances, such as carbohydrates, that are generally present in algal cultures.