Sensitization of three strains of chlorococcal algae for UV- effects by 5- bromodeoxyuridine

The sensitization of chlorococcal algae by 5-BdU for the purpose of UV-light mutagenesis was studied. The results obtained were compared with our earlier findings on the sensitization of the same algal strains by 5-BU. No shielding effect of the 5-BdU molecules against UV-light was observed. Probably, the uptake of them from the liquid medium did not result in such excess as compared with the treatment by 5-BU, even if the cells were long enough (24 h) exposed to the concentration of 5-BdU. Likewise, neither stimulating nor inhibiting growth effects on the growing cell colonies were observed after treatment with 5-BdU. The sensitization of the algal cells for UV-light effects was effective in all the experiments. An increased damage of the algal cells by UV-light after sensitization was proved in all the parameters recorded. The frequencies of permanent changes of the cells or their colonies were also increased, but their spectrum did not change significantly. A suitable combination of the 5-BdU sensitization of the cells before their influencing by UV-light and the induction of their repair mechanisms by visible light may decrease the frequencies of the lethal or sublethal damage and increase the frequencies of the useful permanent changes in the characteristics of the chlorococcal algae. The results obtained are discussed from the viewpoint of the regulated mutation process in the breeding of algae.     

Herbivorous animals can mitigate unfavourable ratios of energy and material supplies by enhancing nutrient recycling

Recent evidence shows that high supply ratios of light and nutrients limit planktonic herbivore growth by lowering the nutritional quality of algae. Over longer time scales, however, grazers may ameliorate this effect by their impact on nutrient cycling. We examine this possibility using two species of the herbivorous zooplankter Daphnia and its algal prey under different light intensities and low phosphorus supply in laboratory microcosms. At high light, Daphnia biomass was limited for a substantial period because of low P content of algal cells. However, a gradual increase in Daphnia density eventually improved food quality through grazing and nutrient cycling and via a novel process involving positive density dependence. Competitive exclusion of one of the two Daphnia species occurred under low light but not under high light when algae were nutritionally unsuitable. Such stoichiometrically mediated interactions among herbivorous animals may represent important mechanisms that affect community structure and material flows in ecosystems.     

Competition between corals and algae on coral reefs: a review of evidence and mechanisms

Despite widespread acceptance that competition between scleractinian corals and benthic algae is important to the structure of coral reef communities, there is little direct experimental evidence that corals and algae do compete, and very little data on the processes and causality of their interactions. Most available evidence is observational or correlative, with intrinsic risks of confounded causality. This paper reviews and categorises the available evidence, concluding that competition between corals and algae probably is widespread on coral reefs, but also that the interaction varies considerably. Widespread replacement of corals by algae may often indicate coral mortality due to external disturbances, rather than competitive overgrowth, but may lead to competitive inhibition of coral recruitment, with consequences for reef recovery. We list eight specific processes by which corals and algae may affect each other, and suggest life history properties that will influence which of these interactions are possible. We propose a matrix for algal effects on corals, which lists the subset of processes possible for each combination of coral life form and algal functional group. This table provides a preliminary framework for improved understanding and interpretation of coral-algal interactions.     

Influence of light on the autospore number of some chlorococcal algae

The method of cultivation of algae on the surface of solid, medium under regulated conditions was used for studying the influence of light on the autospore number with three strains of chlorococcal algae:Scenedesmus quadricauda, Scenedesmus obliquus andChlorella kessleri. The results of these experiments show that not only light but the type of medium as well, exert a very important influence upon both nuclear and cell division and the whole course of the life cycle of algal cells. The number of autospores produced by single cells can be ascertained reliably on the surface of the solid medium. Owing to this fact the relations in cellular populations can be expressed with greater precision in comparison with the evaluation of cultures in liquid media.     

Comparison of N-ethyl-N-nitrosourea Effects in three strains of chlorococcal algae

Three strains of three different species of chlorococcal algae(Chlorella kesslerii Scenedesmus quadricauda andScenedesmus obliquus) were compared in their physiological and genetical responses to N-ethyl-N-nitrosourea (NEU). The mutagen was applied in the basic doses corresponding to their specific tolerance to it. Exponentially-graded doses derived from the basic ones acted for the same period of time and single basic doses acted at linearly-increased periods of time in parallel experiments. The influence of the mutagen on the cell cycle just in progress was characterized by the increase in the frequency of cell divisions which yielded a lower number of autospores. The conditions of the cells during the first three days after treatment were determined according to the average increase of their lag phase. The relative toxicity of the mutagen was expressed as the survival frequencies. The mutation effects were evaluated according to the frequency of permanent changes observed in the growing cell colonies : lethal, morphological and pigmentation. NEU was found to be a relatively suitable mutagen for the chlorococcal algae studied.     

Changes in photosynthetic rate and pigment content of blue-green algae in Lake Mendota.

Blue-green algal blooms were present in Lake Mendota (Dane County, Wis.) from June to November 1976. Concentrations of total algal biomass and of particular algal species were monitored and compared with the pigment contents (chlorophyll a and phycocyanin) and photosynthetic rate of the algal populations. The specific photosynthetic rate (micrograms of C fixed per microgram of chlorophyll a per hour) was a good measure of the physiological state of the algae because this quantity increased just before each population increase and decreased before algal densities diminished. Since the quantity of light in the epilimnion which was available for photosynthesis by algal cells decreased in summer when the high algal densities attenuated incoming radiation, we investigated the possibility that the organisms would utilize lower light intensities more efficiently by increasing their pigment contents. Although some evidence of enhanced utilization of low light levels was found in the period from July to October, this result was not due to increasing chlorophyll and phycocyanin contents. There was a decrease in the phycocyanin content of the algae during this period, perhaps related to the availability of inorganic nitrogen.     

Changes in photosynthetic rate and pigment content of blue-green algae in Lake Mendota.

Blue-green algal blooms were present in Lake Mendota (Dane County, Wis.) from June to November 1976. Concentrations of total algal biomass and of particular algal species were monitored and compared with the pigment contents (chlorophyll a and phycocyanin) and photosynthetic rate of the algal populations. The specific photosynthetic rate (micrograms of C fixed per microgram of chlorophyll a per hour) was a good measure of the physiological state of the algae because this quantity increased just before each population increase and decreased before algal densities diminished. Since the quantity of light in the epilimnion which was available for photosynthesis by algal cells decreased in summer when the high algal densities attenuated incoming radiation, we investigated the possibility that the organisms would utilize lower light intensities more efficiently by increasing their pigment contents. Although some evidence of enhanced utilization of low light levels was found in the period from July to October, this result was not due to increasing chlorophyll and phycocyanin contents. There was a decrease in the phycocyanin content of the algae during this period, perhaps related to the availability of inorganic nitrogen.     

Responses of cell populations of three chlorococcal algae to the action of streptomycin

Time doses of a single concentration of streptomycin and its concentration doses acting for the same time period in a liquid medium had different effects on three strains of chlorococcal algae. This concerned both the physiological responses and permanent changes in the characteristics of cell colonies growing from treated cells. Significant differences were recorded in: the number of autospores produced during the first division of the treated cells on the surface of a solid medium, the length of the lag phase, the growth rate of the diameter of cell colonies, and the survival of the treated cells. The permanent changes in the characteristics of the growing colonies were very different in the individual algal strains in quality and frequency. Physiological and the mutation effects were compared and discussed.     

Photosynthetic acclimation of Chlorella saccharophila to heat stress

Photosynthesis is one of the most important metabolic processes of algae; which is altered as a stress response. During mass cultivation of algae, temperature rise and high light are major factors that affect biomass productivity. High temperature affects photosystem II (PSII) complex irreversibly, damaging intermolecular interactions in it. However, the impact of high temperature on photosynthesis is highly variable among different algal species, depending on the prior acclimation to environmental conditions they were exposed to. The acclimation plays an important role in combating high temperature stress via regulation of photosynthetic responses. Chlorophyll a fluorescence is a highly sensitive, non‐destructive and reliable tool for such measurements of photosynthetic parameters, which provides information about algal photosynthetic performance under given conditions. To understand the effect of heat stress on the responses of high light acclimated alga Chlorella saccharophila, chlorophyll a fluorescence transients were measured after heat exposure at 40°C. Our study demonstrates that rise in temperature for short duration; during open field cultivation reversibly affects the efficiency of PSII in light acclimated alga C. saccharophila. The effects of heat stress on chlorophyll a fluorescence in this alga, grown under high light (max‐1600 μmol photons m^?2 s^?1) are presented here; they are used to infer changes in photosynthetic process during its exposure to heat, as well as their recovery after 72 h. We speculate that heat resistance may have been acquired due to prior exposures to high light.     

Variety of cell cycle patterns in the alga Scenedesmus quadricauda (Chlorophyta) as revealed by application of illumination regimes and inhibitors

In the course of the cell cycles of synchronous cultures of the chlorococcal alga Scenedesmus quadricauda, the following were monitored: total protein and RNA accumulation as a measure of growth processes, the timing of the commitment points at which the cells trigger the sequence of reproductive processes (DNA replication, nuclear and cellular division) and the course of the reproductive processes. The synchronous cultures were grown either under various lighting regimes, or in the temporary presence of specific inhibitors of either proteosynthesis (cycloheximide) or DNA replication (5-fluorodeoxyuridine). By adjusting the length of the light period, the cell cycle could be manipulated. Cell cycle patterns could be altered to give different numbers of sequences of reproductive processes. The extent of their mutual overlap could be influenced and the number of daughter cells produced could be altered. Schematic illustrations of various cell cycle patterns and comparisons with those of higher plants and other algal species are presented.     

The Effect of Puromycin and Cycloheximide on the Infection of Algae-Free Paramecium bursaria by Symbiotic Chlorellae1

It has been suggested that the infection of algae-free Paramecium bursaria by symbiotic algae involves an induction in the ciliate. Such a process suggests a need for the synthesis of specific proteins. Therefore, an attempt was made to determine the role of protein synthesis during the initial phases of host-symbiont interaction by examining the capacity of the ciliate to form a stable association with algae when the ciliate is exposed to puromycin (PURO) or cycloheximide (CYC) during the first 1–3 h of algal insestion. Cycloheximide (100 μg/ml) blocked algal but not ciliate growth and protein synthesis while PURO (250 μg/ml) appeared to inhibit these processes in both Puromycin significantly inhibited the infection when presented to the ciliate during the first hour of algal exposure and had little effect when added after that period. Inhibition of ciliate, as compared to the alga, protein synthesis appears to be significant in relationship to those processes leading to infection, as CYC when presented during the first hour of algae-ciliate exposure has no inhibitory effects. Experiments on algal sugar secretion and ciliate ingestion of algae indicated that neither process was significantly affected by these inhibitors. These results point to a need for host protein synthesis during the initial phase of ingestion of algae which appears to be important to establishment of the symbiotic association.     

深圳大鹏湾海域锥状斯氏藻赤潮期间细菌群落结构变化研究

目的:近年来,赤潮在我国的发生呈增加的趋势,并造成了极大的经济损失。过去研究赤潮发生的机理主要集中在理化因素的影响,而越来越多的证据表明仅凭借营养盐等环境因素并不能解释大部分赤潮现象,藻际微生物可能发挥着重要作用。本文跟踪观测了2010年7月深圳大鹏湾海域爆发的锥状斯氏藻赤潮生消过程中细菌群落丰度种类的变化,从微生物与赤潮藻相互作用的角度探讨了赤潮的生消过程,讨论了不同时期不同关键菌群的特殊作用,为解释赤潮爆发和消亡提供了新的视角,为赤潮的监控和防治新方法的建立奠定了理论基础。方法:本文按时间顺序共采集该赤潮9次样本,利用末端限制性酶切片段长度多态性分析(T-RFLP)等分子生物学方法,通过主成分分析、克隆文库的构建,研究了微生物群落的变化过程,并探讨了特定种属的微生物在赤潮发生、发展和消亡过程中的作用。结果:从浮游细菌丰度来看,随着锥状斯氏藻细胞数量的波动,浮游细菌总数也随之呈现相应的变化。从浮游细菌的种类来看,它们主要属于变形杆菌门(Proteobacteria)、拟杆菌门(Bacteroidetes)和厚壁菌门(Firmicutes)。从浮游细菌的动态变化过程来看,赤潮生消过程中,浮游细菌群落呈现出一定的演替现象,特别是在赤潮后期,群落主成分变化尤为显著。从关键菌群的作用来看,属于γ变形杆菌门的Alteromonas sp.一直占有较高的丰度,赤潮中后期受到菌群相互作用导致比例下降,而赤潮后期其他关键菌群的丰度的增高可能是导致赤潮消亡的重要原因。结论:本文利用T-RFLP这一DNA指纹技术分析微生物群落结构和多样性特征,通过研究赤潮生消过程中藻际浮游细菌群落的动态变化,发现随着赤潮的发展,浮游细菌群落发生着相应的变化。结果说明赤潮藻体丰度数量的改变影响着浮游细菌群落的组成。相对地,细菌群落的适应调整迅速造成赤潮藻体局部生长环境的改变,从而影响赤潮的发展过程。     

Analysis of the self-shading effect on algal vertical distribution in natural waters

Self-shading of light by algae growing in a column of water plays an important role in the dynamics of algal blooms. Thus without self-shading the algal concentration would increase more rapidly, making the nutrient limitation too strong. Apart from the practical importance of self-shading, its inherent nonlinearity in the growth dynamics leads to an interesting mathematical problem, which warrants detailed analytical investigation. Our mathematical model for the self-shading effect includes vertical diffusion, algal settling, gross production, and collective losses of algae. Steady-state solutions of the model equation are investigated in detail by the phase plane method, and their stability examined. Finally we discuss the vertical profile of algal concentration.Contribution No. 291 of the Marine Sciences Research Center     

赤潮过程中“藻-菌”关系研究进展

微生物对促进海洋物质循环,维持水生环境的生态平衡具有重要作用。在赤潮事件中,基于微生物(尤其是细菌)的多样性和重要性,它们与藻类之间的相互关系成为了研究的热点。过去20年里,人们从不同角度对"藻-菌"间的关系进行了探索,包括物理学过程、生物学过程、环境过程以及化学过程。就化学过程而言,它作为一种较早出现的技术,在以往的研究中带给人们许多认识藻菌关系的方法。随着学科的渗透,化学法有了拓展与延伸,为人们认识藻菌关系带来了新的契机。从化学生态学领域来梳理"藻-菌"关系中涉及的现象和行为,包括菌对藻的有益面、菌对藻的有害面、以及藻类应答细菌行为的化学途径;并从信号语言(群体感应、化感作用)的角度来阐释两者之间的互生或克生关系。通过文献综述的方式来解读藻菌关系的互作过程和机理,为认识赤潮的发生和防控方法提供借鉴。     

PHOTOINHIBITION IN RED ALGAL SPECIES WITH DIFFERENT CAROTENOID PROFILES1

Members of the Rhodophyta present different carotenoid profiles. In a majority of the species, lutein constitutes >50% of the total carotenoid content, while in other species, it is replaced by zeaxanthin or antheraxanthin. Given that carotenoids have specific roles in photoprotection, different carotenoid profiles of red algae species could be related to their capacity to cope with photoinhibitory stress. Therefore, in the present work, the sensitivity to light stress of red algal species with different carotenoid profiles was investigated. Photoinhibition of photosynthesis induced by high‐light stress and the subsequent recovery in dim‐light conditions was measured using maximal PSII quantum efficiency (F_v/F_m). The degree of decrease and recovery of F_v/F_m and their respective kinetics were related to the carotenoid profile of the species. Although no relationship between sensitivity to high‐light stress and the carotenoid profile was observed, there were clear carotenoid profile‐related differences in the decrease and recovery kinetics. In species with zeaxanthin or antheraxanthin as the major carotenoid, F_v/F_m reduction and recovery was principally associated with slowly activated and relaxed processes. In contrast, in species with lutein as the major carotenoid, rapidly activated processes appear to play a major role in the down‐regulation of photosynthesis during light‐stress conditions. In these species, the repair of D1 is also important during light‐stress conditions. This finding could imply differential expression of mechanisms involved in photoprotection in red algae that seems to be related to the carotenoid profile of the species.     

The effect of synchronizing dark period on populations ofScenedesmus quadricauda

Populations ofScenedesmus quadricauda grown in a continuous chemostatic regime and synchronized by light and dark intervals were exposed to continuous illumination. The effect of light on synthetic and reproduction processes during the time of the omitted dark period and in the subsequent cell cycle was studied. In general, the sequence of cellular processes and their mutual coupling remain the same as in the darkened population. Synthetic processes and photosynthetic activity are depressed during the period of protoplast fission also in the light. The synchronizing effect of the dark period in chlorococcal algae consists in reducing the developmental variability in the population. The developmental state of daughter cells at the end of the dark interval varies in the span of two (as a rule) or four (at maximum) genomic cycles, while at the end of the light period this variability comprises up to eight genomic states. The more advanced autospores start the next cycle with a greater lag.     

Flow cytometry as a strategy to study the endosymbiosis of algae in Paramecium bursaria

BACKGROUND: The stable symbiotic association between Paramecium bursaria and algae is of interest to study such mechanisms in biology as recognition, specificity, infection, and regulation. The combination of algae-free strains of P. bursaria, which have been recently established by treating their stocks of green paramecia with herbicide paraquat (Hosoya et al.: Zool Sci 12: 807-810, 1995), with the cloned symbiotic algae isolated from P. bursaria (Nishihara et al.: Protoplasma 203: 91-99, 1998), provides an excellent clue to gain fundamental understanding of these phenomena. METHODS: Flow cytometry and light microscopy have been employed to characterize the algal cells after they have been released from the paramecia by ultrasonic treatment. Algal optical properties such as light scattering and endogenous chlorophyll fluorescence intensity have been monitored for symbiotic and free-living strains, and strains at stages of interaction with a host. RESULTS: Neither algal morphology nor chlorophyll content has been found to be altered by sonication of green paramecia. This fact allows to interpret in adequate degree changes in the optical properties of symbiont that just has been released from the association with a host (decreased forward light scatter and chlorophyll fluorescence signals). Optical characterization of both symbiotic and free-living algal strains with respect to their ability to establish symbioses with P. bursaria showed that chlorophyll content per cell volume seems to be a valuable factor for predicting a favorable symbiotic relationship between P. bursaria and algae. CONCLUSIONS: Flow cytometry combined with algae-free paramecia and cloned symbiotic algae identifies algal populations that may be recognized by host cells for the establishment of symbioses.     

The effect of dose and time on the induction of genetic alterations insaccharomyces cerevisiae by aminoacridines in the presence and absence of visible light irradiation in comparison with the dose-effect-curves of mutagens with other type of action

Summary Aminoacridines induce frameshift mutations and are photodynamically active, depending on whether visible light is absent or present. Therefore, a test system which allows to compare quantitatively the genetic effects of aminoacridines irradiated or unirradiated by visible light ought to be susceptible to the different DNA alterations which can be induced by these substances. For this reason in most experiments mitotic gene conversion and only in some selected experiments reverse mutation was chosen as the indicator of genetic activity. In contrast to mutation systems mitotic gene conversion has never shown a response specific to only some types of mutagens. The three aminoacridine derivatives used-acridine orange (AO), proflavine (PF), and acridine yellow (AY)—were successful in the induction of convertants at two different loci. No locus-specificity could be observed. The time-dependent induction of convertants proceeds quickly but soon reaches—especially after treatment without light—a saturation point. The dose/effect-curve after treatment in the dark has a slope increasing with increasing concentration. Irradiation with visible light results in a dose/effect-curve consisting of three parts. At first the increase of convertants is nearly linear extending one (AY) to three (AO) orders of magnitude. After that a saturation effect begins at the point at which an effectiveness of the acridines in the dark is apparent. At high concentrations an induction of convertants can again be observed which is nearly the same as that after treatment in the dark. To determine whether the dose/effect-curves obtained for gene conversion refer to similar curves for gene mutations after treatment with AO at the same locus not only gene conversions but also reverse mutations were scored for. AO-treatment in the dark is ineffective in inducing reverse mutations. Irradiation with visible light results in a dose/effect-curve beeing parallel only in its first part to the dose/effect-curve obtained for gene conversion, while in its second part a mutation frequency decline can be observed. Comparing the dose/effect-curves of AO resulting from the induction of gene conversion and gene mutation, and taking into account that no mutants can be induced by AO-treatment in the dark, the increase in convertants at high acridine-concentrations can be explained as an addition of light-dependent and light-independent effects. That means, in mutation systems at low concentrations of aminoacridines irradiation with visible light should cause transitions, transversions and microlesions, at intermediate concentrations frameshift lesions should begin to appear, and at very high concentrations nearly exclusively frameshift lesions should occur. The dose/effect-curves of aminoacridines compared with those of other mutagens are very complex. The dose/effect-curves of the mutagens of other type of action tested are linear in a double logarithmic scale, and parallel for induced gene conversion and induced gene mutation. These results indicate that the gene conversion ability of a given compound depends on its mutagenic property. That means, many mutagens may exert specific genetic effects not directly but mainly in indirect ways by leading to DNA damage, a situation for repair synthesis resulting as well in mutations as recombinations.     

Changes in the condition of photosynthetic apparatus of a diatom alga <Emphasis Type="Italic">Thallassiosira weisflogii</Emphasis> during photoadaptation and photodamage

Two populations of a diatom alga Thallassiosira weisflogii were grown at photon flux densities (PFD) of 0.8 and 8 μmol/(m² s). For both diatom populations, the recovery of chlorophyll fluorescence parameters (F ₀, F _m, F _v/F _m, and NPQ) was monitored after nondestructive irradiation by visible light at PFD of 40 μmol/(m² s) and after high-intensity irradiation by visible light (1000–4000 μmol/(m² s)). The exposure of diatoms to PFD of 40 μmol/(m² s)—higher than PFD used for algal growth but still nondamaging to photosynthetic apparatus—induced nonphotochemical quenching (NPQ), which was stronger in algae grown at higher PFD (8 μmol/(m² s)) than in algae grown at low light. After irradiation with high-intensity light, the recovery of chlorophyll fluorescence parameters was more pronounced in algae grown at elevated PFD level. During short-term irradiation of diatoms with high-intensity visible light (1000 μmol/(m² s)), a stronger NPQ was observed in the culture adapted to high irradiance. After the treatment of algae with dithiothreitol (an inhibitor of carotenoid deepoxidase in the diadinoxanthin cycle) or NH₄Cl (an agent abolishing the proton gradient at thylakoid membranes), a short exposure of algae to PFD of 40 μmol/(m² s) induced hardly any nonphotochemical quenching. The results indicate the dominant contribution of xanthophyll cycle carotenoids to energy-dependent quenching.     

A review of the harvesting of micro-algae for biofuel production

Many researchers consider efficient harvesting is the major challenge of commercialising micro-algal biofuel. Although micro-algal biomass can be ‘energy rich’, the growth of algae in dilute suspension at around 0.02–0.05 % dry solids poses considerable challenges in achieving a viable energy balance in micro-algal biofuel process operations. Additional challenges of micro-algae harvesting come from the small size of micro-algal cells, the similarity of density of the algal cells to the growth medium, the negative surface charge on the algae and the algal growth rates which require frequent harvesting compared to terrestrial plants. Algae can be harvested by a number of methods; sedimentation, flocculation, flotation, centrifugation and filtration or a combination of any of these. This paper reviews the various methods of harvesting and dewatering micro-algae for the production of biofuel. There appears to be no one method or combination of harvesting methods suited to all micro-algae and harvesting method will have a considerable influence on the design and operation of both upstream and downstream processes in an overall micro-algal biofuel production process.