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PubMed1995

Factors Affecting Development of Peroxisomes and Glycolate Metabolism among Algae of Different Evolutionary Lines of the Prasinophyceae.

Leaf-type peroxisomes are not present in the primitive unicellular Prasinophycean line of algae but are present in the multicellular algae Mougeotia, Chara, and Nitella, which are in the one evolutionary line, Charophyceae, that led to higher plants. Processes related to glycolate metabolism that may have been modified or induced with the appearance of peroxisomes have been examined. The algal dissolved inorganic carbon-concentrating mechanism and alkalization of the medium during photosynthesis were not lost when peroxisomes appeared in the members of the Charophycean line of algae. Therefore, it is unlikely that lowering of the CO2 concentration in the environment was a major factor in the evolutionary appearance of peroxisomes. Multicellular Mougeotia, early members of the Charophycean line of algae, have peroxisomes, but they excrete excess glycolate into the medium. The cytosolic pyruvate reductase for D-lactate synthesis and the glycolate dehydrogenase activity almost disappeared when peroxisomal glycolate oxidase, which also oxidizes L-lactate, appeared. These biochemical changes do not indicate what caused the induction of leaf-type peroxisomes in this evolutionary line of algae. The oxygenase activity of ribulose-1,5-bisphosphate carboxylase/oxygenase and glycolate oxidase require about 200 to 400 [mu]M O2 for 0.5 Vmax. These high-O2-requiring steps in glycolate metabolism would have functioned faster with increasing atmospheric O2, which might have been the causative factor in the induction of peroxisomes.

Journal Article↗
PubMed1968

Comparative Studies on Plastoquinones. IV. Plastoquinones in Algae.

Plastoquinones A and C have been found in all classes of algae, including representatives of greens, yellow-greens, blue-greens, reds, browns and the flagellate, Euglena. Plastoquinone C from red and brown algae can be separated into 6 different types. An additional plastoquinone C has been found in Gigartina and Rhydomela. From chromatographic evidence this may be equivalent to plastoquinone C(o), a C type with a hydroxyl group on the first isoprene unit of the terpenoid sidechain of this substituted benzo-quinone. The ubiquinone, vitamin K and alpha-tocopherylquinone content of several algae is also reported. The presence of plastoquinone A in all green plants and many algae indicates that it may be a functional element in photosynthesis. Our study shows that plastoquinone C is more regularly present in algae than has been previously shown.

Journal Article↗
PubMed1970

Glycolate pathway in green algae.

By three criteria, the glycolate pathway of metabolism is present in unicellular green algae. Exogenous glycolate-1-(14)C was assimilated and metabolized to glycine-1-(14)C and serine-1-(14)C. During photosynthetic (14)CO(2) fixation the distributions of (14)C in glycolate and glycine were similar enough to suggest a product-precursor relationship. Five enzymes associated with the glycolate pathway were present in algae grown on air. These were P-glycolate phosphatase, glycolate dehydrogenase (glycolate:dichloroindophenol oxidoreductase), l-glutamate:glyoxylate aminotransferase, serine hydroxymethylase, and glycerate dehydrogenase. Properties of glycerate dehydrogenase and the aminotransferase were similar to those from leaf peroxisomes. The specific activity of glycolate dehydrogenase and serine hydroxymethylase in algae was 1/5 to 1/10 that of the other enzymes, and both these enzymes appear ratelimiting for the glycolate pathway.Labeling patterns for products of the glycolate pathway during (14)CO(2) fixation are not the same as those obtained with higher plants. In higher plants glycolate, glycine, and serine are uniformly labeled at shortest time periods. In algae, serine was predominately carboxyl-labeled, similarly to 3-phosphoglycerate. This result, plus the lower specific activity of serine hydroxymethylase, indicates that the glycine-serine interconversin in algae is slower than in plants. Initially (2 to 4 seconds) glycolate and glycine were more C-2 labeled. They rapidly became uniformly labeled, with glycine becoming uniformly labeled first. In the presence of isonicotinylhydrazide, labeled glycolate and glycine accumulated, and only a trace of serine-(14)C was detected. Then glycolate and glycine were initially carboxyl-labeled, and glycolate became uniformly labeled almost immediately and before glycine. These results suggest rapid metabolism of glycolate and glycine, in addition to the glycolate pathway.

Journal Article↗
PubMed1975

H(2) metabolism in photosynthetic organisms: I. Dark h(2) evolution and uptake by algae and mosses.

Dark H(2) metabolism was studied in marine and fresh water red algae, the green alga, Chlamydomonas, and mosses. A time variable and temperature-sensitive anaerobic incubation was required prior to H(2) evolution. H(2) evolution was sensitive to disalicylidenepropanediamine. An immediate H(2) uptake was observed in these algae. Immediate dark H(2) uptake but no evolution was observed in the mosses.A cell-free hydrogenase preparation was obtained from anaerobically adapted Chlamydomonas reinhardii by means of sonic oscillation. The hydrogenase was not sedimented at 100,000g. It catalyzed the reduction of methylene blue, p-benzoquinone, NAD, NADP, but not spinach ferredoxin. H(2) evolution was noted with dithionite and with reduced methyl viologen as donors but not with reduced spinach ferredoxin. Similarly, hydrogenase activities were not affected by disalicylidenepropanediamine. The pH optima for H(2) evolution and for H(2) uptake were 7.2 and 7.5 to 9.5, respectively. Extracts prepared from the anaerobically adapted red alga, Chondrus crispus, and the moss, Leptobryum pyriforme, consumed but did not evolve H(2). Uptake was slightly stimulated by methylene blue. It is proposed that red algae and mosses appear to metabolize H(2) by a different pathway than Chlamydomonas.

Journal Article↗
PubMed1980

Light-driven Uptake of Oxygen, Carbon Dioxide, and Bicarbonate by the Green Alga Scenedesmus.

Mass spectrometric techniques were used to study several aspects of the competition between O(2) and species of inorganic carbon for photosynthetically generated reducing power in the green alga, Scenedesmus.In contrast to wild type, no appreciable light-driven O(2) uptake was observed in a mutant lacking photosystem I. It is concluded that the carbon cycle-independent reduction of O(2) occurs at the expense of photosystem I-generated reducing equivalents.The commonly observed differences between CO(2)-grown and air-grown Scenedesmus with respect to CO(2) uptake and glycolate formation cannot be ascribed to differences in their capacity for light-driven O(2) uptake. There were no intrinsic differences found in O(2) uptake capacity between the two physiological types under conditions in which CO(2) was saturating or CO(2) uptake was inhibited. It was only under CO(2)-limited conditions that pronounced differences between the two physiological types were observed. This fact suggests that differences in O(2) metabolism and sensitivity between the two types really reflect differences in their capacity to assimilate inorganic carbon; in this respect they are analogous to C(3) and C(4) plants.The hypothesis that air-grown Scenedesmus can assimilate HCO(3) (-) by directly monitoring the time course of dissolved CO(2), O(2) uptake, and O(2) evolution in illuminated algal suspensions at alkaline pH was tested. Inasmuch as the measuring technique employed was fast compared to the nonenzymic equilibration of the inorganic carbon species, it was possible to determine the degree to which the CO(2) concentration deviated from equilibrium (with the other inorganic carbon species) during the course of illumination. The observed kinetics in air-grown and CO(2)-grown algae in the presence and absence of carbonic anhydrase, and a comparison of these kinetics with theoretical (computer-generated) time courses, support the idea that air-adapted algae are able to assimilate HCO(3) (-) actively at a high rate. The data suggest that these algae preferentially assimilate CO(2) and supply the balance of their needs by taking up HCO(3) (-). Since (unlike C(4) plants) these algae have no special CO(2) pump, and thus have a relatively low affinity for CO(2), HCO(3) (-) assimilation is the major carbon uptake process at alkaline pH even when the total CO(2) is present in millimolar concentrations.

Journal Article↗
PubMed1988

Stereoisomers of beta-Carotene and Phytoene in the Alga Dunaliella bardawil.

Dunaliella bardawil, a halotolerant green alga, was previously shown to accumulate high concentrations of beta-carotene when grown outdoors under defined conditions. The beta-carotene of algae cultivated under high light intensity in media containing a high salt concentration is composed of approximately 50% all-trans beta-carotene and 40% 9-cis beta-carotene. We show here that the 9-cis to all-trans ratio is proportional to the integral light intensity to which the algae are exposed during a division cycle. In cells grown under a continuous white light of 2000 microeinsteins per square meter per second, the ratio reached a value of around 1.5, while in cells grown under a light intensity of 50 microeinsteins per square meter per second, the ratio was around 0.2. As previously shown, algae treated with the herbicide norflurazon accumulate phytoene in place of beta-carotene. Electron micrographs showed that the phytoene is accumulated in many distinct globules located in the interthylakoid spaces of the chloroplast. Here too, two isomers are present, apparently all-trans and 9-cis phytoene, and their ratio is dependent upon the integral light intensity to which the algae are exposed during a division cycle. In the presence of norflurazon, Dunaliella bardawil grown under a light intensity of 2000 microeinsteins per square meter per second contained about 8% phytoene with a 9-cis to all-trans ratio of about 1.0. This ratio decreased to about 0.1 when the light intensity was reduced to 50 microeinsteins per square meter per second. These data suggest that the isomerization reaction which leads to the production of the 9-cis isomer occurs early in the path of carotene biosynthesis, at or before the formation of all-trans phytoene. The presence of the 9-cis isomer of beta-carotene and the dependence of its preponderance on light intensity seem to be a common feature of many plant parts. Thus carrots which are exposed to minimal light contain no 9-cis isomer while sun-exposed leaves, fruits, and flowers contain 20 to 50% of the 9-cis isomer.

Journal Article↗
PubMed2004

Variation in natural selection for growth and phlorotannins in the brown alga Fucus vesiculosus.

Directional selection for plant traits associated with resistance to herbivory tends to eliminate genetic variation in such traits. On the other hand, balancing selection arising from trade-offs between resistance and growth or spatially variable selection acts against the elimination of genetic variation. We explore both the amount of genetic variation and variability of natural selection for growth and concentration of phenolic secondary compounds, phlorotannins, in the brown alga Fucus vesiculosus. We measured variation in selection at two growing depths and two levels of nutrient availability in algae that had faced two kinds of past growing environments. Genetic variation was low for growth but high for phlorotannins. The form and strength of selection for both focal traits depended on the past growing environment of the algae. We found strong directional selection for growth rate in algae previously subjected to higher ultraviolet radiation, but not in algae previously subjected to higher nutrient availability. Stabilizing selection for growth occurred especially in the deep growing environment. Selection for phlorotannins was generally weak, but in some past-environment-current-environment combinations we detected either directional selection against phlorotannins or stabilizing selection. Thus, phlorotannins are not selectively neutral but affect the fitness of F. vesiculosus. In particular, there may be a fitness cost of producing phlorotannins, but the realization of such a cost varies from one environment to another. Genetic correlations between selective environments were high for growth but nonexistent for phlorotannins, emphasizing the high phenotypic plasticity of phlorotannin production. The highly heterogeneous selection, including directional, stabilizing, and spatially variable selection as well as temporal change in selection due to responses to past environmental conditions, probably maintains a high amount of genetic variation in phlorotannins. Such variation provides the potential for rapid evolutionary response of phlorotannins under directional selection.

Analysis of Variance↗
PubMed1997

Ear infections with Shewanella alga: a bacteriologic, clinical and epidemiologic study of 67 cases.

OBJECTIVE: To present bacteriologic and clinical data on 67 patients from the island of Funen, Denmark, with Shewanella alga, a bacterium rarely seen in Scandinavia, isolated from ear swabs. Included in the study is an examination of the occurrence of S. alga in sea water around the island. METHODS: Bacteriologic examination and antibiotic susceptibility testing of 67 clinical isolates, 11 sea-water isolates and two reference strains were conducted. Clinical information was obtained from the referring physicians. RESULTS: During 6 months S. alga was isolated from 67 patients, in 33 cases in pure culture. Seventy per cent of the patients were children between 3 and 15 years old who had clinical symptoms of acute or chronic otitis media. Previous ear disease was common (76%). Most of the cases (85%) occurred in August or September, and 47 of 55 patients reported contact with sea water shortly before symptoms developed. From seven of the patients, S. alga was isolated more than once. The species was also isolated from five of 10 bathing areas around the island of Funen. CONCLUSIONS: The patients were probably infected with S. alga during sea-water bathing in the unusually warm summer of 1994. Infections with marine bacteria are possible in countries with a temperate climate; patients with previous ear disease are at special risk.

Journal Article↗
PubMed2005

Shewanella algae and Shewanella putrefaciens: clinical and microbiological characteristics.

The occurrence of the two Shewanella species found in clinical specimens, Shewanella algae and Shewanella putrefaciens, correlates with the temperature and salinity of seawater. This means that Shewanella infections occur in warm climates or during especially warm summers in temperate climates. The infections described most commonly involve ears, skin and soft tissue, with or without bacteraemia. Primary bacteraemia with a fulminant course is also seen in immunocompromised patients. Important differential characteristics between the two species include the ability of S. algae to produce mucoid colonies with beta-haemolysis on sheep blood agar, to grow at 42 degrees C and in NaCl 6% w/v, and to reduce nitrite, and an inability to produce acid from maltose, all of which are in contrast to the characteristics of S. putrefaciens. Automated identification systems fail to differentiate between S. algae and S. putrefaciens, as S. algae is not included in the databases of these systems. Presumably for this reason, most Shewanella infections reported during recent years have been attributed to S. putrefaciens. However, when extensive phenotypic characterisation is performed, most human infections are seen to be caused by S. algae. As the two species seem to have different pathogenic potential for humans, correct identification is important, and this is possible in routine clinical microbiology laboratories.

Animals↗
PubMed1968

Fatty acids in blue-green algae: possible relation to phylogenetic position.

Analyses of the lipids in five species of blue-green algae show that the fatty acids are largely the C(16) and C(18) acids. The only alga that could be grown heterotrophically, Chlorogloea, formed the triply unsaturated C(18) acid in the light but only the doubly unsaturated C(18) acid in the dark. Examination of these results and the results of others suggest that, except for one species, the more highly unsaturated acids are found in the morphologically more complex algae. The fatty acid compositions of blue-green algae are different from the fatty acid composition of the other prokaryotic organisms, the bacteria. It is speculated that the diversity of the patterns of fatty acid composition among the blue-green algae could be of phylogenetic significance.

Alkenes↗
PubMed1978

Effect of temperature on blue-green algae (cyanobacteria) in lake mendota.

The temperature optimum for photosynthesis of natural populations of blue-green algae (cyanobacteria) from Lake Mendota was determined during the period of June to November 1976. In the spring, when temperatures ranged from 0 to 20 degrees C, there were insignificant amounts of blue-green algae in the lake (less than 1% of the biomass). During the summer and fall, when the dominant phytoplankton was blue-green algae, the optimum temperature for photosynthesis was usually between 20 and 30 degrees C, whereas the environmental temperatures during this period ranged from 24 degrees C in August to 12 degrees C in November. In general, the optimum temperature for photosynthesis was higher than the environmental temperature. More importantly, significant photosynthesis also occurred at low temperature in these samples, which suggests that the low temperature alone is not responsible for the absence of blue-green algae in Lake Mendota during the spring. Temperature optima for growth and photosynthesis of laboratory cultures of the three dominant blue-green algae in Lake Mendota were determined. The responses of the two parameters to changes in temperature were similar; thus, photosynthesis appears to be a valid index of growth. However, there was little photosynthesis by laboratory cultures at low temperatures, in contrast to the natural samples. Evidence for an interaction between temperature and low light intensities in their effect on photosynthesis of natural samples is presented.

Journal Article↗
PubMed1980

Laboratory comparison of the effectiveness of several algicides on isolated swimming pool algae.

The most frequently encountered species of algae found in swimming pools in the Phoenix metropolitan area were used to evaluate the laboratory effectiveness of five commercially available pool chemicals used for algal control. The pool algae used were the xanthophyte Pleurochloris pyrenoidosa, the chlorophyte Oocystis sp., and the cyanophytes Phormidium minnesotense and Plectonema sp. Pad Algae Kill (a chlorine derivative) was effective in the control of all test organisms. Algaedyn, a silver-containing algicide, was effective on P. minnesotense and Plectonema sp., but caused only a slight inhibition in the growth of P. pyrenoidosa and Oocystis sp. Quarternary ammonium (Padicide) was more effective in controlling the growth of Phormidium and Plectonema than Pleurochloris and Oocystis. Algimycin (herbicide) only reduced the growth of Oocystis and was ineffective on the other species. Bio-Gard (copper) reduced the growth of Pleurochloris, but had no effect on the other test organisms. The technique used to quantify the influence of algicides on isolated pool algae appears to be adaptable to those algae that form distinct colonies on an agar substratum.

Journal Article↗
PubMed1986

Bacterial enhancement of vinyl fouling by algae.

The role of bacteria in the development of algae on low-density vinyl was investigated. Unidentified bacterial contaminants in unialgal stock cultures of Phormidium faveolarum and Pleurochloris pyrenoidosa enhanced, by 1 to 2 orders of magnitude, colonization of vinyl by these algae, as determined by epifluorescence microscopy counts and chlorophyll a in extracts of colonized vinyl. Colonization by bacteria always preceded that by algae. Scanning electron microscopy of the colonized Phormidium-bacteria mixture revealed the presence of a slime matrix engulfing both bacteria and algae that may have facilitated algal attachment. Slime was not evident in the Pleurochloris-bacteria mixture, suggesting that the attachment mechanisms differ for the two algae.

Journal Article↗
PubMed2002

Melanin production and use as a soluble electron shuttle for Fe(III) oxide reduction and as a terminal electron acceptor by Shewanella algae BrY.

Dissimilatory metal-reducing bacteria (DMRB) utilize numerous compounds as terminal electron acceptors, including insoluble iron oxides. The mechanism(s) of insoluble-mineral reduction by DMRB is not well understood. Here we report that extracellular melanin is produced by Shewanella algae BrY. The extracted melanin served as the sole terminal electron acceptor. Upon reduction the reduced, soluble melanin reduced insoluble hydrous ferric oxide in the absence of bacteria, thus demonstrating that melanin produced by S. algae BrY is a soluble Fe(III)-reducing compound. In the presence of bacteria, melanin acted as an electron conduit to Fe(III) minerals and increased Fe(III) mineral reduction rates. Growth of S. algae BrY occurred in anaerobic minimal medium supplemented with melanin extracted from previously grown aerobic cultures of S. algae BrY. Melanin produced by S. algae BrY imparts increased versatility to this organism as a soluble Fe(III) reductant, an electron conduit for iron mineral reduction, and a sole terminal electron acceptor that supports growth.

Cytochromes↗
PubMed1975

Factors affecting the contribution by epiphytic algae to the primary productivity of an oligotrophic freshwater lake.

A diatom-dominated population of epiphytic algae was studied in an oligotrophic lake to determine the factors which limit epiphyte growth and to measure their contribution to primary productivity. Algae were collected from plants growing at four sites in Lake George, N.Y., during the spring, summer, and fall of 1974. Samples were taken from 3 m, corresponding to the depth at which macrophytes were most productive. Algae exhibited an optimum temperature for HCO(3) uptake at 30 C, although the summer littoral lake temperature ranged from 18 to 25 C. Light saturation occurred at an intensity of 8,608 lux, approximating the environmental intensity at the depth from which algae were taken. Epiphytes exhibited their maximum photosynthetic capacity of 0.6 mg of carbon fixed/m of macrophyte surface area per h in the early afternoon in mid-August. They assimilated approximately 5% as much inorganic carbon as the macrophytes from which they were taken. Epiphyte population densities followed the seasonal growth patterns of the macrophytes, with maximal leaf colonization remaining essentially constant relative to the leaf position on the plant. There was little change in density between sampling sites at any given time. Productivities of epiphytes from bottom leaves were 10-fold greater than those of epiphytes from top leaves. Addition of PO(4), NO(3), NH(3), Si, and SO(4) had no stimulatory effect on photosynthesis. Addition of HCO(3) stimulated photosynthesis greater than 30%, suggesting that carbon may be a limiting nutrient for epiphytic algae in Lake George.

Journal Article↗
PubMed1986

Cadmium transport, resistance, and toxicity in bacteria, algae, and fungi.

Cadmium is an important environmental pollutant and a potent toxicant to bacteria, algae, and fungi. Mechanisms of Cd toxicity and resistance are variable, depending on the organism. It is very clear that the form of the metal and the environment it is studied in, play an important role in how Cd exerts its effect and how the organism(s) responds. A wide range of Cd concentrations have been used to designate resistance in organisms. To date, no concentration has been specified that is applicable to all species studied under standardized conditions. Cadmium exerts its toxic effect(s) over a wide range of concentrations. In most cases, algae and cyanobacteria are the most sensitive organisms, whereas bacteria and fungi appear to be more resistant. In some bacteria, plasmid-encoded resistance can lead to reduced Cd2+ uptake. However, some Gram-negative bacteria without plasmids are just as resistant to Cd as are bacteria containing plasmids encoding for Cd resistance. According to Silver and Misra (1984), there is no evidence for enzymatic or chemical transformations associated with Cd resistance. Insufficient information is available on the genetics of Cd uptake and resistance in cyanobacteria and algae. Mechanisms remain largely unknown at this point in time. Cadmium is toxic to these organisms, causing severe inhibition of such physiological processes as growth, photosynthesis, and nitrogen fixation at concentrations less than 2 ppm, and often in the ppb range (Tables 2 and 3). Cadmium also causes pronounced morphological aberrations in these organisms, which are probably related to deleterious effects on cell division. This may be direct or indirect, as a result of Cd effects on protein synthesis and cellular organelles such as mitochondria and chloroplasts. Cadmium is accumulated internally in algae (Table 4) as a result of a two-phase uptake process. The first phase involves a rapid physicochemical adsorption of Cd onto cell wall binding sites, which are probably proteins and (or) polysaccharides. This is followed by a lag period and then a slow, steady intracellular uptake. This latter phase is energy dependent and may involve transport systems used to accumulate other divalent cations, such as Mn2+ and Ca2+. Some data indicate that Cd resistance, and possibly uptake, in algae and cyanobacteria is controlled by a plasmid-encoded gene(s). Although considerable information is available on Cd toxicity to, and uptake in fungi, further work is clearly needed in several areas. There is little information about Cd uptake by filamentous fungi, and even in yeasts, information on the specificity, kinetics, and mechanisms of Cd uptake is limited.(ABSTRACT TRUNCATED AT 400 WORDS)

Bacillus subtilis↗
PubMed2007

A clade uniting the green algae Mesostigma viride and Chlorokybus atmophyticus represents the deepest branch of the Streptophyta in chloroplast genome-based phylogenies.

BACKGROUND: The Viridiplantae comprise two major phyla: the Streptophyta, containing the charophycean green algae and all land plants, and the Chlorophyta, containing the remaining green algae. Despite recent progress in unravelling phylogenetic relationships among major green plant lineages, problematic nodes still remain in the green tree of life. One of the major issues concerns the scaly biflagellate Mesostigma viride, which is either regarded as representing the earliest divergence of the Streptophyta or a separate lineage that diverged before the Chlorophyta and Streptophyta. Phylogenies based on chloroplast and mitochondrial genomes support the latter view. Because some green plant lineages are not represented in these phylogenies, sparse taxon sampling has been suspected to yield misleading topologies. Here, we describe the complete chloroplast DNA (cpDNA) sequence of the early-diverging charophycean alga Chlorokybus atmophyticus and present chloroplast genome-based phylogenies with an expanded taxon sampling. RESULTS: The 152,254 bp Chlorokybus cpDNA closely resembles its Mesostigma homologue at the gene content and gene order levels. Using various methods of phylogenetic inference, we analyzed amino acid and nucleotide data sets that were derived from 45 protein-coding genes common to the cpDNAs of 37 green algal/land plant taxa and eight non-green algae. Unexpectedly, all best trees recovered a robust clade uniting Chlorokybus and Mesostigma. In protein trees, this clade was sister to all streptophytes and chlorophytes and this placement received moderate support. In contrast, gene trees provided unequivocal support to the notion that the Mesostigma + Chlorokybus clade represents the earliest-diverging branch of the Streptophyta. Independent analyses of structural data (gene content and/or gene order) and of subsets of amino acid data progressively enriched in slow-evolving sites led us to conclude that the latter topology reflects the true organismal relationships. CONCLUSION: In disclosing a sister relationship between the Mesostigmatales and Chlorokybales, our study resolves the long-standing debate about the nature of the unicellular flagellated ancestors of land plants and alters significantly our concepts regarding the evolution of streptophyte algae. Moreover, in predicting a richer chloroplast gene repertoire than previously inferred for the common ancestor of all streptophytes, our study has contributed to a better understanding of chloroplast genome evolution in the Viridiplantae.

Algal Proteins↗
PubMed1986

The cell cycle of symbiotic Chlorella. IV. DNA content of algae slowly increases during host starvation of green hydra.

The distribution of DNA content of symbiotic Chlorella algae freshly isolated from green hydra was compared with that of cultured Chlorella of the NC64A strain, using flow cytometry. In nonlogarithmic cultures of NC64A most cells had accumulated in G1 phase, while in logarithmic cultures a peak containing cells in S phase and mitosis could be distinguished from the larger G1 peak. However, symbiotic algae showed a single broad peak in which there was no clear distinction between G1 and S phase/mitosis. When hydra were starved for a prolonged period, inhibiting host cell and algal division, the DNA content of the symbiotic algae slowly increased, and the number of daughter cells produced after a single feeding increased with the length of the preceding period of starvation. This suggests that symbiotic algae are able to cycle slowly through S phase, but unless the host is fed they cannot traverse into mitosis and complete the cell division cycle. No significant difference in cell size was found between algae producing either four or eight daughter cells after 1-day- or 22-day-starved hydra were fed, suggesting that algal cell size did not determine the number of daughter cells produced. Instead, this may be dependent upon the length of time the cell had spent in S phase prior to receiving the, as yet unknown, stimulus to enter into mitosis.

Animals↗