Synechococcus Species Research Articles

Identification of a Novel Vinyl Reductase Gene Essential for the Biosynthesis of Monovinyl Chlorophyll in Synechocystis sp. PCC6803

The vast majority of oxygenic photosynthetic organisms use monovinyl chlorophyll for their photosynthetic reactions. For the biosynthesis of this type of chlorophyll, the reduction of the 8-vinyl group that is located on the B-ring of the macrocycle is essential. Previously, we identified the gene encoding 8-vinyl reductase responsible for this reaction in higher plants and termed it DVR. Among the sequenced genomes of cyanobacteria, only several Synechococcus species contain DVR homologues. Therefore, it has been hypothesized that many other cyanobacteria producing monovinyl chlorophyll should contain a vinyl reductase that is unrelated to the higher plant DVR. To identify the cyanobacterial gene that is responsible for monovinyl chlorophyll synthesis, we developed a bioinformatics tool, correlation coefficient calculation tool, which calculates the correlation coefficient between the distributions of a certain phenotype and genes among a group of organisms. The program indicated that the distribution of a gene encoding a putative dehydrogenase protein is best correlated with the distribution of the DVR-less cyanobacteria. We subsequently knocked out the corresponding gene (Slr1923) in Synechocystis sp. PCC6803 and characterized the mutant. The knock-out mutant lost its ability to synthesize monovinyl chlorophyll and accumulated 3,8-divinyl chlorophyll instead. We concluded that Slr1923 encodes the vinyl reductase or a subunit essential for monovinyl chlorophyll synthesis. The function and evolution of 8-vinyl reductase genes are discussed.

Characterization of temperate cyanophages active against freshwater phycocyanin‐rich Synechococcus species

Summary1. This study addressed the prevalence of lysogeny within 19 strains of freshwater Synechococcus sp. rich in phycocyanin (PC) that were isolated from a temperate lake or obtained, in four cases, from a culture collection.2. Lysis of 16 Synechococcus strains (84%) was inducible with mitomycin C, but the required concentration (20 μg mL−1) was higher than in other studies. Mitomycin C induction yielded burst sizes of 3.5–23.7 phages per cell.3. Transmission Electron Microscopy of the resultant temperate phages showed that all belonged to the family Siphoviridae with capsid diameters ranging from 40.3 to 53.5 nm and tail lengths from 129 to 186 nm. None of the cyanophages could be maintained in the lytic cycle using the three non‐lysogenic strains, or any of the other 16 lysogenic strains of Synechococcus.4.These results suggest a potentially high level of lysogeny within PC‐rich Synechococcus species in natural freshwaters, but that the presence of these temperate cyanosiphoviruses may go undetected with the lower mitomycin C concentrations commonly used.

The Structure of Isolated Synechococcus Strain WH8102 Carboxysomes as Revealed by Electron Cryotomography

Carboxysomes are organelle-like polyhedral bodies found in cyanobacteria and many chemoautotrophic bacteria that are thought to facilitate carbon fixation. Carboxysomes are bounded by a proteinaceous outer shell and filled with ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO), the first enzyme in the CO 2 fixation pathway, but exactly how they enhance carbon fixation is unclear. Here we report the three-dimensional structure of purified carboxysomes from Synechococcus species strain WH8102 as revealed by electron cryotomography. We found that while the sizes of individual carboxysomes in this organism varied from 114 nm to 137 nm, surprisingly, all were approximately icosahedral. There were on average ∼250 RuBisCOs per carboxysome, organized into three to four concentric layers. Some models of carboxysome function depend on specific contacts between individual RuBisCOs and the shell, but no evidence of such contacts was found: no systematic patterns of connecting densities or RuBisCO positions against the shell's presumed hexagonal lattice could be discerned, and simulations showed that packing forces alone could account for the layered organization of RuBisCOs.

The ancestor of the Paulinella chromatophore obtained a carboxysomal operon by horizontal gene transfer from a Nitrococcus-like gamma-proteobacterium.

BackgroundPaulinella chromatophora is a freshwater filose amoeba with photosynthetic endosymbionts (chromatophores) of cyanobacterial origin that are closely related to free-living Prochlorococcus and Synechococcus species (PS-clade). Members of the PS-clade of cyanobacteria contain a proteobacterial form 1A RubisCO (ribulose-1,5-bisphosphate carboxylase/oxygenase) that was acquired by horizontal gene transfer (HGT) of a carboxysomal operon. In rDNA-phylogenies, the Paulinella chromatophore diverged basal to the PS-clade, raising the question whether the HGT occurred before or after the split of the chromatophore ancestor.ResultsPhylogenetic analyses of the almost complete rDNA operon with an improved taxon sampling containing most known cyanobacterial lineages recovered the Paulinella chromatophore as sister to the complete PS-clade. The sequence of the complete carboxysomal operon of Paulinella was determined. Analysis of RubisCO large subunit (rbcL) sequences revealed that Paulinella shares the proteobacterial form 1A RubisCO with the PS-clade. The γ-proteobacterium Nitrococcus mobilis was identified as sister of the Paulinella chromatophore and the PS-clade in the RubisCO phylogeny. Gene content and order in the carboxysomal operon correlates well with the RubisCO phylogeny demonstrating that the complete carboxysomal operon was acquired by the common ancestor of the Paulinella chromatophore and the PS-clade through HGT. The carboxysomal operon shows a significantly elevated AT content in Paulinella, which in the rbcL gene is confined to third codon positions. Combined phylogenies using rbcL and the rDNA-operon resulted in a nearly fully resolved tree of the PS-clade.ConclusionThe HGT of the carboxysomal operon predated the divergence of the chromatophore ancestor from the PS-clade. Following HGT and divergence of the chromatophore ancestor, diversification of the PS-clade into at least three subclades occurred. The γ-proteobacterium Nitrococcus mobilis represents the closest known relative to the donor of the carboxysomal operon. The isolated position of the Paulinella chromatophore in molecular phylogenies as well as its elevated AT content suggests that the Paulinella chromatophore has already undergone typical steps in the reductive evolution of an endosymbiont.

Spatial distribution of sponge-associated bacteria in the Mediterranean sponge Tethya aurantium

The local distribution of the bacterial community associated with the marine sponge Tethya aurantium Pallas 1766 was studied. Distinct bacterial communities were found to inhabit the endosome and cortex. Clear differences in the associated bacterial populations were demonstrated by denaturing gradient gel electrophoresis (DGGE) and analysis of 16S rRNA gene clone libraries. Specifically associated phylotypes were identified for both regions: a new phylotype of Flexibacteria was recovered only from the sponge cortex, while Synechococcus species were present mainly in the sponge endosome. Light conduction via radiate spicule bundles conceivably facilitates the unusual association of Cyanobacteria with the sponge endosome. Furthermore, a new monophyletic cluster of sponge-derived 16S rRNA gene sequences related to the Betaproteobacteria was identified using analysis of 16S rRNA gene clone libraries. Members of this cluster were specifically associated with both cortex and endosome of T. aurantium.

Temperate and lytic cyanophages from the Gulf of Mexico

The unicellular cyanobacterial species Synechococcus and Prochlorococcus are known to be vital components of marine ecosystems, especially in the vast oligotrophic areas. Lytic cyanophages infecting unicellular phytoplankton are prevalent and have been demonstrated to act as important constraints on community composition contributing to the seasonal succession in genotypes. Lysogeny in Synechococcus has been documented experimentally in natural environments by prophage induction. At this time it is completely unknown how prevalent lysogeny is among Synechococcus populations. This study was performed to document important features such as size, morphology and the incidence of the T4-like capsid portal protein gene (g20) in a group of lytic Synechococcus cyanophages (35 isolates) isolated from the Gulf of Mexico. A group of Synechococcus isolates (24 strains) were isolated concurrently to investigate the virulence and cross-infectivity of the lytic cyanophages and to determine the frequency of lysogeny by detection of inducible prophage. The host range of the cyanophages toward these Synechococcus strains ranged from 1 of 25 (host of isolation only) to 17 of 25 (68%). Of the 35 cyanophage isolates the large majority were myoviruses (94%) and only two (6%) were of the podovirus type. The expected polymerase chain reaction product for g20 was detected in 20 of the phages (63%). The presence of a detectable g20 was associated with low-infectivity cyanophages at the 90% confidence interval. The Synechococcus strains varied in their resistance to lytic infection from 11% to resistance to all of the phage isolates utilized in testing. The prevalence of inducible prophage-like particles was determined in the Synechococcus strains using mitomycin C and enumerating viruses by epifluorescence microscopy. A statistically significant increase in viruses was detected in 11 of the strains (46%) in response to mitomycin C. There was no observed relationship between the occurrence of prophage induction in the Synechococcus isolates and their resistance to lytic infection. One putative lysogen was induced by continuous high light and contained a prophage-like particle with a single-stranded DNA (ssDNA) genome. Such a prophage-like particle is unlike any prophage described to date, implying that the process of lysogeny is unique in certain marine Synechococcus strains.

Abundance, morphological diversity, and spatial distribution of autotrophic picoplankton in Lake Hovsgol (Mongolia)

Hovsgol is the largest deep lake in Central Asia located in the south-west of the Baikal Rift zone. Until now there has been only one study on the autotrophic picoplankton in Lake Hovsgol. The present work summarizes results of picoplankton studies obtained with light, epifluorescence and scanning electron microscopy. Microscopic analysis showed the presence of picoplankton cyanobacteria and algae in Lake Hovsgol. Autotrophic picoplankton of the lake is characterized by morphotype diversity of Synechococcus species, Synechocystis-like aggregates, and picocyanobacteria cells of small sizes. Picocyanobacteria are dominated by Synechococcus species with single, rarely double, coccoid cells. There is also a picoplankton form of the diatom Cyclotella ocellata reaches 4–13 percent of the total species abundance. Three picocyanobacterial cultures belonging to the genus Synechococcus and exhibiting distinct morphological and ultrastructural characteristics were isolated from the plankton samples. Chlorophyll a content in the pelagic zone of Lake Hovsgol in August was 0.182–0.374 μ g l− 1. In February, the abundance of picoplankton cyanobacteria in the surface layer, which make up the basic autotrophic picoplankton mass, was 2.78 × 105 cells ml−1, in March 1.36 × 105 cells ml−1, and in July 6.06 × 104 cells ml−1. In August, picocyanobacteria abundance fell to 3.42 × 104 cells ml−1 in the 0 to 10 m layer and 7.52 × 104 cells ml−1 in the 0 to 50 m layer. Quantitative variations in autotrophic picoplankton development throughout the lake are negligible. The greatest abundance of picocyanobacteria is recorded in the hypolimnion, 25–50 m deep.

The Biogeography and Phylogeny of Unicellular Cyanobacterial Symbionts in Sponges from Australia and the Mediterranean

The distribution, host associations, and phylogenetic relationships of the unicellular cyanobacterial symbionts of selected marine sponges were investigated with direct 16s rDNA sequencing. The results indicate that the symbionts of the marine sponges Aplysina aerophoba, Ircinia variabilis, and Petrosia ficiformis from the Mediterranean, four Chondrilla species from Australia and the Mediterranean, and Haliclona sp. from Australia support a diversity of symbionts comprising at least four closely related species of Synechococcus. These include the symbionts presently described as Aphanocapsa feldmannii from P. ficiformis and Chondrilla nucula. A fifth symbiont from Cymbastela marshae in Australia is an undescribed symbiont of sponges, related to Oscillatoria rosea. One symbiont, Candidatus Synechococcus spongiarum, was found in diverse sponge genera in the Mediterranean Sea and the Indian, Pacific, and Southern oceans, whereas others were apparently more restricted in host association and distribution. These results are discussed in terms of the biodiversity and biogeographic distributions of cyanobacterial symbionts.

Molecular inference of dominant picocyanobacterial populations by denaturing gradient gel electrophoresis of PCR amplified 16S rRNA gene fragments

SUMMARY Quantitative accuracy based on the fluorescent intensity of bands in a denaturing gradient gel electrophoresis (DGGE) profile of polymerase chain reaction (PCR)-amplified 16S rRNA gene fragments was evaluated for the molecular inference of dominant populations using a cyanobacterial primer pair in a picocyanobacterial community. A serial dilution technique of the template prior to PCR of extracted nucleic acids allowed for elimination of minor strains (less than 10% of the whole cell number) using a cell mixture of three known cultured Synechococcus species with different ratios. When the most abundant strain among the three accounted for more than 80% of the cells, the single band derived from the most abundant one was detected exclusively after the template dilution. In the case of two or three strains evenly distributed in the sample, all strains remained as bands after template dilution. The technique used in the present study was also applied to lake water samples collected from depths of 1 and 5 m on 27 August 1999. The same dominant Synechococcus population was detected in both samples. Thus, the template-dilution technique prior to PCR is useful to determine dominant picocyanobacterial populations in the DGGE profiling.

Integrative Microbiology, 2003

OMICS: A Journal of Integrative BiologyVol. 6, No. 4 EditorialIntegrative Microbiology, 2003Eugene KolkerEugene KolkerSearch for more papers by this authorPublished Online:8 Jul 2004https://doi.org/10.1089/153623102321112728AboutSectionsPDF/EPUB Permissions & CitationsPermissionsDownload CitationsTrack CitationsAdd to favorites Back To Publication ShareShare onFacebookTwitterLinked InRedditEmail "Integrative Microbiology, 2003." , 6(4), p. 285FiguresReferencesRelatedDetailsCited byUnraveling the Complexities of Life Sciences Data Roger Higdon, Winston Haynes, Larissa Stanberry, Elizabeth Stewart, Gregory Yandl, Chris Howard, William Broomall, Natali Kolker, and Eugene Kolker13 February 2013 | Big Data, Vol. 1, No. 1 Volume 6Issue 4Oct 2002 To cite this article:Eugene Kolker.Integrative Microbiology, 2003.OMICS: A Journal of Integrative Biology.Oct 2002.285-285.http://doi.org/10.1089/153623102321112728Published in Volume: 6 Issue 4: July 8, 2004PDF download

Cyanobacterial picoplankton and its colonial formations in two eutrophic canyon reservoirs (Czech Republic)

Autotrophic picoplankton (APP) was studied in a one year cycle in two canyon-type reservoirs in the Czech Republic. APP was present in both reservoirs during the whole year, although in low numbers: In general, picoplankton formed only 0.05-10 % of the total biomass (biovolume, fresh mass). The main proportion was formed by Cyanobacteria (CPP), eucaryotic species played a negligible role. Several morphotypes of CPP were distinguished during the year (April 1998-May 1999): Two rod-shaped Synechococcus species, one spherical type (2 μm diam.) dividing in one plane (Cyanobium), and another spherical type (0.7 μm diam.) dividing in two planes (Synechocystis). During the summer, a proportion of the CPP formed small groups at the beginning, while later the same cell shapes occurred in groups inside of mucilage that corresponded to colonial genera Aphanothece, Cyanodictyon and Aphanocapsa, respectively. Such a life cycle occurred in all the morphotypes except for one (Synechococcus cf. capitatus BAILY-WATTS et KOMAREK). Its appearance and spring maximum in the Slapy reservoir in 1998 was the only evident difference between both reservoirs as far as diversity of CPP morphotypes is concerned. In the year studied, unicellular picoplankton was about two times more abundant in the Slapy reservoir, while the abundance of total picoplankton (unicellular and in colonies) was almost the same in both reservoirs, i.e. about 0.4 million cells maximum and 70-80 10 3 cells/ml average. The fresh mass of the total picoplankton (unicellular + colonial) was larger in the R˙imov reservoir.

Phytoplankton abundances and community structure in the equatorial Pacific

Abstract In both the warm pool region and the high-nutrient low-chlorophyll (HNLC) region of the equatorial Pacific, the phytoplankton community is dominated by high concentrations of picophytoplankton regardless of whether El Nino, La Nina or normal conditions prevail. Flow cytometry measurements indicate that the picoplankton community consists of two species of prokaryotes, Prochlorococcus and Synechococcus, and a diverse mixture of picoeukaryotes that cannot be differentiated. Analyses of chlorophyll and carotenoid pigments, determined by HPLC, confirm the importance of Prochlorococcus and Synechococcus and indicate that the eukaryotes are predominantly haptophytes. There are at least three ecotypes of Prochlorococcus and, possibly, various ecotypes of Synechococcus. These ecotypes have quite different pigment ratios and, possibly, pigment to carbon ratios, which complicates comparisons between cell counts by flow cytometry and the contribution that prokaryotes make to total chlorophyll as calculated from pigment analysis. Increased productivity is associated with the transient influx of nutrients, El Nino conditions in the warm pool, or surface nutrients in HNLC waters. Under these conditions there seems to be a small increase in the relative abundances of Synechococcus, diatoms and chlorophytes. Grazing of picophytoplankton by macro-grazers may make an important contribution to the ‘biological pump’, which may not be dominated by large phytoplankton such as diatoms.

Effects of environmental factors on the seasonally change of phytoplankton populations in a closed freshwater pond

The effect of environmental factors affecting the population dynamic of phytoplankton population was studied seasonally in a closed freshwater pond with the natural water of Lake Kasumigaura, Japan. The predominant phytoplankton species in the pond were classified as Oscillatoria tenuis, Synedra ulna, Chlamydomonas cingulata and Cyclotella kutzingiana, with dominant species of Melosira italica, Synechococcus sp. and Cryptomonas ovata. The most important limiting factor for filament length and cell size of most of the phytoplankton community was temperature. Availability of most nutrients had profound effects on the phytoplankton growth as nonlimiting factors. Based on our results, it is suggested that cell cycle progression was also temporally regulated by a multiplicity of external factors such as temperature, nutrients, dissolved oxygen (DO) and pH. At high pH and high temperature, consistent increase of cell division of some phytoplanketers such as Synedra, Cyclotella, Chlamydomonas and Melosira occurs, and there also may be species-specific responses for other species of phytoplankters. In addition, the cell divisions of phytoplankters are differentially regulated in different phytoplankton species.

Phylogenetic analyses of Synechococcus strains (cyanobacteria) using sequences of 16S rDNA and part of the phycocyanin operon reveal multiple evolutionary lines and reflect phycobilin content.

The genus Synechococcus (cyanobacteria), while containing morphologically similar isolates, is polyphyletic and organisms presently classified as such require reclassification into several independent genera. Studies based on analysis of 16S rRNA gene sequences have shown that members of the genus Synechococcus are affiliated to three of seven deeply branching cyanobacterial lineages. In addition, some strains do not appear to be associated with any of these lineages and may represent novel clades. In this report, a cyanobacterial phylogeny based on 16S rDNA sequences, including 14 newly sequenced Synechococcus isolates, is presented. One newly sequenced Synechococcus strain (PCC 7902) did not have any close relatives amongst cyanobacterial isolates currently contained in 16S rDNA sequence databases and was only loosely affiliated to a cyanobacterial lineage in which no other Synechococcus strains were found. Three hot-spring Synechococcus isolates, including two that were newly sequenced in this study (PCC 6716 and PCC 6717), formed an additional cyanobacterial lineage. These results indicated that Synechococcus species are affiliated to five of eight deeply branching cyanobacterial lineages. Part of the phycocyanin (PC) gene sequence (cpc), including the intergenic spacer (IGS) between cpcB and cpcA and the corresponding flanking regions (cpcBA-IGS), was used to investigate relationships between closely related Synechococcus isolates. Previously described PCR primers did not amplify this region from the majority of strains under investigation, so a new set of primers was designed that allowed amplification and sequencing of the cpcBA-IGS and flanking regions from 38 Synechococcus species. Phylogenetic analysis of this region was largely consistent with that obtained from 16S rDNA sequence analysis and revealed a relationship between the primary PC DNA sequence and the phycobilin content of cells.

Nitrate transport and not photoinhibition limits growth of the freshwater Cyanobacterium synechococcus species PCC 6301 at low temperature.

The effect of low temperature on cell growth, photosynthesis, photoinhibition, and nitrate assimilation was examined in the cyanobacterium Synechococcus sp. PCC 6301 to determine the factor that limits growth. Synechococcus sp. PCC 6301 grew exponentially between 20 degreesC and 38 degreesC, the growth rate decreased with decreasing temperature, and growth ceased at 15 degreesC. The rate of photosynthetic oxygen evolution decreased more slowly with temperature than the growth rate, and more than 20% of the activity at 38 degreesC remained at 15 degreesC. Oxygen evolution was rapidly inactivated at high light intensity (3 mE m-2 s-1) at 15 degreesC. Little or no loss of oxygen evolution was observed under the normal light intensity (250 microE m-2 s-1) for growth at 15 degreesC. The decrease in the rate of nitrate consumption by cells as a function of temperature was similar to the decrease in the growth rate. Cells could not actively take up nitrate or nitrite at 15 degreesC, although nitrate reductase and nitrite reductase were still active. These data demonstrate that growth at low temperature is not limited by a decrease in the rate of photosynthetic electron transport or by photoinhibition, but that inactivation of the nitrate/nitrite transporter limits growth at low temperature.

The twelfth Tansley Lecture. Small is beautiful: the picophytoplankton

1. Picophytoplankton are planktonic photosynthetic O2‐evolvers that can pass through 2 μm‐diameter pores; they include prokaryotic (eubacterial) and eukaryotic members and occur in freshwater and marine habitats. There are no photosynthetic reproductive and dispersal stages of benthic macrophytes of picoplanktonic size. The picophytoplankton condition appears to be derived and polyphyletic in both prokaryotes and eukaryotes. 2. Picophytoplankton are among the smallest free‐living cells, despite having to contain the photosynthetic apparatus, which occupies about half of the cell volume, as well as core cellular machinery. The size of the smallest prokaryotic (0·6 μm diameter) and eukaryotic (0·95 μm diameter) picophytoplankton are close to the minimum possible size estimated from the occurrence of non‐scalable essential components such as the genome and plasmalemma and other membranes. 3. Picophytoplankton cells have advantages relative to larger phytoplankton cells in terms of resource acquisition and the subsequent use of the resources in catalysing cell growth and reproduction. The smaller package effect in light harvesting means smaller resource (energy, C, N, Fe, Mn, Cu) costs of photon harvesting and transformation into chemical energy in small than in large cells. The smaller diffusion boundary layer around small cells, coupled with smaller nutrient fluxes per unit plasmalemma area needed to attain a given fraction of the maximum specific growth rate in smaller cells, increases the availability of low concentrations of nutrients to small relative to larger cells. If the supply of CO2 to the core photosynthetic carboxylase ribulose bisphosphate carboxylase‐oxygenase is purely by diffusion then smaller cells could satisfy their catalytic requirements with less of this enzyme whose synthesis has high energy, C and N costs. Overall, resources can be acquired, and used in growth, more effectively in smaller than in larger cells. 4. Some factors work against the conclusion in (3.) but, in most habitats, do not negate these conclusions. Examples related to non‐scalable essential cell components are the use of energy, C, N and P in the genome and of energy, C, N, P and Fe in the plasma membrane. Transport‐related factors include the increased potential cell volume‐specific leakage of accumulated resources, and the greater cell volume‐specific energy costs of motility at a given speed, in smaller than in larger cells. The smaller package effect in smaller cells involves a greater potential for photodamage by both photosynthetically active radiation and by UV‐B. 5. Picophytoplankton occurrence is also a function of factors which lead to cell loss. Factors such as sinking out of the euphotic zone and parasitism by eukaryotes such as chytrids are less significant for picophytoplankton than for larger cells, whereas viral parasitism and grazing by appropriately sized grazers are likely to be at least as great for picophytoplankton as for larger cells. 6. The totality of the effects mentioned in (3.) above suggests that picophytoplankton should generally have higher specific growth rates (probably) in resource‐saturated (photons, C, N, P, Fe, etc.) and (certainly) in resource‐limited environments than do larger cells. The distribution of picophytoplankton is certainly consistent with their ability to capitalize on resource‐limited environments: they contribute a larger fraction of biomass and productivity relative to larger cells in low‐nutrient than in high‐nutrient environments, and in low‐light (e.g. the deep chlorophyll maximum) than in high‐light environments. 7. Sexual reproduction is apparently rare in picophytoplankton, with implications for species definition. There are probably relatively few species (hundreds or thousands) with very wide biogeographical ranges in marine or in freshwater habitats. The small size and (probably) low biodiversity means large numbers of individuals worldwide, e.g. c.1026 individuals of the commonest species of the marine cyanobacterium Synechococcus. Picophytoplankton contribute at least one‐tenth (i.e. in excess of 3 Pg C per year) to global aquatic net primary productivity.

Biopan-survival I: Exposure of the osmophiles Synechococcus SP. (Nageli) and Haloarcula SP. to the space environment

The objective of this study was to determine the survivability of osmophilic microorganisms in space, as well as examine the DNA breakage in osmophilic cells exposed to solar UV-radiation plus vacuum and to vacuum only. The organisms used were an unidentified species of Synechococcus (Nägeli) that inhabits the evaporitic gypsum-halite crusts that form along the marine intertidal, and an unidentified species of the extremely halophilic genus Haloarcula (designated as isolate G) isolated from a evaporitic NaCl crystal. Because these organisms are desiccation resistant and gypsum-halite as well as NaCl attenuate UV-radiation, we hypothesized that these organisms would survive in the space environment, better than most others. The organisms were exposed to the space environment for 2 weeks while in earth orbit aboard the Biopan facility. Ground controls were tested in a space simulation facility. All samples were compared to unexposed samples. Survivability was determined by plate counts and the most probable number technique. DNA breakage was determined by labeling breaks in the DNA with 32P followed by translation. Results indicate that the osmophilic microbes survived the 2 week exposure. The major cause of cell death was DNA damage. The number of strand breaks in the DNA from vacuum UV exposed cells was greater than the vacuum only exposed cells.

THE EFFECT OF PHOSPHATE STATUS ON THE KINETICS OF CYANOPHAGE INFECTION IN THE OCEANIC CYANOBACTERIUM SYNECHOCOCCUS SP. WH78031

ABSTRACTPhycoerythrin‐containing Synechococcus species are considered to be major primary producers in nutrient‐limited gyres of subtropical and tropical oceanic provinces, and the cyanophages that infect them are thought to influence marine biogeochemical cycles. This study begins an examination of the effects of nutrient limitation on the dynamics of cyanophage/Synechococcus interactions in oligotrophic environments by analyzing the infection kinetics of cyanophage strain S‐PM2 (Cyanomyoviridae isolated from coastal water off Plymouth, UK) propagated on Synechococcus sp. WH7803 grown in either phosphate‐deplete or phosphate‐replete conditions. When the growth of Synechococcus sp. WH7803 in phosphate‐deplete medium was followed after infection with cyanophage, an 18‐h delay in cell lysis was observed when compared to a phosphate‐replete control. Synechococcus sp. WH7803 cultures grown at two different rates (in the same nutritional conditions) both lysed 24 h postinfection, ruling out growth rate itself as a factor in the delay of cell lysis. One‐step growth kinetics of S‐PM2 propagated on host Synechococcus sp. WH7803, grown in phosphate‐deplete and‐replete media, revealed an apparent 80% decrease in burst size in phosphate‐deplete growth conditions, but phage adsorption kinetics ofS‐PM2 under these conditions showed no differences. These results suggested that the cyanophages established lysogeny in response to phosphate‐deplete growth of host cells. This suggestion was supported by comparison of the proportion of infected cells that lysed under phosphate‐replete and‐deplete conditions, which revealed that only 9.3% of phosphate‐deplete infected cells lysed in contrast to 100% of infected phosphate‐replete cells. Further studies with two independent cyanophage strains also revealed that only approximately 10% of infected phosphate‐deplete host cells released progeny cyanophages. These data strongly support the concept that the phosphate status of the Synechococcus cell will have a profound effect on the eventual outcome of phage‐host interactions and will therefore exert a similarly extensive effect on the dynamics of carbon flow in the marine environment.

Nutrient Requirement and Growth of a Synechococcus Species Isolated from Lake Balaton

AbstractA pico sized Synechococcus species isolated from Lake Balaton was studied in batch and continuous cultures. This picocyanobacterium had a pH optimum at 8.5 and a temperature optimum at 28‐30°C. The Ik value for growth was 52 μEinstein m−2 S−1, the maximum growth rate 2.27 d−1, the half saturation Constant of growth 1.2 μg PO4‐P I−1 and the minimal cell quota 1.74 nig P g dry weight−1. The dry weight of cells showed a minimum, the chlorophyll‐a/biomass ratio a maximum as a function of growth rate. Above the quota of 3.4 fg P Cell−1 significant amounts of non‐reactive dissolved Phosphorous were released.

Self-electrophoresis is not the mechanism for motility in swimming cyanobacteria.

Swimming cyanobacteria do not have flagella. In principle, they could be propelled by streams of ions flowing from head to tail, i.e., by a self-electrophoretic mechanism. We have ruled out this possibility by showing that cells of a swimming Synechococcus species fail to drift in an external electric field.