Ni Uptake and Limitation in Marine Synechococcus Strains

Ni accumulation and utilization were studied in two strains of marine Synechococcus, isolated from both coastal (CC9311; clade I) and open-ocean (WH8102; clade III) environments, for which complete genome sequences are available. Both strains have genes encoding an Ni-containing urease and when grown on urea without Ni become Ni-N colimited. The Ni requirements of these strains also depend upon the genomic complement of genes encoding superoxide dismutase (SOD). WH8102, with a gene encoding only an Ni-SOD, has a novel obligate requirement for Ni, regardless of the N source. Reduced SOD activity in Ni-depleted cultures of WH8102 supports the link of this strain's Ni requirement to Ni-SOD. The genome of CC9311 contains a gene for a Cu/Zn-SOD in addition to a predicted pair of Ni-SODs, yet this strain cannot grow without Ni on NO₃⁻ and can grow only slowly on NH₄⁺ without Ni, implying that the Cu/Zn-SOD cannot completely replace Ni-SOD in marine cyanobacteria. CC9311 does have a greater tolerance for Ni starvation. Both strains increase their Ni uptake capabilities and actively bioconcentrate Ni in response to decreasing extracellular and intracellular Ni. The changes in Ni uptake rates were more pronounced in WH8102 than in CC9311 and for growth on urea or nitrate than for growth on ammonia. These results, combined with an analysis of fully sequenced marine cyanobacterial genomes, suggest that the growth of many marine Synechococcus and all Prochlorococcus strains is dependent upon Ni.     

Different physiological responses of cyanobacteria to ultraviolet‐B radiation under iron‐replete and iron‐deficient conditions: Implications for underestimating the negative effects of UV‐B radiation

Iron deficiency has been considered one of the main limiting factors of phytoplankton productivity in some aquatic systems including oceans and lakes. Concomitantly, solar ultraviolet‐B radiation has been shown to have both deleterious and positive impacts on phytoplankton productivity. However, how iron‐deficient cyanobacteria respond to UV‐B radiation has been largely overlooked in aquatic systems. In this study, physiological responses of four cyanobacterial strains (Microcystis and Synechococcus), which are widely distributed in freshwater or marine systems, were investigated under different UV‐B irradiances and iron conditions. The growth, photosynthetic pigment composition, photosynthetic activity, and nonphotochemical quenching of the different cyanobacterial strains were drastically altered by enhanced UV‐B radiation under iron‐deficient conditions, but were less affected under iron‐replete conditions. Intracellular reactive oxygen species (ROS) and iron content increased and decreased, respectively, with increased UV‐B radiation under iron‐deficient conditions for both Microcystis aeruginosa FACHB 912 and Synechococcus sp. WH8102. On the contrary, intracellular ROS and iron content of these two strains remained constant and increased, respectively, with increased UV‐B radiation under iron‐replete conditions. These results indicate that iron‐deficient cyanobacteria are more susceptible to enhanced UV‐B radiation. Therefore, UV‐B radiation probably plays an important role in influencing primary productivity in iron‐deficient aquatic systems, suggesting that its effects on the phytoplankton productivity may be underestimated in iron‐deficient regions around the world.     

GROWTH REGULATION OF rRNA CONTENT IN PROCHLOROCOCCUS AND SYNECHOCOCCUS (MARINE CYANOBACTERIA) MEASURED BY WHOLE‐CELL HYBRIDIZATION OF rRNA‐TARGETED PEPTIDE NUCLEIC ACIDS1

The cyanobacteria Synechococcus and Prochlorococcus are important primary producers in marine ecosystems. Because currently available approaches for estimating microbial growth rates can be difficult to apply in the field, we have been exploring the feasibility of using quantitative rRNA measurements as the basis for making such estimates. In this study we examined the relationship between rRNA and growth rate in several Synechococcus and Prochlorococcus strains over a range of light‐regulated growth rates. Whole‐cell hybridization with fluorescently labeled peptide nucleic acid (PNA) probes was used in conjunction with flow cytometry to quantify rRNA on a per cell basis. This PNA probing technique allowed rRNA analysis in a phycoerythrin‐containing Synechococcus strain (WH7803) and in a non–phycoerythrin‐containing strain and in Prochlorococcus. All the strains showed a qualitatively similar tri‐phasic relationship between rRNA·cell^?1 and growth rate, involving relatively little change in rRNA·cell^?1 at low growth rates, linear increase at intermediate growth rates, and a plateau and/or decrease at the highest growth rates. The onset of each phase was associated with the relative, rather than absolute, growth rate of each strain. In the Synechococcus strains, rRNA normalized to flow cytometrically measured forward angle light scatter (an indicator of size) was well‐correlated with growth rate across strains. These findings support the idea that cellular rRNA may be useful as an indicator of in situ growth rate in natural Synechococcus and Prochlorococcus populations.     

Effects of iron on the growth and minimal fluorescence yield of three marine Synechococcus strains (Cyanophyceae)

Two coastal Synechococcus stains PCC 7002 and CC9311 and one oceanic strain WH8102 were cultured with 4–1000 nM Fe in Aquil medium. Compared with those under iron‐replete conditions, their growth rates were significantly decreased by 59% for WH8102 at 15 nM Fe, by 37% for CC9311 at 15 nM Fe and by 57% for PCC 7002 at 4 nM Fe. Among these three strains, PCC 7002 was the most tolerant to iron limitation while WH8102 was the most sensitive to iron limitation. For each strain under the same iron concentration, the growth rates calculated from the minimal fluorescence yield and cell concentration showed no significant difference. The linear correlation was established between the minimal fluorescence yield and cell concentration although the minimal fluorescence yield per cell varied depending on the strains and iron levels. Under iron‐replete conditions, the minimal fluorescence yield per cell was 100‐fold higher for the phycoerythrin‐lacking strain PCC 7002 than two phycoerythrin‐containing strains WH8102 and CC9311. Under iron‐deplete conditions, it was increased respectively by 128% and 7% for WH8102 and CC9311 but was decreased by 30% for PCC 7002. Furthermore, the minimal fluorescence yield per cell for PCC 7002 and CC9311 showed little difference throughout the light and dark diel cycle. However, it was significantly higher for WH8102 in the daytime than in the dark.     

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

Phycoerythrin-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.     

Comparative membrane proteomics reveal contrasting adaptation strategies for coastal and oceanic marine Synechococcus cyanobacteria

Marine cyanobacteria genus Synechococcus are among the most abundant and widespread primary producers in the open ocean. Synechococcus strains belonging to different clades have adapted distinct strategies for growth and survival across a range of marine conditions. Clades I and IV are prevalent in colder, mesotrophic, coastal waters, while clades II and III prefer warm, oligotrophic open oceans. To gain insight into the cellular resources these unicellular organisms invest in adaptation strategies we performed shotgun membrane proteomics of four Synechococcus spp. strains namely CC9311 (clade I), CC9605 (clade II), WH8102 (clade III) and CC9902 (clade IV). Comparative membrane proteomes analysis demonstrated that CC9902 and WH8102 showed high resource allocation for phosphate uptake, accounting for 44% and 38% of overall transporter protein expression of the species. WH8102 showed high expression of the iron uptake ATP-binding cassette binding protein FutA, suggesting that a high binding affinity for iron is possibly a key adaptation strategy for some strains in oligotrophic ocean environments. One protein annotated as a phosphatase 2c (Sync_2505 and Syncc9902_0387) was highly expressed in the coastal mesotrophic strains CC9311 and CC9902, constituting 14%–16% of total membrane protein, indicating a vital, but undefined function, for strains living in temperate mesotrophic environments.     

A Suppression Subtractive Hybridization Approach Reveals Niche-Specific Genes That May Be Involved in Predator Avoidance in Marine Synechococcus Isolates

Picocyanobacteria of the genus Synechococcus are important contributors to marine primary production and are ubiquitous in the world's oceans. This genus is genetically diverse, and at least 10 discrete lineages or clades have been identified phylogenetically. However, little if anything is known about the genetic attributes which characterize particular lineages or are unique to specific strains. Here, we used a suppression subtractive hybridization (SSH) approach to identify strain- and clade-specific genes in two well-characterized laboratory strains, Synechococcus sp. strain WH8103 (clade III) and Synechococcus sp. strain WH7803 (clade V). Among the genes that were identified as potentially unique to each strain were genes encoding proteins that may be involved in specific predator avoidance, including a glycosyltransferase in strain WH8103 and a permease component of an ABC-type polysaccharide/polyol phosphate export system in WH7803. During this work the genome of one of these strains, WH7803, became available. This allowed assessment of the number of false-positive sequences (i.e., sequences present in the tester genome) present among the SSH-enriched sequences. We found that approximately 9% of the WH8103 sequences were potential false-positive sequences, which demonstrated that caution should be used when this technology is used to assess genomic differences in genetically similar bacterial strains.     

Clade-Specific 16S Ribosomal DNA Oligonucleotides Reveal the Predominance of a Single Marine Synechococcus Clade throughout a Stratified Water Column in the Red Sea

Phylogenetic relationships among members of the marine Synechococcus genus were determined following sequencing of the 16S ribosomal DNA (rDNA) from 31 novel cultured isolates from the Red Sea and several other oceanic environments. This revealed a large genetic diversity within the marine Synechococcus cluster consistent with earlier work but also identified three novel clades not previously recognized. Phylogenetic analyses showed one clade, containing halotolerant isolates lacking phycoerythrin (PE) and including strains capable, or not, of utilizing nitrate as the sole N source, which clustered within the MC-A (Synechococcus subcluster 5.1) lineage. Two copies of the 16S rRNA gene are present in marine Synechococcus genomes, and cloning and sequencing of these copies from Synechococcus sp. strain WH 7803 and genomic information from Synechococcus sp. strain WH 8102 reveal these to be identical. Based on the 16S rDNA sequence information, clade-specific oligonucleotides for the marine Synechococcus genus were designed and their specificity was optimized. Using dot blot hybridization technology, these probes were used to determine the in situ community structure of marine Synechococcus populations in the Red Sea at the time of a Synechococcus maximum during April 1999. A predominance of genotypes representative of a single clade was found, and these genotypes were common among strains isolated into culture. Conversely, strains lacking PE, which were also relatively easily isolated into culture, represented only a minor component of the Synechococcus population. Genotypes corresponding to well-studied laboratory strains also appeared to be poorly represented in this stratified water column in the Red Sea.     

DNA POLYMORPHISM WITHIN THE WH7803 SEROGROUP OF MARINE SYNECHOCOCCUS SPP. (CYANOBACTERIA)1,2

Genetic differences among ten strains of chroococcoid cyanobacteria (Synechococcus spp.) were identified by Southern blot hybridization. Data on shared number of restriction fragment length polymorphisms were used to identify the pattern and degree of genetic relatedness among the strains by two different methods of phylogenetic analysis. All the marine strains in the study contained phycoerythrin (PE) and cross-reacted with antisera directed against strain WH7803. Five contained a PE composed of phycourobilin (PUB) and phycoerythrobilin (PEB) Chromophores, and three contained a PE composed of only PEB chromophores. Two freshwater strains which do not contain PE and do not cross-react with the anti-WH7803 serum were included in the study for comparison. Dollo Parsimony analysis and cluster analysis showed that the WH7803 serogroup includes at least four widely separated genetic lineages. Strains within each lineages were closely related but the differences between lineages were as great as those between any of the marine lineages and the freshwater lineage. Strains cultured simultaneously from the same water mass were associated with different lineages. Thus, we conclude that natural assemblages of marine. Synechococcus are, at least occasionally, composed of individuals as genetically distinct from each other as members of different species or genera in other taxa.     

Examination of Genetic Relatedness of Marine Synechococcus spp. by Using Restriction Fragment Length Polymorphisms

The relatedness of several marine Synechococcus spp. was estimated by DNA hybridization. Strains isolated from various geographical locations and representing a diversity of DNA base compositions and phycobiliprotein profiles were compared by restriction fragment length polymorphisms for a number of genes. DNAs from two marine red algae and a cryptomonad alga (which exhibit a phycobiliprotein composition similar to that of the marine Synechococcus spp.) and Synechococcus strain PCC6301 (Anacystis nidulans) were also included in the comparison. Strains WH8008, WH8018, and WH7805 were shown to be very similar to one another, as were strains WH7802 and WH7803. Strains WH8110 and WH5701 were clearly unrelated to any of the other strains, and no marine Synechococcus isolate showed any similarity to the freshwater Synechococcus strain PCC6301 or the eucaryotic algae. The method is relatively straightforward and sensitive and uses a variety of basic molecular biology techniques. Its utility in ascertaining the genetic relatedness and diversity of marine Synechococcus spp. and possible extension to field studies are discussed.     

Aminopeptidase Activity in Marine Chroococcoid Cyanobacteria

Synechococci are important primary producers in the ocean and can also utilize some components of the dissolved organic matter (DOM). The readily utilizable DOM in seawater is mainly polymeric (e.g., protein, polysaccharide) or phosphorylated and requires hydrolysis prior to uptake. We examined whether synechococci express ectoenzymes to hydrolyze DOM components and considered the possible significance of ectohydrolases for Synechococcus ecology and organic matter cycling in the sea. Five strains of non-nitrogen-fixing synechococci in axenic cultures were tested for enzyme activities with fluorogenic substrates. All strains show ectocellular aminopeptidase activity, but other enzymes were undetectable. The aminopeptidase level was in the range determined for five marine heterotrophic bacterial isolates tested for comparison. Aminopeptidase was not secreted into the medium; the majority (74%; tested in WH 7803) was cell surface bound, and a small fraction was periplasmic. The periplasmic activity was not released by cold osmotic shock of WH 7803. Phenylmethylsulfonyl fluoride and EDTA, inhibitors of serine and metalloproteases, strongly or completely inhibited WH 7803 aminopeptidase. The enzyme seemed constitutive; per-cell activity did not change during incubations in unenriched seawater, bovine serum albumin, or nitrate-replete mineral medium. In natural planktonic assemblages in the Southern California Bight, aminopeptidase activity was correlated with Synechococcus abundance as well as the abundance of other bacteria. Ectocellular aminopeptidase may be common in marine synechococci and play roles in their nitrogen nutrition, particularly in low-nitrate and low-light environments. Since synechococci are much less abundant than heterotrophic bacteria in seawater, the impact of Synechococcus aminopeptidase on proteolysis in the sea is likely to be episodic and restricted to specialized microenvironments.     

Growth regulation in irradiance limited marine Synechococcus sp. WH 7803

Examinations of the macromolecular components of the protein synthesizing system (RNA, DNA and protein) have been made in the marine cyanobacterium, Synechococcus sp. WH 7803. Slowly growing, irradiance limited cells have less RNA and lower rates of RNA synthesis than do those growing at rapid rates. RNA content and synthesis increase in conjunction with division rate. Protein content is variable. Protein synthesis increases up to a plateau at division rates less the maximum observed. The results imply that there is extra protein synthetic capacity produced at high, irradiance limited growth rates. Synechococcus sp. WH 7803 responds to an increase in irradiance through a rapid shiftup in macromolecular synthesis. RNA, protein and DNA increase in a sequential fashion which precedes the onset of cell division. After decreases in irradiance, protein synthesis is maintained despite reductions in RNA. This suggests that there is some degree of physiological buffering which occurs in this species. These studies indicate that, as in more extensively studied procaryotic models, the protein synthesizing system plays a central role in the global mechanisms regulating growth in Synechococcus sp. WH 7803.Abbreviations PSS protein synthesizing system - HMW high molecular weight - LMW low molecular weight - TCA trichloroacetic acid     

EFFECT OF SPECTRAL QUALITY ON GROWTH AND PIGMENTATION OF PICOCYANOBACTERIA1

The influence of spectral quality on growth and pigmentation was compared among five strains of marine and freshwater picocyanobacteria grown under the same photon flux density (28 μE · m^?2·s^?1). Growth and phycoerythrin (PE) concentration per unit carbon increased when marine Synechococcus WH7803 was grown under green light as compared to red light, but no change in phycocyanin concentration occurred. Marine Synechococcus strain 48B66 also showed greater levels of PE when grown under green light than under red light, but no concomitant growth increase occurred. Both strains thus exhibited Group II chromatic adaptation. Additionally, strain 48B66 increased the relative level of phycourobilin compared to phycoerythrobilin when grown under red light. In contrast, both marine and freshwater Synechococcus strains containing no PE showed decreased growth under green light. Chlorophyll a concentrations were greatest or among the greatest in all strains grown under green light. These results suggest that light quality, through its effects on growth rate, may be an important factor controlling the distribution and abundance of the various pigment types of Synechococcus.     

Identification of glycine betaine as compatible solute in Synechococcus sp. WH8102 and characterization of its N-methyltransferase genes involved in betaine synthesis

Biosynthesis of glycine betaine from simple carbon sources as compatible solute is rare among aerobic heterotrophic eubacteria, and appears to be almost exclusive to the non-halophilic and slightly halophilic phototrophic cyanobacteria. Although Synechococcus sp. WH8102 (CCMP2370), a unicellular marine cyanobacterium, could grow up to additional 2.5% (w/v) NaCl in SN medium, natural abundance ¹³C nuclear magnetic resonance spectroscopy identified glycine betaine as its major compatible solute. Intracellular glycine betaine concentrations were dependent on the osmolarity of the growth medium over the range up to additional 2% NaCl in SN medium, increasing from 6.8 ± 1.5 to 62.3 ± 5.5 mg/g dw. The ORFs SYNW1914 and SYNW1913 from Synechococcus sp. WH8102 were found as the homologous genes coding for glycine sarcosine N-methyltransferase and sarcosine dimethylglycine N-methyltransferase, heterologously over-expressed respectively as soluble fraction in Escherichia coli BL21(DE3)pLysS and purified by Ni-NTA His•bind resins. Their substrate specificities and the values of the kinetic parameters were determined by TLC and ¹H NMR spectroscopy. RT-PCR analysis revealed that the two ORFs were both transcribed in cells of Synechococcus sp. WH8102 growing in SN medium without additional NaCl, which confirmed the pathway of de novo synthesizing betaine from glycine existing in these marine cyanobacteria.     

DIEL PATTERNS OF GROWTH AND DIVISION IN MARINE PICOPLANKTON IN CULTURE

The effect of a 12:12-h light:dark (LD) cycle on the phasing of several cell parameters was explored in a variety of marine picophytoplanktonic strains. These included the photosynthetic prokaryotes Prochlorococcus (strains MED 4, PCC 9511, and SS 120) and Synechococcus (strains ALMO 03, ROS 04, WH 7803, and WH 8103) and five picoeukaryotes (Bathycoccus prasinos Eikrem et Throndsen, Bolidomonas pacifica Guillou et Chrétiennot-Dinet, Micromonas pusilla Manton et Parke, Pelagomonas calceolata Andersen et Saunders, and Pycnococcus provasolii Guillard et al.). Flow cytometric analysis was used to determine the relationship between cell light scatter, pigment fluorescence, DNA (when possible), and the LD cycle in these organisms. As expected, growth and division were tightly coupled to the LD cycle for all of these strains. For both Prochlorococcus and picoeukaryotes, chl and intracellular carbon increased throughout the light period as estimated by chl fluorescence and light scatter, respectively. In response to cell division, these parameters decreased regularly during the early part of the dark period, a decrease that either continued throughout the dark period or stopped for the second half of the dark period. For Synechococcus, the decrease of chl and scatter occurred earlier (in the middle of the light period), and for some strains these cellular parameters remained constant throughout the dark period. The timing of division was very similar for all picoeukaryotes and occurred just before the subjective dusk, whereas it was more variable between the different Prochlorococcus and Synechococcus strains. The burst of division for Prochlorococcus SS 120 and PCC 9511 was recorded at the subjective dusk, whereas the MED 4 strain divided later at night. Synechococcus ALMO 03, ROS 04, and WH 7803, which have a low phycourobilin to phycoerythrobilin (PUB:PEB) ratio, divided earlier, and their division was restricted to the light period. In contrast, the high PUB:PEB Synechococcus strain WH 8103 divided preferentially at night. There was a weak linear relationship between the FALS_max:FALS_min ratio and growth rate calculated from cell counts (r = 0.83, n = 11, P < 0.05). Because of the significance of picoplanktonic populations in marine systems, these results should help to interpret diel variations in oceanic optical properties in regions where picoplankton dominates.     

CHARACTERIZATION OF A FUNCTIONAL VANADIUM‐DEPENDENT BROMOPEROXIDASE IN THE MARINE CYANOBACTERIUM SYNECHOCOCCUS SP. CC93111

Vanadium‐dependent bromoperoxidases (VBPOs) are characterized by the ability to oxidize halides using hydrogen peroxide. These enzymes are well‐studied in eukaryotic macroalgae and are known to produce a variety of brominated secondary metabolites. Though genes have been annotated as VBPO in multiple prokaryotic genomes, they remain uncharacterized. The genome of the coastal marine cyanobacterium Synechococcus sp. CC9311 encodes a predicted VBPO (YP_731869.1, sync_2681), and in this study, we show that protein extracts from axenic cultures of Synechococcus possess bromoperoxidase activity, oxidizing bromide and iodide, but not chloride. In‐gel activity assays of Synechococcus proteins separated using PAGE reveal a single band having VBPO activity. When sequenced via liquid chromatography/mass spectrometry/mass spectrometry (LC/MS/MS), peptides from the band aligned to the VBPO sequence predicted by the open reading frame (ORF) sync_2681. We show that a VBPO gene is present in a closely related strain, Synechococcus sp. WH8020, but not other clade I Synechococcus strains, consistent with recent horizontal transfer of the gene into Synechococcus. Diverse cyanobacterial‐like VBPO genes were detected in a pelagic environment off the California coast using PCR. Investigation of functional VBPOs in unicellular cyanobacteria may lead to discovery of novel halogenated molecules and a better understanding of these organisms’ chemical ecology and physiology.     

Selection and Characterization of Cyanophage Resistance in Marine Synechococcus Strains

Marine viruses are an important component of the microbial food web, influencing microbial diversity and contributing to bacterial mortality rates. Resistance to cooccurring cyanophages has been reported for natural communities of Synechococcus spp.; however, little is known about the nature of this resistance. This study examined the patterns of infectivity among cyanophage isolates and unicellular marine cyanobacteria (Synechococcus spp.). We selected for phage-resistant Synechococcus mutants, examined the mechanisms of phage resistance, and determined the extent of cross-resistance to other phages. Four strains of Synechococcus spp. (WH7803, WH8018, WH8012, and WH8101) and 32 previously isolated cyanomyophages were used to select for phage resistance. Phage-resistant Synechococcus mutants were recovered from 50 of the 101 susceptible phage-host pairs, and 23 of these strains were further characterized. Adsorption kinetic assays indicate that resistance is likely due to changes in host receptor sites that limit viral attachment. Our results also suggest that receptor mutations conferring this resistance are diverse. Nevertheless, selection for resistance to one phage frequently resulted in cross-resistance to other phages. On average, phage-resistant Synechococcus strains became resistant to eight other cyanophages; however, there was no significant correlation between the genetic similarity of the phages (based on g20 sequences) and cross-resistance. Likewise, host Synechococcus DNA-dependent RNA polymerase (rpoC1) genotypes could not be used to predict sensitivities to phages. The potential for the rapid evolution of multiple phage resistance may influence the population dynamics and diversity of both Synechococcus and cyanophages in marine waters.     

Comparative phosphorus nutrition of the marine cyanobacterium Synechococcus WH7803 and the marine diatom Thalassiosira weissflogii

Phosphate uptake kinetics of Synechococcus sp. WH7803 and Thalassiosiraweissflogii were studied in axenic batch culture. Phosphate-repleteSynechococcus sp. WH7803 cells have a lower affinity for inorganicphosphate (Pi) (K_s = 67 µmol l^–1) than Pi-starvedcells (K_s = 3.1 µmol l^–1). The K_s of Pi-starvedcells increased