Amoebic grazing of freshwater Synechococcus strains rich in phycocyanin

Fifteen strains of naked amoebae were presented with 19 strains of Synechococcus on an agar surface. After 14 days of incubation, each of the 285 combinations yielded one of three responses. 42.1% of combinations showed clearing (digestion) of the Synechococcus (C), 56.5% of combinations showed no clearing of the Synechococcus (N) while 1.4% of combinations showed partial clearing of the Synechococcus (P). In general, the Synechococcus strains showed variability in their susceptibility to digestion by the amoebae and the amoebae showed variability in their ability to digest the Synechococcus strains. There was no evidence for amoebae actively selecting profitable prey and equivalent-sized Synechococcus strains were ingested at the same rate, irrespective of their fate. There was some evidence of 'size-selective' grazing in that amoebae ingested the smaller Synechococcus strains at higher rates than the larger strains. However, there was no correlation between prey size and their ultimate fate. These data suggest that amoebae are not selective with regard to the ingestion of synechococci, but that 'selection' occurs at the digestion stage, i.e. whether the synechococci are digested or not.     

Abundance and distribution of Synechococcus spp. and cyanophages in the Chesapeake Bay

Despite the increasing knowledge of Synechococcus spp. and their co-occurring cyanophages in oceanic and coastal water, little is known about their abundance, distribution, and interactions in the Chesapeake Bay estuarine ecosystem. A 5-year interannual survey shows that Synechococcus spp. and their phages are persistent and abundant members of Chesapeake Bay microbial communities. Synechococcus blooms (10⁶ cells ml⁻¹) were often observed in summer throughout the Bay, contributing 20 to 40% of total phytoplankton chlorophyll a. The distribution of phycoerythrin-containing (PE-rich) Synechococcus cells appeared to mostly correlate with the salinity gradient, with higher abundances at higher salinities. Cyanophages infectious to Synechococcus were also abundant (up to 6 × 10⁵ viruses ml⁻¹ by the most probable number assay) during summer months in the Bay. The covariation in abundance of Synechococcus spp. and cyanophages was evident, although the latitude of observed positive correlation varied in different years, mirroring the changing environmental conditions and therefore the host-virus interactions. The impacts of cyanophages on host Synechococcus populations also varied spatially and temporally. Higher phage-related Synechococcus mortality was observed in drought years. Virus-mediated host mortality and subsequent liberation of dissolved organic matter (DOM) may substantially influence oceanic biogeochemical processing through the microbial loop as well as the microbial carbon pump. These observations emphasize the influence of environmental gradients on natural Synechococcus spp. and their phage population dynamics in the estuarine ecosystem.     

Distribution of Synechococcus spp. determined by immunofluorescent assay

By using two polyclonal antisera against WH 7803 strain (Synechococcus sp.) and WH 5701 strain (Synechococcus bacillaris) it is possible to detect and to enumerate cells of the two cyanobacterial serogroups. The immunofluorescence technique was used to study the distribution of the two serogroups in the estuarine, coastal and upwelling waters of the Mediterranean Sea surrounding Messina. In the estuarine waters of the Alcantara River (Ionian Sea), the WH 7803 serogroup was present at a concentration in the order of 10² cells ml⁻¹ and the WH 5701 serogroup at a concentration of 5·5 × 10² cellsml⁻¹. In the coastal waters of Messina, where urban and industrial wastes are usuallydumped, the concentration of total phycoerythrin- Synechococcus ranged from 1·3 × 10² to 4·1 × 10³ cells ml⁻¹; the WH 7803 serogroup accounted for 50–94% of the totalpopulation in Ionian stations, whereas the WH 5701 serogroup ranged from1·4 × 10¹ to6·7 × 102cells ml⁻¹. In the upwelling area (Straits of Messina) bothserogroups were found. Vertical distribution of two Synechococcus strains had anopposite trend and their concentrations were of the order of 10¹–10²cells ml⁻¹. Theuse of the Scan laser system allows both autofluorescent and labelled organismsto be distinguished in a preparation for optical microscopy. It also allows false-positivecells to be distinguished.     

Characterization of phycoerythrin-containing Synechococcus spp. populations by immunofluorescence

Using an immunofluorescence assay developed to identify serogroups(i.e. clusters of strains labelled by one antiserum), the compositionof natural populations of phycoerythrin-containing Synechococcusspp. was examined. The 7803 (open ocean clone)-serogroup wasfound in most oceanic regions, but was most prevalent (up to85%) in tropical and subtropical waters during spring and summer.At coastal Long Island stations it was most abundant (up to65%) when water temperatures were >22°C. The seasonaland geographic distribution of the 7803-serogroup appeared tobe limited by water temperature. No consistent pattern was observedin the per cent composition with depth in the Sargasso Sea orat coastal to offshore stations in the North-west Atlantic Oceanor eastern tropical North Pacific Ocean. The 8016 (coastal clone)-serogroupwas abundant at coastal and estuarine stations off Long Island(up to 95 %) and its appearance was also correlated with warmwater temperature (> 15°C). However, this serogroup remaineda constant proportion of the population at the Long Island Soundstation during early winter months (through January) when abundanceof the 7803-serogroup was negligible. Owing to limited data,the oceanic distribution of the 8016-serogroup is not yet discernible.Lastly, antisera to the phycocyanin-dominant Synechococcus spp.clones failed to label any cells in samples collected from severaloceanic stations. Thus, these strains appear to be limited tocoastal and estuarine regions, which is consistent with predictionsfrom experiments comparing the photosynthetic performance ofthe phycoerythrin-dominant and phycocyanin-dominant clones. ¹Present address: Department of Oceanography, University ofHawaii, Honolulu, HI 96822, USA     

Effect of Temperature on Photosynthesis and Growth in Marine Synechococcus spp.

In this study, we develop a mechanistic understanding of how temperature affects growth and photosynthesis in 10 geographically and physiologically diverse strains of Synechococcus spp. We found that Synechococcus spp. are able to regulate photochemistry over a range of temperatures by using state transitions and altering the abundance of photosynthetic proteins. These strategies minimize photosystem II (PSII) photodamage by keeping the photosynthetic electron transport chain (ETC), and hence PSII reaction centers, more oxidized. At temperatures that approach the optimal growth temperature of each strain when cellular demand for reduced nicotinamide adenine dinucleotide phosphate (NADPH) is greatest, the phycobilisome (PBS) antenna associates with PSII, increasing the flux of electrons into the ETC. By contrast, under low temperature, when slow growth lowers the demand for NADPH and linear ETC declines, the PBS associates with photosystem I. This favors oxidation of PSII and potential increase in cyclic electron flow. For Synechococcus sp. WH8102, growth at higher temperatures led to an increase in the abundance of PBS pigment proteins, as well as higher abundance of subunits of the PSII, photosystem I, and cytochrome b6f complexes. This would allow cells to increase photosynthetic electron flux to meet the metabolic requirement for NADPH during rapid growth. These PBS-based temperature acclimation strategies may underlie the larger geographic range of this group relative to Prochlorococcus spp., which lack a PBS.Marine picocyanobacteria are the most abundant phytoplankton, inhabiting nearly every area of the surface ocean and dominating in tropical and subtropical waters. The smallest and most abundant marine picocyanobacteria belong to the genera Synechococcus and Prochlorococcus, which together account for one-third of the total primary production on Earth (Partensky et al., 1999b). Marine Synechococcus spp. are genetically diverse (Scanlan et al., 2009; Mazard et al., 2012), play an important role in the biogeochemical cycling of carbon (Grob et al., 2007), and are found from the equator to the polar circle, though they are less abundant at higher latitudes (Agusti, 2004; Scanlan et al., 2009; Huang et al., 2012). Temperature is a major factor that controls photosynthetic rates, and the biogeography of Synechococcus spp. strains in the modern ocean has been linked to temperature (Zwirglmaier et al., 2008). In this study, we explore the effect of temperature on growth and photosynthesis in several Synechococcus spp. strains.Photosynthetic electron transport in cyanobacteria, including Synechococcus spp., shares similarities with that of plants and green algae (Fig. 1). Photosynthetic organisms are commonly able to perform photosynthesis efficiently over a range of temperatures bracketing the optimal growth temperature (T_opt). However, decreased metabolic rates at temperatures too far below T_opt can cause an imbalance between photochemistry and metabolism, leading to photodamage (Huner et al., 1996). By contrast, elevated temperatures may affect membrane fluidity and denature proteins, which can also lead to a decline in photosynthetic efficiency (Falk et al., 1996). A range of diverse acclimation strategies have evolved among algae and plants to balance electron flow through the electron transport chain (ETC) during temperature fluctuations (Maxwell et al., 1994; Krol et al., 1997; Gray et al., 1998; Miśkiewicz et al., 2000).Open in a separate windowFigure 1.PBS structure and linear photosynthetic electron flow in cyanobacteria. In this schematic, the PBS is in “state 1,” indicating it is associated with a PSII dimer. Photosynthetic electron flow pathways are indicated by black arrows, and chemical reactions are indicated by blue arrows. Major ETC components include PSII, PSI, PQ/plastoquinol (PQH₂), cytochrome b6f (Cyt b6f), plastocyanin (PLC), ferredoxin (FX), flavodoxin (FL), and ferredoxin/flavodoxin NADP reductase (FNR). Other proteins depicted include the phycobiliproteins APC, PC, two forms of PE (PE I and PE II), PSII chlorophyll-binding proteins CP47 and CP43, the PSII core polypeptides D1 and D2, the PSI chlorophyll-binding core proteins PsaA and PsaB, and the PSI reaction center subunit PsaD. [See online article for color version of this figure.]Less is known about mechanisms marine cyanobacteria use to acclimate to temperature. Cyanobacteria differ from plants and green algae in that photosynthesis and respiration occur in the same membrane. In addition, the ratios of PSII:PSI are more variable in cyanobacteria (Campbell et al., 1998; Bailey et al., 2008), which can impact the flow of electrons through the ETC. Cells must prevent overreduction of the ETC because this can lead to damage of the D1 polypeptide of PSII in a process called photoinhibition; to sustain PSII activity, replacement of the damaged D1 by de novo protein synthesis is required (Aro et al., 1993). Cyanobacteria have evolved a suite of strategies to balance electron flow in the thylakoid membrane when the cells are exposed to high light; important strategies include nonphotochemical quenching (El Bissati et al., 2000; Bailey and Grossman, 2008) and alternative electron flow pathways (Asada, 1999; Bailey et al., 2008; Mackey et al., 2008). Cyanobacteria may also selectively funnel light energy to PSII or PSI to regulate the amount of electrons entering and exiting the ETC (Campbell et al., 1998).In cyanobacteria, including Synechococcus spp., the main light-harvesting antennae are water-soluble pigment-protein complexes called phycobilisomes (PBSs; Grossman et al., 1993; Six et al., 2007). Unlike the antenna of plants and algae that are embedded within the thylakoid membrane, PBSs are located on the cytoplasmic surface of the membrane (Fig. 1). Structurally, the PBS consists of phycobiliproteins, including the PBS core allophycocyanin (APC) and lateral rods of phycocyanin (PC) and phycoerythrin (PE; Fig. 1). The PBS core has evolved together with the core genome of Synechococcus spp., whereas the rod components appear to have evolved separately through gene duplication, DNA exchange between cells, and possibly virally mediated lateral gene transfer (Six et al., 2007). Each phycobiliprotein binds chromophores called phycobilins (linear tetrapyrroles) that selectively absorb different wavelengths of green-red light, thereby extending the range of photosynthetically active radiation the cell can use beyond that of chlorophyll (Campbell et al., 1998). The PBS is capable of rapid diffusion over the thylakoid membrane surface (Mullineaux et al., 1997), where it can associate with either PSI or PSII. The PBS is a mobile antenna element that does not bind chlorophyll and that likely associates with reaction centers by weak interactions with lipid head groups (Sarcina et al., 2001).State transitions, the movements of PBS or other antenna pigments between reaction centers, allow the cells to avoid PSII photodamage by balancing electron flow such that electrons do not accumulate within the ETC. Whether the PBS associates with PSI or PSII is determined by the redox poise of the plastoquinone (PQ) pool (Fig. 1), which serves as an indicator of electron flow through the ETC. When the PQ pool is oxidized, the PBS becomes associated with PSII (state 1) such that the rate of linear electron flow increases. By contrast, a reduced PQ pool elicits affiliation of the PBS with PSI (state 2), which could increase the withdrawal of electrons from the ETC. In the dark, the PQ pool tends to be reduced due to respiratory electron flow, and the PBS affiliates primarily with PSI.Recent ocean basin scale research has shed light on the role of temperature on the global distributions of Synechococcus spp. in the ocean. Collectively, these studies have shown that marine Synechococcus spp. tolerate a broad range of temperatures, likely due to high genetic diversity among strains. For example, of the four clades that dominate in natural communities, clades I and IV typically inhabit cooler waters north of 30°N and south of 30°S (Brown et al., 2005; Zwirglmaier et al., 2007, 2008), while clades II and III generally inhabit warmer tropical and subtropical waters (Fuller et al., 2006; Zwirglmaier et al., 2008). Other Synechococcus spp. sequences have been recently identified from colder waters in the northern Bering Sea and Chukchi Sea, suggesting that a possible cold adaptation could exist in some strains present at high latitudes (Huang et al., 2012). Still, other studies have found no relationship between Synechococcus spp. abundance and temperature (Zinser et al., 2007), suggesting that additional factors (e.g. nutrient availability) may be responsible for shaping Synechococcus spp. community structure (Palenik et al., 2003, 2006; Scanlan et al., 2009).While field surveys have made great strides in understanding the role of temperature in controlling picocyanobacteria distributions, much remains to be learned about the range of growth responses to temperature that can occur in marine Synechococcus spp. To date, characterization of individual Synechococcus spp. strains includes work with two isolates from the Sargasso Sea, showing variable responses to temperature (Moore et al., 1995; Fu et al., 2007). These studies demonstrate the potential for changing sea surface temperature (SST) to influence the biogeochemical role of Synechococcus spp. in the Sargasso Sea; however, little is known about whether these responses can be generalized to other strains or environments. Changes in growth rate and photosynthetic efficiency, if they occur, could alter global Synechococcus spp. distributions, affect ecosystem structure, and ultimately impact marine biogeochemical cycles and Earth’s climate, and thus could have important implications for the earth system.A mechanistic understanding of how temperature affects growth and photosynthesis in geographically and physiologically diverse strains of Synechococcus spp. is needed to clarify how temperature influences Synechococcus spp. biogeography, as well as to provide insights into how populations are likely to respond to increased SST in the future. The goal of this study is to characterize the growth, photosynthetic efficiency, and light-harvesting characteristics of 10 diverse Synechococcus spp. isolates over a range of temperatures. Using chlorophyll fluorescence analysis, we show that regulation of light harvesting via state transitions is an important acclimation process that allows cells to increase photosynthetic electron flow under high temperature conditions. This effect is enhanced for strains with higher proportions of phycoerythrobilin and phycouribilin. We use global proteome data from Synechococcus sp. WH8102 to show that this temperature-dependent enhancement is brought about in part by an increase in the abundance of PBS proteins, as well as proteins from PSII, PSI, and other ETC components. The results are discussed in the context of Synechococcus spp. biogeography in the modern ocean, and potential implications for how cells could respond to future increases in SST are considered.     

Patterns and regulation of silicon accumulation in Synechococcus spp.

Six clones of the marine cyanobacterium Synechococcus, representing four major clades, were all found to contain significant amounts of silicon in culture. Growth rate was unaffected by silicic acid, Si(OH)₄, concentration between 1 and 120 μM suggesting that Synechococcus lacks an obligate need for silicon (Si). Strains contained two major pools of Si: an aqueous soluble and an aqueous insoluble pool. Soluble pool sizes correspond to estimated intracellular dissolved Si concentrations of 2–24 mM, which would be thermodynamically unstable implying the binding of intracellular soluble Si to organic ligands. The Si content of all clones was inversely related to growth rate and increased with higher [Si(OH)₄] in the growth medium. Accumulation rates showed a unique bilinear response to increasing [Si(OH)₄] from 1 to 500 μM with the rate of Si acquisition increasing abruptly between 80 and 100 μM Si(OH)₄. Although these linear responses imply some form of diffusion‐mediated transport, Si uptake rates at low Si (~1 μM Si) were inhibited by orthophosphate, suggesting a role of phosphate transporters in Si acquisition. Theoretical calculations imply that observed Si acquisition rates are too rapid to be supported by lipid‐solubility diffusion of Si through the plasmalemma; however, facilitated diffusion involving membrane protein channels may suffice. The data are used to construct a working model of the mechanisms governing the Si content and rate of Si acquisition in Synechococcus.     

Survival ability of cytotoxic strains of motile Aeromonas spp. in different types of water

The ability of motile Aeromonas spp. to survive in drinking water (mineral and tap water) and in sea water was experimentally tested. Clinically isolated cytotoxic strains of A. hydrophila, A. caviae and A. sobria were selected for this study. After contamination of water samples, the survival of Aeromonas strains was studied for at least three months using viable counts. The results obtained show that the survival of the Aeromonas spp. varies considerably depending on species and water type. For all three species, the survival time was longest in mineral water, where viable bacteria of each strain were still detected after 100 d. Moreover, A hydrophila and A. caviae also re-grew on the first day. In tap water all strains showed marked survival, although to a lesser extent than in mineral water. Aeromonas cells showed a rapid decline in sea water (90% reduction in viable cells after about two d) and thus seem to be more sensitive to saline/marine stress than chlorination.     

Dynamics and Distribution of Cyanophages and Their Effect on Marine Synechococcus spp.

Cyanophages infecting marine Synechococcus cells were frequently very abundant and were found in every seawater sample along a transect in the western Gulf of Mexico and during a 28-month period in Aransas Pass, Tex. In Aransas Pass their abundance varied seasonally, with the lowest concentrations coincident with cooler water and lower salinity. Along the transect, viruses infecting Synechococcus strains DC2 and SYN48 ranged in concentration from a few hundred per milliliter at 97 m deep and 83 km offshore to ca. 4 × 10⁵ ml^-1 near the surface at stations within 18 km of the coast. The highest concentrations occurred at the surface, where salinity decreased from ca. 35.5 to 34 ppt and Synechococcus concentrations were greatest. Viruses infecting strains SNC1, SNC2, and 838BG were distributed in a similar manner but were much less abundant (<10 to >5 × 10³ ml^-1). When Synechococcus concentrations exceeded ca. 10³ ml^-1, cyanophage concentrations increased markedly (ca. 10² to > 10⁵ ml^-1), suggesting that a minimum host density was required for efficient viral propagation. Data on the decay rate of viral infectivity d (per day), as a function of solar irradiance I (millimoles of quanta per square meter per second), were used to develop a relationship (d = 0.2610I - 0.00718; r² = 0.69) for conservatively estimating the destruction of infectious viruses in the mixed layer of two offshore stations. Assuming that virus production balances losses and that the burst size is 250, ca. 5 to 7% of Synechococcus cells would be infected daily by viruses. Calculations based on contact rates between Synechococcus cells and infectious viruses produce similar results (5 to 14%). Moreover, balancing estimates of viral production with contact rates for the farthest offshore station required that most Synechococcus cells be susceptible to infection, that most contacts result in infection, and that the burst size be about 324 viruses per lytic event. In contrast, in nearshore waters, where ca. 80% of Synechococcus cells would be contacted daily by infectious cyanophages, only ca. 1% of the contacts would have to result in infection to balance the estimated virus removal rates. These results indicate that cyanophages are an abundant and dynamic component of marine planktonic communities and are probably responsible for lysing a small but significant portion of the Synechococcus population on a daily basis.     

Nonribosomal peptide synthetase genes occur in most cyanobacterial genera as evidenced by their distribution in axenic strains of the PCC

Previous studies largely carried out with environmental samples or axenic and non-axenic cultures suggested that cyanobacteria may be a rich source of hitherto unexplored bioactive compounds. This has been confirmed in the present study by a screening of 146 axenic strains from the Pasteur Culture Collection (PCC) of cyanobacteria. Use of degenerate PCR primers, designed on the basis of conserved sequence motifs in the aminoacyl-adenylation domain of peptide synthetases, revealed the presence of the corresponding genes in the majority (75.3%) of the strains examined. Among unicellular cyanobacteria, only Chamaesiphon sp. strain PCC 6605, two strains of Gloeocapsa and most Microcystis isolates (22 out of 24) contained these genes; no amplicons were detected for any members of the genera Cyanothece, Gloeobacter and Gloeothece and the genetically diverse representatives of Synechococcus and Synechocystis. By contrast, eight out of ten pleurocapsalean members, 16 out of 25 oscillatorian strains, and all but two of the 63 filamentous heterocystous cyanobacteria tested gave positive amplification results. This information will be highly valuable for further exploring the corresponding cyanobacterial peptides and for elucidating the bioactivity of such non-ribosomally synthesized molecules.     

Novel miniature transposable elements in thermophilic Synechococcus strains and their impact on an environmental population

The genomes of the two closely related freshwater thermophilic cyanobacteria Synechococcus sp. strain JA-3-3Ab and Synechococcus sp. strain JA-2-3B′a(2-13) each host several families of insertion sequences (ISSoc families) at various copy numbers, resulting in an overall high abundance of insertion sequences in the genomes. In addition to full-length copies, a large number of internal deletion variants have been identified. ISSoc2 has two variants (ISSoc2∂-1 and ISSoc2∂-2) that are observed to have multiple near-exact copies. Comparison of environmental metagenomic sequences to the Synechococcus genomes reveals novel placement of copies of ISSoc2, ISSoc2∂-1, and ISSoc2∂-2. Thus, ISSoc2∂-1 and ISSoc2∂-2 appear to be active nonautonomous mobile elements derived by internal deletion from ISSoc2. Insertion sites interrupting genes that are likely critical for cell viability were detected; however, most insertions either were intergenic or were within genes of unknown function. Most novel insertions detected in the metagenome were rare, suggesting a stringent selective environment. Evidence for mobility of internal deletion variants of other insertion sequences in these isolates suggests that this is a general mechanism for the formation of miniature insertion sequences.     

Comparative evaluation of different preservation methods for cyanobacterial strains

Maintaining pure cultures using preservation methods is of high importance for biotechnological purposes. However, preservation does not necessarily guarantee the genetic stability of these cultures. Therefore, preservation methods are currently needed to assure viability as well as genetic, physiological, and morphological integrity across storage periods. In this study, preservation of five isolates from the microalgae and cyanobacteria collection of the Plant Biology Department, Federal University of Viçosa, Minas Gerais, Brazil was investigated via monthly analyses of cell viability, biomass recovery, and contaminant concentrations over a period of 120 days. Lyophilization was adequate for both heterocystous cyanobacteria and other strains that were able to differentiate hormogones or to synthesize thick layers of exopolysaccharides. Lyophilization was also able to maintain cultures with low levels of contaminants. Dimethyl sulfoxide was relatively efficient, though some of the strains were susceptible to its cytotoxic effects. Our results demonstrated that cryopreservation with glycerol was the most efficient method. The ability to routinely preserve cyanobacterial strains reduces costs associated with maintaining large culture collections and reduces the risks of losing particular strains or species through contamination and genetic drift. The results obtained in this study are therefore discussed in the context of the efficiency of the methods and the current need to develop suitable methods for maintenance of cyanobacterial collections.     

Chemotaxis toward Nitrogenous Compounds by Swimming Strains of Marine Synechococcus spp.

Many of the open-ocean isolates of the marine unicellular cyanobacterium Synechococcus spp. are capable of swimming motility, whereas coastal isolates are nonmotile. Surprisingly, the motile strains do not display phototactic or photophobic responses to light, but they do demonstrate positive chemoresponses to several nitrogenous compounds. The chemotactic responses of Synechococcus strain WH8113 were investigated using blind-well chemotaxis chambers fitted with 3.0-μm-pore-size Nuclepore filters. One well of each chamber contained cells suspended in aged Sargasso Sea water, and the other well contained the potential chemoattractant in seawater. The number of cells that crossed the filter into the attractant-seawater mixture was measured by direct cell counts and compared with values obtained in chambers lacking gradients. Twenty-two compounds were tested, including sugars, amino acids, and simple nitrogenous substrates, at concentrations ranging from 10⁻⁵ to 10⁻¹⁰ M. Strain WH8113 responded positively only to ammonia, nitrate, β-alanine, glycine, and urea. Typically, there was a 1.5- to 2-fold increase in cell concentrations above control levels in chambers containing these compounds, which is comparable to results from similar experiments using enteric and photoheterotrophic bacteria. However, the threshold levels of 10⁻⁹ to 10⁻¹⁰ M found for Synechococcus spp. chemoresponses were lower by several orders of magnitude than those reported for other bacteria and fell within a range that could be ecologically significant in the oligotrophic oceans. The presence of chemotaxis in motile Synechococcus spp. supports the notion that regions of nutrient enrichment, such as the proposed microzones and patches, may play an important role in picoplankton nutrient dynamics.     

Comparison of methods for detection of Erysipelothrix spp. and their distribution in some Australasian seafoods

For many years, Erysipelothrix rhusiopathiae has been known to be the causative agent of the occupationally related infection erysipeloid. A survey of the distribution of Erysipelothrix spp. in 19 Australasian seafoods was conducted, and methodologies for the detection of Erysipelothrix spp. were evaluated. Twenty-one Erysipelothrix spp. were isolated from 52 seafood parts. Primary isolation of Erysipelothrix spp. was most efficiently achieved with brain heart infusion broth enrichment followed by subculture onto a selective brain heart infusion agar containing kanamycin, neomycin, and vancomycin after 48 h of incubation. Selective tryptic soy broth, with 48 h of incubation, was the best culture method for the detection of Erysipelothrix spp. with PCR. PCR detection was 50% more sensitive than culture. E. rhusiopathiae was isolated from a variety of different fish, cephalopods, and crustaceans, including a Western rock lobster (Panulirus cygnus). There was no significant correlation between the origin of the seafoods tested and the distribution of E. rhusiopathiae. An organism indistinguishable from Erysipelothrix tonsillarum was isolated for the first time from an Australian oyster and a silver bream. Overall, Erysipelothrix spp. were widely distributed in Australasian seafoods, illustrating the potential for erysipeloid-like infections in fishermen.     

Isolation of Dunaliella spp. from a hypersaline lake and their ability to accumulate glycerol

The purpose of the present work was to study the potential biotechnological use of Dunaliella species isolated from a hypersaline lake in Turkey. Dunaliella spp. grown in Johnson's medium were isolated and their glycerol production was studied in a batch system in order to determine the optimal conditions required for the highest glycerol accumulation. In the experiments performed with four newly isolated Dunaliella spp., the maximum glycerol accumulation was obtained at 20% NaCl concentration, and pH 6 (for strains T1 and T2) and pH 9 (for strains T3 and T4). Biomass production by strain T2 was significantly higher that by the other strains but the highest glycerol production in broth was obtained by strain T1 followed by strain T2. Strain T1 showed high glycerol production, i.e. 452.57microg/ml of culture broth at 20% NaCl concentration. The highest glycerol accumulation on both dry weight and cell basis was obtained with strain T1, followed by strains T3 and T4 (55.01, 50.16, and 40.23microg/10(6) cells (or pg/cell), respectively) at 25% NaCl concentration. When the high initial inoculum concentration was used at 25% NaCl concentration, strain T1 had the shortest (approximately 10-15days) lag period. This study shows that the isolated strains T1 and T2 can be used for glycerol production because of their high productivity.     

Chroococcoid cyanobacteria Synechococcus spp. in the Black Sea: pigments, size, distribution, growth and diurnal variability

Phycoerythrin-containing unicellular cyanobacteria Synechococcusspp. were studied for the first time during April–May,1994 and September–October, 1996, in the western and southernBlack Sea for pigments, size and abundance distribution viaspectrometry, epifluorescence microscopy and flow cytometry.Abundance distribution in the surface mixed layer in April–May,1994, revealed that cells were more concentrated in offshorewaters than in coastal regions under the direct influence ofthe river Danube. However, in the south, higher surface cellconcentrations were characteristic of the nearshore areas duringSeptember–October, 1996. A highly significant correlationwas observed between cell abundance and ambient physico-chemicalparameters with depth. Visual inspection of the individual cellsunder the epifluorescence microscope revealed that cells atthe subsurface, chlorophyll a maximum layer (SCML, based onin situ fluorometer readings) fluoresce more brightly and forlonger than those at the surface and at lower depths. Spectralproperties of a total of 64 Synechococcus spp. clonal isolatesfrom different depths within the euphotic layer (about the top60 m) in the southern Black Sea coast showed that all have type2 phycoerythrobilin in common, lacking phycourobilin. In vivofluorescence emission maxima for phycoerythrobilin were aboutthe same (~578 nm) for all isolates. All isolates had in vivoabsorption maxima at between 435 and 442 nm, and at about 681nm due to chlorophyll a. It was shown from the flow cytometermean forward light scatter data for size distribution that cellsat the surface mixed layer (0–10 m) were larger than cellsat lower depths (20–60 m). Based on in vivo fluorescencemeasurements, significant differences in the acclimated growthrates of clones from different depths were observed. Time versuscell count plots showed that cells of the cyanobacteria Synechococcusspp. are under grazing pressure, from midnight until noon, andslowly begin to rebuild their population in the afternoon bydividing throughout the evening.