Effects of PCB on interspecific competition in natural and gnotobiotic phytoplankton communities in continuous and batch cultures

The toxicity of polychlorinated biphenyls (PCB) to the diatomThalassiosira pseudonana (formerlyCyclotella nana), grown in pure and mixed cultures, was greatest when in competition with other species. Continuous cultures were superior to batch cultures for studying competitive interactions, and PCB caused greater alteration of species composition in continuous cultures than it did in batch cultures. Natural phytoplankton communities from Vineyard Sound, maintained in continuous culture, responded to PCB stress the same as did gnotobiotic communities, withT. pseudonana showing similar responses in both communities. A PCB concentration of 0.1 μg/liter (0.1 part per billion), a level not uncommon in natural waters, did not affect algal growth in pure cultures but caused substantial disruption of continuous culture communities. The possible impact of PCB pollution on natural phytoplankton communities is discussed. Contribution No. 3181 from the Woods Hole Oceanographic Institution.     

Conservation of PHO pathway in ascomycetes and the role of Pho84

In budding yeast, Saccharomyces cerevisiae, the phosphate signalling and response pathway, known as PHO pathway, monitors phosphate cytoplasmic levels by controlling genes involved in scavenging, uptake and utilization of phosphate. Recent attempts to understand the phosphate starvation response in other ascomycetes have suggested the existence of both common and novel components of the budding yeast PHO pathway in these ascomycetes. In this review, we discuss the components of PHO pathway, their roles in maintaining phosphate homeostasis in yeast and their conservation across ascomycetes. The role of high-affinity transporter, Pho84, in sensing and signalling of phosphate has also been discussed     

Phosphorus supply drives rapid turnover of membrane phospholipids in the diatom Thalassiosira pseudonana

In low-phosphorus (P) marine systems, phytoplankton replace membrane phospholipids with non-phosphorus lipids, but it is not known how rapidly this substitution occurs. Here, when cells of the model diatom Thalassiosira pseudonana were transferred from P-replete medium to P-free medium, the phospholipid content of the cells rapidly declined within 48 h from 45±0.9 to 21±4.5% of the total membrane lipids; the difference was made up by non-phosphorus lipids. Conversely, when P-limited T. pseudonana were resupplied with P, cells reduced the percentage of their total membrane lipids contributed by a non-phosphorus lipid from 43±1.5 to 7.3±0.9% within 24 h, whereas the contribution by phospholipids rose from 2.2±0.1 to 44±3%. This dynamic phospholipid reservoir contained sufficient P to synthesize multiple haploid genomes, suggesting that phospholipid turnover could be an important P source for cells. Field observations of phytoplankton lipid content may thus reflect short-term changes in P supply and cellular physiology, rather than simply long-term adjustment to the environment.     

Novel Trichoderma polysporum Strain for the Biocontrol of Pseudogymnoascus destructans,the Fungal Etiologic Agent of Bat White Nose Syndrome

White-nose syndrome (WNS), an emerging disease of hibernating bats, has rapidly spread across eastern North America killing millions of bats. Pseudogymnoascus destructans (Pd), the sole etiologic agent of WNS, is widespread and persistent in bat hibernacula. Control of Pd in the affected sites is urgently needed to break the transmission cycle while minimizing any adverse impact on the native organisms. We isolated a novel strain of Trichoderma polysporum (Tp) from one of the caves at the epicenter of WNS zoonotic. Detailed experimental studies revealed: (1) Tp WPM 39143 was highly adapted to grow at temperatures simulating the cave environment (6°C-15°C), (2) Tp WPM 39143 restricted Pd colony growth in dual culture challenges, (3) Tp WPM 39143 caused four logs reduction of Pd colony forming units and genome copies in autoclaved soil samples from one of the WNS affected caves, (4) Tp WPM 39143 extract showed specific fungicidal activity against Pd in disk diffusion assay, but not against closely related fungus P. pannorum (Pp), (5) Tp WPM 39143 extract retained inhibitory activity after exposure to high temperatures, light and proteinase K, and (6) Inhibitory metabolites in Tp WPM 39143 extract comprised of water-soluble, high polarity compounds. These results suggest that Tp WPM 39143 is a promising candidate for further evaluation as a biocontrol agent of Pd in WNS affected sites.     

Differential Growth Responses of Marine Phytoplankton to Herbicide Glyphosate

Glyphosate is a globally popular herbicide to kill weeds and its wide applications may lead to accumulation in coastal oceans as a source of phosphorus (P) nutrient or growth inhibitor of phytoplankton. We studied the physiological effects of glyphosate on fourteen species representing five major coastal phytoplankton phyla (haptophyta, bacillariophyta, dinoflagellata, raphidophyta, and chlorophyta). Based on growth responses to different concentrations of glyphosate under contrasting dissolved inorganic phosphorus (DIP) conditions, we found that phytoplankton species could be classified into five groups. Group I (Emiliania huxleyi, Skeletonema costatum, Phaeodactylum tricornutum) could utilize glyphosate as sole P-source to support growth in axenic culture, but in the presence of DIP, they were inhibited by both 36-μM and 360-μM glyphosate. Group II (Karenia mikimotoi, Prorocentrum minimum, Dunaliella tertiolecta, Symbiodinium sp., Heterosigma akashiwo and Alexandrium catenella) could not utilize glyphosate as sole P-source to support growth, and in the presence of DIP growth was not affected by 36-μM but inhibited by 360-μM glyphosate. Glyphosate consistently enhanced growth of Group III (Isochrysis galbana) and inhibited Group IV (Thalassiosira weissflogii, Thalassiosira pseudonana and Chattonella marina) regardless of DIP condition. Group V (Amphidinium carterae) exhibited no measurable response to glyphosate regardless of DIP condition. This grouping is not congruent with the phylogenetic relationships of the phytoplankton species suggesting functional differentiation driven by environmental pressure. We conclude that glyphosate could be used as P-source by some species while is toxic to some other species and yet has no effects on others. The observed differential effects suggest that the continued use of glyphosate and increasing concentration of this herbicide in the coastal waters will likely exert significant impact on coastal marine phytoplankton community structure.     

Long-distance movement and differential targeting of microRNA399s

We have previously demonstrated that miR399s control phosphate (Pi) homeostasis by regulating the expression of a ubiquitin-conjugating E2 enzyme (UBC24/PHO2) in Arabidopsis. Changes in miR399-dependent PHO2 gene expression modulate Pi uptake, allocation and remobilization. More recently, we provided evidence that miR399s are able to move in the phloem stream and across grafting junctions from the scions overexpressing miR399 to the wild-type rootstocks. Movement of miR399s serves as a long-distance signal to report and balance the Pi status between shoots and roots. Of note, results from grafting experiments indicate that miR399b is less efficient in cleaving the PHO2 mRNA than is miR399f, despite the similar mobility of the two miR399s. We propose that nucleotide 13 of miR399s, which gives rise to the sequence variation among different miR399 species, could be involved in regulating the abundance of PHO2 mRNA through sequence complementarity to the target sequences of PHO2 mRNA and mimicking target sequence of At4/IPS1 noncoding RNAs.Key words: phosphate, microRNA399, PHO2, UBC24, long-distance movement, At4/IPS1     

A study of phosphate limitation in Lake Maarsseveen: phosphate uptake kinetics versus bioassays

In order to assess possible phosphate limitation for the phytoplankton community of Lake Maarsseveen, two techniques (phosphate uptake experiments and bioassays) were employed simultaneously in February–March 1982. In that period the ambient phosphate concentration of the lake water was less than 0.03 µM P and the diatom Asterionella formosa constituted more than 90% of the phytoplankton population. The phosphate uptake experiments showed relatively high uptake capacities and low cell phosphorus contents for the natural phytoplankton community. This suggested phosphate limitation throughout the test period. The growth stimulation of the phytoplankton after enrichment with phosphate, however, only revealed phosphate limitation from the beginning of March and bioassays may therefore be regarded as a less sensitive method.     

Effect of biodegradable chelating ligands on Fe uptake in and growth of marine microalgae

Iron (Fe) is an important nutrient for phytoplankton. The low solubility of Fe in oxic waters can be a growth-limiting factor for phytoplankton. Synthetic aminopolycarboxylates (APCs) such as ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA) are widely used as Fe complexing agents for microalgae culture. However, the presence of these non-ready biodegradable APC_S in aquatic systems may have serious environmental consequences. In the present study, the effects of biodegradable chelating ligands (hydroxyiminodisuccinic acid (HIDS), methylglycinediacetic acid (MGDA), and iminodisuccinate (IDS)) on Fe uptake in and growth of three coastal microalgae (Heterosigma akashiwo, Prymnesium parvum, and Skeletonema marinoi-dohrnii complex) were investigated, and the results were compared with those of non-ready biodegradable APCs (EDTA, ethylenediamine tetra-methylene phosphonic acid (EDTMP), and DTPA). The biodegradable chelating ligands did not have significant growth inhibition effect on the phytoplankton. Although the growth of the algae (except S. marinoi-dohrnii complex) was not affected substantially by 1.5 and 7.5 μM of DTPA, growth inhibition occurred by 7.5 μM of EDTMP and 150 μM of EDTA, DTPA, and EDTMP. The effect of chelating ligands on microalgal growth was likely to be associated with the intracellular Fe uptake influenced by the chelating ligands. On average, intracellular Fe concentrations for biodegradable chelating ligands were substantially higher than those for non-ready biodegradable APCs. Except H. akashiwo, the ratio of intra/extracellular Fe concentrations was highest for MGDA followed by IDS and HIDS. The results indicate that biodegradable chelating ligands are more efficient than non-ready biodegradable APCs in intracellular Fe uptake and algal growth.     

OsCYCP1;1, a PHO80 homologous protein,negatively regulates phosphate starvation signaling in the roots of rice (Oryza sativa L.)

Phosphorus is one of the most essential and limiting nutrients in all living organisms, thus the organisms have evolved complicated and precise regulatory mechanisms for phosphorus acquisition, storage and homeostasis. In the budding yeast, Saccharomyces cerevisiae, the modification of PHO4 by the PHO80 and PHO85 complex is a core regulation system. However, the existence and possible functions in phosphate signaling of the homologs of the PHO80 and PHO85 components in plants has yet to be determined. Here we describe the identification of a family of seven PHO80 homologous genes in rice named OsCYCPs. Among these, the OsCYCP1;1 gene was able to partially rescue the pho80 mutant strain of yeast. The OsCYCP1;1 protein was predominantly localized in the nucleus, and was ubiquitously expressed throughout the whole plant and during the entire growth period of rice. Consistent with the negative role of PHO80 in phosphate signaling in yeast, OsCYCP1;1 expression was reduced by phosphate starvation in the roots. This reduction was dependent on PHR2, the central regulator of phosphate signaling in rice. Overexpression and suppression of the expression of OsCYCP1;1 influenced the phosphate starvation signaling response. The inducible expression of phosphate starvation inducible and phosphate transporter genes was suppressed in the OsCYCP1;1 overexpression lines and was relatively enhanced in the OsCYCP1;1 RNAi plants by phosphate starvation. Together, these results demonstrate the role of PHO80 homologs in the phosphate starvation signaling pathway in rice.     

Nutrient interactions between phytoplankton and bacterioplankton under different carbon dioxide regimes

Light, nutrients, temperature, pH, and salinity are important factors in controlling the growth of phytoplankton and bacterioplankton. Supply of key nutrients to these communities can result in mutualistic or competitive relationships between bacterioplankton and phytoplankton. In this study, we investigated growth and uptake of nutrients by the marine prasinophyte flagellate Tetraselmis chui (strain PLY429) in the presence and absence of a community of bacterioplankton at two pH levels. Growth of PLY429 and total nutrient uptake were calculated for each treatment. The addition of bacterioplankton resulted in lower growth rates of PLY429, but the removal of ammonium was greater in those cultures with bacterioplankton present. The division rate of PLY429 was affected by pH; however, pH changes did not result in different uptake rates of nitrate, ammonium, or phosphate by the mixed algal and bacterial assemblage. These findings suggest that bacterioplankton and phytoplankton were competing for ammonium and that a lower pH resulted in more rapid algal growth. Mention of a trade name does not imply endorsement by the National Marine Fisheries Service.     

Impact of Light and Temperature on the Uptake of Algal Symbionts by Coral Juveniles

The effects of temperature and light on the breakdown of the coral-Symbiodinium symbiosis are well documented but current understanding of their roles during initial uptake and establishment of symbiosis is limited. In this study, we investigate how temperature and light affect the uptake of the algal symbionts, ITS1 types C1 and D, by juveniles of the broadcast-spawning corals Acropora tenuis and A. millepora. Elevated temperatures had a strong negative effect on Symbiodinium uptake in both coral species, with corals at 31°C showing as little as 8% uptake compared to 87% at 28°C. Juveniles in high light treatments (390 µmol photons m⁻² s⁻¹) had lower cell counts across all temperatures, emphasizing the importance of the light environment during the initial uptake phase. The proportions of the two Symbiodinium types taken up, as quantified by a real time PCR assay using clade C- and D-specific primers, were also influenced by temperature, although variation in uptake dynamics between the two coral species indicates a host effect. At 28°C, A. tenuis juveniles were dominated by C1 Symbiodinium, and while the number of D Symbiodinium cells increased at 31°C, they never exceeded the number of C1 cells. In contrast, juveniles of A. millepora had approximately equal numbers of C1 and D cells at 28°C, but were dominated by D at 30°C and 31°C. This study highlights the significant role that environmental factors play in the establishment of coral-Symbiodinium symbiosis and provides insights into how potentially competing Symbiodinium types take up residence in coral juveniles.     

Diatom growth responses to photoperiod and light are predictable from diel reductant generation

Light drives phytoplankton productivity, so phytoplankton must exploit variable intensities and durations of light exposure, depending upon season, latitude, and depth. We analyzed the growth, photophysiology and composition of small, Thalassiosira pseudonana, and large, Thalassiosira punctigera, centric diatoms from temperate, coastal marine habitats, responding to a matrix of photoperiods and growth light intensities. T. pseudonana showed fastest growth rates under long photoperiods and low to moderate light intensities, while the larger T. punctigera showed fastest growth rates under short photoperiods and higher light intensities. Photosystem II function and content responded primarily to instantaneous growth light intensities during the photoperiod, while diel carbon fixation and RUBISCO content responded more to photoperiod duration than to instantaneous light intensity. Changing photoperiods caused species‐specific changes in the responses of photochemical yield (e^?/photon) to growth light intensity. These photophysiological variables showed complex responses to photoperiod and to growth light intensity. Growth rate also showed complex responses to photoperiod and growth light intensity. But these complex responses resolved into a close relation between growth rate and the cumulative daily generation of reductant, across the matrix of photoperiods and light intensities.     

Phosphate uptake by blue green algae in vitro and in a lake during an algal bloom: Useful application of a force-flow relationship

A bioenergetic model, developed by M. Thellier, was applied to the ³²P-phosphate uptake data obtained with blue green algae and allowed the determination of a threshold concentration for the absorption of phosphate. Data obtained during an algal bloom of Oscillatoria rubescens showed that algal growth ceased when the phosphate concentration in the lake dropped below this threshold value. The resulting starvation led to an increase in the permeability of the membrane for phosphate.     

Utilization of dissolved organic phosphorus by different groups of phytoplankton taxa

The utilization of nine dissolved organic phosphorus (DOP) compounds by five bloom-causing phytoplankton species was studied under batch culture conditions. The DOP compounds included were adenosine 5-triphosphate (ATP), adenosine 5-monophosphate (AMP), cytidine 5-monophosphate (CMP), guanosine 5-monophosphate (GMP), uridine 5-monophosphate (UMP), glucose-6-phosphate (G6P), sodium glycerophosphate (GYP), 4-nitrophenyl phosphate (NPP), and triethyl phosphate (TEP), and the phytoplankton taxa were Skeletonema costatum, Prorocentrum micans, Alexandrium tamarense, Chattonella marina, and Heterosigma akashiwo. The four flagellate taxa, P. micans, A. tamarense, C. marina, and H. akashiwo, grew well under various DOP regimes. P. micans and C. marina were the most capable of using DOP compounds, sustaining better growth on a majority of nucleotides (ATP, AMP, CMP, GMP, and UMP) and phosphomonoesters (G6P and GYP) than in inorganic phosphorus (P) controls. A. tamarense and H. akashiwo showed equivalent growth in most organic and inorganic P cultures, while the diatom species, S. costatum, could only utilize AMP and GMP. Furthermore, A. tamarense and C. marina could endure N, P-depleted conditions. Among the nine DOP compounds tested, the nucleotide compounds had the highest nutritional value for algal cell growth, while TEP could not sustain growth as the sole source of P. These results suggest that enhanced DOP utilization and the endurance of nutrient-limitation by harmful flagellate taxa offer their competitive advantages, which may account for the frequent occurrence of their blooms in coastal waters.     

Identification of a Streptococcus pneumoniae Gene Locus Encoding Proteins of an ABC Phosphate Transporter and a Two-Component Regulatory System

The Escherichia coli Pst system belongs to the family of ABC transporters. It is part of a phosphate (PHO) regulon which is regulated by extracellular phosphate. Under conditions of phosphate limitation, the response regulator PhoB is phosphorylated by the histidine kinase PhoR and binds to promoters that share a consensus PHO box. Under conditions of phosphate excess, PhoR, Pst, and PhoU downregulate the PHO regulon. Screening of a library of pneumococcal mutants with defects in exported proteins revealed a putative two-component regulatory system, PnpR-PnpS, and a downstream ABC transporter, similar to the Pst system in E. coli including a gene encoding a PhoU protein. Similar to E. coli, mutagenesis of the ATP-binding cassette gene, pstB, resulted in decreased uptake of phosphate. The effects of the loss of the pneumococcal Pst system extended to decreased transformation and lysis. Withdrawal of phosphate led to transformation deficiency in the parent strain R6x but not to penicillin tolerance, suggesting that reduced bacterial death was independent of phosphate. None of these phenotypes was observed in the pneumococcal loss-of-function mutant phoU. By using a lacZ reporter construct, it was demonstrated that expression of the two-component regulatory system PnpR-PnpS was not influenced by different concentrations of phosphate. These results suggest a more complex role of the Pst system in pneumococcal physiology than in that of E. coli.