Charles G. Trick

Growth at Low Temperature Mimics High-Light Acclimation in Chlorella vulgaris'

Structural and functional alterations to the photosynthetic apparatus after growth at low temperature (5[deg]C) were investigated in the green alga Chlorella vulgaris Beijer. Cells grown at 5[deg]C had a 2-fold higher ratio of chlorophyll a/b, 5-fold lower chlorophyll content, and an increased xanthophyll content compared to cells grown at 27[deg]C even though growth irradiance was kept constant at 150 [mu]mol m-2 s-1. Concomitant with the increase in the chlorophyll a/b ratio was a lower abundance of light-harvesting polypeptides in 5[deg]C-grown cells as observed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and confirmed by western blotting.The differences in pigment composition were found to be alleviated within 12 h of transferring 5[deg]C-grown cells to 27[deg]C. Furthermore, exposure of 5[deg]C-grown cells to a 30-fold lower growth irradiance (5 [mu]mol m-2 s-1) resulted in pigment content and composition similar to that in cells grown at 27[deg]C and 150 [mu]mol m-2 s-1. Although both cell types exhibited similar measuring-temperature effects on CO2-saturated O2 evolution, 5[deg]C-grown cells exhibited light-saturated rates of O2 evolution that were 2.8-and 3.9-fold higher than 27[deg]C-grown cells measured at 27[deg]C and 5[deg]C, respectively. Steady-state chlorophyll a fluorescence indicated that the yield of photosystem II electron transport of 5[deg]C-grown cells was less temperature sensitive than that of 27[deg]C-grown cells. This appears to be due to an increased capacity to keep the primary, stable quinone electron acceptor of photosystem II (QA) oxidized at low temperature in 5[deg]C- compared with 27[deg]C-grown cells regardless of irradiance. We conclude that Chlorella acclimated to low temperature adjusts its photosynthetic apparatus in response to the excitation pressure on photosystem II and not to the absolute external irradiance. We suggest that the redox state of QA may act as a signal for this photosynthetic acclimation to low temperature in Chlorella.

Collection and detection of natural iron-binding ligands from seawater

Abstract Iron (Fe) is an essential element for the biochemical and physiological functioning of terrestrial and oceanic organisms, including phytoplankton, which are responsible for the primary productivity in the worlds oceans. However, due to the low solubility of Fe in seawater, phytoplankton are often limited by their inability to incorporate enough Fe to allow for optimal growth rates in regions with dissolved Fe concentrations below 1 nM. It has been postulated that certain phytoplankton may produce compounds to facilitate the uptake of Fe from seawater to overcome this limitation. Dissolved Fe in the oceans is overwhelmingly complexed (>99%) by strong organic ligands that may control the uptake of Fe by microbiota; however, the identity, origin, and chemical characteristics of these organic chelates are largely unknown. Although it has been implied that some components of natural Fe-binding ligands are siderophores, no direct analyses of such compounds from natural seawater have been conducted. Here, we present a simple solid-phase extraction technique employing Biobeads SM-2 and Amberlite XAD-16 resins for concentrating naturally occurring dissolved iron-binding compounds from large volumes (>200 l) of seawater. Additionally, we report on the first successful determination of molecular weight size classes and preliminary iron-binding functional group characterization within those size classes for isolates collected from the surface and below the photic zone (150 m) in the central California coastal upwelling system. Electrochemical analyses using competitive ligand equilibration/adsorptive cathodic stripping voltammetry (CLE-ACSV) showed that isolated compounds had conditional Fe-binding affinities (with respect to inorganic iron—Fe′) of K FeL,Fe′ cond =10 11.5 –10 11.9 M −1 , similar to purified marine siderophores produced in laboratory cultures and to the ambient Fe-binding ligands observed in seawater. In addition, 63% of the extracted compounds from surface-collected samples fall within the defined size range of siderophores (300–1000 Da). Hydroxamate or catecholate Fe-binding functional groups were present in each compound for which Fe binding was detected. These results illustrate that the functional groups previously shown to be present in marine and terrestrial siderophores extracted and purified from laboratory cultures are also present in the natural marine environment. These data provide evidence that a significant fraction of the organic Fe-binding compounds we collected contain Fe-binding functional groups consistent with biologically produced siderophores. These results provide further insight into characteristics of the Fe-binding ligands that are thought to be important in controlling the biological availability of Fe in the oceans.

The Growing Need for Sustainable Ecological Management of Marine Communities of the Persian Gulf

The Persian Gulf is a semi-enclosed marine system surrounded by eight countries, many of which are experiencing substantial development. It is also a major center for the oil industry. The increasing array of anthropogenic disturbances may have substantial negative impacts on marine ecosystems, but this has received little attention until recently. We review the available literature on the Gulf’s marine environment and detail our recent experience in the United Arab Emirates (U.A.E.) to evaluate the role of anthropogenic disturbance in this marine ecosystem. Extensive coastal development may now be the single most important anthropogenic stressor. We offer suggestions for how to build awareness of environmental risks of current practices, enhance regional capacity for coastal management, and build cooperative management of this important, shared marine system. An excellent opportunity exists for one or more of the bordering countries to initiate a bold and effective, long-term, international collaboration in environmental management for the Gulf.

Hydroxamate-siderophore production and utilization by marine eubacteria

Siderophore (iron-binding chelator) production was examined in 30 strains of open ocean bacteria from the generaVibrio, Alteromonas, Alcaligenes, Pseudomonas, andPhotobacterium. The results showed that hydroxamate-type siderophore production was widely distributed in various marine species, except for isolates ofAlteromonas macleodii andV. nereis. In all cases, the ability to produce siderophores was under the control of iron levels in the medium and satisfied the iron requirements of the siderophore bioassay organism. On the basis of chemical assay and bacterial bioassays, none of the examined isolates produced phenolate-type siderophores. Several isolates produces siderophores that were neither hydroxamatenor phenolate-type siderophores. Some strains such asAlteromonas communis produce siderophores that could be used by many other isolates. In contrast, the siderophore produced byAlcaligenes venustus had little cross-strain utilization. These findings suggest that the ability to produce siderophores may be common to open ocean bacteria.

Voltammetric estimation of iron(III) thermodynamic stability constants for catecholate siderophores isolated from marine bacteria and cyanobacteria

Abstract Thermodynamic stability constants have been estimated for the complexation of iron(III) with catecholate-type siderophores isolated from the marine bacterium Alteromonas luteoviolacea and from the marine cyanobacterium Synechococcus sp. PCC 7002. Stability constants were determined utilizing the “chelate scale” of Taylor et al. (1994). The scale is based upon a linear relationship between the reduction potentials and the pH-independent thermodynamic stability constants for known iron(III) complexes. Log K values for the alterobactin B ferric iron complex are 43.6 ± 1.5 at pH 8.2 and 37.6 ± 1.2 at pH 6, consistent with a shift from bis-catecholate to monosalicylate/monocatecholate iron coordination with decreasing pH. Synechococcus isolates PCC 7002 Nos. 1 and 3 formed iron(III) complexes with stability constants of approximately 38.1 ± 1.2 and 42.3 ± 1.5, respectively. The binding strengths of the iron(III) complexes examined in this study are quite high, suggesting that catecholate siderophores may play a role in the solubilization and biological uptake of iron in the marine environment.

Influence of iron limitation and nitrogen source on growth and siderophore production by cyanobacteria

To characterize the mobilization and uptake of iron by cyanobacteria, 14 species were screened for ability to scavenge iron in a competitive system. The cyanobacteria exhibited a range of growth responses to iron limitation which could be separated into three groups, and a representative species from each group was chosen for further study.

Iron enrichment stimulates toxic diatom production in high-nitrate, low-chlorophyll areas

Oceanic high-nitrate, low-chlorophyll environments have been highlighted for potential large-scale iron fertilizations to help mitigate global climate change. Controversy surrounds these initiatives, both in the degree of carbon removal and magnitude of ecosystem impacts. Previous open ocean enrichment experiments have shown that iron additions stimulate growth of the toxigenic diatom genus Pseudonitzschia. Most Pseudonitzschia species in coastal waters produce the neurotoxin domoic acid (DA), with their blooms causing detrimental marine ecosystem impacts, but oceanic Pseudonitzschia species are considered nontoxic. Here we demonstrate that the sparse oceanic Pseudonitzschia community at the high-nitrate, low-chlorophyll Ocean Station PAPA (50° N, 145° W) produces approximately 200 pg DA L−1 in response to iron addition, that DA alters phytoplankton community structure to benefit Pseudonitzschia, and that oceanic cell isolates are toxic. Given the negative effects of DA in coastal food webs, these findings raise serious concern over the net benefit and sustainability of large-scale iron fertilizations.

Physiological changes in the coastal marine cyanobacterium Synechococcus sp. PCC 7002 exposed to low ferric ion levels

Cyanobacteria are ubiquitous in marine waters. These prokaryotic cells are of particular interest in areas of the ocean where the availability of iron may be limiting for cell growth since these organisms commonly excrete iron-specific organic ligands (siderophores) in response to low levels of iron. It is generally considered that the production of siderophores provides a competitive advantage over the competing microorganisms that do not produce these ligands. In order to ascertain the influence of iron availability on the physiology of picoplanktonic cyanobacteria we performed a series of experiments on the coastal coccoid cyanobacterium, Synechococcus sp. PCC 7002. Physiological responses were examined in cells grown in a continuous cuture system with influx media containing a range of iron concentrations (from 4.2 x 10 -5 to 5.1 x 10 -9 M FeCl 3 ). Steady-state growth rates, combined with growth data from batch cultures demonstrated a non-linear response between iron availability and cell proliferation : cell yields were considerably higher in the lowest-iron chemostats than predicted based on the yields in the higher-iron chemostats. The higher yields during low-iron growth corresponded with the production of the extracellular siderophores and the induction of the specific iron-siderophore membrane transport proteins. A comparison of iron transport and carbon acquisition rates between the low-iron grown cells and the high-iron grown cells indicates that under low-iron growth conditions, iron and carbon acquisition meets the growth demands of the cells, whereas growth at higher iron levels enabled excessive (luxury) carbon acquisition and storage. We conclude that cyanobacteria are efficiently adapted to grow in low-iron environments (providing sufficient light for photosynthesis is available) and the luxury-uptake of carbon may serve as the source material for the extracellular ligands released by these cells. Since the release of siderophores was at iron levels in excess of the levels that induce the siderophore-mediated transport of iron, cyanobacteria growing in an environment with varying levels of iron may contribute substantial amounts of their stored carbon reserves into the DOC as iron-specific ligands.

Impacts on phytoplankton biomass and productivity in the Pacific Northwest during the warm ocean conditions of 2005

[1] Delayed onset of the spring transition and upwellingfavorable winds in the Pacific Northwest during springsummer 2005 resulted in a positive temperature anomaly and a pronounced negative anomaly in surface phytoplankton biomass (chlorophyll a )a nd primary productivity. Compared to time periods before and after the warm water event, total biomass was reduced by ca. 50% along a hydrographic line extending seaward from Grays Harbor, WA (47 N), with a concomitant decrease of ca. 40% in surface and depth-integrated primary productivity. Associated with these declines in biomass and productivity was a change in mean phytoplankton size, with >50% of the nearshore assemblage less than 5m mi n size during the warm event, compared to <30% during more normal conditions. Unlike higher trophic levels, the phytoplankton rapidly recovered with the onset of upwelling, returning to more typical size structure, biomass, and productivity within one week of the onset of upwelling-favorable winds. Citation: Kudela, R. M., W. P. Cochlan, T. D. Peterson, and C. G. Trick (2006), Impacts on phytoplankton biomass and productivity in the Pacific Northwest during the warm ocean conditions of 2005, Geophys. Res. Lett., 33, L22S06, doi:10.1029/2006GL026772.

A profile of an endosymbiont-enriched fraction of the coral Stylophora pistillata reveals proteins relevant to microbial-host interactions

This study examines the response of Symbiodinium sp. endosymbionts from the coral Stylophora pistillata to moderate levels of thermal “bleaching” stress, with and without trace metal limitation. Using quantitative high throughput proteomics, we identified 8098 MS/MS events relating to individual peptides from the endosymbiont-enriched fraction, including 109 peptides meeting stringent criteria for quantification, of which only 26 showed significant change in our experimental treatments; 12 of 26 increased expression in response to thermal stress with little difference affected by iron limitation. Surprisingly, there were no significant increases in antioxidant or heat stress proteins; those induced to higher expression were generally involved in protein biosynthesis. An outstanding exception was a massive 114-fold increase of a viral replication protein indicating that thermal stress may substantially increase viral load and thereby contribute to the etiology of coral bleaching and disease. In the absence of a sequenced genome for Symbiodinium or other photosymbiotic dinoflagellate, this proteome reveals a plethora of proteins potentially involved in microbial-host interactions. This includes photosystem proteins, DNA repair enzymes, antioxidant enzymes, metabolic redox enzymes, heat shock proteins, globin hemoproteins, proteins of nitrogen metabolism, and a wide range of viral proteins associated with these endosymbiont-enriched samples. Also present were 21 unusual peptide/protein toxins thought to originate from either microbial consorts or from contamination by coral nematocysts. Of particular interest are the proteins of apoptosis, vesicular transport, and endo/exocytosis, which are discussed in context of the cellular processes of coral bleaching. Notably, the protein complement provides evidence that, rather than being expelled by the host, stressed endosymbionts may mediate their own departure.