Photosystem II and Pigment Dynamics among Ecotypes of the Green Alga Ostreococcus

We investigated the photophysiological responses of three ecotypes of the picophytoplankter Ostreococcus and a larger prasinophyte Pyramimonas obovata to a sudden increase in light irradiance. The deepwater Ostreococcus sp. RCC809 showed very high susceptibility to primary photoinactivation, likely a consequence of high oxidative stress, which may relate to the recently noted plastid terminal oxidase activity in this strain. The three Ostreococcus ecotypes were all capable of deploying modulation of the photosystem II repair cycle in order to cope with the light increase, but the effective clearance of photoinactivated D1 protein appeared to be slower in the deepwater Ostreococcus sp. RCC809, suggesting that this step is rate limiting in the photosystem II repair cycle in this strain. Moreover, the deepwater Ostreococcus accumulated lutein and showed substantial use of the xanthophyll cycle under light stress, demonstrating its high sensitivity to light fluctuations. The sustained component of the nonphotochemical quenching of fluorescence correlated well with the xanthophyll deepoxidation activity. Comparisons with the larger prasinophyte P. obovata suggest that the photophysiology of Ostreococcus ecotypes requires high photosystem II repair rates to counter a high susceptibility to photoinactivation, consistent with low pigment package effects in their minute-sized cells.The prasinophytes are marine planktonic green algae with a phylogenetic position branching near the base of the green lineage (Baldauf, 2003; Turmel et al., 2009). They are widespread in temperate (Diez et al., 2001; Zhu et al., 2005) and polar (Lovejoy et al., 2007) marine habitats, in which they are often significant contributors to primary production (Not et al., 2004). The prasinophytes include the smallest known eukaryotic photoautotroph, Ostreococcus tauri (Courties et al., 1994; Chrétiennot-Dinet et al., 1995), whose particularly simple structure makes it an attractive model minimal chlorophyte, and indeed, minimal eukaryote (Derelle et al., 2006). Recently, genomic sequences for three Ostreococcus strains, isolated from different ecological niches, have become available (Derelle et al., 2006; Palenik et al., 2007), thus increasing the interest of these models for understanding acclimation processes in this deep-branching group of chlorophytes.Photoacclimation strategies differ in two Ostreococcus strains (Cardol et al., 2008; Six et al., 2008), which, although belonging to different phylogenetic clades, are nonetheless morphologically indistinguishable (Rodríguez et al., 2005). O. tauri, a eutrophilic lagoon species, modulates PSII content to enable acclimation and growth over a wide range of irradiances. In marked contrast, Ostreococcus sp. (O. sp.) RCC809, isolated at 105 m depth in the tropical Atlantic Ocean, modulates the size of its large PSII antenna in a strategy that accommodates a narrower range of light levels but that incurs lower nutrient costs compared with photoacclimation in O. tauri (Six et al., 2008). The evidence for different light acclimation strategies between these two Ostreococcus ecotypes raises the question of the underlying physiological processes for niche adaptation in these closely related organisms. Cardol et al. (2008) recently analyzed the coastal O. tauri and the deepwater O. sp. RCC809 grown under low to moderate light and found exciting evidence for a plastid terminal oxidase electron flow path in O. sp. RCC809 from PSII back to oxygen, short-circuiting the usual Z scheme in a mechanism to generate a transthylakoidal pH gradient without net generation of reductant. Like all oxygenic photoautotrophs, the prasinophytes suffer photoinactivation of PSII (Aro et al., 1993; Tyystjarvi, 2008; Guskov et al., 2009) at a rate approximately proportional to the incident irradiance (Nagy et al., 1995; Hakala et al., 2005). To counter this photoinactivation, a PSII repair cycle proteolytically removes the photoinactivated D1 protein (Silva et al., 2003) and replaces it through de novo synthesis and reassembly with the remaining subunits (Aro et al., 1993). If photoinactivation outruns the rate of repair, the PSII pool suffers net photoinhibition (Aro et al., 2005; Nishiyama et al., 2005, 2006; Murata et al., 2007), leading to a decrease in photosynthetic capacity and potentially to a decrease in growth. To limit photoinhibition, photosynthetic cells use physiological processes that dissipate excess light energy into heat, thereby preempting the generation of toxic reactive oxygen species (Baroli et al., 2004; Holt et al., 2004) that can inhibit metabolism, notably including the PSII repair processes (Nishiyama et al., 2006; Murata et al., 2007). These excitation dissipation mechanisms manifest as a drop in PSII fluorescence yield termed nonphotochemical quenching of fluorescence (NPQ). In land plants and characterized chlorophytes, NPQ is notably associated with changes in light-harvesting complex conformation along with pigmentation changes (Demmig-Adams and Adams, 1992; Baroli et al., 2004; Holt et al., 2004; Li et al., 2004).The specialization of Ostreococcus ecotypes to contrasting environments suggests that they may have evolved distinct capacities to cope with rapid fluctuations in light. Here, we investigate this question by subjecting three different Ostreococcus ecotypes to short-term increases in light irradiance to uncover their capacities for PSII repair and susceptibilities to photoinactivation. We use a target theory approach (Nagy et al., 1995; Sinclair et al., 1996) to parameterize their susceptibility to primary photoinactivation in a form useful for predicting and modeling responses to changes in irradiance. We moreover compare the Ostreococcus strains to a much larger prasinophyte derived from temperate surface waters, Pyramimonas obovata, to explore how cell size can influence photophysiology in the prasinophytes.     

Frequent fire promotes diversity and cover of biological soil crusts in a derived temperate grassland

The intermediate disturbance hypothesis (IDH) predicts that species diversity is maximized at moderate disturbance levels. This model is often applied to grassy ecosystems, where disturbance can be important for maintaining vascular plant composition and diversity. However, effects of disturbance type and frequency on cover and diversity of non-vascular plants comprising biological soil crusts are poorly known, despite their potentially important role in ecosystem function. We established replicated disturbance regimes of different type (fire vs. mowing) and frequency (2, 4, 8 yearly and unburnt) in a high-quality, representative Themeda australis–Poa sieberiana derived grassland in south-eastern Australia. Effects on soil crust bryophytes and lichens (hereafter cryptogams) were measured after 12 years. Consistent with expectations under IDH, cryptogam richness and abundance declined under no disturbance, likely due to competitive exclusion by vascular plants as well as high soil turnover by soil invertebrates beneath thick grass. Disturbance type was also significant, with burning enhancing richness and abundance more than mowing. Contrary to expectations, however, cryptogam richness increased most dramatically under our most frequent and recent (2 year) burning regime, even when changes in abundance were accounted for by rarefaction analysis. Thus, from the perspective of cryptogams, 2-year burning was not an adequately severe disturbance regime to reduce diversity, highlighting the difficulty associated with expression of disturbance gradients in the application of IDH. Indeed, significant correlations with grassland structure suggest that cryptogam abundance and diversity in this relatively mesic (600 mm annual rainfall) grassland is maximised by frequent fires that reduce vegetation and litter cover, providing light, open areas and stable soil surfaces for colonisation. This contrasts with detrimental effects of 2-year burning on native perennial grasses, indicating that this proliferation of cryptogams has potentially high functional significance for situations where vegetation cover is depleted, particularly for reducing soil erosion.     

Vegetation communities in continental boreal wetlands along a salinity gradient: Implications for oil sands mining reclamation

Oil sands mining is a major disturbance to boreal landscapes in north-eastern Alberta, Canada. Freshwater peatlands dominate the landscape prior to mining, but the post-mining reclamation landscape will have wetlands that span a salinity gradient. Little is known about the native vegetation communities in subsaline and saline marshes in the boreal region, yet these communities offer the best potential for reclamation of wetlands after oil sands mining. The overall intent of this study is to provide information on natural wetland communities along a gradient of salinities that can be used to enhance oil sands wetland reclamation. Our specific study objectives were to: (1) characterize environmental conditions of industrial and natural wetlands, (2) characterize vegetation communities (composition and diversity) in these wetlands, (3) and explore how vegetation communities (composition and diversity) may be influenced by environmental conditions. We surveyed vegetation communities and environmental variables in 25 natural boreal wetlands along a salinity gradient and in 10 industrial marshes in the oil sands mining region. We observed an electrical conductivity (EC) range of 0.5-28 mS cm⁻¹ in the wetlands, indicating that salinity similar to or higher than anticipated for oil sands reclamation is naturally present in some boreal wetlands. We observed low species richness in both industrial and natural wetlands. There were 101 plant species observed in all the wetlands, with 82 species recorded in the natural wetlands and 44 species in industrial wetlands. At the plot level, richness decreased with increasing EC and pH, but increased with soil organic matter. Using Cluster Analysis and indicator species analysis we defined 16 distinct vegetation community types, each dominated by one or two species of graminoid vegetation. In general these communities resembled those of boreal or prairie marshes. Electrical conductivity, pH, and water depth were important factors correlating with community composition of the wetlands, however peat depth and soil organic content did not differ among community types. Not all community types were present in industrial wetlands, indicating that these communities may need to be planted to enhance overall diversity in future reclaimed oil sands wetlands.     

Prognostic significance of tumor iNOS and COX-2 in stage III malignant cutaneous melanoma

Purpose  New prognostic markers are needed for malignant melanoma. Inducible nitric oxide synthase (iNOS) and cyclooxygenase type 2 (COX-2) have been described to correlate with progression of melanoma. Moreover, activating mutations in BRAF/NRAS oncogenes are often detected in melanoma. The BRAF/NRAS mutation status and expression of COX-2 and iNOS were examined to compare their prognostic value for overall survival (OS) in stage III malignant cutaneous melanoma. Experimental design  The expression of iNOS and COX-2 in metastatic lymph nodes from 21 rapidly progressing (OS from date of diagnosis of stage III disease ≤14 months) and 17 slowly progressing (OS ≥60 months) stage III cutaneous melanoma patients was examined by immunohistochemistry. The presence of BRAF/NRAS mutations was analyzed using direct DNA sequencing. χ² exact trend test and logistic regression analysis were used for statistical analysis. Results  Both iNOS (P = 0.002) and COX-2 (P = 0.048) alone significantly predicted OS. The BRAF/NRAS mutation status did not significantly differ between patient groups, although iNOS significantly (P = 0.013) correlated with BRAF mutation frequency. Furthermore, the odds ratio (OR) with respect to OS of iNOS (OR = 10.4) was higher than that of COX-2 (OR = 5.6) and was stable in the multivariate analysis of OS together with disease stage IIIB/C, ulceration, number of metastatic lymph nodes, and Breslow tumor thickness. Conclusion  Our data show that iNOS is an independent and stronger prognostic factor for OS in stage III malignant cutaneous melanoma than COX-2.     

Cancer/testis antigens can be immunological targets in clonogenic CD133<Superscript>+</Superscript> melanoma cells

“Cancer stem cells” that resist conventional treatments may be a cause of therapeutic failure in melanoma. We report a subpopulation of clonogenic melanoma cells that are characterized by high prominin-1/CD133 expression in melanoma and melanoma cell lines. These cells have enhanced clonogenicity and self-renewal in vitro, and serve as a limited in vitro model for melanoma stem cells. In some cases clonogenic CD133⁺ melanoma cells show increased expression of some cancer/testis (CT) antigens. The expression of NY-ESO-1 in an HLA-A2 expressing cell line allowed CD133⁺ clonogenic melanoma cells to be targeted for killing in vitro by NY-ESO-1-specific CD8⁺ T-lymphocytes. Our in vitro findings raise the hypothesis that if melanoma stem cells express CT antigens in vivo that immune targeting of these antigens may be a viable clinical strategy for the adjuvant treatment of melanoma. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

<Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis> PAO1 Resistance to Zinc Pyrithione: Phenotypic Changes Suggest the Involvement of Efflux Pumps

The aim of this study is to investigate the involvement of an efflux pump in the development of Pseudomonas aeruginosa resistance to zinc pyrithione (ZnPT). In the presence of efflux inhibitor carbonyl cyanide m-chlorophenyl-hydrazone (CCCP), the minimum inhibitory concentration of ZnPT for P. aeruginosa resistant cells is reduced significantly (p < 0.05). In addition, the concentration of ZnPT excluded by the resistant bacteria was reduced significantly (p < 0.01). However, the above reductions did not reach the levels measured for P. aeruginosa PAO1 sensitive strain. Furthermore, such changes in P. aeruginosa resistant cells were correlated with the overexpression of outer membrane proteins, reduced sensitivity toward imipenem (p < 0.01) and increased sensitivity toward sulphatriad and chloramphenicol (p < 0.05). In a continuation to a previous study, we conclude that P. aeruginosa resistance to ZnPT is multifactorial and involves induced efflux systems. Suzanne Abdel Malek is currently on leave from Petra University, and a member at the Faculty of Applied Medical Sciences, King Abdulaziz University, Jeddah, Saudi Arabia.     

Will male advertisement be a reliable indicator of paternal care,if offspring survival depends on male care?

Existing theory predicts that male signalling can be an unreliable indicator of paternal care, but assumes that males with high levels of mating success can have high current reproductive success, without providing any parental care. As a result, this theory does not hold for the many species where offspring survival depends on male parental care. We modelled male allocation of resources between advertisement and care for species with male care where males vary in quality, and the effect of care and advertisement on male fitness is multiplicative rather than additive. Our model predicts that males will allocate proportionally more of their resources to whichever trait (advertisement or paternal care) is more fitness limiting. In contrast to previous theory, we find that male advertisement is always a reliable indicator of paternal care and male phenotypic quality (e.g. males with higher levels of advertisement never allocate less to care than males with lower levels of advertisement). Our model shows that the predicted pattern of male allocation and the reliability of male signalling depend very strongly on whether paternal care is assumed to be necessary for offspring survival and how male care affects offspring survival and male fitness.