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The effects of mixing different leaf litter species on litter decomposition in streams have received considerable attention in recent years. However, contrasting results have been reported and the mechanisms behind the effects of litter diversity have been poorly examined. We compared the decomposition rates and associated fungi for two contrasting litter species, when incubated individually and in mixture, at two different current velocities. Coarse-mesh bags with alder litter individually, oak litter individually and with a mixture of both were incubated in a forest headwater stream over 32 days, under fast or slow current velocities. We determined litter decomposition rates, microbial oxygen consumption rates, and aquatic hyphomycete sporulation rates, species richness and community composition; litter species in the mixture were processed individually. Our results provided weak evidences for diversity effects on leaf litter decomposition. Generally, litter decomposition was unaffected by mixing contrasting litter species, with litter species in the mixture decomposing at the same rate as when incubated individually at both current velocities. The same pattern was observed for microbial variables. Decomposition rates and microbial colonization and activity depended primarily on the traits of the target litter species and were not affected by those of the companion species. However, litter-mixing effects were detected on oak litter at late decomposition stages under fast current velocity conditions, suggesting that both current velocity and the incubation time might influence diversity effects on litter decomposition in streams. This finding contributes to explain the lack of litter-mixing effects reported previously by many studies.

14 pags., 4 figs., Background: Amyloids are ordered, insoluble protein aggregates, characterized by a cross-β sheet quaternary structure in which molecules in a β-strand conformation are stacked along the filament axis via intermolecular interactions. While amyloids are typically associated with pathological conditions, functional amyloids have also been identified and are present in a wide variety of organisms ranging from bacteria to humans. The cytoplasmic polyadenylation element-binding (CPEB) prion-like protein is an mRNA-binding translation regulator, whose neuronal isoforms undergo activity-dependent aggregation, a process that has emerged as a plausible biochemical substrate for memory maintenance. CPEB aggregation is driven by prion-like domains (PLD) that are divergent in sequence across species, and it remains unknown whether such divergent PLDs follow a similar aggregating assembly pathway. Here, we describe the amyloid-like features of the neuronal Aplysia CPEB (ApCPEB) PLD and compare them to those of the Drosophila ortholog, Orb2 PLD. Results: Using in vitro single-molecule and bulk biophysical methods, we find transient oligomers and mature amyloid-like filaments that suggest similarities in the late stages of the assembly pathway for both ApCPEB and Orb2 PLDs. However, while prior to aggregation the Orb2 PLD monomer remains mainly as a random coil in solution, ApCPEB PLD adopts a diversity of conformations comprising α-helical structures that evolve to coiled-coil species, indicating structural differences at the beginning of their amyloid assembly pathways. Conclusion: Our results indicate that divergent PLDs of CPEB proteins from different species retain the ability to form a generic amyloid-like fold through different assembly mechanisms., The work was funded by two joint grants from the Ministry of Economy and Competitiveness to MCV (SAF2013-49179-C2-1-R and SAF2016-76678-C2-1-R) and DVL (SAF2013-49179-C2-2-R and SAF2016-76678-C2-2-R) and grants of the Ministry of Economy and Science (BFU2015-70072-R) and the CIBER de Enfermedades Respiratorias (CIBERES; ISCIII) to MM.

14 p.-6 fig.-1 tab., Endolysins are bacteriophage-encoded peptidoglycan hydrolases targeting the cell wall of host bacteria via their cell wall-binding domains (CBDs). The molecular basis for selective recognition of surface carbohydrate ligands by CBDs remains elusive. Here, we describe, in atomic detail, the interaction between the Listeria phage endolysin domain CBD500 and its cell wall teichoic acid (WTA) ligands. We show that 30O-acetylated GlcNAc residues integrated into the WTA polymer chain are the key epitope recognized by a CBD binding cavity located at the interface of tandem copies of beta-barrel, pseudosymmetric SH3b-like repeats. This cavity consists of multiple aromatic residues making extensive interactions with two GlcNAc acetyl groups via hydrogen bonds and van der Waals contacts, while permitting the docking of the diastereomorphic ligands. Our multidisciplinary approach tackled an extremely challenging protein–glycopolymer complex and delineated a previously unknown recognition mechanism by which a phage endolysin specifically recognizes and targets WTA, suggesting an adaptable model for regulation of endolysin specificity., E. T. S. has been supported by the Swiss National Science Foundation (SNF) grant 310030_156947/1. F. J. C.and M. M. have been supported by the Spanish Ministry of Science Innovation and Universities and FEDER funding (grants RTI2018-094751-B-C22 and BFU2015-70072R) and CIBERES, an initiative from the Spanish Institute of Health Carlos III.

Endolysins are bacteriophage-encoded peptidoglycan hydrolases targeting the cell wall of host bacteria via their cell wall-binding domains (CBDs). The molecular basis for selective recognition of surface carbohydrate ligands by CBDs remains elusive. Here, we describe, in atomic detail, the interaction between the Listeria phage endolysin domain CBD500 and its cell wall teichoic acid (WTA) ligands. We show that 3’ O-acetylated GlcNAc residues integrated into the WTA polymer chain are the key epitope recognized by a CBD binding cavity located at the interface of tandem copies of beta-barrel, pseudo-symmetric SH3b-like repeats. This cavity consists of multiple aromatic residues making extensive interactions with two GlcNAc acetyl groups via hydrogen bonds and van der Waals contacts, while permitting the docking of the diastereomorphic ligands. The multidisciplinary approach described here delineates a previously unknown recognition mechanism by which a phage endolysin specifically recognizes and targets WTA, suggesting an adaptable model for regulation of endolysin specificity.

Mitochondrial endonuclease G from Leishmania infantum (LiEndoG) participates in the degradation of double-stranded DNA (dsDNA) during parasite cell death and is catalytically inactive at a pH of 8.0 or above. The presence, in the primary sequence, of an acidic amino acid-rich insertion exclusive to trypanosomatids and its spatial position in a homologybuilt model of LiEndoG led us to postulate that this peptide stretch might act as a pH sensor for selfinhibition. We found that a LiEndoG variant lacking residues 145-180 is indeed far more active than its wild-Type counterpart at pH values >7.0. In addition, we discovered that (i) LiEndoG exists as a homodimer, (ii) replacement of Ser211 in the active-site SRGH motif with the canonical aspartate from the DRGH motif of other nucleases leads to a catalytically deficient enzyme, (iii) the activity of the S211D variant can be restored upon the concomitant replacement of Ala247 with Arg and (iv) a C-Terminal extension is responsible for the observed preferential cleavage of single-stranded DNA (ssDNA) and ssDNA- dsDNA junctions. Taken together, our results support the view that LiEndoG is a multidomain molecular machine whose nuclease activity can be subtly modulated or even abrogated through architectural changes brought about by environmental conditions and interaction with other binding partners.

Changes in hydrology are one of the main causes of mangrove degradation; however, the reforestation of mangrove has been the main restoration activity and very little information on how pioneer species can facilitate the colonization and development of the mangrove species is available. After carrying out a water reconnection as the sole restoration action, secondary succession has occurred in the mangrove rehabilitation area of Celestun (Yucatan, SE Mexico). Two pioneer species, Batis maritima and Salicornia virginica were observed in plots with different coverage (0%, 20%, 100%) where the three natural mangrove species were established, with Laguncularia racemosa as the dominant species in density. The greatest interstitial mean salinity (79.9 g/kg) was recorded in the plots with 20% cover, while the lowest salinity (40.7 g/kg) was recorded in the plots with 100% of coverage. At the end of sampling period nutrient content (carbon, nitrogen and phosphorus) and organic matter in the sediment were greatest in the plots with 100% cover, whereas the lowest concentrations were observed in the site devoid of vegetation. The percentage cover of S. virginica and B. maritima changed over time; in the plot that started with 100% cover it decreased until it disappeared at the end of the study period, whereas it increased in the plots with 20% and 0% cover. This study shows that B. maritima and S. virginica has a function as “facilitator species” initially colonizing the bare soil and modifying its conditions (decreasing interstitial salinity and increasing nutrient), which favored colonization and growing of mangrove seedlings.

Drought, an important environmental factor affecting the functioning of stream ecosystems, is likely to become more prevalent in the Mediterranean region as a consequence of climate change and enhanced water demand. Drought can have profound impacts on leaf litter decomposition, a key ecosystem process in headwater streams, but there is still limited information on its effects at the regional scale. We measured leaf litter decomposition across a gradient of aridity in the Ebro River basin. We deployed coarse- and fine-mesh bags with alder and oak leaves in 11 Mediterranean calcareous streams spanning a range of over 400km, and determined changes in discharge, water quality, leaf-associated macroinvertebrates, leaf quality and decomposition rates. The study streams were subject to different degrees of drought, specific discharge (Ls−1km−2) ranging from 0.62 to 9.99. One of the streams dried out during the experiment, another one reached residual flow, whereas the rest registered uninterrupted flow but with different degrees of flow variability. Decomposition rates differed among sites, being lowest in the 2 most water-stressed sites, but showed no general correlation with specific discharge. Microbial decomposition rates were not correlated with final nutrient content of litter nor to fungal biomass. Total decomposition rate of alder was positively correlated to the density and biomass of shredders; that of oak was not. Shredder density in alder bags showed a positive relationship with specific discharge during the decomposition experiment. Overall, the results point to a complex pattern of litter decomposition at the regional scale, as drought affects decomposition directly by emersion of bags and indirectly by affecting the functional composition and density of detritivores.

In temporary Mediterranean streams, flow fragmentation during summer droughts originates an ephemeral mosaic of terrestrial and aquatic habitat types. The heterogeneity of habitat types implies a particular ecosystem functioning in temporary streams that is still poorly understood. We assessed the initial phases of leaf litter decomposition in selected habitat types: running waters, isolated pools and moist and dry streambed sediments. We used coarse-mesh litter bags containing Populus nigm leaves to examine decomposition rates, microbial biomass, macroinvertebrate abundance and dissolved organic carbon (DOC) release rates in each habitat type over an 11-clay period in late summer. We detected faster decomposition rates in aquatic (limning waters and isolated pools) than in terrestrial habitats (moist and dry streambed sediments). Under aquatic conditions, decomposition was characterized by intense leaching and early microbial colonization, which swiftly started to decompose litter. Microbial colonization in isolated pools was primarily dominated by bacteria, whereas in running waters fungal biomass predominated. Under terrestrial conditions, leaves were most often affected by abiotic processes that resulted in small mass losses. We found a substantial decrease in DOC release rates in both aquatic habitats within the first days of the study, whereas DOC release rates remained relatively stable in the moist and dry sediments.This suggests that leaves play different roles as a DOC source during and after flow fragmentation. Overall, our results revealed that leaf decomposition is heterogeneous during flow fragmentation, which has implications related to DOC utilization that should be considered in future regional carbon budgets. (C) 2016 Elsevier B.V. All rights reserved.

The study of leaf litter as a resource for shredders has emerged as a key topic in trophic links in ecology. However, thus far, most studies have emphasized the leaf quality as one of the main determinants of shredder behaviour and growth without simultaneously considering the leaf quantity availability. Nevertheless, the combined effects of leaf quantity and quality on shredder behaviour and growth is particularly crucial to further understand how ecosystem functioning may respond to the increasing flow intermittency due to climate change. In this study, we explore how changes in the leaf litter quality and quantity influence the feeding preferences and growth of an invertebrate shredder (Potamophylax latipennis). To do so, we used black poplar leaves conditioned in two streams with different flow regimens as a food resource. Afterwards, using a microcosm approach, we offered leaf discs that varied in terms of leaf quantity and quality to P. latipennis. Our results showed that flow intermittency had a negative effect on the quality of the food resource, and a lower quality had a negative effect on the consumption and growth rates of P. latipennis. Furthermore, we found that P. latipennis fed selectively on higher quality leaves even though the availability (quantity) of this resource was lower. In the context of climate change, with higher aridity/drier conditions/scenarios, our findings suggest that a decrease in the availability (quantity) of high-quality resources could potentially threaten links in global fluvial food webs and thus threaten ecosystem functioning.

This paper reviews the current knowledge on the diversity, distribution and ecology of the genus Ruppia L. in the Mediterranean region. The genus Ruppia, a cosmopolitan aquatic plant complex, is generally restricted to shallow waters such as coastal lagoons and brackish habitats characterized by fine sediments and high salinity fluctuations. In these habitats Ruppia meadows play an important structural and functional role. Molecular analyses revealed the presence of 16 haplotypes in the Mediterranean region, one corresponding to Ruppia maritima L., and the others to various morphological forms of Ruppia cirrhosa (Petagna) Grande, all together referred to as the “R. cirrhosa s.l. complex”, which also includes Ruppia drepanensis Tineo. Populations of hybrid origin between R. maritima and R. cirrhosa and polyploidy have been detected.

Streptococcus suis is a Gram-positive bacterium that infects humans and various animals, causing human mortality rates ranging from 5 to 20%, as well as important losses for the swine industry. In addition, there is no effective vaccine for S. suis and isolates with increasing antibiotic multiresistance are emerging worldwide. Facing this situation, wild type or engineered bacteriophage lysins constitute a promising alternative to conventional antibiotics. In this study, we have constructed a new chimeric lysin, Csl2, by fusing the catalytic domain of Cpl-7 lysozyme to the CW-7 repeats of LySMP lysin from an S. suis phage. Csl2 efficiently kills different S. suis strains and shows noticeable activity against a few streptococci of the mitis group. Specifically, 15 μg/ml Csl2 killed 4.3 logs of S. suis serotype 2 S735 strain in 60 min, in a buffer containing 150 mM NaCl and 10 mM CaCl, at pH 6.0. We have set up a protocol to form a good biofilm with the non-encapsulated S. suis mutant strain BD101, and the use of 30 μg/ml Csl2 was enough for dispersing such biofilms and reducing 1-2 logs the number of planktonic bacteria. In vitro results have been validated in an adult zebrafish model of infection.

In forest headwater streams where the riparian canopy limits autochthonous primary production, leaf litter decomposition is a key process controlling nutrient and carbon cycling. Any alteration of the riparian vegetation may influence litter decomposition and detrital food webs. We evaluated the effect of non-native Platanus hybrida riparian plantations on leaf litter decomposition in Mediterranean streams. The experiment was conducted in six headwater streams; three lined by native riparian vegetation and three crossing P. hybrida plantations. We have characterized the processing rates of alder leaves and the assemblages of shredder macroinvertebrates and fungi. Litter decomposition was significantly faster in the P. hybrida than in the reference streams. Although the dissolved inorganic nitrogen concentration was higher in P. hybrida, no significant effect was observed in decomposition rates. Differences in decomposition rates reflected the macroinvertebrate and shredder colonization in alder litter, with higher abundance and richness in the P. hybrida streams. However, aquatic hyphomycete sporulation rate was higher in reference streams, suggesting that the variation in decomposition rates is a direct consequence of shredder abundance. Our findings support part of the substrate quality-matrix quality (SMI) hypothesis, which expects that high-quality litter will show increased decomposition rates in a low-quality litter matrix. © 2013 Springer Science+Business Media Dordrecht.

13 p.-7 fig.-1 tab., The emergence and spread of antibiotic-resistant bacteria is pushing the need of alternative treatments. In this context, phage therapy is already a reality to successfully fight certain multiresistant bacteria. Among different phage gene products, murein hydrolases responsible of phage progeny liberation (also called lysins or endolysins) are weapons that target specific peptidoglycan bonds, leading to lysis and death of susceptible bacteria when added from the outside. In the pneumococcal system, all but one phage murein hydrolases reported to date share a choline-binding domain that recognizes cell walls containing choline residues in the (lipo)teichoic acids. Some purified pneumococcal or phage murein hydrolases, as well as several chimeric proteins combining natural catalytic and cell wall-binding domains (CBDs) have been used as effective antimicrobials. In this work we have constructed a novel chimeric N-acetylmuramoyl-L-alanine amidase (PL3) by fusing the catalytic domain of the Pal amidase (a phage-coded endolysin) to the CBD of the LytA amidase, the major pneumococcal autolysin. The physicochemical properties of PL3 and the bacteriolytic effect against several pneumococci (including 48 multiresistant representative strain) and related species, like Streptococcus pseudopneumoniae, Streptococcus mitis, and Streptococcus oralis, have been studied. Results have shown that low doses of PL3, in the range of 0.5–5 mg/ml, are enough to practically sterilize all choline-containing strains tested. Moreover, a single 20-mg dose of PL3 fully protected zebrafish embryos from infection by S. pneumoniae D39 strain. Importantly, PL3 keeps 95% enzymatic activity after 4 weeks at 37 C and can be lyophilized without losing activity, demonstrating a remarkable robustness. Such stability, together with a prominent efficacy against a narrow spectrum of human pathogens, confers to PL3 the characteristic to be an effective therapeutic. In addition, our results demonstrate that the structure/functionbased domain shuffling approach is a successful method to construct tailor-made endolysins with higher bactericidal activities than their parental enzymes., Research wasfunded by grants from the Ministerio de Economía y Competitividad (MINECO) to PG (SAF2012-39444- C02-01) and MM (BFU2012-36825 and BFU2015-70052-R), the Consejería de Educación de la Comunidad de Madrid (S2010/BMD/2457) to MM. Additional funding was provided by the CIBER de Enfermedades Respiratorias (CIBERES),an initiative of the Instituto de Salud Carlos III (ISCIII).

In this work, we analyzed at high resolution the sugar-binding mode of the recombinant N-terminal ricin-B domain of the hemolytic protein LSLa (LSL150) from the mushroom Laetiporus sulphureus and also provide functional in vitro evidence suggesting that, together with its putative receptor-binding role, this module may also increase the solubility of its membrane pore-forming partner. We first demonstrate that recombinant LSL150 behaves as an autonomous folding unit and an active lectin. We have determined its crystal structure at 1.47 Å resolution and also that of the [LSL150:(lactose)β, γ)] binary complex at 1.67 Å resolution. This complex reveals two lactose molecules bound to the β and γ sites of LSL150, respectively. Isothermal titration calorimetry indicates that LSL150 binds two lactoses in solution with highly different affinities. Also, we test the working hypothesis that LSL150 exhibits in vivo properties typical of solubility tags. With this aim, we have fused an engineered version of LSL150 (LSLt) to the N-terminal end of various recombinant proteins. All the designed LSL150-tagged fusion proteins were successfully produced at high yield, and furthermore, the target proteins were purified by a straightforward affinity procedure on agarose-based matrices due to the excellent properties of LSL150 as an affinity tag. An optimized protocol for target protein purification was devised, which involved removal of the LSL150 tag through in-column cleavage of the fusion proteins with His6-tagged TEV endoprotease. These results permitted to set up a novel, lectin-based system for production and purification of recombinant proteins in E. coli cells with attractive biotechnological applications., Financial support from the Ministerio de Ciencia e Innovación (BFU2010-17929/BMC; BFU2009-10052) and the Factoría de Cristalización (Consolider-Ingenio-2007), and CIBER de Enfermedades Respiratorias (CIBERES), an initiative of Instituto de Salud Carlos III, is greatly appreciated.

The main goal of this study was to examine the natural variability of alder (Alnus glutinosa (L.) GAERTN.) leaf processing and explore its potentiality as a functional indicator to assess the ecological status of Spanish headwater streams. Breakdown of leaf litter was studied during autumn-winter in reference headwater streams of two regions of northern Spain: the Basque Country (on the Atlantic) and Catalonia (on the Mediterranean). Spring experiments were also carried out in the Atlantic region in order to study seasonal changes. Leaf mass loss rates were slightly higher in Catalonian streams. Temperature was not the main factor for explaining differences between the two regions. In the Atlantic one, however, water temperature determined the spatial and seasonal variability of leaf litter processing. Because of the high natural variability in breakdown rates, our results highlight the difficulty in detecting moderate impairments on stream functioning through the analysis of leaf litter decomposition if this process is not accompanied by the study of other factors affecting it.

The response of early Ruppia cirrhosa Petagna (Grande) litter decomposition to external nitrogen and phosphorus availability in La Tancada (Ebro River, NE Spain), a coastal lagoon that receives agricultural freshwater runoff from rice fields has been examined. Recently abscised dead R. cirrhosa stems were collected and 25 g of fresh weight was placed in litter bags with a mesh size of 100 μm and 1 mm. These bags were fertilised by adding nitrogen (N), a mixture of nitrogen plus phosphorus (N + P), or phosphorus (P), or were left untreated (CT). Macroinvertebrates were retrieved from the bags and the ash-free dry weight, and carbon, and N and P content of the remaining plant material were measured after 0, 3, 7, 14, 22 and 32 days. Litter decomposition rates, k (day −1 ), were estimated using a simple exponential model. Litter decay was clearly accelerated by the addition of P in the fine (100 μm) litter bags (0.042), but when N was added alone (0.0099) the decomposition rate was lower than in the CT treatments (0.022). No significant difference was observed between the N (0.0099–0.018) and N + P (0.0091–0.015) treatments in either the fine or the coarse (1 mm) litter bags. These results could be attributed to the relatively high availability of external (environmental) and internal (detritus contents) N. No significant effect of macro invertebrates was observed in the CT treatment or under N or P or N + P addition. The ratio between the decomposition rates in coarse and fine litter bags (k c /k f ) was lower in disturbed Tancada lagoon (0.82) than in Cesine lagoon (2.11), a similar Mediterranean coastal water body with almost pristine conditions. These results indicate that, in addition to data on macroinvertebrate community structure, decomposition rates could also be used to assess water quality in coastal lagoons.

In this study, the growth, senescence, leaf loss and nutrient dynamics of Juncus maritimus were followed to examine litter decay in a Mediterranean coastal marsh. Decomposition was studied in dead leaves still attached to the plant and in leaves placed in litterbags (detached leaves/litter) on the sediment surface. The dynamics of fungi, meiofauna and epiphytes associated with detached litter were also followed. No significant differences were observed between decay rates in dead leaves attached to plants (0.0017 day−1) and detached leaves (0.0015 day−1) in litter bags. The percentage of ash-free dry weight lost was inversely proportional to the C:N and C:P ratios in plant detritus during decay, indicating N and P limitation for the decomposer community inhabiting decaying J. maritimus litter and uptake of these nutrients from the environment. Water availability and high temperatures on the sediment surface increased the density of meiofauna and epiphyton and decreased fungal biomass during the first 20 days of the experiment. The density of ciliates and nematodes in decomposing litter was inversely related to the C:N ratio and directly related to the percentage of AFDW lost. On the basis of these observations, it was concluded that meiofauna are primary colonizers of J. maritimus leaf litter.

Most studies on plant decomposition in salt marshes have been carried out in Spartina -dominated marshes in North America. In contrast, few have focused on marshes in Mediterranean systems. Moreover, research into litter decay in estuarine systems has been conducted with plant material collected before natural senescence and death. Here we followed the growth, senescence, leaf fall, and nutrient dynamics of Spartina versicolor to examine litter decay in a Mediterranean coastal system. We studied the dynamics of fungi, meiofauna and algae associated with detached S. versicolor litter, and the effect of the microenvironment (above and underneath wracks of dead Spartina ) on decomposition. The exponential decay coefficient rate ( k , day −1 ) was higher for leaves attached to standing plants (0.0019) than after leaf abscission (0.0002–0.001). The decomposition rate of detached leaves was highly variable and depended on the position of the litter. The large differences in decomposition rates between the two experimental conditions indicate that the microenvironment affected the associated litter community during the initial phase of decay. Water availability and high temperatures over the sediment surface increased the density of meiofauna and epiphyton and decreased fungal biomass during the first 20 days of the experiment. Fungal biomass was at the lower end of reported values, probably as a result of the drier conditions and high salinity in the Mediterranean marsh. Spartina versicolor detritus acted as a nutrient sink by immobilizing large amounts of N and P for at least one year.

This work aims to characterise the current autotrophic compartment of the Albufera des Grau coastal lagoon (Menorca, Balearic Islands) and to assess the relationship between the submerged macrophytes and the limnological parameters of the lagoon. During the study period the submerged vegetation was dominated by the macrophyte Ruppia cirrhosa, which formed dense extensive meadows covering 79% of the surface. Another macrophyte species, Potamogeton pectinatus, was also observed but only forming small stands near the rushing streams. Macroalgae were only occasionally observed. Macrophyte biomass showed a clear seasonal trend, with maximum values in July. The biomass of R. cirrhosa achieved 1760 g DW m-2, the highest biomass ever reported for this species in the literature. The seasonal production-decomposition cycle of the macrophyte meadows appears to drive the nutrient dynamics and carbon fluxes in the lagoon. Despite the significant biomass accumulation and the absence of a washout of nutrients and organic matter to the sea, the lagoon did not experience a dystrophic collapse. These results indicate that internal metabolism is more important than exchange processes in the lagoon. El presente estudio pretende caracterizar el componente autotrófico de la laguna litoral de s’Albufera des Grau (Menorca, Islas Baleares) y determinar la relación entre los macrófitos acuáticos y la dinámica de los principales parámetros limnológicos del sistema. Durante el periodo estudiado, la vegetación sumergida estuvo dominada por el macrófito Ruppia cirrhosa, que formaba extensas praderas en toda la laguna. También se observó otra especie de macrófito, Potamogeton pectinatus, pero sólo formando pequeñas formaciones cerca de la entrada de los torrentes a la laguna. La biomasa de macrófitos mostró un claro ciclo estacional, con los valores máximos centrados en verano. La biomasa de R. cirrhosa alcanzó 1760 g DW m-2, que supone el valor más alto de biomasa descrito para esta especie en la literatura. El ciclo estacional de producción-descomposición de las praderas de macrófitos parece ser el responsable de la dinámica de nutrientes y de los flujos de carbono en la laguna. A pesar de las elevadas biomasas acumuladas y de la ausencia de un lavado de nutrientes y materia orgánica hacia el mar, la laguna no mostró un colapso distrófico, sugiriendo la importancia del metabolismo interno de la laguna por encima de los procesos de intercambio con el mar.

The spatial variability of plant organic matter processing was studied experimentally in a shallow coastal lagoon (Tancada lagoon, average depth: 37 cm, area: 1.8 km 2 ) in the Ebro River Delta (NE Spain). To determine theeffect of hydrology and sediment characteristics on plant organic matter processing, leaves of Phragmites australis at the end of its vegetative cycle and whole plants of Ruppia cirrhosa (PETAGNA) GRANDE, just abscised, were enclosed in litter bags. Two different mesh sizes (100 μm and 2 mm) were used to study the effect of macroinvertebrates on decomposition. The bags were placed in the water column and approximately 15 cm above the sediment at 6 different locations in the lagoon. The experiment was performed twice, in autumn-winter and spring-summer. The effect of macroinvertebrates on decomposition rate was not significant in Tancada lagoon. Breakdown rates showed spatial differences only in spring-summer. In the autumn-winter experiment, the effect of strong wind masked the effects of environmental variables and hydrology on decomposition rate. In the spring-summer experiment, characterised by high stability of the water column, dissolved inorganic nitrogen (DIN) concentration in the water column and organic matter in the sediment were the main factors determining the variability of organic matter processing. A positive relationship was calculated between P. australis decomposition rate and dissolved inorganic nitrogen in spring-summer (r 2 = 0.92, p < 0.001).

11 p.-7 fig.-3 tab., This work was supported by Dirección General de Investigación Científica y Técnica Grants BIO2000-1307, BMC2000-1002, BIO2003-01952, BMC2003-00074, and by a Comunidad Autónoma de Madrid Grant of the Program for Strategic Groups.

We have analyzed the in vitro disassembly of the capsid of the minute virus of mice, and the stability of capsid chimeras carrying heterologous epitope insertions. Upon heating in a physiological buffer, empty capsids formed by 60 copies of protein VP2 underwent first a reversible conformational change with a small enthalpy change detected by fluorescence. This change was associated with, but not limited to, externalization of the VP2 N terminus. Irreversible capsid dissociation as detected by changes in fluorescence, hemagglutination activity, and electrophoretic mobility occurred at much higher temperatures. Differential scanning calorimetry in the same conditions indicated that the dissociation/denaturation transition involved a high enthalpy change and proceeded through one or more intermediates. In contrast, in the presence of 1.5 M guanidinium chloride, heat-induced disassembly fitted a two-state irreversible process. Both thermally and chemically induced dissociation/denaturation yielded a form that had lost a part of the tertiary structure, but still retained the native secondary structure. Data from chemical dissociation indicates this form may correspond to a molten globule-like monomeric state of the capsid protein. All five antigenic peptide insertions attempted in exposed loops, despite being perhaps among the least disruptive, led to defects in folding/assembly of the capsid and, in most cases, to reduced capsid stability against thermal dissociation. The results with one of the simplest viral capsids reveal a complex pathway for disassembly, and a reduction in capsid assembly and stability upon insertion of peptides, even within the most exposed capsid loops.

The litter-bag technique was used to study the effect of seasonality (spring–summer versus autumn–winter) and nutrient availability on leaf decomposition in two Mediterranean watercourses: the Ebro river, which is eutrophic, and the Senia stream. To establish the effect of macroinvertebrates on litter breakdown, we used air-dried leaves from the two dominant species of riparian vegetation (Populus alba and Populus nigra) along each watercourse and litter bags of two mesh sizes (100 μm and 5 mm). Macroinvertebrates were collected from the bags and ash free dry weight and carbon, nitrogen and phosphorus contents of the plant detritus remaining were measured. Litter decomposition rates, in days and degree-days, were estimated using a simple exponential model. A significant effect of macroinvertebrates and seasonality on litter decay was observed only in the Ebro river. Decomposition rates were faster in this river, P. alba showing the highest rates in spring–summer (0.022–0.038 day−1). The macroinvertebrates collected from the bags were mostly collector-gatherers of the genus Chironomus. Their density increased over time and was greater in the experiments performed in spring–summer (two to ten fold higher). Higher temperatures together with increased macroinvertebrate densities led to augmented decomposition rates in the Ebro river but no effect was observed in the Senia stream. Our data show that leaf decay is both quantitatively and qualitatively affected by inorganic nutrient levels and temperature in the ambient environment, regardless of initial C:N and C:P ratios.

Chemotherapy. All rights reserved. Objectives: Streptococcus pneumoniae is becoming increasingly antibiotic resistant worldwide and new antimicrobials are urgently needed. Our aim was new chimeric phage endolysins, or lysins, with improved bactericidal activity by swapping the structural components of two pneumococcal phage lysozymes: Cpl-1 (the best lysin tested to date) and Cpl-7S. Methods: The bactericidal effects of four new chimeric lysins were checked against several bacteria. The purified enzymes were added at different concentrations to resuspended bacteria and viable cells were measured after 1 h. Killing capacity of the most active lysin, Cpl-711, was tested in a mouse bacteraemia model, following mouse survival after injecting different amounts (25-500 mg) of enzyme. The capacity of Cpl-711 to reduce pneumococcal biofilm formation was also studied. Results: The chimera Cpl-711 substantially improved the killing activity of the parental phage lysozymes, Cpl-1 and Cpl-7S, against pneumococcal bacteria, including multiresistant strains. Specifically, 5 mg/mL Cpl-711 killed ≥7.5 log of pneumococcal R6 strain. Cpl-711 also reduced pneumococcal biofilm formation and killed 4 log of the bacterial population at 1 mg/mL. Mice challenged intraperitoneally with D39_IU pneumococcal strain were protected by treatment with a single intraperitoneal injection of Cpl-711 1 h later, resulting in about 50% greater protection than with Cpl-1. Conclusions: Domain swapping among phage lysins allows the construction of new chimeric enzymes with high bactericidal activity and a different substrate range. Cpl-711, the most powerful endolysin against pneumococci, offers a promising therapeutic perspective for the treatment of multiresistant pneumococcal infections.

The effect of dissolved nutrients on growth, nutrient content and uptake rates of Chaetomorpha linum in a Mediterranean coastal lagoon (Tancada, Ebro delta, NE Spain) was studied in laboratory experiments. Water was enriched with distinct forms of nitrogen, such as nitrate or ammonium and phosphorus. Enrichment with N, P or with both nutrients resulted in a significant increase in the tissue content of these nutrients. N-enrichment was followed by an increase in chlorophyll content after 4 days of treatment, although the difference was only significant when nitrate was added without P. P-enrichment had no significant effect on chlorophyll content. In all the treatments an increase in biomass was obseved after 10 days. This increase was higher in the N+P treatments. In all the treatments the uptake rate was significantly higher when nutrients were added than in control jars. The uptake rate of N, as ammonium, and P were significantly higher when they were added alone while that of N as nitrate was higher in the N+P treatment. In the P-enriched cultures, the final P-content of macroalgal tissues was ten-fold that of the initial tissue concentrations, thereby indicating luxury P-uptake. Moreover, at the end of the incubation the N:P ratio increased to 80, showing that P rather than N was the limiting factor for C. linum in the Tancada lagoon. The relatively high availability of N is related to the N inputs from rice fields that surround the lagoon and to P binding in sediments. A partir de experimentos en laboratorio se ha estudiado la influencia de la disponibilidad de nutrientes disueltos en el crecimiento, contenido en nutrientes y sus tasas de absorción en la especie de macroalga Chaetomorpha linum procedente de una laguna costera típicamente mediterránea (La Tancada, Delta del Ebro, NE España). Se fertilizó con diferentes formas de nitrógeno, nitrato o amonio y fósforo. Se ha observado un incremento significativo en el contenido de N y P en los tejidos vegetales tanto en las fertilizaciones con P o N como con N+P. La fertilización con N dio como resultado un aumento de la concentración de clorofila a los 4 días de iniciado el experimento aunque sólo se han observado diferencias significativas en el tratamiento con nitrato. La fertilización con P no produjo efecto significativo sobre la concentración en clorofila. En todos los tratamientos se ha observado un aumento de biomasa al cabo de 10 días y este incremento fue mayor cuando se fertilizaba con N+P. La tasa de absorción ha sido siempre más elevada en los microcosmos fertilizados que en los controles sin fertilizar. Las tasas de absorción de amonio y P fueron significativamente más elevadas en los tratamientos simples, con sólo amonio o P, sin embargo en el caso del nitrato la tasa de absorción fue mayor cuando se fertilizaba con N+P. Se ha observado un aumento en 10 veces el contenido inicial en los cultivos enriquecidos con P lo cual sería indicador de un consumo extra de fósforo, lo que unido al valor bajo inicial de N:P de 80 sería indicador de limitación del crecimiento por P en la laguna de la Tancada. La relativa disponibilidad alta de N con respecto al P podría estar relacionada con la entrada de N disuelto de los arrozales y la inmovilización de P en el sedimento.

The distribution biomass and photosynthesis of three species of rooted macrophytes, Ruppia cirrhosa (Petagna) Grande, Potamogeton pectinatus L. and Zostera noltii Hornem and a floating macroalga Chaetomorpha linum Kutz, were studied in Buda lagoon (River Ebro delta, NE Spain) during spring (May), summer (July) and autumn (October) 1995. Buda lagoon was characterized by a marked gradient of conductivity due to freshwater discharges from rice fields from June to October and by seawater input due to the regression of the delta of the River Ebro during the last 10 years. A typical spatial distribution was observed: monospecific stands of P. pectinatus developed near freshwater inputs in the inner part of the lagoon and mixed stands of R. cirrhosa and P. pectinatus developed in transitional zones between freshwater and seawater influence. The part of the lagoon where the influence of seawater was highest was covered by dense mixed stands of Z. noltii , R. cirrhosa and C. linum . Maximum biomass and production of P. pectinatus were reached in July (biomass of 501 gDW m −2 , and maximum photosynthetic rates, Pm, of 14 mgO 2 g −1 DW h −1 ). Maximum biomass of R. cirrhosa and Z. noltii (456·5 and 250 gDW m −2 respectively) and photosynthetic rate of R. cirrhosa (23·9 mgO 2 g −1 DW h −1 ) occurred in May, whereas no significant differences in production were detected between May and July in Z. noltii . Maximum C. linum production was reached in October (5·4 mgO 2 g −1 DW h −1 ). In October P. pectinatus coverage and production decreased, which was related to high turbidity and density of benthivorous fish due to freshwater inflows. Implications of lower freshwater inflow and higher seawater intrusion in the spatial distribution of aquatic macrophytes in this coastal lagoon are discussed.

The main objective of this work was to devise a method to measure the production and turnover rate of a macrophyte with thin leaves such as Ruppia cirrhosa (Petagna) Grande. Net production was calculated from values of biomass, decomposition rates and mortality obtained in a Mediterranean coastal lagoon (Tancada lagoon, Ebro Delta, NE Spain). Overall, the biomass of rhizomes and roots was constant during the annual cycle, but stem biomass varied substantially. Above-ground biomass peaked in September with 532 g AFDW m −2 and reached a minimum in April with 30 g AFDW m −2 . The net production was calculated to be 361.1 g C m −2 per year, which is the highest value for R. cirrhosa reported in the literature, and a turnover rate of 1.34. The net production obtained by this method is within the estimates based on harvesting techniques (303–545 g C m −2 per year).

This study examines the effect of pH changes on photosynthetic characteristics and the role of dissolved inorganic carbon (DIC) in determining the dominance of three species of macroalgae Chaetomorpha linum (O.F. Muller) Kutzing, Gracilaria verrucosa (Hudson) Papenfuss and Ulva sp. in a Mediterranean coastal lagoon. Fluctuations of pH were measured in the lagoon in summer. Water column CO 2 and HCO 3 − concentrations inside the algal mat showed significant diurnal fluctuations, from a morning peak to an afternoon low, decreasing 96 and 40%, respectively. The response of photosynthesis to increased pH was examined in laboratory conditions in spring (May) and summer (July). The photosynthetic rate declined rapidly at pH above 8.5 and below 6.5. G. verrucosa responded differently in spring and summer showing acclimation to higher pH in summer than in spring. In Ulva sp. incubations, we observed optimum photosynthesis between pH 6 and 7.5. The decrease in photosynthetic rate below pH 6 was lower (12.30%) than above pH 8 (81.03%). This difference may be related to the origin of the macroalgae, suggesting acclimation to the original pH of the environment. Results from instantaneous photosynthesis measurements indicate that low DIC-availability limits the photosynthetic capacity of G. verrucosa,, C. linum and Ulva sp. in spring and of C. linum at high irradiances in summer. Our results also show that G. verrucosa has a higher efficiency at low CO 2 concentrations than C. linum and Ulva sp. It is suggested that G. verrucosa may be better adapted to maintain higher photosynthetic rates than other macroalgae in conditions of tissue N sufficiency and low water DIC concentrations which are typical of shallow coastal environments in summer.

During the last 10 years, a drastic change in the structure of the community of primary producers has been observed in Tancada Lagoon (Ebro Delta, NE Spain). This consisted of a decrease in the abundance of submerged rooted macrophyte cover and a spring and summer increase in floating macroalgae. Two spatial patterns have been observed. In the west part of the lagoon, Chaetomorpha linum Kutzing, dominated during winter and decreased progressively in spring when Cladophora sp. reached its maximum development. In the east part of the lagoon, higher macroalgal diversity was observed, together with lower cover in winter and early spring. Cladophora sp., Gracilaria verrucosa Papenfuss and Chondria tenuissima Agardh, increased cover and biomass in summer. Maximum photosynthetic production was observed in spring for G. verrucosa (10·9 mg O 2 g −1 DW h −1 ) and C. tenuissima (19·0 mg O 2 g −1 DW h −1 ) in contrast with Cladophora sp. (15·9 mg O 2 g −1 DW h −1 ) and Chaetomorpha linum (7·2 mg O 2 g −1 DW h −1 ) which reached maximum production in summer. Increased conductivity from reduced freshwater inflow, and higher water temperatures during periods of lagoon isolation, mainly in summer, were the main physical factors associated with an increase in floating macroalgal biomass across the lagoon. Reduced nitrogen availability and temperature-related changes in carbon availability during summer were related to a decrease in abundance of C. linum and increases in G. verrucosa and Cladophora sp.

The relationship between primary production and irradiance was analyzed over an annual cycle in the submerged macrophytes, Chara hispida and Potamogeton pectinatus, of two mediterranean stream ponds. The effect of temperature on photosynthesis was also studied. The population of P. pectinatus reached maximum production values of 19.67 mgO2 g−1 AFDW h−1 in December at 20°C. In summer and owing to the development of floating filamentous algae, P. pectinatus growth decreased. This can be observed in a decrease in production and chlorophyll content. At the end of autumn a `self-pruning' mechanism in P. pectinatus caused increase of light penetration and new shoots were observed. C. hispida showed maximum production values of 10.86 mg O2 g−1 AFDW h−1 in May. In summer, in agreement with temperature increase C. hispida fructifies and decays, increasing P. pectinatus growth and cover in the same pond. Photoinhibition was observed in C. hispida in October, in agreement with a low radiation adaptation owing to an unusual decrease in light penetration in the pond, caused by inputs of suspended material from a fire suffered in the watershed at the end of summer. Variations in temperature had no effect on Pm/R ratio in P. pectinatus and decreased sharply from young to old tissue. The effect of temperature on the Pm/R ratio in C. hispida was significant. P. pectinatus showed great adaptation capacity to temperature fluctuations and light and this adaptation is higher than in C. hispida, which is affected by temperature increase and light penetration reduction.

Actinoporins are water-soluble proteins with the ability to form pores upon insertion into biological membranes. They constitute a family of proteins with high degree of sequence identities but different hemolytic activities, suggesting that minor conformational arrangements result in major functional changes. A good example of this situation is the sea anemone Stichodactyla helianthus which produces two very similar actinoporins, sticholysins I (StnI) and II (StnII), but of very different hemolytic efficiency. Within this idea, given that the high resolution three-dimensional structure of StnII is already known, we have now solved that one corresponding to StnI in order to analyze the influence of particular residues on the conformation and activity of these proteins. In addition, random mutagenesis has been also used to produce five less hemolytic variants of StnI. All these mutations map to functionally relevant regions because they are probably involved in conformational changes associated with pore formation, which take place after membrane binding, and involve long-distance rearrangements of the polypeptide chain of actinoporins., This work was supported by the Spanish Ministerio de Ciencia e Innovación through projects CTQ2008-00080/BQU, CTQ2011-22514, and BFU2009-10185, and one FPU fellowship granted to S.G.-L.

11 p.-4 tab.-7 fig., Endolysins comprise a novel class of selective antibacterials refractory to develop resistances. The Cpl-7 endolysin, encoded by the Streptococcus pneumoniae bacteriophage Cp-7, consists of a catalytic module (CM) with muramidase activity and a cell wall-binding module (CWBM) made of three fully conserved CW_7 repeats essential for activity. Firstly identified in the Cpl-7 endolysin, CW_7 motifs are also present in a great variety of cell wall hydrolases encoded, among others, by human and live-stock pathogens. However, the nature of CW_7 receptors on the bacterial envelope remains unknown. In the present study, the structural stability of Cpl-7 and the target recognized by CW_7 repeats, relevant for exploitation of Cpl-7 as antimicrobial, have been analyzed, and transitions from the CM and the CWBM assigned, using circular dichroism and differential scanning calorimetry. Cpl-7 stability is maximum around 6.0–6.5, near the optimal pH for activity. Above pH 8.0 the CM becomes extremely unstable, probably due to deprotonation of the N-terminal amino-group, whereas the CWBM is rather insensitive to pH variation and its structural stabilization by GlcNAc-MurNAc-L-Ala-D-isoGln points to the cell wall muropeptide as the cell wall target recognized by the CW_7 repeats. Denaturation data also revealed that Cpl-7 is organized into two essentially independent folding units, which will facilitate the recombination of the CM and the CWBM with other catalytic domains and/or cell wall-binding motifs to yield new tailored chimeric lysins with higher bactericidal activities or new pathogen specificities., This work was supported by grants SAF2009-10824, and BFU2009-10052 from Ministerio de Ciencia e Innovacio´n (MICINN), and BIPPEP2 from Comunidad Autónoma de Madrid (S2010/BMD-2457). Additional funding was provided by the CIBER de Enfermedades Respiratorias (CIBERES), an initiative of the ISCIII. P. Rico-Lastres was supported by a fellowship from MICINN.

Leaf litter decomposition is a crucial process providing matter and energy to communities inhabiting headwater streams. This process could be affected by many man-made landscape transformations and its response can vary depending on the climate setting. In this study, we test the hypothesis that the presence of small headwater reservoirs decreases litter decomposition downstream, as reported for temperate Oceanic climatic regions, and that this effect is more accentuated in the Mediterranean. The effect of small dams on the decomposition of alder (Alnus glutinosa) leaves was studied in four headwater streams in Catalonia (NE Spain). The presence of a dam affected litter decomposition rates in three of the four streams studied, and this depended on reservoir typology. In those with seasonal surface release, decomposition rates were slower downstream from the dams, but in the case of a continuous hypolimnetic release, it was faster, with higher DIN and temperature and abundance of shredders. Alder litter decomposition rates were twice those reported for Oceanic climatic conditions. In Mediterranean headwaters, the effect of small dams will even be more evident at an annual scale due to the diminished flow rates in summer and this effect will be more pronounced than in the more Oceanic. © 2012 Springer Science+Business Media B.V., This study was funded by the Spanish Ministry of Education and Science (projects CGL2007-462 66664-C04 and CGL2011-30474-C02).

The main purpose of our work was to elucidate factors responsible for the geographical differences in leaf-litter decomposition rates in Spanish oligotrophic headwater streams. Decomposition experiments with alder (Alnus glutinosa) leaf litter were carried out in 22 headwater streams in 4 different climatic regions across the Iberian Peninsula (Cornisa Cantbrica, Cordillera Litoral Catalana, Sierra de Guadarrama, and Sierra Nevada). Streams that were similar in size, flowed mainly over siliceous substrate in catchments with scarce human settlements and activities, and fell within a range of low nutrient concentrations were chosen in each region. Breakdown rates were regionally variable and were low (0.1090.198% ash-free dry mass [AFDM]/degree day [dd]) in the Cornisa Cantbrica, the most mesic and Atlantic region, and high (0.3020.639% AFDM/dd) in Sierra de Guadarrama, one of the coldest and most inland areas. Temperature was not the determining factor affecting differences in breakdown rates among regions, and breakdown rates were not related to concentrations of dissolved nutrients. However, microbial reproductive activity (sporulation rates) was significantly correlated with dissolved P concentration. Breakdown rates were explained better by presence and feeding activities of detritivores than by decomposer activity. Incorporation of breakdown rates in assessment schemes of stream ecological status will be difficult because leaf processing does not respond unequivocally to environmental factors when climatic regions are considered. Thus, regional adjustments of baseline standards in reference conditions will be required. © 2011 by The North American Benthological Society., This study was funded by the Spanish Ministry of Education and Science (project CGL2007-66664-C04), by the University of the Basque Country (Research grant GIU05/38), and by the Basque Government (Research grants IT-422-07 and IT-302-10)

21 p.- 7 fig.- 4 tab.-2 fig. supl.-1 tab. supl., Bacteriophage endolysins include a group of new antibacterials reluctant to development of resistance. We present here the first structural study of the Cpl-7 endolysin, encoded by pneumococcal bacteriophage Cp-7. It contains an N-terminal catalytic module (CM) belonging to the GH25 family of glycosyl hydrolases and a C-terminal region encompassing three identical repeats of 42 amino acids (CW_7 repeats). These repeats are unrelated to choline-targeting motifs present in other cell wall hydrolases produced by Streptococcus pneumoniae and its bacteriophages, and are responsible for the protein attachment to the cell wall. By combining different biophysical techniques and molecular modeling, a three-dimensional model of the overall protein structure is proposed, consistent with circular dichroism and sequence-based secondary structure prediction, small angle x-ray scattering data, and Cpl-7 hydrodynamic behavior. Cpl-7 is an ∼115-Å long molecule with two well differentiated regions, corresponding to the CM and the cell wall binding region (CWBR), arranged in a lateral disposition. The CM displays the (βα)5β3 barrel topology characteristic of the GH25 family, and the impact of sequence differences with the CM of the Cpl-1 lysozyme in substrate binding is discussed. The CWBR is organized in three tandemly assembled three-helical bundles whose dispositions remind us of a super-helical structure. Its approximate dimensions are 60 × 20 × 20 Å and presents a concave face that might constitute the functional region involved in bacterial surface recognition. The distribution of CW_7 repeats in the sequences deposited in the Entrez Database have been examined, and the results drastically expanded the antimicrobial potential of the Cpl-7 endolysin, This work was supported by Grants BFU2006-10288, SAF2009-10824, BIO2007-61336, and BFU2009-10052 from Ministerio de Ciencia e Innovación, Grant BIPPED-CM from the Comunidad de Madrid, the CIBER de Enfermedades Respiratorias (CIBERES), an initiative of the ISCIII, Glycodynamics Network Grant FP6-UE MCTN-CT-2005-019561, and European Community beam time Proposal 48086

The LytC lysozyme of Streptococcus pneumoniae forms part of the autolytic system of this important pathogen. This enzyme is composed of a C-terminal CM (catalytic module), belonging to the GH25 family of glycosyl hydrolases, and an N-terminal CBM (choline-binding module), made of eleven homologous repeats, that specifically recognizes the choline residues that are present in pneumococcal teichoic and lipoteichoic acids. This arrangement inverts the general assembly pattern of the major pneumococcal autolysin, LytA, and the lytic enzymes encoded by pneumococcal bacteriophages that place the CBM (made of six repeats) at the C-terminus. In the present paper, a three-dimensional model of LytC built by homology modelling of each module and consistent with spectroscopic and hydrodynamic studies is shown. In addition, the putative catalytic-pair residues are identified. Despite the inversion in the modular arrangement, LytC and the bacteriophage-encoded Cpl-1 lysozyme most probably adopt a similar global fold. However, the distinct choline-binding ability and their substrate-binding surfaces may reflect a divergent evolution directed by the different roles played by them in the host (LytC) or in the bacteriophage (Cpl-1). The tight binding of LytC to the pneumococcal envelope, mediated by the acquisition of additional choline-binding repeats, could facilitate the regulation of the potentially suicidal activity of this autolysin. In contrast, a looser attachment of Cpl-1 to the cell wall and the establishment of more favourable interactions between its highly negatively charged catalytic surface and the positively charged chains of pneumococcal murein could enhance the lytic activity of the parasite-encoded enzyme and therefore liberation of the phage progeny. © 2005 Biochemical Society., This work was supported by DGICYT (Dirección General de Investigación Científica y Técnica) Grants BIO2000-1307, BMC2000-1002, BIO2003-01952, BMC2003-00074 and by CAM Grant of the Program for Strategic Groups. B. M. was supported by a fellowship from the Spanish Ministerio de Ciencia y Tecnología.

10 p.-2 tab.-7 fig., Ceragenin CSA-13, a cationic steroid, is here reported to show a concentration-dependent bactericidal/bacteriolytic activity against pathogenic streptococci, including multidrug-resistant Streptococcus pneumoniae. The autolysis promoted by CSA- 13 in pneumococcal cultures appears to be due to the triggering of the major S. pneumoniae autolysin LytA, an Nacetylmuramoyl-L-alanine amidase. CSA-13 also disintegrated pneumococcal biofilms in a very efficient manner, although at concentrations slightly higher than those required for bactericidal activity on planktonic bacteria. CSA-13 has little hemolytic activity which should allow testing its antibacterial efficacy in animal models., This work was supported by Dirección General de Investigación Científica y Técnica (grant numbers SAF2009-10824, BFU2009-10052, BFU2012-36825,and SAF2012-39444-C02-01) and Centro de Investigación Biomédica en Red de Enfermedades Respiratorias (CIBERES), which is an initiative of the ISCIII.

The spatial distribution of macrophytes (Ruppia drepanensis Tineo and Lamprothamnium papulosum (Wallr.) J. Gr. was studied along transects perpendicular to the shoreline in Lake Gallocanta (Aragon, NE Spain) in 1988 and 1990. In the shallow zone, a gradient from the shoreline to offshore waters was clear: Small R. drepanensis plants were the only colonizers of near shore waters affected by wave action and desiccation. R. drepanensis and L. papulosum coexisted at intermediate depths in the shallow zone. L. papulosum reached higher biomasses than R. drepanensis in the deepest parts of the shallow zone. In the deepest zone of the lake, stands of the two species did not overlap. Individual plants of R. drepanensis occured patchily within a sparse prairie of L. papulosum.

The influence of C-6 alpha- or C-7 alpha-methoxylation of the beta-lactam ring in the catalytic action of class A and B beta-lactamases has been investigated. For this purpose the kinetic behaviour of beta-lactamases I (class A) and II (class B) from Bacillus cereus was analysed by using several cephamycins, moxalactam, temocillin and related antibiotics. These compounds behaved as poor substrates for beta-lactamase II, with high Km values and very low catalytic efficiencies. In the case of beta-lactamase I, the substitution of a methoxy group for a H atom at C-7 alpha or C-6 alpha decreased the affinity of the substrates for the enzyme. Furthermore, the acylation of cephamycins was completely blocked, whereas that of penicillins was slowed down by a factor of 10(4)-10(5), acylation being the rate-determining step of the process.

Based on the comparison of environmental requirements for Ruppia cirrhosa and Potamogeton pectinatus growth, macrophyte versus phytoplankton biomass and production features, and differences in hydrological and nutrient balances between Tancada lagoon (where macrophytes form dense beds) and Encanizada lagoon (with no macrophytes at all), several proposals for macrophyte restoration are presented. The highest photosynthetic efficiency of R. cirrhosa takes place at high irradiance and it grows over a wide range of salinity. P. pectinatus is better adapted to lower light intensity and salinity than Ruppia. R. cirrhosa transplanted from Tancada to Encanizada was successful in enclosures, where light availability increased ( μ = 0.013 cm−1), but not in open waters where light extinction coefficient was 0.032 cm−1. Phytoplankton biomass (0.11–2.15 g C m−2) is much lower than macrophyte biomass (16–200 g C m−2) in Tancada lagoon. However, phytoplankton production (165 g C m−2 yr−1 in Tancada, 480 g C m−2 yr−1 in Encanizada) is the same order of magnitude as macrophyte production (244–467 g C m−2 yr−1). Turnover rates are 0.3–0.9 day−1 for phytoplankton and 1.2–2.5 yr−1 for macrophytes. Phytoplankton and inorganic particles are responsible for high turbidity of the water in Encanizada lagoon. Phytoplankton blooms in Encanizada lagoon are supported by high freshwater inflows from rice field drains from May to November. The Qs (seawater discharge)/QF (Freshwater discharge) ratios are, respectively, 0.24 and 0.48, which denotes a higher seawater influence in Tancada than in Encanizada lagoon. Decreasing freshwater inputs to Encanizada lagoon both in May and November thus allowing greater inputs of sea water, is proposed as the most effective way to restore this eutrophic coastal lagoon.