Attività Fotosintetica di Alghe Marine Nella Grotta Delle Viole (Isola S. Domino - Tremiti)

Abstract

Photosynthetic rates of some algae in the marine cave « Grotta delle Viole » (Is. S. Domino - Tremiti). — The « Grotta delle Viole » is one of the several marine caves located along the calcareous rocky southern littoral of the Island S. Domino (Tremiti) in the Adriatic Sea. Morphologically this cave is a tunnel, which connects the open littoral sea with a little bay. Availing of these environmental factors, we have chosen three stations to measure the photosyn-thetic yield, under completely natural conditions, of algae particularly important for some marine communities, described in an other paper (see, Pignatti S. et al. 1967). In station 1 (fig. 1) we have a biotope with strongly reduced light and in the neighbouring stations 2 and 3, two biotopes exposed to sun-light. We have studied three species living in dark places (« Peyssonelia » cfr. « harveyana », « Palmophyllum crassum » and « Pseudolithophyllum expansum » two of well lighted habitas (« Padina pavonia » and « Dictyota dichotoma » and one of intermediate place (« Codium difforme ») Some information on the optical conditions of the seawater have been obtained with a photoelectric cell, filters were used to measure the red and blue light penetration (Tab. 1, 2). This part of the Adriatic Sea is characterized by high penetration of blue light. In the cave this light is highly predominant. The photosynthetic rates were measured in natural conditions by determining the output in time O₂ using the Winkler method (Tab. 3) and the CO₂ changes by measuring pH-changes in short time intervals with an original method using a submarine incubation cell, of our design, equipped with the electrodes of a pH-meter and a spot-light galvanometer as measure instrument. The data obtained with the latter method have been statistically analized, their significance discussed and reported in Tab. 4. On the basis of the results, the species, which are confined in places with reduced light intensity, show a low but measurable photosynthetic surplus only in their natural habitats, transferred in high-light intensity they show a deficit. This fact can suggest the hypotheses: deactivation of the chlorophyll in green and blue light or competitive inhibition due to the presence of accessory pigments. The species of sunny habitats transferred in low-light intensity show an assimilatory deficit, that in this case, with great probability, is due to the progressive reduction of the photosynthetic process. These considerations explaine also the observed distributions of the species and of the algal communities (fig. 1), since each of them is connected with a light optimum. It seems important moreover to note that here, for the first time, data are given also on photosynthetic activity of Lithothamnia.     

Relitti Mediterranei all'imboccatura di Cavità Ipogee Carsiche

Abstract

Mediterranean relicts at the mouth of karstic caves. — Far away from the mediterranean maquis stretched along the coast of Trieste, we can still find some groups of rank evergreen-oaks with several other mediterranean species.

The survival of these thermophile species is probably due to warm ascensional drafts, coming just in winter from the underneath caves.     

Fis targets assembly of the Xis nucleoprotein filament to promote excisive recombination by phage lambda

The phage-encoded Xis protein is the major determinant controlling the direction of recombination in phage lambda. Xis is a winged-helix DNA binding protein that cooperatively binds to the attR recombination site to generate a curved microfilament, which promotes assembly of the excisive intasome but inhibits formation of an integrative intasome. We find that lambda synthesizes surprisingly high levels of Xis immediately upon prophage induction when excision rates are maximal. However, because of its low sequence-specific binding activity, exemplified by a 1.9 A co-crystal structure of a non-specifically bound DNA complex, Xis is relatively ineffective at promoting excision in vivo in the absence of the host Fis protein. Fis binds to a segment in attR that almost entirely overlaps one of the Xis binding sites. Instead of sterically excluding Xis binding from this site, as has been previously believed, we show that Fis enhances binding of all three Xis protomers to generate the microfilament. A specific Fis-Xis interface is supported by the effects of mutations within each protein, and relaxed, but not completely sequence-neutral, binding by the central Xis protomer is supported by the effects of DNA mutations. We present a structural model for the 50 bp curved Fis-Xis cooperative complex that is assembled between the arm and core Int binding sites whose trajectory places constraints on models for the excisive intasome structure.     

Structure and Identification of a Pterin Dehydratase-like Protein as a Ribulose-bisphosphate Carboxylase/Oxygenase (RuBisCO) Assembly Factor in the α-Carboxysome

Carboxysomes are proteinaceous bacterial microcompartments that increase the efficiency of the rate-limiting step in carbon fixation by sequestering reaction substrates. Typically, α-carboxysomes are genetically encoded as a single operon expressing the structural proteins and the encapsulated enzymes of the microcompartment. In addition, depending on phylogeny, as many as 13 other genes are found to co-occur near or within α-carboxysome operons. One of these genes codes for a protein with distant homology to pterin-4α-carbinolamine dehydratase (PCD) enzymes. It is present in all α-carboxysome containing bacteria and has homologs in algae and higher plants. Canonical PCDs play an important role in amino acid hydroxylation, a reaction not associated with carbon fixation. We determined the crystal structure of an α-carboxysome PCD-like protein from the chemoautotrophic bacterium Thiomonas intermedia K12, at 1.3-Å resolution. The protein retains a three-dimensional fold similar to canonical PCDs, although the prominent active site cleft present in PCD enzymes is disrupted in the α-carboxysome PCD-like protein. Using a cell-based complementation assay, we tested the PCD-like proteins from T. intermedia and two additional bacteria, and found no evidence for PCD enzymatic activity. However, we discovered that heterologous co-expression of the PCD-like protein from Halothiobacillus neapolitanus with RuBisCO and GroELS in Escherichia coli increased the amount of soluble, assembled RuBisCO recovered from cell lysates compared with co-expression of RuBisCO with GroELS alone. We conclude that this conserved PCD-like protein, renamed here α-carboxysome RuBisCO assembly factor (or acRAF), is a novel RuBisCO chaperone integral to α-carboxysome function.     

The crystal structure of the primary Ca2+ sensor of the Na+/Ca2+ exchanger reveals a novel Ca2+ binding motif

The Na+/Ca2+ exchanger is a plasma membrane protein that regulates intracellular Ca2+ levels in cardiac myocytes. Transport activity is governed by Ca2+, and the primary Ca2+ sensor (CBD1) is located in a large cytoplasmic loop connecting two transmembrane helices. The binding of Ca2+ to the CBD1 sensory domain results in conformational changes that stimulate the exchanger to extrude Ca2+. Here, we present a crystal structure of CBD1 at 2.5A resolution, which reveals a novel Ca2+ binding site consisting of four Ca2+ ions arranged in a tight planar cluster. This intricate coordination pattern for a Ca2+ binding cluster is indicative of a highly sensitive Ca2+ sensor and may represent a general platform for Ca2+ sensing.     

The crystal structure of the mycobacterium tuberculosis Rv3019c-Rv3020c ESX complex reveals a domain-swapped heterotetramer

Mycobacterium tuberculosis encodes five gene clusters (ESX‐1 to ESX‐5) for Type VII protein secretion systems that are implicated in mycobacterial pathogenicity. Substrates for the secretion apparatus are encoded within the gene clusters and in additional loci that lack the components of the secretion apparatus. The best characterized substrates are the ESX complexes, 1:1 heterodimers of ESAT‐6 and CFP‐10, the prototypical member that has been shown to be essential for Mycobacterium tuberculosis pathogenesis. We have determined the structure of EsxRS, a homolog of EsxGH of the ESX‐3 gene cluster, at 1.91 Å resolution. The EsxRS structure is composed of two four‐helix bundles resulting from the 3D domain swapping of the C‐terminal domain of EsxS, the CFP‐10 homolog. The four‐helix bundles at the extremities of the complex have a similar architecture to the structure of ESAT‐6·CFP‐10 (EsxAB) of ESX‐1, but in EsxRS a hinge loop linking the α‐helical domains of EsxS undergoes a loop‐to‐helix transition that creates the domain swapped EsxRS tetramer. Based on the atomic structure of EsxRS and existing biochemical data on ESX complexes, we propose that higher order ESX oligomers may increase avidity of ESX binding to host receptor molecules or, alternatively, the conformational change that creates the domain swapped structure may be the basis of ESX complex dissociation that would free ESAT‐6 to exert a cytotoxic effect.     

Biochemical characterization of Bacillus subtilis type II isopentenyl diphosphate isomerase, and phylogenetic distribution of isoprenoid biosynthesis pathways.

An open reading frame (Acc. no. P50740) on the Bacillus subtilis chromosome extending from bp 184,997-186,043 with similarity to the idi-2 gene of Streptomyces sp. CL190 specifying type II isopentenyl diphosphate isomerase was expressed in a recombinant Escherichia coli strain. The recombinant protein with a subunit mass of 39 kDa was purified to apparent homogeneity by column chromatography. The protein was shown to catalyse the conversion of dimethylallyl diphosphate into isopentenyl diphosphate and vice versa at rates of 0.23 and 0.63 micromol.mg(-1).min(-1), respectively, as diagnosed by 1H spectroscopy. FMN and divalent cations are required for catalytic activity; the highest rates were found with Ca2+. NADPH is required under aerobic but not under anaerobic assay conditions. The enzyme is related to a widespread family of (S)-alpha-hydroxyacid oxidizing enzymes including flavocytochrome b2 and L-lactate dehydrogenase and was shown to catalyse the formation of [2,3-13C2]lactate from [2,3-13C2]pyruvate, albeit at a low rate of 1 nmol.mg(-1).min(-1). Putative genes specifying type II isopentenyl diphosphate isomerases were found in the genomes of Archaea and of certain eubacteria but not in the genomes of fungi, animals and plants. The analysis of the occurrence of idi-1 and idi-2 genes in conjunction with the mevalonate and nonmevalonate pathway in 283 completed and unfinished prokaryotic genomes revealed 10 different classes. Type II isomerase is essential in some important human pathogens including Staphylococcus aureus and Enterococcus faecalis where it may represent a novel target for anti-infective therapy.     

Chlorophyll Content Observations of the Near-Surface Scattering Layers in the Mediterranean Sea

Abstract

In several areas of the Mediterranean Sea near-surface sound-reflecting layers have been studied. The amount of total pigment occurring in these layers has been determined. Since these layers occur near the basis of the euphotic zone, the degree of degradation of the pigments has been determined by a fluorimetric method. An increase in total pigment has been noticed in the scattering layer as compared to the over and under-lying water layers. A low degree of decomposition of pigment has been found in the scattering layer compared with that in the immediate over and under-lying layers of the wather column. When a scattering layer is lacking the degradation state of the pigment increases progressively with depth. These results suggest that the plants present in the scattering layers are healthy with regard to photosyntetic pigment.     

Saxifraga Berica (Béguinot) D. A. Webb E Asplenium Lepidum Presl Sui Colli Berici

Abstract

«Saxifraga berica» (Béguinot) D. A. Webb and «Asplenium lepidum» Presl on the «Colli Berici». – We have identified a new association in the small caverns of the calcareous rocks in the hills of the north-eastern zone of the «Colli Berici», rising from the Italian plain near Vicenza. We have adopted for this association the name: ADIANTO-SAXIFRAGETUM BERICAE. This phytocoenose is characterized by the endemic «Saxifraga berica». We have found new stations of this remarkable plant and reported some features of this species to complete the diagnosis of D. A. Webb. In two station of this association we have found also the rare «Asplenium lepidum», new for this region.