Structural styles and Neogene petroleum system around the Yusuf-Habibas Ridge (Alboran Basin, Mediterranean Sea)

International audienceThe Algerian offshore is part of the southern margin of the western Mediterranean Sea. The western part of this offshore area represents the transitional margin between the South Algero-Balearic Basin and the Alboran Basin. The study area includes the southern and eastern parts of the Alboran Basin and the northwestern part of the Algerian margin and is in the western part of the plate boundary between Eurasia and Africa (Figure 1). The Yusuf-Habibas Ridge is a major EW-striking structure of this complex plate boundary, separating the eastern and southern parts of the Alboran Basin from the South Algero-Balearic Basin (Martinez-Garcia et al., 2011, and references therein). The ridge played an important role during the Neogene Alboran westward block migration between the Africa and Iberia plates, while the Kabylies blocks migrated southward and accreted to Africa. Furthermore, the ongoing NW-SE convergence between Africa and Iberia has induced a new stress field, since 7 Ma ago, replacing an earlier stress field (Fernandez-Ibañez et al., 2007) and leading to reactivation and polyphased deformation on the main structures in the basin, including the Yusuf-Habibas Ridge

Tyrosine metabolism: identification of a key residue in the acquisition of prephenate aminotransferase activity by 1β aspartate aminotransferase

International audienceAlternative routes for the post-chorismate branch of the biosynthetic pathway leading to tyrosine exist, the 4-hydroxyphenylpyruvate or the arogenate route. The arogenate route involves the transamination of prephenate into arogenate. In a previous study, we found that, depending on the microorganisms possessing the arogenate route, three different aminotransferases evolved to perform prephenate transamination, that is, 1β aspartate aminotransferase (1β AAT), N-succinyl-l,l-diaminopimelate aminotransferase, and branched-chain aminotransferase. The present work aimed at identifying molecular determinant(s) of 1β AAT prephenate aminotransferase (PAT) activity. To that purpose, we conducted X-ray crystal structure analysis of two PAT competent 1β AAT from Arabidopsis thaliana and Rhizobium meliloti and one PAT incompetent 1β AAT from R. meliloti. This structural analysis supported by site-directed mutagenesis, modeling, and molecular dynamics simulations allowed us to identify a molecular determinant of PAT activity in the flexible N-terminal loop of 1β AAT. Our data reveal that a Lys/Arg/Gln residue in position 12 in the sequence (numbering according to Thermus thermophilus 1β AAT), present only in PAT competent enzymes, could interact with the 4-hydroxyl group of the prephenate substrate, and thus may have a central role in the acquisition of PAT activity by 1β AAT

Long term evolution and internal architecture of a high-energy banner ridge from seismic survey of Banc du Four (Western Brittany, France)

International audienceThe recent completion of a coupled seismic and swath bathymetric survey, conducted across the sand ridge system of the Banc du Four located on the Atlantic continental shelf of Brittany (Mer d’Iroise, France), provided new data for the study of the long term evolution of deep tidal sand ridges. Five seismic units are distinguished within the ridge, separated by pronounced major bounding surfaces. The basal unit is interpreted to be shoreface deposits forming the core of the ridge. It is overlaid by a succession of marine sand dunes fields forming the upper units. Sandwave climbing, which combines progradation and accretion, is the major process controlling the growth of the ridge. The elevation of the preserved dune foresets reaches values of about 20–30 m within the ridge. The foresets indicate a combination of giant dunes characterized by numerous steep (up to 20°) clinoforms corresponding to a high-energy depositional environment. Moreover, the presence of scour pits linked to the 3D geometries of giant dunes allow the growth of bedforms migrating oblique to the orientation of giant dune crest lines. All of the radiocarbon ages of the biogenic surficial deposits of the Banc du Four range from 10,036 to 2748 cal years B.P. and suggest the Banc du Four has grown during the last sea-level rise. The apparent absence of recent surface deposits could be caused by a change in benthic biogenic productivity or the non-conservation of recent deposits. In contrast, the presence of relatively old sands at the top of the ridge could be explained by the reworking and leakage of the lower units that outcrop locally at the seabed across the ridge. Moreover, the long-term evolution of the ridge appears strongly controlled by the morphology of the igneous basement. The multiphase accretion of the ridge is closely linked to the presence of a residual tidal current eddy, consecutive with the progressive flooding of the coastal promontories and straits that structured the igneous basement.Therefore, the Banc du Four should be thought of as a representative example of a large-scale high-energy banner bank

Reply to Comment by A. Argnani on "Geometry of the Deep Calabrian Subduction from Wide‐Angle Seismic Data and 3‐D Gravity Modeling"

Keypoints This contribution is a reply on a comment submitted by A. Argnani. The alternate interpretation of the wide-angle seismic model is discussed. The Alfeo Fault system is proposed to be the current location of STEP fault. Abstract Andrea Argnani in his comment on Dellong et al., 2020 (Geometry of the deep Calabrian subduction (Central Mediterranean Sea) from wide‐angle seismic data and 3D gravity modeling), proposes an alternate interpretation of the wide-angle seismic velocity models presented by Dellong et al., 2018 and Dellong et al., 2020 and proposes a correction of the literature citations in these paper. In this reply, we discuss in detail all points raised by Andrea Argnani

Recent and active deformation pattern off the easternmost Algerian margin, Western Mediterranean Sea: New evidence for contractional tectonic reactivation

International audienceWe describe for the first time a set of large active thrusts and folds near the foot of the easternmost Algerian margin, Western Mediterranean, from swath bathymetry and high-resolution seismic data acquired in 2005 during the Maradja2/Samra cruise. This active system resumes a previous passive margin and creates growth strata deposition on the limbs of large folds, resulting in the development of perched basins at the foot of the margin since less than ~ 1 Ma. They form a set of overlapping fault segments verging toward the Algerian basin, in a way similar to what has been observed off eastern Algiers on the rupture zone of the 2003 Mw 6.8 Boumerdes earthquake. The horizontal shortening rate across large folds is estimated to be of the order of 1 mm/yr. Although no historical earthquakes are reported here, these fault segments could have been responsible for large (M ~ 7.5) events in the past. This young tectonic system further supports the hypothesis of subduction inception of the Neogene oceanic lithosphere in the context of the Africa–Eurasia convergence

Calmodulin-like proteins localized to the conoid regulate motility and cell invasion by Toxoplasma gondii

Toxoplasma gondii contains an expanded number of calmodulin (CaM)-like proteins whose functions are poorly understood. Using a combination of CRISPR/Cas9-mediated gene editing and a plant-like auxin-induced degron (AID) system, we examined the roles of three apically localized CaMs. CaM1 and CaM2 were individually dispensable, but loss of both resulted in a synthetic lethal phenotype. CaM3 was refractory to deletion, suggesting it is essential. Consistent with this prediction auxin-induced degradation of CaM3 blocked growth. Phenotypic analysis revealed that all three CaMs contribute to parasite motility, invasion, and egress from host cells, and that they act downstream of microneme and rhoptry secretion. Super-resolution microscopy localized all three CaMs to the conoid where they overlap with myosin H (MyoH), a motor protein that is required for invasion. Biotinylation using BirA fusions with the CaMs labeled a number of apical proteins including MyoH and its light chain MLC7, suggesting they may interact. Consistent with this hypothesis, disruption of MyoH led to degradation of CaM3, or redistribution of CaM1 and CaM2. Collectively, our findings suggest these CaMs may interact with MyoH to control motility and cell invasion

Applying laser reflectometry to study active submarine faults: the FOCUS project (FOCUS = Fiber Optic Cable Use for Seafloor studies of earthquake hazard and deformation)

Laser reflectometry (BOTDR), commonly used for structural health monitoring (bridges, dams, etc.), will for the first time be applied to study movements of an active fault on the seafloor, 25 km offshore Catania Sicily (an urban area of 1 million people). This technique can measure and locate micro-strains (< 1 mm) across very large distances (10 - 200 km). The goal of the European funded FOCUS project (ERC Advanced Grant) is to connect a dedicated 6-km long strain cable to the EMSO (European Multidisciplinary water-column and Seafloor Observatory) seafloor observatory in 2100 m water depth. Here, in May 2017, between the onshore fault system on the SE flank of Mount Etna and the deeper offshore Alfeo fault system, 4 cm of dextral strike-slip movement was documented as a slow slip event by seafloor acoustic ranging. For the planned seafloor operations, a detailed site survey of the seafloor will first be performed to determine the best path for deployment of the new strain cable. The next step will be to connect this 6-km long fiber optic cable to the EMSO station TSS (Test Site South) using a deep-water cable-laying system with an integrated plow to bury the cable 20 cm in the soft sediments in order to increase coupling between the cable and the seafloor. The targeted track for the cable will cross the North Alfeo Fault at three locations. Laser reflectometry measurements will be calibrated by a three-year deployment of seafloor geodetic instruments to quantify relative displacement across the fault. During the implementation of the laser reflectometry, a passive seismological experiment is planned to record regional seismicity. This will involve deployment of a temporary network of OBS (Ocean Bottom Seismometers) on the seafloor and seismic stations on land, supplemented by INGV permanent land stations. The simultaneous use of laser reflectometry, seafloor geodetic stations as well as seismological land and sea stations will provide an integrated system for monitoring a wide range of types of slipping events along the North Alfeo Fault. A long-term goal is the development of dual-use telecom cables with industry partners