Extinction of herbivorous dinosaurs linked to Early Jurassic global warming event.

Sauropods, the giant long-necked dinosaurs, became the dominant group of large herbivores in terrestrial ecosystems after multiple related lineages became extinct towards the end of the Early Jurassic (190-174 Ma). The causes and precise timing of this key faunal change, as well as the origin of eusauropods (true sauropods), have remained ambiguous mainly due to the scarce dinosaurian fossil record of this time. The terrestrial sedimentary successions of the Cañadón Asfalto Basin in central Patagonia (Argentina) document this critical interval of dinosaur evolution. Here, we report a new dinosaur with a nearly complete skull that is the oldest eusauropod known to date and provide high-precision U-Pb geochronology that constrains in time the rise of eusauropods in Patagonia. We show that eusauropod dominance was established after a massive magmatic event impacting southern Gondwana (180-184 Ma) and coincided with severe perturbations to the climate and a drastic decrease in the floral diversity characterized by the rise of conifers with small scaly leaves. Floral and faunal records from other regions suggest these were global changes that impacted the terrestrial ecosystems during the Toarcian warming event and formed part of a second-order mass extinction event.

Exploring the interior of cuticles and compressions of fossil plants by FIB-SEM milling and image microscopy.

We present the first study of cuticles and compressions of fossil leaves by Focused Ion Beam Scanning Electron Microscopy (FIB-SEM). Cavities preserved inside fossil leaf compressions corresponding to substomatal chambers have been observed for the first time and several new features were identified in the cross-section cuts. These results open a new way in the investigation of the three-dimensional structures of both micro- and nanostructural features of fossil plants. Moreover, the application of the FIB-SEM technique to both fossils and extant plant remains represent a new source of taxonomical, palaeoenvironmental and palaeoclimatic information.

The role of GlpR repressor in Pseudomonas putida KT2440 growth and PHA production from glycerol.

Pseudomonas putida KT2440 has evolved a tightly regulated system for metabolizing glycerol implying a prolonged growth lag-phase. We have learnt that this fact can be avoided by the addition of small amounts of some growth precursors. The addition of 1 mM octanoic acid as co-feeder completely eliminated the lag-phase, resulting in an improvement, in terms of invested time, of both growth and polyhydroxyalkanoates (PHA) accumulation. To investigate this phenomenon, we have followed co-metabolic approaches combined with mutations of the specific and global regulatory networks that connect glycerol catabolism and PHA synthesis. By using mutant strains in metabolic genes from the PHA and tricarboxylic acid (TCA) cycles, we have demonstrated that the co-feeding effect is independent of PHA accumulation, but driven on active glyoxylate shunt and Entner-Doudoroff (ED) routes. These findings suggested that the effect of octanoate on glycerol metabolism could rely, either on a global activation of the cell energy state, or on the generation of specific metabolites or cofactors needed for the activation of glycerol metabolism. Our results addressed GlpR as the key factor controlling the efficient utilization of glycerol as growth precursor in P. putida KT2440. Accordingly, a glpR knockout mutant of P. putida KT2440 showed an elimination of the lag-phase when cultured on glycerol in the absence of co-feeder. Besides, the production of PHA in this strain was increased near twofold, resulting in a higher final yield in terms of PHA accumulation. The repressor activity of the GlpR protein over the glp genes in the absence of glycerol was finally demonstrated by qRT-PCR. This work contributed to unravel the physiological causes of the long lag-phase produced by glycerol in the model strain P. putida KT2440 that hinders its use as carbon source in biotechnological applications for generating valuable products.

The polyhydroxyalkanoate metabolism controls carbon and energy spillage in Pseudomonas putida.

The synthesis and degradation of polyhydroxyalkanoates (PHAs), the storage polymer of many bacteria, is linked to the operation of central carbon metabolism. To rationalize the impact of PHA accumulation on central carbon metabolism of the prototype bacterium Pseudomonas putida, we have revisited PHA production in quantitative physiology experiments in the wild-type strain vs. a PHA negative mutant growing under low nitrogen conditions. When octanoic acid was used as PHA precursor and as carbon and energy source, we have detected higher intracellular flux via acetyl-CoA in the mutant strain than in the wild type, which correlates with the stimulation of the TCA cycle and glyoxylate shunt observed on the transcriptional level. The mutant defective in carbon and energy storage spills the additional resources, releasing CO(2) instead of generating biomass. Hence, P. putida operates the metabolic network to optimally exploit available resources and channels excess carbon and energy to storage via PHA, without compromising growth. These findings demonstrate that the PHA metabolism plays a critical role in synchronizing global metabolism to availability of resources in PHA-producing microorganisms.

Nucleoid-associated PhaF phasin drives intracellular location and segregation of polyhydroxyalkanoate granules in Pseudomonas putida KT2442.

The PhaF is a nucleoid-associated like protein of Pseudomonas putida KT2442 involved in the polyhydroxyalkanoate (PHA) metabolism. Its primary structure shows two modular domains; the N-terminal PHA granule-binding domain (phasin domain) and the C-terminal half containing AAKP-like tandem repeats characteristic of the histone H1 family. Although the PhaF binding to PHA granules and its role as transcriptional regulator have been previously demonstrated, the cell physiology meaning of these properties remains unknown. This work demonstrates that PhaF plays a crucial role in granule localization within the cell. TEM and flow cytometry studies of cells producing granules at early growth stage demonstrated that PhaF directs the PHA granules to the centre of the cells, forming a characteristic needle array. Our studies demonstrated the existence of two markedly different cell populations in the strain lacking PhaF protein, i.e. cells with and without PHA. Complementation studies definitively demonstrated a key role of PhaF in granule segregation during the cell division ensuring the equal distribution of granules between daughter cells. In vitro studies showed that PhaF binds DNA through its C-terminal domain in a non-specific manner. All these findings suggested a main role of PhaF in PHA apparatus through interactions with the segregating chromosome.