Pablo M. Fernández

Synergistic roles of climate warming and human occupation in Patagonian megafaunal extinctions during the Last Deglaciation

Patagonian megafaunal extinctions reveal synergistic roles of climate change and human impacts. The causes of Late Pleistocene megafaunal extinctions (60,000 to 11,650 years ago, hereafter 60 to 11.65 ka) remain contentious, with major phases coinciding with both human arrival and climate change around the world. The Americas provide a unique opportunity to disentangle these factors as human colonization took place over a narrow time frame (~15 to 14.6 ka) but during contrasting temperature trends across each continent. Unfortunately, limited data sets in South America have so far precluded detailed comparison. We analyze genetic and radiocarbon data from 89 and 71 Patagonian megafaunal bones, respectively, more than doubling the high-quality Pleistocene megafaunal radiocarbon data sets from the region. We identify a narrow megafaunal extinction phase 12,280 ± 110 years ago, some 1 to 3 thousand years after initial human presence in the area. Although humans arrived immediately prior to a cold phase, the Antarctic Cold Reversal stadial, megafaunal extinctions did not occur until the stadial finished and the subsequent warming phase commenced some 1 to 3 thousand years later. The increased resolution provided by the Patagonian material reveals that the sequence of climate and extinction events in North and South America were temporally inverted, but in both cases, megafaunal extinctions did not occur until human presence and climate warming coincided. Overall, metapopulation processes involving subpopulation connectivity on a continental scale appear to have been critical for megafaunal species survival of both climate change and human impacts.

Modos de ocupación del bosque patagónico de la vertiente oriental de Los Andes: aportes desde la Ecología Isotópica

En este trabajo se discute el aporte de los isotopos estables del carbono y del nitrogeno al problema de los modos de ocupacion humana del bosque de la vertiente oriental de los Andes. Se presenta una caracterizacion inicial de su ecologia isotopica sobre la base de 58 valores de plantas y herbivoros y dos de restos oseos humanos, comprobandose que es posible discriminar senales isotopicas asociadas a recursos de bosque y evaluar el grado de permanencia y/o intensidad de empleo de este bioma en el pasado.

Oleaginous yeasts from Antarctica: Screening and preliminary approach on lipid accumulation

The capability of 17 Rhodotorula spp. isolated from Antarctica to accumulate intracellular lipids in nitrogen‐limited medium was investigated. As results, 10 isolates were selected by Nile red staining, while 12 isolates were selected as oleaginous by analysis of total lipid content (20.4–73%, w/w of dry biomass). The higher lipid production and accumulation was exhibited for six strains belonging to three species of Rhodotorula (Rhodotorula glutinis, Rhodotorula glacialis, and Rhodotorula laryngis). This is the first report where R. laryngis have been identified within oleaginous specie. Lipid accumulation was evaluated comparatively in two nitrogen‐limited glucose‐based media (MI and MII). MI (low C/N ratio) was more suitable for biomass and lipid production while in MII (high C/N ratio) total lipid content was improved. R. glutinis R4, R. glacialis R15, and R. glutinis R48 showed high lipid concentrations (4.65–6.93 g L−1) and they were able to accumulate large amounts of lipids per gram of biomass (47–77%, w/w). A similar profile in fatty acids composition and content of neutral lipids to vegetable oils was observed, indicating that lipids produced by oleaginous Antarctic yeasts can be considered an alternative feedstock for biodiesel production. Antarctica represents an important source of oleaginous yeasts with adaptive capabilities to accumulate considerable amounts of lipids with biotechnological interest at 15 °C and 25 °C.

Removal efficiency of Cr6+ by indigenous Pichia sp. isolated from textile factory effluent.

Resistance of the indigenous strains P. jadinii M9 and P. anomala M10, to high Cr6+ concentrations and their ability to reduce chromium in culture medium was studied. The isolates were able to tolerate chromium concentrations up to 104 μg mL−1. Growth and reduction of Cr6+ were dependent on incubation temperature, agitation, Cr6+ concentration, and pH. Thus, in both studied strains the chromium removal was increased at 30°C with agitation. The optimum pH was different, with values of pH 3.0 and pH 7.0 in the case of P. anomala M10 and pH 7.0 using P. jadinii M9. Chromate reduction occurred both in intact cells (grown in culture medium) as well as in cell-free extracts. Chromate reductase activity could be related to cytosolic or membrane-associated proteins. The presence of a chromate reductase activity points out a possible role of an enzyme in Cr6+ reduction.

Bioremediation strategies for chromium removal: Current research, scale-up approach and future perspectives

Industrial applications and commercial processes release a lot of chromium into the environment (soil, surface water or atmosphere) and resulting in serious human diseases because of their toxicity. Biological Cr-removal offers an alternative to traditional physic-chemical methods. This is considered as a sustainable technology of lower impact on the environment. Resistant microorganisms (e.g. bacteria, fungi, and algae) have been most extensively studied from this characteristic. Several mechanisms were developed by microorganisms to deal with chromium toxicity. These tools include biotransformation (reduction or oxidation), bioaccumulation and/or biosorption, and are considered as an alternative to remove the heavy metal. The aim of this review is summarizes Cr(VI)-bioremediation technologies oriented on practical applications at larger scale technologies. In the same way, the most relevant results of several investigations focused on process feasibility and the robustness of different systems (reactors and pilot scale) designed for chromium-removal capacity are highlighted.

Zooarchaeology in the Neotropics

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Bioprospection of cold-adapted yeasts with biotechnological potential from Antarctica

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Draft Genome Sequence of Achromobacter sp. Strain AR476-2, Isolated from a Cellulolytic Consortium

The aim of this study was to investigate the ability to produce extracellular hydrolytic enzymes at low temperature of yeasts isolated from 25 de Mayo island, Antarctica, and to identify those exhibiting one or more of the evaluated enzymatic activities. A total of 105 yeast isolates were obtained from different samples and 66 were identified. They belonged to 12 basidiomycetous and four ascomycetous genera. Most of the isolates were ascribed to the genera Cryptococcus, Mrakia, Cystobasidium, Rhodotorula, Gueomyces, Phenoliferia, Leucosporidium, and Pichia. Results from enzymes production at low temperatures revealed that the Antarctic environment contains metabolically diverse cultivable yeasts, which represent potential tools for biotechnological applications. While most the isolates proved to produce 2‐4 of the investigated exoenzymes, two of them evidenced the six evaluated enzymatic activities: Pichia caribbica and Guehomyces pullulans, which were characterized as psycrotolerant and psycrophilic, respectively. In addition, P. caribbica could assimilate several n‐alkanes and diesel fuel. The enzyme production profile and hydrocarbons assimilation capacity, combined with its high level of biomass production and the extended exponential growth phase make P. caribbica a promising tool for cold environments biotechnological purposes in the field of cold‐enzymes production and oil spills bioremediation as well.

Perspective in Bioremediation: Enhancing the Hexavalent Chromium Removal Using Native Yeasts from Tucumán, Argentina

ABSTRACT Achromobacter sp. AR476-2 is a noncellulolytic strain previously isolated from a cellulolytic consortium selected from samples of insect gut. Its genome sequence could contribute to the unraveling of the complex interaction of microorganisms and enzymes involved in the biodegradation of lignocellulosic biomass in nature.

Chromate removal by yeasts isolated from sediments of a tanning factory and a mine site in Argentina

The occurrence of indigenous Cr(VI)-reducing eukaryotic microorganisms, including those with no history of Cr(VI) contamination, has provided important non-conventional yeasts with significant biological relevance and biotechnological applications. Based on physiological/biochemical characterization and molecular taxonomy analysis, these isolates were identified as Cyberlindnera jadinii M9 and Wickerhamomyces anomalus M10. Cy. jadinii M9 and W. anomalus M10 were grown in medium plus 1 mM Cr(VI) at 25 °C, causing complete chromium removal before reaching 48 h of cultivation. Flame Atomic Absorption Spectroscopy (FAAS) assays suggested that Cr(VI) disappearance was coupled to the Cr(III) concomitant production. These results indicated that reducing capacity of chromate-resistant yeasts would be the main detoxification mechanism. Crude chromate reductase (CChRs) of strains M9 and M10, were characterized based on optimal temperature, pH, use of electron donors, metal ions and initial Cr(VI) concentration in the reaction mixture. Both CChRs showed an increase in Cr(VI) reductase activity with addition of NAD(P)H as electron donor and were highly inhibited by Hg2+ and Mn2+. The CChR from Cy. jadinii M9 showed the highest chromate reductase activity at 60 °C and pH 6.0 in the presence of Cu2+ or Na+, while W. anomalus M10 CChR had the maximum activity at 50 °C and pH 7.0 in presence of Cu2+. Initial Cr(VI) concentrations of 1.3 and 1.7 mM for CChRs of Cy. jadinii M9 and W. anomalus M10 respectively were inhibitory. This chapter presents evidence of the significant potential of native selected yeasts for chromium bioremediation, thus being promising candidates for alleviating this polluting metal from environment.