Catalytic properties of a highly thermoactive polygalacturonase from the mesophilic fungus Penicillium occitanis and use in juice clarification

A new polygalacturonase (PG1) is purified to homogeneity from the hyper-pectinolytic mutant (CT1) of Penicillium occitanis by using two chromatographic steps. The purified PGI exhibited a very high specific activity toward PGA, namely 57533.2 U/mg of protein and a high optimal temperature, 70 degrees C. In our knowledge, it is one of the highest temperature optima described till now, even among those reported for thermophilic fungi; recalling here that our fungus is a mesophilic one. The N-terminal sequence was almost identical to that deduced from the previously cloned pga1 gene. The mass spectrometry analysis of PG1 further confirmed its belonging to the pga1 gene. As the peptide sequence of the pga1 bears the signature of endopolygalacturonases, we brought in this work evidences that it belongs to enzymes that hydrolyze pectin by endo-fashion. Indeed, during the hydrolysis of polygalacturonic acid by PG1, the viscosity drops very quickly while reducing sugars were released very slowly. In addition, thin layer chromatography showed that mainly oligosaccharides were released from PGA, namely tetra and trigalacturonic acids. The purified PGI was able to enhance the clarification of citrus juice. Considering all these properties, this novel fungal would be an interesting biocatalyst for future application in fruit and vegetable transformation. (C) 2016 Elsevier B.V. All rights reserved

Assessing seasonal variations and aquifer vulnerability in coastal aquifers of semi-arid regions using a multi-tracer isotopic approach: the case of Grombalia (Tunisia)

The Grombalia aquifer (NE Tunisia) is an example of an important source of water supply for regional and national development, where the weak controls over abstraction, fertilizer application and waste disposal, coupled with limited knowledge of aquifer dynamics, is causing aquifer over-exploitation and water quality degradation. Assessing the key role of groundwater in water-resources security is therefore of paramount importance to support new actions to preserve water quality and quantity in the long-run. This study presents one of the first investigations targeted at a complete assessment of aquifer dynamics in the Grombalia aquifer. A multi-tracer hydrogeochemical and isotopic (δ2H, δ18O and 3H) approach was used to study the influence of seasonal variation on piezometric levels, chemical and isotopic compositions, and groundwater recharge. A total of 116 samples were collected from private wells and boreholes during three periods in a 1 year monitoring campaign (February–March 2014, September 2014 and February 2015). Results revealed the overall unsuitability of groundwater for drinking and irrigation purposes (NO3 > 50 mg/L in 51% of the wells; EC >1,000 μS/cm in 99% of the wells). Isotopic balance coupled to piezometric investigation indicated the contribution of the shallow aquifer to deep groundwater recharge. The study also revealed the weakness of ‘business as usual’ management practices, highlighting possible solutions to tackle water-related challenges in the Grombalia region, where climate change, population growth and intensive agricultural activities have generated a large gap between demand and available water reserves, hence becoming a possible driver for social insecurity