No abstract

DDT (1,1,1-trichloro-2,2-bis(4-chlorophenyl) ethane) is probably the best known and most useful organochlorine insecticide in the world which was used since 1945 for agricultural purposes and also for vector-borne disease control such as malaria since 1955, until its banishment in most countries by the Stockholm convention for ecologic considerations. However, the World Health Organization allowed its reintroduction only for control of vector-borne diseases in some tropical countries in 2006. Due to its physicochemical properties and specially its persistence related with a half-life up to 30 years, DDT linked to several health and social problems which are due to its accumulation in the environment and its biomagnification properties in living organisms. This manuscript compiles a multidisciplinary review to evaluate primarily (i) the worldwide contamination of DDT and (ii) its (eco) toxicological impact onto living organisms. Secondly, several ways for DDT bioremediation from contaminated environment are discussed. For this, reports on DDT biodegradation capabilities by microorganisms and ways to enhance bioremediation strategies to remove DDT are presented. The different existing strategies for DDT bioremediation are evaluated with their efficiencies and limitations to struggle efficiently this contaminant. Finally, rising new approaches and technological bottlenecks to promote DDT bioremediation are discussed.

The factors regulating soil microbial stability (e.g. resistance and resilience) are poorly understood, even though microorganisms are essential for ecosystem functioning. In this study, we tested whether a functional microbial community subjected to different primary mild stresses was equally resistant or resilient to a subsequent severe stress. The nitrate reducers were selected as model community and analysed in terms of nitrate reduction rates and genetic structure by narG PCR-restriction fragment length polymorphism fingerprinting. Heat, copper and atrazine were used as primary stresses and mercury at a high concentration as a severe stress. None of the primary stresses had any significant impact on the nitrate reducer community. Although primary stress with heat, copper or atrazine had no effect on the resilience of the nitrate reducer activity to mercury stress, pre-exposure to copper, another heavy metal, resulted in increased resilience. In contrast, the resistance of both structure and activity of the nitrate reducer community to severe mercury stress was not affected by any of the primary stresses tested. Our experiment suggests that the hypothetical effect of an initial stress on the response of a microbial community to an additional stress is complex and may depend on the relatedness of the two consecutive stresses and the development of positive cotolerance.

Arylsulfatases allow microorganisms to satisfy their sulfur (S) requirements as inorganic sulfate after sulfate ester hydrolysis. Our objectives were to investigate the arylsulfatase activities among soil isolates, especially Streptomyces sp., Microbacterium sp. and Rhodococcus sp., because such investigations are limited for these bacteria, which often live in sulfate-limited conditions. Physiological and biochemical analyses indicated that these isolates possessed strong specific arylsulfatase activities ranging from 6 to 8 U. Moreover, for Streptomyces sp., an arylsulfatase localization study revealed 2 forms of arylsulfatases. A first form was located in the membrane, and a second form was located in the intracellular compartment. Both arylsulfatases had different patterns of induction. Indeed, the intracellular arylsulfatase was strictly induced by inorganic sulfate limitation, whereas the membrane arylsulfatase was induced both by substrate presence or S demand independently. For Microbacterium and Rhodococcus isolates, only a membrane arylsulfatase was found. Consequently, our results suggest the presence of a previously undescribed arylsulfatase in these microorganisms that allows them to develop an alternative strategy to fulfill their S requirements compared to bacteria previously studied in the literature.