SUMMARY Aromatic compounds belong to one of the most widely distributed classes of organic compounds in nature, and a significant number of xenobiotics belong to this family of compounds. Since many habitats containing large amounts of aromatic compounds are often anoxic, the anaerobic catabolism of aromatic compounds by microorganisms becomes crucial in biogeochemical cycles and in the sustainable development of the biosphere. The mineralization of aromatic compounds by facultative or obligate anaerobic bacteria can be coupled to anaerobic respiration with a variety of electron acceptors as well as to fermentation and anoxygenic photosynthesis. Since the redox potential of the electron-accepting system dictates the degradative strategy, there is wide biochemical diversity among anaerobic aromatic degraders. However, the genetic determinants of all these processes and the mechanisms involved in their regulation are much less studied. This review focuses on the recent findings that standard molecular biology approaches together with new high-throughput technologies (e.g., genome sequencing, transcriptomics, proteomics, and metagenomics) have provided regarding the genetics, regulation, ecophysiology, and evolution of anaerobic aromatic degradation pathways. These studies revealed that the anaerobic catabolism of aromatic compounds is more diverse and widespread than previously thought, and the complex metabolic and stress programs associated with the use of aromatic compounds under anaerobic conditions are starting to be unraveled. Anaerobic biotransformation processes based on unprecedented enzymes and pathways with novel metabolic capabilities, as well as the design of novel regulatory circuits and catabolic networks of great biotechnological potential in synthetic biology, are now feasible to approach.

Artemisinin (ART)-based combination therapies (ACTs) are the first-line drugs-and often the last treatments-that can effectively cure Plasmodium falciparum infections. Unfortunately, the decreased clinical efficacy of artesunate, one of the major ART derivatives, was recently reported along the Thailand-Cambodia border. Through long-term artemisinin pressure in vitro, we have obtained an ART-tolerant strain that can survive extremely high doses of ART. We showed that drug pressure could induce a subpopulation of ring stages into developmental arrest, which can explain the ART tolerance in P. falciparum. We also observed interesting transcriptomic modifications possibly associated with the acquisition of ART tolerance. These modifications include the overexpression of heat shock and erythrocyte surface proteins and the downexpression of a cell cycle regulator and a DNA biosynthesis protein. This study highlights a new phenomenon in the Plasmodium response to ART that may explain the delayed clearance of parasites after artesunate treatment observed on the Thailand-Cambodia border and that provides important information for achieving a better understanding of the mechanisms of antimalarial resistance.Plasmodium falciparum malaria remains the worst parasitic disease in developing countries, with nearly 200 million cases and 800,000 deaths being reported each year (28). Quinolines (mefloquine, amodiaquine, chloroquine, quinine) and antifolate (pyrimethamine, proguanil, sulfadoxine) have been the major antimalarial drugs in areas of endemicity for decades. Nevertheless, the emergence of multidrug-resistant P. falciparum parasites has made these drugs useless in many areas where they are endemic. This situation was particularly threatening, until the introduction of artemisinin (ART) and its derivatives. ART combination therapy (ACT) has become the first-line treatment of uncomplicated falciparum malaria in most countries where it is endemic. More than a million doses of ACT are administered to treat malaria each year, particularly after the recommendation of World Health Organization (WHO) in 2005 (26).Artemisinin is isolated from a plant (Artemisia annua) that has been used for the treatment of fever for more than 2,000 years in Chinese traditional medicine. ART shows rapid antimalarial activity, has few side effects, and is active against parasite strains that are resistant to many traditional antimalarial drugs, such as quinolines and antifolates. To reduce the risk of drug resistance, ART and its derivatives are generally used in combination with other antimalarial agents. Although it is still being debated whether there are parasites that can be considered to have real resistance to ART (23), e.g., greatly increased 50% inhibitory concentrations (IC 50 s), the delayed clearance of parasites has been reported (6,16,17). Delayed clearance suggests that some parasites can survive ART treatment for a longer period of time than expected, but they are eventually killed by the drug, raising the possibility of a surviva...

We report here that the bzd genes for anaerobic benzoate degradation in Azoarcus sp. strain CIB are organized as two transcriptional units, i.e., a benzoate-inducible catabolic operon, bzdNOPQMSTUVWXYZA, and a gene, bzdR, encoding a putative transcriptional regulator. The last gene of the catabolic operon, bzdA, has been expressed in Escherichia coli and encodes the benzoate-coenzyme A (CoA) ligase that catalyzes the first step in the benzoate degradation pathway. The BzdA enzyme is able to activate a wider range of aromatic compounds than that reported for other previously characterized benzoate-CoA ligases. The reduction of benzoyl-CoA to a nonaromatic cyclic intermediate is carried out by a benzoyl-CoA reductase (bzdNOPQ gene products) detected in Azoarcus sp. strain CIB extracts. The bzdW, bzdX, and bzdY gene products show significant similarity to the hydratase, dehydrogenase, and ring-cleavage hydrolase that act sequentially on the product of the benzoyl-CoA reductase in the benzoate catabolic pathway of Thauera aromatica. Benzoate-CoA ligase assays and transcriptional analyses based on lacZ-reporter fusions revealed that benzoate degradation in Azoarcus sp. strain CIB is subject to carbon catabolite repression by some organic acids, indicating the existence of a physiological control that connects the expression of the bzd genes to the metabolic status of the cell.