In a gram-negative isolate (DSM 9103) able to grow with EDTA as the sole source of carbon, nitrogen, and energy, the first two steps of the catabolic pathway for EDTA were elucidated. They consisted of the sequential oxidative removal of two acetyl groups, resulting in the formation of glyoxylate. An enzyme complex that catalyzes the removal of two acetyl groups was purified and characterized. EDTA is a chelating agent from the group of aminopolycarboxylic acids with the ability to form stable, water-soluble complexes with most metal ions. Because of the high stability of its complexes, EDTA is employed for various industrial and domestic applications (41). It was estimated that about 28,000 tonnes of EDTA (calculated as H 4 EDTA) per year was used in western Europe in 1987 and 1988 (41). Because its use is water based, high amounts of EDTA enter the aqueous environment and wastewater treatment plants. It has been shown that EDTA is rather recalcitrant towards biological degradation (3, 26). Consequently, little or no elimination of EDTA is usually observed during wastewater treatment (1). The only known sink of EDTA in surface waters is the photolysis by sunlight of Fe III EDTA, the most important photolabile EDTA species (19). Therefore, EDTA is found in rivers in high concentrations ranging from 10 to 100 g liter Ϫ1 (6, 10, 31). Concentrations between 1 and 10 g liter Ϫ1 are typical for lakes and groundwater (16).Despite its persistence in wastewater treatment plants, reports on the biological degradation of EDTA exist. Studies of Tiedje (35) indicated that EDTA is degraded slowly by microorganisms present in a variety of aerobic soils and river sediments. Belly and coworkers (2) also observed degradation of EDTA by using a mixed culture obtained from an aerated lagoon that received EDTA-containing sewage. Meanwhile, it was reported that enrichment of mixed (12) and also pure (25, 29) cultures can mineralize EDTA under strictly aerobic conditions. Starting from the mixed culture enriched by Gschwind (12), we isolated a bacterial strain that is able to grow with EDTA as the sole source of carbon, nitrogen, and energy (40). It was deposited in the German Culture Collection as strain DSM 9103.In their mixed culture, Belly and coworkers (2) identified several compounds which they proposed to be intermediates of the degradation of EDTA, primarily iminodiacetate (IDA) and ethylenediaminetriacetate (ED3A). Based on these intermediates, a pathway for EDTA degradation was suggested that consisted of two types of reactions: firstly, successive removal of the four acetyl groups in the form of glyoxylate and secondly, cleavage of the molecule within the ethylenediamine part. The former mechanism would be similar to the degradation of nitrilotriacetate (NTA), a structural analog of EDTA. The biochemical pathway of NTA degradation, first proposed by Cripps and Noble (5) and Firestone and Tiedje (9), was later confirmed in the NTA-degrading bacterium Chelatobacter heintzii. For this chelating agent, the successive removal o...

The oomycete Phytophthora sojae is a severe pathogen of soybean. Several resistance genes against races of P. sojae exist in soybean but the nature of corresponding avirulence genes is unknown. Clones encoding four different isoforms of a protein elicitor from P. sojae (sojein 1–4) belonging to the class of acidic α‐elicitins have been isolated. These 98 amino acid proteins show high homology to elicitins from other Phytophthora species. The different sojein isoforms were expressed in Escherichia coli as His‐tagged fusion proteins. Purified sojein as well as recombinant sojein isoforms induce hypersensitive reaction (HR)‐like lesions in tobacco but are not active as race‐specific elicitors in soybean. However all sojein isoforms induce defence‐related genes like those encoding phenylalanine ammonia lyase, glutathione‐S‐transferase and chalcone synthase in tobacco and soybean plants and cell cultures. It is concluded that sojeins contribute to the induction of defence responses but that they are not involved in race specific recognition of the P. sojae races by soybean plants.

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