, 2001; García-González et al., 2005). The atzR-atzDEF cluster is physically separated from the unstable region containing

atzA, atzB and atzC by two large gene clusters, which include the functions for the replication, segregation and conjugational transfer of pADP-1 (Martinez et al., 2001). Cya− (unable to degrade cyanuric acid) mutants arise due to the spontaneous loss of the complete pADP-1 plasmid, but independent loss of atzD, atzE or atzF is not detected, suggesting that these genes do not share the genetic instability of atzA, atzB and atzC (V. García-González & F. Govantes, unpublished data). Because atrazine is used primarily as a nitrogen source by degrading strains, the effect of nitrogen availability on atrazine degradation rates has been documented extensively. Generally, nitrogen amendments reduce the rates of atrazine degradation both in soil microbial populations (Entry et al., 1993; Alvey & Crowley, 1995; selleck Abdelhafid et al., 2000a, b; Guillén-Garcés et al., 2007) and in pure cultures of degrading bacteria (Bichat et al., 1999; Gebendinger & Radosevich, 1999; García-González et al., 2003), although exceptions to this rule

have been documented (Bichat et al., 1999). Pseudomonas sp. strain ADP is the best-characterized bacterial strain in nitrogen control of atrazine utilization (reviewed by Govantes et al., 2009). Atrazine selleck products degradation by resting cell suspensions of Pseudomonas sp. strain ADP is inhibited when cells are grown on nitrogen sources that support fast growth, whereas cells grown on growth-limiting nitrogen sources or metabolites of the pathway (including atrazine) Progesterone support efficient degradation. Atrazine does not induce the pathway in the presence of other nitrogen sources (Bichat et al.,

1999; García-González et al., 2003). Similarly, nitrate amendment significantly inhibited atrazine mineralization by Pseudomonas sp. strain ADP when tested in soil microcosms. The negative effect of added nitrogen sources on atrazine elimination limits the use of Pseudomonas sp. strain ADP bioremediation of atrazine-polluted agricultural soils (García-González et al., 2003). It should be noted that inhibition of atrazine metabolism by nitrate is only relevant when it is provided as a nitrogen source, as Pseudomonas sp. ADP appears to mineralize atrazine normally when nitrate is provided as an electron acceptor under anoxic conditions (Katz et al., 2000). This observation highlights the notion that inhibition is not the result of the mere presence of nitrate in the medium, but of its contribution to nitrogen availability. Attempts to study the expression of the atzA, atzB and atzC genes in Pseudomonas sp. strain ADP failed to demonstrate regulation in response to atrazine (Martinez et al., 2001; Devers et al., 2004) or nitrogen limitation (O. Porrúa & F. Govantes, unpublished data).