Microbial utilization of heterocyclic nitrogen from atrazine

Radiotracer studies have provided indirect evidence that heterocyclic N in atrazine [2-chloro-4(ethylamino)-6-(isopropylamino)-1,3,5-triazine] may be utilized by microorganisms as a source of IV; however, no data are availabl e from investigations using N-15 as a tracer. Studies were conducted to exa mine microbial utilization of atrazine ring-N-15 in soil and pure cultures of Pseudomonas sp. strain ADP, Agrobacterium radiobacter J14a, or bacterium M91-3. Atrazine [U-N-15-ring] was synthesized from labeled urea. To invest igate the effect of exogenous N on atrazine degradation, pure cultures were supplemented with unlabeled atrazine and labeled N as (NH4)(2)SO4, KNO3, u rea, or glycine. Under C-limiting conditions, cells of Pseudomonas sp. stra in ADP incorporated side chain-N into biomass and liberated ring-IV as NH4. When N was limiting, ring-IV Has also recovered in biomass. Degradation of atrazine by Pseudomonas strain sp. ADP and A. radiobacter was unaffected b y the presence of exogenous N, whereas no degradation occurred with bacteri um M91-3 in media containing urea or NH4-N. The fate of double-labeled [U-C -14, U-N-15-ring]-atrazine (15 mg kg(-1)) was examined after incubation of a Bloomfield soil (sandy, mired, mesic Psammentic Hapludalf) amended with N H4- or NO3-N (75 mg kg(-1)), with or without an inoculum of Pseudomonas sp. strain ADP (1.06 x 10(13) cells kg(-1)). In uninoculated soil, mineralizat ion of atrazine-C-14 was inhibited by inorganic N, whereas in the inoculate d soil, 87% of the atrazine was mineralized, regardless of the N treatment. The C/N ratio was much loner for amino acids isolated from soil than for t he atrazine ring, suggesting preferential assimilation of N over C by micro organisms.