MICROBIAL UTILIZATION OF ATRAZINE-NITROGEN

Authors: BICHAT, FREDERQUE - UNIV OF ILLINOIS; MULVANEY, RICHARD - UNIV OF ILLINOIS; SIMS, GERALD

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/4/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: Atrazine is a well-known contaminant of natural waters, due to mobility and stability in the environment. Recent studies examining reasons for the resistance of atrazine to degradation suggest that the herbicide is a poor energy and carbon source, but may serve as a nitrogen source for specific soil microorganisms isolated from soil. Studies were conducted to examine use of atrazine nitrogen by a soil microbial community and by pure cultures of soil bacteria (Pseudomonas sp. strain ADP, Agrobacterium radiobacater J14a, or M91-3). Atrazine, labeled with a non-radioactive isotope of N, was synthesized from labeled urea. Cultures of P. ADP, as well as the soil microbial community, did not use atrazine as a carbon source, but did incorporate atrazine N into cell biomass. Atrazine degradation was not affected by the presence of other N sources in P. ADP or A. radiobacter, whereas such N sources inhibited degradation by M91-3, an organism that is similar to the soil microbial community. Nitrogen sources found in agricultural fertilizers inhibited atrazine degradation in soil, unless an insensitive organism, such as P. ADP was introduced. Based on these studies, degradation of atrazine in soil is primarily due to its use as an N source, while other N sources reduce degradation. It appears unlikely that atrazine concentrations in soil can be maintained low enough that native organisms will degrade the herbicide rapidly. The results may also have important implications for natural water, as much lower N levels are desirable in aquatic environments. This new evidence for a relationship between the nitrogen cycle and atrazine fate is probably relevant to all triazine herbicides, and may be applied to strategies for reducing contamination of natural waters by triazines.

Technical Abstract: Radiotracer studies have provided indirect evidence that the heterocyclic N in atrazine (2-Chloro-4(ethylamino)-6-(isopropylamino)-1,3,5-triazine) may be utilized by microorganisms as a source of N; however, no data are available from investigations using 15N as a tracer. Studies were conducted to examine microbial utilization of atrazine-ring-15N in soil and pure cultures of Pseudomonas sp. Strain ADP, Agrobacterium radiobacter J14a, or M92-3. Atrazine (U-15N-ring) was synthesized from labeled urea. To investigate the effect of exogenous N on degradation of atrazine, pure cultures were supplemented with unlabeled atrazine and labeled N as (NH4)2SO4, KNO3, urea, or glycine. Under C-limiting conditions, cells of P. ADP incorporated side-chain N into biomass and liberated ring-N as N4. When N was limiting, ring-N was also recovered in biomass. Degradation of atrazine by P. ADP and A. Radiobacter was unaffected by the presence of exogenous N, whereas no degradation occurred with M91-3 in media containing urea or NH4-N. The fate of double-labeled (U-14C, U-15N- ring)atrazine(15 mg kg-1) was examined after incubation for 6 to 53 d of Bloomfield soil (sandy, mixed, mesic Psammentic Hapludalf) amended with NH4- or NO3-N (75 mg kg-1), with or without an inoculum of P.ADP (1.06 x 10 13 cells kg-1). Mineralization of atrazine-14C by indigenous microorganisms in soil was inhibited by inorganic N during the first 42 d, whereas 87% of the atrazine was mineralized after 6 d, regardless of the N treatment applied to the inoculated soil. The C\N ratio was much lower for amino acids isolated from soil than for the atrazine ring suggesting preferential assimilation of N over C by microorganisms.