Effects of Adaptation on Biodegradation Rates in Sediment/Water Cores from Estuarine and Freshwater Environments

Abstract

Experiments were devised to determine whether exposure to xenobiotics would cause microbial populations to degrade the compounds more rapidly during subsequent exposures. Studies were done with water/sediment systems (ecocores) taken from a salt marsh and a river. Systems were tested for adaptation to the model compounds methyl parathion and p -nitrophenol. 14 CO 2 released from radioactive parent compounds was used as a measure of mineralization. River populations preexposed to p -nitrophenol at concentrations as low as 60 μg/liter degraded the nitrophenol much faster than did control populations. River populations preexposed to methyl parathion also adapted to degrade the pesticide more rapidly, but higher concentrations were required. Salt marsh populations did not adapt to degrade methyl parathion. p -Nitrophenol-degrading bacteria were isolated from river samples but not from salt marsh samples. Numbers of nitrophenol-degrading bacteria increased 4 to 5 orders of magnitude during adaptation. Results indicate that the ability of populations to adapt depends on the presence of specific microorganisms. Biodegradation rates in laboratory systems can be affected by concentration and prior exposure; therefore, adaptation must be considered when such systems are used to predict the fate of xenobiotics in the environment.

MINERALIZATION AND SORPTION OF p-NITROPHENOL IN ESTUARINE SEDIMENT

“…These results were based on degradation in river water and on concentrations of up to 20 mg/L p-nitrophenol. Earlier studies of p-nitrophenol degradation in coastal sediments indicated that sediment preexposure affects the rate of degradation of the compounds by the sediment on reexposure [6,7]. p-Nitrophenol has been listed as priority pollutant by the U.S. Environmental Protection Agency.…”

Adaptation of Periphytic Communities in Model Streams to a Quaternary Ammonium Surfactant

“…Pignatello et al [16] also attributed adaptation to an increase in the population of initially low numbers of pentachlorophenol (PCP) degraders. Although adaptation to C12-TMAC by periphyton in our experiments may be the result of a rapid increase in degrader populations within a two-week period, we cannot entirely rule out enzyme induction as a possible mechanism for a fairly rapid acclimation response [28].…”

“…Three mechanisms have been proposed for adaptations that result in an increase in mineralization of xenobiotics by natural microbial communities [28]: (a) selection of specific degrader populations, (b) induction or derepression of specific enzyme systems, and (c) genetic changes in microbial populations. Shimp et al [8] hypothesized that exposure of seston to C12TMAC resulted in selection for C12TMAC degraders.…”

A COMPARISON of the effects of two methods of acclimation on aerobic biodegradability

“…Organic substances may be transformed by nonbiological mechanisms such as photolysis, hydrolysis, and oxidation, but biodegradation is the predominant mechanism in soil and water [ 1,2]. Many factors have been found to affect biodegradation, including temperature [3,4], nitrogen and phosphorus levels [4,5], chemical concentration [6-91, molecular weight [ 101, the availability of alternate carbon sources [ll-141, basal salts medium [15], salinity [16,17], water hardness [ 181, source and concentration of the inoculum [17][18][19][20], and microbial acclimation due to prior exposure of the microbial population to the chemical [7,16,19,21,22]. In certain situations, for example, lake or river sediments, the presence of oxic-anoxic conditions is very important, and in the absence of oxygen the availability of alternative electron accep-~ The current address of H.M. Watson is 105 Shirewood Dr., Rochester, NY 14625. tors (NO3, SO4, Fe(III), etc.)…”

“…This acclimation may result in subsequent chemical biodegradation or in the enhancement of existing biodegradation by several orders of magnitude [30]. The actual mechanisms are not well understood [2] but are thought to include both physiological adaptation such as genetic change, enzyme induction, and plasmidexchange [17,19,, and achangeintherelative abundance of microbial populations [34]. Another aspect of acclimation that needs to be addressed is the question of what influence different methods of acclimation have on subsequent biodegradability in laboratory tests, which in turn affects our ability to predict fate in the environment.…”