Metabolic diversity and activity of heterotrophic bacteria in ground water

Abstract

The number and metabolic diversity of bacteria were studied in groundwaters collected in the United States and Canada. Bacterial numbers were determined by acridine orange direct counts, viable plate counts and I4C most-probable-number counts. Metabolic diversity was determined by heterotrophic activity and biodegradation potential assays using several classes of natural and xenobiotic substrates. Rates of metabolism in diversity studies (uptake and/or mineralization to carbon dioxide) were measured by radiotracer techniques and rate data were analyzed by nonlinear regression models to generate appropriate kinetic constants. Overall, the density and activity of groundwater bacteria were comparable to values reported for oligotrophic marine and freshwater systems. Bacterial numbers ranged from approximately lo2 to lo6 cells/ml, depending on the enumeration technique used and the particular sample tested. Turnover times for natural compounds in heterotrophic activity assays (i.e., glucose, amino acids) ranged from less than 100 to more than 2,000 h. Degradation half-lives for xenobiotic and natural substrates in biodegradation potential studies exhibited a comparable range of values. In general, our results indicate that groundwater bacteria have the potential to metabolize several classes of natural and xenobiotic substrates, although at reduced rates compared with those of surface water systems.

Chemical fate and transport in a domestic septic system: Biodegradation of linear alkylbenzene sulfonate (LAS) and nitrilotriacetic acid (NTA)

“…If biodegradation rates change as a function of chemical exposure, this may not be a valid assumption. Rather, the more accurate fate model for such materials might be one in which biodegradation rates are varied as a function of distance from the discharge point This consideration might be especially im portant for compounds with slow biodegradation rates, whereby a gradient of detectable chemical occurs some distance downgradient from a source LAS and NTA biodegradation rates in the vicinity of the septic tank tile field were rapid relative to their residence time and were generally comparable to the biodegradation kinetics of naturally occurring chemicals [32,33] Rapid rates are reflected in the extensive removal (>99%) of both chemicals from the tile field and aquifer For perspective, the typical removal of septic tank effluent organic matter by tile fields, as represented by BOD, ranges from 75 to 95% [34,35] The observed rates and extent of LAS and NTA mineralization in the vicinity of the septic tank tile field are also consistent with the observations of other researchers in similar environmental settings For example, Federle and Pastwa [ 141 examined the biodegradation of LAS beneath a pond in northern Wisconsin that received "grey" water discharge from a nearby laundromat LAS half-lives ranged from 3 2 to 16 5 d over depths from 0 6 to 3 7 m below the pond bottom On average, the extent of LAS mineralization was 33% Larson et a1 [22] observed similar results in a variety of soil and groundwater systems For NTA, Ward [36] measured mineralization rates in soils collected from the vicinity of two septic tank systems in Canada He observed half-lives of 3 to 7 d and approximately 60% mineralization Similar results have been obtained in studies using ground water from the same location [32], a variety of surface and subsurface soils [29], and in soil columns using ground water from a water infiltration site in Switzerland [28] In summary, this work demonstrated that (a) microbial communities adapt to LAS and NTA in infiltrating tank effluents, (b) there is a marked spatial variation in the distribution of degraders and biodegradative activity in subsurface soil, sediment, and ground water, and (c) biodegradation in the above mentioned compartments is an important removal mechanism for LAS and NTA Coupled with the slowing of chemical transport via adsorption, biodegradation in func tioning septic tank systems effectively eliminates groundwater contamination by such materials…”

Environmental Biotechnology Group Meeting biotechnology in the clean water industries

“…As a result ' bioremediation has been seen as more of an occult than a science'. 16 In most cases where bioremediation has been successful, indigenous aquifer organisms have been stimulated by the addition of nutrients and oxygen. Although claims have been made that introduced genotypes may be maintained in aquifers, experience has shown that the inoculation of especially bred or engineered organisms seldom results in the desired strain becoming established.…”

Use of biodegradation data in chemical assessment

“…Second, biodegradation can be a practical removal mechanism in ground water at distances that are very close to a site of discharge. Even as close as 10 m, greater than 80% of a chemical will be removed if the BHL is less than 40 d. For reference, under aerobic conditions (e.g., in shallow unconfined systems), chemicals like toluene [17], nitrilotriacetic acid [18], linear alkylbenzene sulfonate [19], phenol, benzoic acid, benzylamine [20], aniline and mcresol [21] fall into this range. As stated above, the practical biodegradation model solution shown in Figure 4 ignores the potentially important role played by adsorption.…”