A comparison of autoclaved and gamma-irradiated soils as media for microbial colonization experiments

Salonius, P. O.; Robinson, J. B. D.; Chase, F. E.

doi:10.1007/bf01373392

Cited by 119 publications

(53 citation statements)

References 16 publications

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“…In the present study, DOC increased by a factor of 1.5 to 3.2 with the 55°C treatment ( Table 1). Autoclaving and fumigation, which kill soil organisms, are known to result, after reinoculation, in peak activities that are much higher than in nontreated soils (30,31). It has also been found that in an agricultural soil, autoclaving and recolonization resulted in TdR and Leu incorporation rates 5 to 20 times higher than preautoclaving values after 1 week (12).…”

Section: Discussionmentioning

confidence: 99%

Temperature-Driven Adaptation of the Bacterial Community in Peat Measured by Using Thymidine and Leucine Incorporation

Ranneklev

Bååth

2001

Appl Environ Microbiol

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The temperature-driven adaptation of the bacterial community in peat was studied, by altering temperature to simulate self-heating and a subsequent return to mesophilic conditions. The technique used consisted of extracting the bacterial community from peat using homogenization-centrifugation and measuring the rates of thymidine (TdR) or leucine (Leu) incorporation by the extracted bacterial community at different temperatures. Increasing the peat incubation temperature from 25°C to 35, 45, or 55°C resulted in a selection of bacterial communities whose optimum temperatures for activity correlated to the peat incubation temperatures. Although TdR and Leu incorporations were significantly correlated, the Leu/TdR incorporation ratios were affected by temperature. Higher Leu/TdR incorporation ratios were found at higher temperatures of incubation of the extracted bacterial community. Higher Leu/TdR incorporation ratios were also found for bacteria in peat samples incubated at higher temperatures. The reappearance of the mesophilic community and disappearance of the thermophilic community when the incubation temperature of the peat was shifted down were monitored by measuring TdR incorporation at 55°C (thermophilic activity) and 25°C (mesophilic activity). Shifting the peat incubation temperature from 55 to 25°C resulted in a recovery of the mesophilic activity, with a subsequent disappearance of the thermophilic activity. The availability of substrate for bacterial growth varied over time and among different peat samples. To avoid confounding effects of substrate availability, a temperature adaptation index was calculated. This index consisted of the log 10 ratio of TdR incorporation at 55 and 25°C. The temperature index decreased linearly with time, indicating that no thermophilic activity would be detected by the TdR technique 1 month after the temperature downshift. There were no differences between the slopes of the temperature adaptation indices over time for peat samples incubated at 55°C 3 or 11 days before incubation at 25°C. Thus, different levels of bacterial activity did not affect the temperature-driven adaptation of the bacterial community.Peat is a common substrate used for plant cultivation. After peat is harvested, it is usually collected into stockpiles, which sometimes during the storage period can undergo self-heating. This results not only in substantial losses of material (losses of up to 50% of the substance have been reported [20]) but also in a peat product that may inhibit seed germination and plant growth (23,38).From a microbiological point of view, self-heating and the subsequent cooling period can be considered two phases with extremely different selection pressures, the first selecting for a more thermophilic community and the second selecting for a mesophilic community when the temperature drops. The usual approach to studying such transition phenomena has been to use agar plates incubated at different temperatures, e.g., at around room temperature to indicate the mesophilic community ...

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Section: Discussionmentioning

confidence: 99%

Temperature-Driven Adaptation of the Bacterial Community in Peat Measured by Using Thymidine and Leucine Incorporation

Ranneklev

Bååth

2001

Appl Environ Microbiol

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“…Autoclaving soil results in nutrient release which normally results in higher microbial activity (Powlson & Jenkinson, 1975). However, depressive effects on microbial growth in autoclaved soil have also been demonstrated (Salonius, Robinson & Chase, 1976). Considering the high content of phenolic substances in humus (Hurst & Burges, 1967), the negative effects on microbial growth might be due to release of toxic substances during heating of the soil.…”

Section: Discussionmentioning

confidence: 99%

Effects of liming on ectomycorrhizal fungi infecting Pinus sylvestris L.

1990

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summary Growth rates of ectomycorrhizal fungi were measured in pure culture at pH 3–8 on MMN‐agar and sterilized peat, with and without nutrients added. Mycorrhizas were synthesized with Pinus sylvestris L. seedlings and the growth rate of the external mycelium was measured in peat at pH 3.8 and 7.3. The fungi were three isolates of Piloderma croceum Erikss. & Hjorts., two isolates of an unidentified (pink) mycorrhizal type and one isolate of another unidentified (white long) mycorrhizal type, all isolated from P. sylvestris roots. All three fungi showed much higher (2–5 times) growth rates when grown as symbionts than when grown in pure culture. The P. croceum isolates also grew as symbionts at pH 7.3, where no growth occurred in pure culture. These findings emphasize the danger of generalizing from data obtained in pure culture studies to explain what may happen when fungi grow in symbiosis with host plants. Generally, growth rates in pure culture were higher and the pH tolerance levels were wider on agar than on peat. The exceptions were one P. croceum isolate, which had the fastest pure culture growth rate on peat with MMN, and the pink isolates, which grew at higher pH on peat than on agar. There were no significant differences between growth on peat with and without MMN.

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“…However, so that this aging process may occur in the absence of indigenous PAH-degrading bacteria, the sediments must be sterile during the aging process. We chose gamma irradiation as the least intrusive method to sterilize the sediments based on earlier soil studies (10,13,35) that reported 2.5 to 3.5 megarads as being adequate to sterilize soils; presumably such doses would also sterilize saturated sediments, as the radiation would likely generate more oxygen radicals in such water-saturated materials (30). However, a review of these and similar papers suggested that the claims of soil sterility were based on inadequate data.…”

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confidence: 99%

Impact of Irradiation and Polycyclic Aromatic Hydrocarbon Spiking on Microbial Populations in Marine Sediment for Future Aging and Biodegradability Studies

Melcher

Apitz²,

Hemmingsen

2002

Appl Environ Microbiol

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Experiments were carried out to develop methods to generate well-characterized, polycyclic aromatic hydrocarbon (PAH)-spiked, aged but minimally altered sediments for fate, biodegradation, and bioavailability experiments. Changes in indigenous bacterial populations were monitored in mesocosms constructed of relatively clean San Diego Bay sediments, with and without exposure to gamma radiation, and then spiked with five different PAHs and hexadecane. While phenanthrene and chrysene degraders were present in the unspiked sediments and increased during handling, PAH spiking of nonirradiated sediments led to dramatic increases in their numbers. Phenotypic characterization of isolates able to grow on phenanthrene or chrysene placed them in several genera of marine bacteria: Vibrio, Marinobacter or Cycloclasticus, Pseudoalteromonas, Marinomonas, and Halomonas. This is the first time that marine PAH degraders have been identified as the latter two genera, expanding the diversity of marine bacteria with this ability. Even at the highest irradiation dose (10 megarads), heterotrophs and endospore formers reappeared within weeks. However, while bacteria from the unirradiated sediments had the capacity to both grow on and mineralize 14 C-labeled phenanthrene and chrysene, irradiation prevented the reappearance of PAH degraders for up to 4 months, allowing spikes to age onto the sediments, which can be used to model biodegradation in marine sediments.

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A comparison of autoclaved and gamma-irradiated soils as media for microbial colonization experiments

Cited by 119 publications

References 16 publications

Temperature-Driven Adaptation of the Bacterial Community in Peat Measured by Using Thymidine and Leucine Incorporation

Temperature-Driven Adaptation of the Bacterial Community in Peat Measured by Using Thymidine and Leucine Incorporation

Effects of liming on ectomycorrhizal fungi infecting Pinus sylvestris L.

Impact of Irradiation and Polycyclic Aromatic Hydrocarbon Spiking on Microbial Populations in Marine Sediment for Future Aging and Biodegradability Studies

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