Effects of low temperature and freeze-thaw cycles on hydrocarbon biodegradation in Arctic tundra soil

Abstract

Degradation of petroleum hydrocarbons was monitored in microcosms with diesel fuel-contaminated Arctic tundra soil incubated for 48 days at low temperatures (-5, 0, and 7 degrees C). An additional treatment was incubation for alternating 24-h periods at 7 and -5 degrees C. Hydrocarbons were biodegraded at or above 0 degrees C, and freeze-thaw cycles may have actually stimulated hydrocarbon biodegradation. Total petroleum hydrocarbon (TPH) removal over 48 days in the 7, 0, and 7 and -5 degrees C treatments, respectively, was 450, 300, and 600 microg/g of soil. No TPH removal was observed at -5 degrees C. Total carbon dioxide production suggested that TPH removal was due to biological mineralization. Bacterial metabolic activity, indicated by RNA/DNA ratios, was higher in the middle of the experiment (day 21) than at the start, in agreement with measured hydrocarbon removal and carbon dioxide production activities. The total numbers of culturable heterotrophs and of hydrocarbon degraders did not change significantly over the 48 days of incubation in any of the treatments. At the end of the experiment, bacterial community structure, evaluated by ribosomal intergenic spacer length analysis, was very similar in all of the treatments but the alternating 7 and -5 degrees C treatment.

FIG. 1

Effect of temperature on petroleum hydrocarbon removal (sum of the five most abundant compounds, C₁₁ to C₁₅ n-alkanes) in Arctic soil microcosms. Symbols: □, 7°C; ▴, 7 and −5°C; ×, 0°C; ◊, −5°C; ○, killed control. Error bars show standard deviations (n = 3). d.w., dry weight.

FIG. 2

Effect of temperature on respiration (as CO₂ production) in Arctic soil microcosms. Symbols: □, 7°C; ▴, 7 and −5°C; ×, 0°C; ◊, −5°C; ○, killed control. Error bars show standard deviations (n = 3). d.w., dry weight.

FIG. 3

HS-SPME analysis of the five most abundant compounds in the Alert soil (C₁₁ to C₁₅ n-alkanes) in the 7°C and 7 and −5°C treatments. Symbols: □, 7°C; ▴, 7 and −5°C; ○, killed control. Error bars show standard deviations (n = 3). d.w., dry weight.

FIG. 4

RISA at day 48: Lanes: 1, pristine soil; 2, contaminated soil; 3, starting soil (after storage at 7°C); 4, −5°C; 5, 0°C; 6, 7°C; 7, 7 and −5°C; 8, enrichment culture on jet fuel (16); 9, enrichment culture grown on PAHs (unpublished data); 10, Pseudomonas sp. isolate from the soil (16); 11, Rhodococcus sp. isolate from the soil (16); 12, 100-bp ladder (Gibco BRL).