Selective biostimulation of cold‐ and salt‐tolerant hydrocarbon‐degrading Dietzia maris in petroleum‐contaminated sub‐Arctic soils with high salinity

Abstract

BACKGROUND: The dual tolerance of hydrocarbon-degrading bacteria to low temperatures and salinity has not been extensively reported. This study identifies cold-and salt-tolerant hydrocarbon degraders obtained from petroleum-contaminated sub-Arctic soils, with the objective of stimulating target populations and assessing hydrocarbon biodegradation in soils abruptly impacted by salinity.

Manipulation of Unfrozen Water Retention for Enhancing Petroleum Hydrocarbon Biodegradation in Seasonally Freezing and Frozen Soil

“…Nutrient-induced osmotic pressure has been regarded as a negative factor for oligotrophic microbial activity in cold-climate soils, and the highest nutrient dose used in this study (249 mg N/kg) falls within the upper range of N doses previously published in the context of hydrocarbon biodegradation in cold-climate soils at low temperatures. ,, However, the high N concentration in freezing contaminated clayey site soils in this study enhanced hydrocarbon biodegradation, reflecting the potential adaptation of indigenous freezing-tolerant hydrocarbon degraders to nutrient-induced osmotic pressure. Cold- and salt-tolerant hydrocarbon-degrading bacteria (5% NaCl, w/v, 10 °C) have been isolated from nonsaline , petroleum-contaminated, sub-Arctic soils, inferring the potential connection between salt tolerance and indigenous cold-adapted microorganisms in cold-climate soils . Salt exclusion was over 90% in saturated clayey silt amended with NaCl under slow freezing at −0.1 °C/d .…”

“…Cold-and salt-tolerant hydrocarbon-degrading bacteria (5% NaCl, w/v, 10 °C) have been isolated from nonsaline, petroleum-contaminated, sub-Arctic soils, inferring the potential connection between salt tolerance and indigenous cold-adapted microorganisms in cold-climate soils. 34 Salt exclusion was over 90% in saturated clayey silt amended with NaCl under slow freezing at −0.1 °C/ d. 13 Slower soil freezing rates below −3 °C/day (field freezing condition) are critical for excluding more salts, compared to faster freezing rates. 13 The slow soil freezing rate of −0.2 °C/d applied in this study mimics the natural soil seasonal freezing rate 12 and corresponded to the remaining unfrozen water contents over 50% of the initial water content of the unfrozen phase (Figure 1) and lowered freezing-point depressions in the treated soils (Figure 4B).…”

“…The duration of the partially frozen soil phase, in which unfrozen water and ice coexist, can be prolonged from a few weeks to months, partly as a result of the zero-curtain effect that holds soil temperatures near freezing during seasonal shifts in cold climates . The soils eventually enter the deeply frozen phase, when unfrozen water content becomes limited at a threshold level that is minimal but vital for cold-adapted microbial populations to survive or possibly remain active at subzero temperatures. − The freezing rate also influences microbial survivability associated with physiological acclimation and the osmoregulation of microbial cells. − Substantial salt tolerance (5–10% NaCl) has been reported for cold-adapted bacteria isolated from polar and subpolar habitats, such as the active layer of freezing soils, permafrost, sea ice, and even petroleum-contaminated sub-Arctic soils. − Laboratory and field bioremediation experiments conducted using petroleum-contaminated cold-climate soils undergoing freezing at natural in situ seasonal rates (near −0.1 °C/d) indicate the emergence of winter microbial populations in partially frozen and deeply frozen soils. , Conventional laboratory studies have been conducted using rapid repeated freeze–thaw cycles that are much faster than seasonal rates, intended to mimic diurnal, periodic, and drastic fluctuation effects (e.g., ±20 °C per day). − However, applying soil freezing rates that are well controlled and site-representative, in combination with a sampling strategy based on the soil thermal phase, is crucial for studying seasonally freezing and thawing soil environments, as noted and similarly discussed in prior work …”

Chemical and Biological Indicators for Evaluation of Arctic Soil Degradation and Its Potential to Remediation

“…oil-polluted arctic soils with high salinity (Rhykerd et al, 1995;Chang et al, 2018;Wang et al, 2017). Therefore, prior to developing an integrated system of measures to eliminate soil pollution in the Arctic zone, it was necessary to evaluate the self-restoration potential of disturbed arctic soils by analyzing chemical and biological indicators.…”

Hydrocarbon Removal by Two Differently Developed Microbial Inoculants and Comparing Their Actions with Biostimulation Treatment

“…Bioremediation of soils contaminated with petroleum hydrocarbons is usually based upon two approaches: biostimulation (an addition of the appropriate nutrients and/or electron acceptors to stimulate the degradation capacity of the indigenous soil microorganisms) and bioaugmentation (an inoculation of soil with high numbers of autochthonous or allochthonous hydrocarbon-degrading microorganisms) [6]. The results obtained in different studies advocate the application of either the former [7][8][9] or the latter method [10][11][12]. Numerous microorganisms possess an ability to use hydrocarbons as the sole source of carbon and energy, but only representatives of a few genera, notably Mycolicibacterium (formerly included in Mycobacterium genus), Pseudomonas, and Rhodococcus, are capable of degrading both aliphatic and aromatic hydrocarbons [13].…”