Biological remediation of agricultural soils contaminated with oil is complicated by the presence of residual amounts of chemical plant protection products, in particular, herbicides, which, like oil, negatively affect the soil microbiome and plants. In this work, we studied five strains of bacteria of the genera Pseudomonas and Acinetobacter, which exhibited a high degree of oil biodegradation (72–96%). All strains showed resistance to herbicides based on 2,4-D, imazethapyr and tribenuron-methyl, the ability to fix nitrogen, phosphate mobilization, and production of indole-3-acetic acid. The presence of pollutants affected the growth-stimulating properties of bacteria in different ways. The most promising strain P. citronellolis N2 was used alone and together with oat and lupine plants for soil remediation of oil, including herbicide-treated oil-contaminated soil. Combined contamination was more toxic to plants and soil microorganisms. Bacterization stimulated the formation of chlorophyll and suppressed the synthesis of abscisic acid and malonic dialdehyde in plant tissues. The combined use of bacteria and oat plants most effectively reduced the content of hydrocarbons in the soil (including in the presence of herbicides). The results obtained can be used to develop new methods for bioremediation of soils with polychemical pollution.

The increasing demand for energy sources is leading to greater contamination of soils, including agricultural, by oil products. It requires the search for effective methods to restore the disturbed territories. This study evaluates the effectiveness of using the hydrocarbon-degrading strain Pseudomonas schmalbachii N3.1, both individually and in combination with Lupinus albus L. and Avena sativa L. plants to purify soil from oil that has been contaminated with imazethapyr- or tribenuron-methyl-based herbicides. The study analyzes changes in the abundance of microorganisms (ammonifying, hydrocarbon oxidizing, oligonitrophilic), soil respiratory and enzyme activity, as well as the soil content of oil products. It was found that oil is less toxic to the soil microbiocenosis than the herbicides, while the combination of plants and bacteria significantly increases the number of microorganisms of the studied groups. When L. albus and bacteria were applied separately, soil respiratory activity in oil-contaminated samples increased by 31–36 %. The highest catalase activity was recorded in A. sativa plantings, including inoculated soils (8.72–12.25 and 9.12–10.95 ml O2/g·min, respectively). Bioremediation promoted an increase in invertase activity (by 1.7–3.5 times), with the maximum effect observed when plants and microorganisms were combined (2.44–4.37 and 2.09–4.51 mg glucose/24 h/g in soils with L. albus and A. sativa, respectively). All types of bioremediation reduced the oil product content in soils. The lowest values were achieved with the combined use of P. schmalbachii N3.1 and A. sativa (2.3–2.8 g/kg). This was probably due to the highest number of hydrocarbon-oxidizing bacteria (up to 13·107 CFU/g) and significant catalase activity (up to 11 ml O2/g . min).

Using plants to restore soils subjected to salinization and polychemic pollution can be an effective way to return agricultural land to circulation and obtain safe products. In this study, experiments were conducted with oats and lupine to evaluate their ability to purify soils contaminated with copper (II) and nickel (II) ions, carbonate and sulfate anions and oil and their combinations. The biological activity of the soil, phytotoxicity, and hydrocarbon content, as well as plant growth and biochemical parameters in polluted soil, were studied. The enzymes most sensitive to soil contamination were catalase, urease, and phosphatase. Copper ions inhibited oat root growth by 45.7% and lupine by 46.6%. Oil and its mixtures with other pollutants inhibited shoot growth by up to 50.3% in oats and up to 28.6% in lupine. The content of malonic dialdehyde increased in oats when exposed to copper, while in lupines, it increased 2.9-fold when exposed to oil. Flavonoids in oats increased with metal contamination (by 9–16.7%), while in lupines with oil (by 8.6%). Chlorophyll fluctuations were less pronounced in oats than in lupine. Despite the stress experienced by plants due to soil pollution, the degradation rate of petroleum hydrocarbons under oat and lupine crops was 33–46%. In general, oats and lupine are promising for the phytoremediation of complexly polluted and saline soils.

A new halotolerant bacterial strain, Bacillus atrophaeus ANT22, was isolated and identified. It possesses growth-promoting properties (i.e., indole-3-acetic acid production, phosphate mobilization, and antagonistic activity) and biofilm-forming capacity. The effects of magnesium sulphate and sodium chloride salts on these properties were studied. A model experiment was conducted to assess the effect of treating lupine seeds with this strain on the morphological and biochemical parameters of plants under normal conditions and in the presence of 0.25% sodium chloride in the soil. B. atrophaeus ANT22 enhanced plant growth, especially under saline conditions. In the presence of NaCl, inoculation increased root length and weight by 46.5% and 48.3%, respectively, led to shoot elongation by 12.0% and an increase in shoot weight by 27.9%, and also contributed to an increase in the number of leaves and their weight (by 36.8% and 30.9%, respectively) relative to uninoculated plants in saline soil. Furthermore, bacterization increased chlorophyll production by 21.3% in plants planted in soil with NaCl and reduced malondialdehyde levels by 1.4 times compared with untreated samples. These results demonstrate the potential of using the halotolerant film-forming strain B. atrophaeus ANT22 to stimulate plant growth in saline soil.