**3.3 Microorganisms**

74 Management of Organic Waste

The addition of exogenous test substrate (oil hydrocarbons) to soil was accompanied by the change in soil microbiota activity: the rate of CO2 production initially increased as a result of substrate and probably SOM mineralization and then, on depletion of the substrate, gradually decreased. The amount of CO2 evolved was divided by means of mass isotope balance into two fractions: from the substrates (oil hydrocarbons) and from SOM mineralization. Thus, the difference between CO2 evolved from SOM mineralization in oil hydrocarbons amended soil (C\*SOM) and in the control soil (CSOM) relative to the control (in percentage) was used to estimate the magnitude of the priming effect (PE) induced by oil hydrocarbons (denoted as SUB). The PE value was determined in two notations as *kinetic* PE(Δti ) calculated as a value for Δti–time intervals using equation [11] and the PE(*total*) calculated as a weighted average value

PE(Δti) [%] = 100×(C\*SOM(i) - CSOM(i))/CSOM(i) (11)

where C\*SOM(i) = Fi×C(SUB+SOM)I; C(SUB+SOM)i is the total C evolved as CO2 in the amended soil during Δti-time; and Fi is the share of CO2-C resulting from the SOM in crude oil amended

PE(*total*) [%]=Σ(PE(Δti)·Δti)/Σ(Δti) (12)

**3. Degradation of oil hydrocarbons by soil microbiota and laboratory bacteria** 

Arable soil samples from the Krasnodar region of Russia were used in the experiment after they had been cultivated with corn (С4-plant). Soil samples were sieved through a 2 mm sieve and then moistened to 60 % of field capacity. The initial organic matter content was about 4.9 % of dry soil (DS) weight or 19.6 mg С g-1 DS. The carbon isotope composition in the initial SOM was characterized by a 13C value of -23.01 0.2 ‰, typical of soils vegetated

The crude oil as hydrophobic compound was applied as follows: crude oil (4 ml of oil corresponding to 3200 mg) was added to 10 g of dried and dispersed soil and then 10 g of the soil was mixed with fresh moist soil equivalent to 100 g of dry material. The final substrate concentration was 27.43 mg C g-1 soil. Since the content of SOM in the initial dry soil sample was about 19.6 mg C/g DS, the share of oil hydrocarbons introduced into the soil exceeded 1.4-fold the quantity of SOM. Assuming that the major part of crude oil spilled over the soil is contained in the upper 10-cm layer, we find that the supposed degree of soil

The carbon isotope composition of the oil hydrocarbons used in these experiments was characterized by a 13C value of -28.4 0.1 ‰, the light and heavy oil hydrocarbon

**2.6 Calculation of priming effects** 

for the whole period of observation using equation [12].

soil in Δti-time, which was calculated by equation [8].

where PE(Δti) was calculated according to Eq. [11].

**introduced into soil** 

**3.2 Crude oil test-substrate** 

pollution will be about 32 tons per 1 ha.

**3.1 Soil samples** 

by С4-plants.

To estimate the potential of microbial mineralization of oil hydrocarbons polluted soils, the CO2 production was determined in 12 glass vials with tested soils (three replicates of each experiment and control) (Table 1). In Experiment 1, crude oil was introduced into vials with native soil containing only native soil microorganisms; in Experiment 2, the laboratory strain *Pseudomonas aureofaciens* BS1393(pBS216) (Kochetkov et al. 1997) was additionally introduced into the same soil with oil. Native soil without oil and the same soil with the strain BS1393(pBS216) were used as controls 1 and 2, respectively (Table 1).

The strain *Pseudomonas aureofaciens* BS1393(pBS216) bears the plasmid pBS216 that controls naphthalene and salicylate biodegradation, is able to utilize aromatic oil hydrocarbons, and has an antagonistic effect on a wide range of phytopathogenic fungi (Kochetkov et al. 1997). The ability of the strain to synthesize phenazine antibiotics and thus staining its colonies bright-orange on LB agar medium allowed its use as a marker of quantitative presence of the above microorganisms in soil in the presence of aboriginal microflora ( Sambrook, et al. 1989].

