Capacity of Pseudomonas Strains to Degrade Hydrocarbons, Produce Auxins and Maintain Plant Growth under Normal Conditions and in the Presence of Petroleum Contaminants

Abstract

The phytoremediation of soil contaminated with petroleum oil products relies on co-operation between plants and rhizosphere bacteria, including the plant growth-promoting effect of the bacteria. We studied the capacity of strains of Pseudomonas, selected as oil degraders, to produce plant hormones and promote plant growth. Strains with intermediate auxin production were the most effective in stimulating the seedling growth of seven plant species under normal conditions. Bacterial seed treatment resulted in about a 1.6-fold increase in the weight of barley seedlings, with the increment being much lower in other plant species. The strains P. plecoglossicida 2.4-D and P. hunanensis IB C7, characterized by highly efficient oil degradation (about 70%) and stable intermediate in vitro auxin production in the presence of oil, were selected for further study with barley. These strains increased the seed germination percentage approximately two-fold under 5% oil concentration in the soil, while a positive effect on further seedling growth was significant when the oil concentration was raised to 8%. This resulted in a 1.3–1.7-fold increase in the seedling mass after 7 days of growth, depending on the bacterial strain. Thus, strains of oil-degrading bacteria selected for their intermediate and stable production of auxin were found to be effective ameliorators of plant growth inhibition resulting from petroleum stress.

Effects of Association of Barley Plants with Hydrocarbon-Degrading Bacteria on the Content of Soluble Organic Compounds in Clean and Oil-Contaminated Sand

“…Both bacterial strains were able to synthesize auxins [ 20 ]. However, IAA levels in the eluate from sand with bacteria was low in the absence of plants ( Figure 5 ).…”

“…Chelyabinskiy 99) were used to study the effects of plant-bacteria association on soluble organic compounds in a sand growing substrate in the presence and absence of petroleum. In preliminary experiments comprising 6 plant species, barley was chosen as the most petroleum-resistant and the most responsive to bacterial inoculation in terms of growth promoting effect [ 20 ]. Six barley seedlings, whose coleoptile had a length of 0.5–1 cm, were planted in each 500 mL vessel with clean or oil-contaminated sand.…”

“…Bacterial strains of P. hunanensis IB C7 and Enterobacter sp. UOM 3 have been previously selected from the collection of Ufa Institute of Biology, Ufa Federal Research Centre, Russian Academy of Sciences (UIB UFRC RAS) as being capable of oxidizing oil products and accumulating indole-3-acetic acid (IAA) in vitro [ 20 , 35 ]. Bacteria were cultured for 72 h in meat-peptone broth (g L −1 ): peptone—5, NaCl—5, at a temperature of 28 °C; aeration of the medium was provided by rotating flasks (160 rpm) in an orbital shaker-incubator ES-20/60 (SIA BIOSAN, Riga, Latvia).…”

“…However, when soil was contaminated with oil, the relationship between auxin production and root exudation has not yet been studied. Plant growth was shown to be influenced by some bacterial strains from genera Pseudomonas and Enterobacter , which are capable of oxidising oil hydrocarbons and producing auxins [ 19 , 20 , 21 ]. Their growth promoting effect was not only due to a decrease in the toxicity of oil components, but also to the immediate effect of bacteria on plant growth brought about by their ability to produce plant hormones [ 20 , 22 ].…”

“…UOM 3 on the accumulation of organic acids and sugars in the substrate under conditions of oil pollution and the presence of barley seedlings. These strains were characterized by a relatively high activity in oxidation of oil components and ability to produce IAA [ 20 ]. Taking into account the presumptive role of hormones in the regulation of root exudation, the concentration of hormones in the substrate solution and in plants was analyzed.…”