The Pseudomonas qingdaonensis ZCR6 strain, isolated from the rhizosphere of Zea mays growing in soil co-contaminated with hydrocarbons and heavy metals, was investigated for its plant growth promotion, hydrocarbon degradation, and heavy metal resistance. In vitro bioassays confirmed all of the abovementioned properties. ZCR6 was able to produce indole acetic acid (IAA), siderophores, and ammonia, solubilized Ca3(PO4)2, and showed surface active properties and activity of cellulase and very high activity of 1-aminocyclopropane-1-carboxylic acid deaminase (297 nmol α-ketobutyrate mg−1 h−1). The strain degraded petroleum hydrocarbons (76.52% of the initial hydrocarbon content was degraded) and was resistant to Cd, Zn, and Cu (minimal inhibitory concentrations reached 5, 15, and 10 mM metal, respectively). The genome of the ZCR6 strain consisted of 5,507,067 bp, and a total of 5055 genes were annotated, of which 4943 were protein-coding sequences. Annotation revealed the presence of genes associated with nitrogen fixation, phosphate solubilization, sulfur metabolism, siderophore biosynthesis and uptake, synthesis of IAA, ethylene modulation, heavy metal resistance, exopolysaccharide biosynthesis, and organic compound degradation. Complete characteristics of the ZCR6 strain showed its potential multiway properties for enhancing the phytoremediation of co-contaminated soils. To our knowledge, this is the first analysis of the biotechnological potential of the species P. qingdaonensis.

The phytoremediation of soil co-contaminated with petroleum hydrocarbons and heavy metals was studied using Zea mays that was supported with the addition of plant growth-promoting Pseudomonas qingdaonensis ZCR6 and meat and bone meal. The introduced ZCR6 strain was able to survive in the soil and colonize the tissues of maize; however, it did not support plant growth and biomass production or have an impact on hydrocarbon removal. The amendment of the soil with meat and bone meal had a negative impact on the growth of maize however it enhanced soil microbial activity and thus the degradation of hydrocarbons. The efficacy of hydrocarbon removal estimated in fertilized soils reached a value of 32% regardless of the treatment. Z. mays was able to accumulate Zn, Cd and Cu in the presence of hydrocarbons, with the highest phytoextraction ability of Zn. The activity of the mechanisms enhancing the phytoremediation was tested through the quantification of the expression of the selected genes. Among them only acdS, encoding ACC deaminase, and CYP153, encoding cytochrome P450-type alkane hydroxylase, were expressed. As far as we are aware, these are the first results tackling the global problem of co-contaminated soils using a slow-release meat and bone meal fertilizer and a plant-growth-promoting microbe.