Abstract
A number of Pseudomonas strains function as inoculants for biocontrol, biofertilization, and phytostimulation, avoiding the use of pesticides and chemical fertilizers. Here, we present a new metabolically versatile plant growth-promoting rhizobacterium, Pseudomonas rhizophila S211, isolated from a pesticide contaminated artichoke field that shows biofertilization, biocontrol and bioremediation potentialities. The S211 genome was sequenced, annotated and key genomic elements related to plant growth promotion and biosurfactant (BS) synthesis were elucidated. S211 genome comprises 5,948,515 bp with 60.4% G+C content, 5306 coding genes and 215 RNA genes. The genome sequence analysis confirmed the presence of genes involved in plant-growth promoting and remediation activities such as the synthesis of ACC deaminase, putative dioxygenases, auxin, pyroverdin, exopolysaccharide levan and rhamnolipid BS. BS production by P. rhizophila S211 grown on olive mill wastewater based media was effectively optimized using a central-composite experimental design and response surface methodology (RSM). The optimum conditions for maximum BS production yield (720.80 ± 55.90 mg/L) were: 0.5% (v/v) inoculum size, 15% (v/v) olive oil mill wastewater (OMWW) and 40°C incubation temperature at pH 6.0 for 8 days incubation period. Biochemical and structural characterization of S211 BS by chromatography and spectroscopy studies suggested the glycolipid nature of the BS. P. rhizophila rhamnolipid was stable over a wide range of temperature (40–90°C), pH (6–10), and salt concentration (up to 300 mM NaCl). Due to its low-cost production, emulsification activities and high performance in solubilization enhancement of chemical pesticides, the indigenous BS-producing PGPR S211 could be used as a promising agent for environmental bioremediation of pesticide-contaminated agricultural soils.
Highlights
Overuse of chemical fertilizers and pesticides to meet the growing demand of food supply has undoubtedly cause pollution and severe damage to soil organisms and insect pollinators (Savci, 2012; Mahanty et al, 2017)
Similar results were reported by Wattanaphon et al (2008) who evaluated the solubilization potential of three pesticides, i.e., methyl parathion, trifluralin and ethyl parathion, in the presence of three surfactants namely Tween 80, sodium dodecyl sulfate (SDS) and a glycolipid produced by Burkholderia cenocepacia BSP3. Given their ability to enhance soil nutrient availability, produce plant growth–stimulating compounds, and protect against pathogens, Plant growth promoting rhizobacteria (PGPR) are widely used as bioinoculants to support survival and development of plants even under various stressing conditions, such as pesticide contamination of soil
By analyzing the complete S211 genome, we identified the key genes that potentially promote plant growth as well as genes involved in xenobiotic biodegradation and BS synthesis
Summary
Overuse of chemical fertilizers and pesticides to meet the growing demand of food supply has undoubtedly cause pollution and severe damage to soil organisms and insect pollinators (Savci, 2012; Mahanty et al, 2017). Biofertilizers are ecofriendly agro-input, more cost-effective than chemical fertilizers, and their prolonged use enhances soil fertility substantially (Mahdi et al, 2010; Singh et al, 2011). It was mentioned that the use of biofertilizers enhances crop yield by 10–40% (Bhardwaj et al, 2014). The use of biofertilizers has many benefits, including cheap source of nutrients, excellent suppliers of micronutrients and organic matter, secretion of growth hormones, no adverse effects to ecosystem and longer shelf life (Gaur, 2010; Mahanty et al, 2017)
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