Plant growth promoting characterization of soil bacteria isolated from petroleum contaminated soil
Abstract
Contaminant -degrading bacteria can be included among the plant -growth promoting bacteria ; because the presence of contaminants, in general produce negatively effects on plant’s growth; thus, the elimination of the inhibiting contaminants will benefit them. Although contaminant -degrading strains have been traditionally isolated from various environments; the number of studies that reported the isolation and identification of soil bacteria with contaminant - degrading abilities have increased. The aim of this study was to characterized microbial strains isolated from petroleum contaminated soil by plant growth promotion traits to recommend them as potential bioinoculants. In this work, five of the six soil isolates were classified as Indole Acetic Acid higher producers and only one of them as lower producer. Sporosarcina aquimarina strain -Q3 and Bacillus cereus strain +F2 tested in Axonopus affinis plantlets bioassay, showed that these isolates were the most effective promoters of this plant species; therefore, these soil bacteria with possible hydrocarbon degradation ability could be considered as potential bioinoculants and can be recommended with a practical importance for the rhizoremediation of petroleum contaminated sites and plant growth promotion.
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Introduction
Even p etroleum is one of the main components of modern industrial society ; an increasing number of sites are seriously contaminated by hydrocarbons (HCs) [1, 2, 3, 4] . It has bee n reported that the use of plants in conjunction with HC degrading and/or plant growth -promoting bacteria (PGPB) offers much more potential for the remediation of HC contaminated soils [5, 6, 7, 8] . There are knowing b acteria that possess HC-degradation pa thways and metabolic activities not only improve plant tolerance to HC pollutants by degrading these organic compounds [9, 10, 11], a dditionally if they are PGPB , they could mitigate plant stress and also enhance plant growth and development [12, 13, 14, 1 5]. Some authors [5, 12, 13, 16, 17, 18, 19, 20] mentioned that rhizobacteria (RB) and endophytic bacteria (EB), contribute d to biodegradation of toxic organic compounds in polluted soil and could have potential for improving phytoremediation. Particularly , the RB colonize the root environment and participate in the degradation of HCs [6, 20, 21, 22, 23] . Vilchez and Manzanera [24] mention that the presence and characterization of beneficial PGPB in petroleum contaminated soils is limited ; even t here have b een reports about adequate plant species to enhance the rhizoremediation of this kind of organic contaminants [25, 26, 27] . The aim of this study was to characterized microbial strains isolated from petroleum contaminated soil by plant growth promotion tra its to recommend them as potential bioinoculants.
Conclusion
In this work, the six isolated bacteria from two contaminated soil samples with petroleum hydrocarbons were characterized by one of the principal plant growth promoting traits, the Indole Acetic Acid production; five of the six isolates were classified as IAA higher producers and only one of them as lower producer. Four of them were affected in the IAA production by the presence and concentration of tryptophan and only two of them were not affected by the amino acid at any concentration. Sporosarcina aquimarina strain -Q3 and Bacillus cereus strain +F2 tested in A. affinis plantlets bioassay to analyze their activity as plant growth promoters, showed that these isolates were the most effective promoters of this plant species; even these strains have the highest and the lowest IAA production, respectively. Therefore, these soil bacteria with possible hydrocarbon degradation ability could be considered as potential bioinoculants and can be recommended with a practical importance for the rhizoremediation of petroleum contaminated sites and plant growth promotion.
