Hydrocarbon degradation potential and plant growth-promoting activity of culturable endophytic bacteria of Lotus corniculatus and Oenothera biennis from a long-term polluted site

Abstract

Many endophytic bacteria exert beneficial effects on their host, but still little is known about the bacteria associated with plants growing in areas heavily polluted by hydrocarbons. The aim of the study was characterization of culturable hydrocarbon-degrading endophytic bacteria associated with Lotus corniculatus L. and Oenothera biennis L. collected in long-term petroleum hydrocarbon-polluted site using culture-dependent and molecular approaches. A total of 26 hydrocarbon-degrading endophytes from these plants were isolated. Phylogenetic analyses classified the isolates into the phyla Proteobacteria and Actinobacteria. The majority of strains belonged to the genera Rhizobium, Pseudomonas, Stenotrophomonas, and Rhodococcus. More than 90% of the isolates could grow on medium with diesel oil, approximately 20% could use n-hexadecane as a sole carbon and energy source. PCR analysis revealed that 40% of the isolates possessed the P450 gene encoding for cytochrome P450-type alkane hydroxylase (CYP153). In in vitro tests, all endophytic strains demonstrated a wide range of plant growth-promoting traits such as production of indole-3-acetic acid, hydrogen cyanide, siderophores, and phosphate solubilization. More than 40% of the bacteria carried the gene encoding for the 1-aminocyclopropane-1-carboxylic acid deaminase (acdS). Our study shows that the diversity of endophytic bacterial communities in tested plants was different. The results revealed also that the investigated plants were colonized by endophytic bacteria possessing plant growth-promoting features and a clear potential to degrade hydrocarbons. The properties of isolated endophytes indicate that they have the high potential to improve phytoremediation of petroleum hydrocarbon-polluted soils.

Keywords: Endophytic bacteria; Lotus corniculatus L.; Oenothera biennis L.; Petroleum hydrocarbons; Plant growth-promoting mechanisms; Plant-bacteria interactions.

Fig. 1

Neighbor-joining phylogenetic tree of partial 16S rDNA sequences of endophytic bacteria isolated from L. corniculatus and O. biennis. GenBank accession numbers of the strains are shown in parentheses. The bar represents 0.02 substitutions per site; bootstrap values (n = 1000) are displayed. The tree was generated using the MEGA 6.0 software

Fig. 2

The graphs showing the classification of L. corniculatus and O. biennis endophytic bacteria to the Alpha-, Beta-, Gammaproteobacteria, or Actinobacteria. The percentages indicate the relative abundance of isolates that were present in the tested plants