Phenanthrene and Pyrene Modify the Composition and Structure of the Cultivable Endophytic Bacterial Community in Ryegrass (Lolium multiflorum Lam)

Abstract

This study provides new insights into the dynamics of bacterial community structure during phytoremediation. The communities of cultivable autochthonous endophytic bacteria in ryegrass exposed to polycyclic aromatic hydrocarbons (PAHs) were investigated with regard to their potential to biodegrade PAHs. Bacterial counts and 16S rRNA gene sequence were used in the microbiological evaluation. A total of 33 endophytic bacterial strains were isolated from ryegrass plants, which represented 15 different genera and eight different classes, respectively. Moreover, PAH contamination modified the composition and structure of the endophytic bacterial community in the plants. Bacillus sp., Pantoea sp., Pseudomonas sp., Arthrobacter sp., Pedobacter sp. and Delftia sp. were only isolated from the seedlings exposed to PAHs. Furthermore, the dominant genera in roots shifted from Enterobacter sp. to Serratia sp., Bacillus sp., Pantoea sp., and Stenotrophomonas sp., which could highly biodegrade phenanthrene (PHE). However, the diversity of endophytic bacterial community was decreased by exposure to the mixture of PAHs, and increased by respective exposure to PHE and pyrene (PYR), while the abundance was increased by PAH exposure. The results clearly indicated that the exposure of plants to PAHs would be beneficial for improving the effectiveness of phytoremediation of PAHs.

Exploration of social spreading reveals behavior is prevalent amongPedobacterandP. fluorescensisolates, and shows variations in induction of phenotype

“…Interestingly, co-isolation of strains did not appear to be an important factor for their ability to engage in a social behavior, and even our canonical two species were not co-isolated, one having been isolated in Dutch dune soil, and the other from sandy-loam soil in a farm in MA, U.S.A (33,34). The vast majority of the species we tested were isolated from soil, but Pseudomonas and Pedobacter can be isolated from a variety of different environments (35)(36)(37)(38)(39)(40). Ultimately, close relationship to our initial two study strains is a better predictor of interaction than the environment from which the strains were isolated.…”

Selection of Endophytic Strains for Enhanced Bacteria-Assisted Phytoremediation of Organic Pollutants Posing a Public Health Hazard

“…Gammaproteobacteria and Alphaproteobacteria endophytes were more abundant in roots, while Betaproteobacteria were predominant in stems [122]. In turn, the abundance analysis indicated that the exposure of ryegrass to increasing concentrations of phenanthrene and pyrene positively correlated with the numbers of endophytic bacteria and negatively correlated with the richness of these communities in roots, while no such relationship was con-firmed for shoots [25]. Similar data related to endophyte biodiversity in wheat depending on the phenanthrene contamination level were reported by Liu et al [26].…”

“…This may suggest their potential for biodegradation of the hydrocarbons tested. Moreover, it was shown that the higher concentrations of individual or combined PAHs were accompanied by lower biodiversity of endophytes [25]. In turn, it was found in another study that inoculation of phenanthrene-contaminated wheat with PAH-degrading endophytic Massilia sp.…”

“…It has been shown that organic contamination of soil may affect the population characteristics of endophytic bacteria [24]. For instance, in their study on bacterial community in ryegrass (Lolium multiflorum Lam) exposed to phenanthrene and pyrene in comparison to non-contaminated plants, Zhu et al [25] showed that strains from the genera Bacillus, Pantoea, Pseudomonas, Arthrobacter, Pedobacter, and Delftia were present only in plants exposed to PAHs. This may suggest their potential for biodegradation of the hydrocarbons tested.…”

Effects of <i>Rhizobium</i> Species Living with the Dark Septate Endophytic Fungus <i>Veronaeopsis simplex</i> on Organic Substrate Utilization by the Host

“…2 ), strain VsBac-Y9 was affiliated with the cluster composed of the above-described clone sequences and Rhizobium sp, enrichment clone N312. A BLAST search of its almost-complete 16S rRNA gene sequence (1387 bp) with the NCBI database showed that isolate VsBac-Y9 was extremely close to the Rhizobium isolates P7 and YIC4260, which were cultured from the rhizospheres of gramineous Lolium multiflorum ( 37 ) and leguminous Sesbania cannabina ( 21 ), respectively.…”