Selection of Specific Endophytic Bacterial Genotypes by Plants in Response to Soil Contamination

Abstract

Plant-bacterial combinations can increase contaminant degradation in the rhizosphere, but the role played by indigenous root-associated bacteria during plant growth in contaminated soils is unclear. The purpose of this study was to determine if plants had the ability to selectively enhance the prevalence of endophytes containing pollutant catabolic genes in unrelated environments contaminated with different pollutants. At petroleum hydrocarbon contaminated sites, two genes encoding hydrocarbon degradation, alkane monooxygenase (alkB) and naphthalene dioxygenase (ndoB), were two and four times more prevalent in bacteria extracted from the root interior (endophytic) than from the bulk soil and sediment, respectively. In field sites contaminated with nitroaromatics, two genes encoding nitrotoluene degradation, 2-nitrotoluene reductase (ntdAa) and nitrotoluene monooxygenase (ntnM), were 7 to 14 times more prevalent in endophytic bacteria. The addition of petroleum to sediment doubled the prevalence of ndoB-positive endophytes in Scirpus pungens, indicating that the numbers of endophytes containing catabolic genotypes were dependent on the presence and concentration of contaminants. Similarly, the numbers of alkB-or ndoB-positive endophytes in Festuca arundinacea were correlated with the concentration of creosote in the soil but not with the numbers of alkB-or ndoB-positive bacteria in the bulk soil. Our results indicate that the enrichment of catabolic genotypes in the root interior is both plant and contaminant dependent.

Engineered endophytic bacteria improve phytoremediation of water-soluble, volatile, organic pollutants

“…Earlier results had indicated that growing plants on contaminated soil could selectively enhance the prevalence of endophytes containing the degradation pathways for specific pollutants 21 . After 21 d of growth without toluene, the plants were transferred to glass cuvettes containing toluene in the lower compartment at final concentrations of 0, 100, 500 or 1,000 mg/l.…”

Diversity of bacterial endophytes in roots of Mexican husk tomato plants (Physalis ixocarpa) and their detection in the rhizosphere

“…Some examples include nitrogen fixation, antibacterial and antifungal activities, as well as plant growth promotion (Brooks et al, 1994;Berg et al, 2005;Tan et al, 2006;Rijavec et al, 2007). Other roles such as synthesis of novel chemicals, resistance to heavy metals and xenobiotic degration have been observed in isolated endophytes (Siciliano et al, 2001;Ryan et al, 2007). Importantly, it has been suggested that investigating the diversity of bacterial endophytes may lead us to identify novel drugs for treatment of diseases in humans, plants and animals (Strobel et al, 2004;Ryan et al, 2008).…”

Hydrocarbon degradation, plant colonization and gene expression of alkane degradation genes by endophytic Enterobacter ludwigii strains

“…The efficiency of a phytoremediation process depends mainly on the presence and activity of plant-associated microorganisms carrying degradation genes required for the enzymatic break-down of contaminants. The rhizosphere and plant endosphere have been reported to host pollutant-degrading bacteria (Siciliano et al, 2001;Andria et al, 2009;) and highly diverse alkane degrading bacteria containing alkane degrading genes have been isolated from the plant environment (Kaimi et al, 2007). Expression analysis of alkane monooxygenase (alkB) and a cytochrome P450 hydroxylase (CYP153 gene) indicated degradation in the rhizosphere as well as in the plant interior (Powell et al, 2006;Andria et al, 2009;Afzal et al, 2011).…”