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Soil pollution has become a major concern in various terrestrial ecosystems worldwide. One in situ soil bioremediation strategy that has gained popularity recently is microbe-assisted phytoremediation, which is promising for remediating pollutants. Sphingomonads, a versatile bacteria group comprising four well-known genera, are ubiquitous in vegetation grown in contaminated soils. These Gram-negative microbes have been investigated for their ability to induce innate plant growth-promoting (PGP) traits, including the formation of phytohormones, siderophores, and chelators, in addition to their evolutionary adaptations enabling biodegradation and microbe-assisted removal of contaminants. However, their capacity for bacterial-assisted phytoremediation has to date been undervalued. Here, we highlight the specific features, roles, advantages, and challenges associated with using sphingomonads in plant-microbe interactions, from the perspective of future phytotechnologies., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Understanding the uptake of organic pollutants by plants is an important part of the assessment of risks from crops grown on contaminated soils. This study was an investigation of the effects of surfactants added to PAHs-contaminated soil on the uptake and accumulation of PAHs in maize tissues during phytoremediation. The accumulation of phenanthrene (PHE) and pyrene (PYR) by maize plant was not influenced significantly by the surfactant amendment to the soil. The distribution of PHE and PYR in maize tissues was not positively correlated with the corresponding lipid contents. Remarkably, the concentrations of PHE (20.9 ng g(-1)) and PYR (0.9 ng g(-1)) in maize grain were similar to or even much lower than those in some foods. Moreover, surfactants could enhance the removal of pollutants from contaminated soil during phytoremediation, which might be due to surfactant desorption ability and microbial activity in soil. The study suggests that use of maize plant with surfactant is an alternative technology for remediation of PAHs-contaminated soils., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Resin acids are tricyclic terpenoids occurring naturally in trees. We investigated the occurrence of resin acid-degrading bacteria on the Arctic tundra near the northern coast of Ellesmere Island (82 degrees N, 62 degrees W). According to most-probable-number assays, resin acid degraders were abundant (10(3) to 10(4) propagules/g of soil) in hydrocarbon-contaminated soils, but they were undetectable (<3 propagules/g of soil) in pristine soils from the nearby tundra. Plate counts indicated that the contaminated and the pristine soils had similar populations of heterotrophs (10(6) to 10(7) propagules/g of soil). Eleven resin acid-degrading bacteria belonging to four phylogenetically distinct groups were enriched and isolated from the contaminated soils, and representative isolates of each group were further characterized. Strains DhA-91, IpA-92, and IpA-93 are members of the genus Pseudomonas. Strain DhA-95 is a member of the genus Sphingomonas. All four strains are psychrotolerant, with growth temperature ranges of 4 degrees C to 30 degrees C (DhA-91 and DhA-95) or 4 degrees C to 22 degrees C (IpA-92 and IpA-93) and with optimum temperatures of 15 to 22 degrees C. Strains DhA-91 and DhA-95 grew on the abietanes, dehydroabietic and abietic acids, but not on the pimaranes, isopimaric and pimaric acids. Strains IpA-92 and IpA-93 grew on the pimaranes but not the abietanes. All four strains grew on either aliphatic or aromatic hydrocarbons, which is unusual for described resin acid degraders. Eleven mesophilic resin acid degraders did not use hydrocarbons, with the exception of two Mycobacterium sp. strains that used aliphatic hydrocarbons. We conclude that hydrocarbon contamination in Arctic tundra soil indirectly selected for resin acid degraders, selecting for hydrocarbon degraders that coincidentally use resin acids. Psychrotolerant resin acid degraders are likely important in the global carbon cycle and may have applications in biotreatment of pulp and paper mill effluents.