Mobilizing agents enhance fungal degradation of polycyclic aromatic hydrocarbons and affect diversity of indigenous bacteria in soil

Abstract

The impact of several mobilizing agents (MAs) (i.e., soybean oil, Tween-20, Tween-80, olive-oil mill wastewaters, and randomly methylated beta-cyclodextrins) on the degradation performances of the white-rot fungi Irpex lacteus and Pleurotus ostreatus was comparatively assessed in a soil spiked with a mixture of seven polycyclic aromatic hydrocarbons (PAHs). Among the different MAs, soybean oil best supported the growth of both fungi that was twice that observed in soil in the absence of MAs. In addition, soybean oil positively affected PAH degradation by both fungi. In this case, the total weight of organic contaminants (TWOC) was lower than that in the absence of MAs (57.7 vs. 201.3 and 26.3 vs. 160.4 mg kg(-1) with I. lacteus and P. ostreatus, respectively). On the other hand, the number of cultivable heterotrophic bacteria was significantly lower in the soil with soybean oil augmented with either one of the two fungi (5.21 vs. 8.71 and 0.22 vs. 0.51 x 10(7) CFU g(-1) soil with I. lacteus and P. ostreatus, respectively). The effect of soybean oil was confirmed by denaturing gradient gel electrophoresis (DGGE) analysis of PCR-amplified 16S rRNA genes that showed a general decrease in biodiversity. The impact of the other MAs on bacterial diversity was either slightly negative or positive in incubation controls. Both richness and Shannon-Weaver index decreased upon treatment with P. ostreatus. Moreover, with this fungus the composition of the indigenous bacteria was not significantly affected by the type of MA used. By contrast, both indices increased in soil with I. lacteus in the presence of randomly methylated beta-cyclodextrins (39 vs. 33 and 1.43 vs. 1.26, respectively) and soybean oil (19 vs. 5 and 1.01 vs. 0.65, respectively).

Irpex lacteus, a white-rot fungus with biotechnological potential — review

“…The effect was studied in detail with a model soil that was artificially contaminated with PAHs. In this case soybean oil and Tween 80 best supported the degradation activity of I. lacteus and their effect was remarkable toward phenanthrene, anthracene, fluoranthene, chrysene and benz[a]pyrene (Leonardi et al 2008) Bhatt et al (2000 tested the degradation of RBBR dye in an artificially contaminated soil (150 mg dye per kg dry soil) using I. lacteus, a bacterial consortium isolated from a soil industrially contaminated with dye effluents, and a coculture comprising both I. lacteus and this bacterial consortium. Both I. lacteus and the coculture removed RBBR gradually during a 49-d experiment to reach a removal of 76 and 78 %, respectively.…”

Application of vegetable oils in the treatment of polycyclic aromatic hydrocarbons-contaminated soils

“…However, Leonardi et al [78] reported that depending on the fungi, the laccase activity in soybean amended soil can be enhanced or reduced (I. Lacteus and P. Ostreatus respectively).…”

“…For PAH degrading white-rot fungi, the use of vegetable oil could significantly serve as an extra carbon and energy source to support fungi growth, either in the soil system [78] or liquid cultures [79,80]. This is of particular significance since 5-ring and above PAHs are mainly degraded by fungi through their non-specific extracellular enzyme.…”

“…Leonardi et al [78] were the only ones who studied treatment of PAH spiked soil using maize stalks previously colonised with whiterot fungi and incubated at 24 • C under dark and moist conditions (15% water). The addition of 2.5% (w/w) soybean oil enhanced the degradation of 7 spiked PAHs with total removal efficiencies within 75-100% after 42 days.…”

Specific detection of bioavailable phenanthrene and mercury by bacterium reporters in the red soil

“…Firstly, on the design of reporter systems, the lux gene expression was used to evaluate the bioavailability of PHE. This is mainly because bacterial luminescence has two major advantages for detecting PAHs and other sparingly soluble compounds: a faster response time and higher shortterm sensitivities (Leonardi et al 2008). Both advantages allow a relatively small number of reporter molecules to produce a sufficient and strong signal.…”