Arbuscular Mycorrhizal Fungi in a Wetland Constructed for Benzene-, Methyl Tert-Butyl Ether- and Ammonia-Contaminated Groundwater Bioremediation
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bs_bs_banner Brief report Arbuscular mycorrhizal fungi in a wetland constructed for benzene-, methyl tert-butyl ether- and ammonia-contaminated groundwater bioremediation Thomas Fester* (arbuscular mycorrhizal fungi, AMF; Smith and Read, Helmholtz-Centre for Environmental Research – UFZ, 2008). The association allows the exchange of nutrients Permoserstraße 15, D-04318 Leipzig, Germany. (carbohydrates provided by the plant, mineral nutrients provided by the fungi), and markedly increases the host plant’s tolerance of various biotic and abiotic stress Summary factors. Arbuscular mycorrhizal fungi also influence the Arbuscular mycorrhizal fungi (AMF), which are transport and distribution of organic pollutants in plants present in most natural environments, have demon- (Debiane et al., 2009; Langer et al., 2010), reportedly strated capacity to promote biodegradation of reducing their concentrations in shoots of colonized organic pollutants in the greenhouse. However, it is plants, while increasing their concentrations in roots, par- not certain whether AMF can spontaneously establish ticularly in the rhizodermis (Huang et al., 2007; Wu et al., in phytoremediation systems constructed to decon- 2009). These effects may help to protect plants from taminate groundwater, because of the unusual condi- damage by organic pollutants. Beneficial effects of the tions during the construction and operation of such presence of AMF on soil bacteria (Toljander et al., 2007), systems. To assess this possibility, root samples notably bacteria capable of degrading organic com- from a wetland constructed for the phytoremediation pounds (Corgié et al., 2006; Alarcon et al., 2008), have of groundwater contaminated with benzene, methyl also been reported. By both protecting plants from tert-butyl ether and ammonia were analysed. Sub- adverse effects of organic pollutants and promoting stantial AMF colonization was observed in plant roots associated bacteria, AMF can accelerate the biodegra- sampled close to the inlet of a basin filled with fine dation of organic pollutants. Several studies have gravel and planted with Phragmites australis. In addi- recently demonstrated beneficial effects of AMF on the tion, analysis of a fragment of the nuclear large ribos- biodegradation of organic pollutants, including: the dissi- omal subunit, amplified by nested PCR, revealed the pation of polycyclic aromatic hydrocarbons (PAHs) by presence of AMF molecular operational taxonomic Lolium multiflorum (Yu et al., 2011), dissipation of PAHs units closely related to Funneliformis mosseae and by Medicago sativa under low water and phosphate Rhizophagus irregularis in the samples. These find- availability (Zhou et al., 2009), and phytoremediation of ings demonstrate the capacity of generalist AMF aged petroleum contamination by Triticum aestivum strains to establish spontaneously, rapidly and (Malachowska-Jutsz and Kalka, 2010). Arbuscular myc- extensively in groundwater bioremediation technical orrhizal fungi can therefore be considered ideal inhabit- installations. ants of technical installations for the plant-based bioremediation of groundwater contaminated by organic pollutants. However, such installations are often con- Introduction structed without including a significant source of AMF An arbuscular mycorrhiza is a type of close, mutualistic propagules. Furthermore, the stressful conditions in such association that forms in root systems between diverse installations – such as poor substrates, and potentially plant species and members of a small group of soil fungi toxic concentrations of organic pollutants for the fungi (Verdin et al., 2006; Debiane et al., 2011) – may hinder the successful establishment of AMF. Received 22 February, 2012; revised 28 June, 2012; accepted 6 July, To investigate the ability of AMF to establish under such 2012. *For correspondence. E-mail [email protected]; Tel. conditions, we analysed AMF colonization levels in plant (+49) 341 2351315; Fax (+49) 341 235451315. doi:10.1111/j.1751-7915.2012.00357.x roots sampled from a wetland constructed to decontami- Funding Information No funding information provided. nate groundwater polluted with benzene, methyl tert-butyl © 2012 The Author Microbial Biotechnology © 2012 Society for Applied Microbiology and Blackwell Publishing Ltd Mycorrhizal fungi from constructed wetlands 81 ether (MTBE) and ammonia. The wetland was continu- legend for details), clearly showing that these fungi suc- ously streamed (inflow rate 6 l h-1) by water containing 20, cessfully colonized this unusual environment within 4 3.7 and 45 mg l-1 of these compounds respectively. Arbus- years. Thus, establishment of AMF does not appear to cular mycorrhizal fungi present in roots from Phragmites have been profoundly hindered in the inlet part of the australis growing in this wetland were phylogenetically wetland, although it was exposed to the highest concen- analysed by cloning and sequencing a 400 bp fragment of trations of organic pollutants. In contrast, no colonization the nuclear large ribosomal subunit, amplified by nested of roots by AMF was observed in the part of the basin PCR. where the plants were growing in free water with no gravel substrate, suggesting that a solid substrate was required for AMF colonization. The likeliest sources of the coloniz- Results and discussion ing fungi were airborne propagules or mycelia already Spontaneous colonization of constructed wetlands present in the P. australis plantlets when they were trans- ferred to the constructed wetland. The constructed wetland investigated in this study was established in March 2007. It consists of a basin that receives a stream of contaminated groundwater. Phrag- Generalist AMF strains as early and rapid colonizers of mites australis plantlets were planted at the inlet end, the constructed wetland which is filled with light gravel. Close to its outlet area Considerable frequencies of very similar patterns were there is a compartment lacking the gravel substrate where detected in restriction fingerprinting of PCR products P. australis is growing in water, forming a dense root mat cloned from a fragment of the large ribosomal subunit, (Fig. 1). Root samples taken from the part of the con- indicating that the AMF community within the constructed structed wetland with the gravel substrate in 2011 were wetland had low diversity at the sampling time. Fifty-one substantially associated with AMF (colonized proportions clones with identical patterns were removed from the by length, 40%, 25%, 25%, 60% and 80%; see Fig. 1 analysis, leaving 34 unique clones for sequence analy- sis, and only two AMF taxa were detected: Rhizophagus irregularis and Funneliformis mosseae. The restriction endonuclease Taq I was used for restriction fingerprint- ing, partly because it has been recommended for Inlet Outlet T-RFLP analysis of the PCR fragment analysed in this Benzene (mg l-1) 20 3.8 MTBE (mg l-1) 3.7 3.1 study (Mummey and Rillig, 2007), and partly because Ammonia N (mg l-1) 45 21 almost all AMF species in the phylogenetic tree shown in Water flow Fig. 2 could be differentiated using this enzyme in a AMF ++ AMF - virtual digest. In particular, it was possible to differentiate all other species from R. irregularis and F. mosseae, the Fig. 1. In March 2011 five samples of roots (each about 10 g) were taken from the ‘front’ (near the inlet) and five from the ‘rear’ (near two AMF found in the wetland samples, excluding the the outlet; 10 samples in total) of the illustrated constructed wetland possibility that AMF species were missed because of (5 m long, 1.15 m wide, 1.25 m deep; inflow rate 6 l h-1) planted the use of Taq I for restriction fingerprinting prior to with P. australis, which is being used in a compartment transfer experiment close to Leuna, Germany (Seeger et al., 2011). Parts of sequence analysis. As the primer pairs used in our the sampled roots were stained with ink (Sheaffer, Middlesex, UK) analysis are not capable of amplifying sequences of and vinegar according to Vierheilig and colleagues (1998) to high- members from the genus Diversispora or the families light AMF structures, and the degree of colonization by AMF was roughly estimated by inspecting the stained roots under a stereomi- Archaeosporaceae and Paraglomaceae (Gamper et al., croscope and estimating approximate ratios of mycorrhizally colo- 2009), however, the possible presence of additional AMF nized to non-colonized root lengths. Substantial degrees of AMF from these groups cannot be excluded. Phylogenetic colonization were observed in all five root samples from the ‘front’ part of the wetland (40%, 25%, 25%, 60% and 80%). In contrast, analysis using the set of consensus sequences for AMF no colonization of P. australis roots was observed in samples from (see fig. 1 in Krüger et al., 2011) clearly showed that the rear part, where there was no gravel substrate and the roots all sequences analysed in our study clustered with the formed a dense root mat. These microscopic observations are con- sistent with results of nested PCR analysis of a 400 bp fragment of AMF genera Rhizophagus or Funneliformis (data not the nuclear large ribosomal subunit using the primer pairs LR1/ shown). Only four sequences clustered with different FLR2 and FLR3/FLR4 (Gollotte et al., 2004) and Taq PCR Master- fungal groups, one of which proved to be a chimeric mix (Qiagen, Hilden, Germany). DNA extracted (using a DNeasy Plant Mini-Kit, Qiagen) from all samples from the front part of the sequence in later analysis, while the other three