Vertical flow constructed wetlands for the treatment of inorganic ...

2000), NOB communities (Maixner et al., 2006, Dionisi et al. 2002; Cebron and Garnier,
2005) and denitrifying communities (Throbäck et al., 2004, Henry et al., 2006) in natural
and engineered systems. Because the construction of clone libraries followed by
sequencing are laborious, they have been routinely applied in conjunction to other
community profiling methods such as DGGE and T-RFLP (Horz et al. 2000, Tietz et al.,
2007).
The following section is a summary of studies characterising microbial
communities in CWs. While general microbial studies are occasionally mentioned, the
focus is on nitrogen transforming bacteria.
It is known that slow growing organism such as AOB often grow attached to
surfaces in an extracellular polymeric matrix, or biofilm, which help them maintain a
stable physiological state in the presence of inhibitory substances (acidic or saline
conditions) and increase their recovery rate after a period of starvation for ammonium
(Powell and Prosser 1992; Phillips et al., 1999; Gorra et al., 2007). The presence of
surfaces for adherence may also select for specific strains of ammonia-oxidizing
bacteria (Stehr et al. 1995; Phillips et al. 1999).
The diversity of the β-proteobacteria AOB was investigated in a
rhyzoremediation system treating municipal wastewater in Germany by Haleem et al.
(2000). Cloning and sequencing of AOB associated with the roots of Phragmites
australis and soil below the root system revealed that the majority of all sequences
belonged to the Nitrosospira cluster and only a few sequences were affiliated with
Nitrosomonas subcluster 7 (classification according to Stephen et al., 1996).
Truu et al. (2005) analysed the diversity and distribution of microbial
communities in a sand HF wetland treating domestic wastewater. Methods used
included PCR-DGGE (with universal 16S rDNA eubacterial and archaeal primers and
AOB specific primers), and also MPN counts. They found significant differences in the
spatial distribution of the microbial communities. In the case of general bacteria and
specific AOB, the communities were very diverse and the most important factors
affecting their distributions were related to depth and differences between the inflow
and outflow wastewater characteristics. For the archaeal community, very high
diversity was verified, with 20 to 30 dominant populations. Archaea was the only group
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