Abstract
SummaryThe bacterial community composition of activated sludge from a wastewater treatment plant (Almería, Spain) with the particularity of using seawater was investigated by applying 454-pyrosequencing. The results showed that Deinococcus-Thermus, Proteobacteria, Chloroflexi and Bacteroidetes were the most abundant retrieved sequences, while other groups, such as Actinobacteria, Chlorobi, Deferribacteres, Firmicutes, Planctomycetes, Spirochaetes and Verrumicrobia were reported at lower proportions. Rarefaction analysis showed that very likely the diversity is higher than what could be described despite most of the unknown microorganisms probably correspond to rare diversity. Furthermore, the majority of taxa could not be classified at the genus level and likely represent novel members of these groups. Additionally, the nitrifiers in the sludge were characterized by pyrosequencing the amoA gene. In contrast, the nitrifying bacterial community, dominated by the genera Nitrosomonas, showed a low diversity and rarefaction curves exhibited saturation. These results suggest that only a few populations of low abundant but specialized bacteria are responsible for removal of ammonia in these saline wastewater systems.
Highlights
Activated sludge constitutes a crucial tool in the biodegradation of organic materials, transformation of toxic compounds into harmless products and nutrient removal in wastewater treatment plants (WWTPs)
A great majority cannot be obtained by conventional techniques (Wagner et al, 1993) and, current molecular techniques such as sequence analysis of 16S rRNA gene clone libraries (Snaidr et al, 1997), fingerprinting methods such as denaturing gradient gel electrophoresis (DGGE; Boon et al, 2002), thermal gradient gel electrophoresis (TGGE; Eichner et al, 1999) and terminal restriction fragment length polymorphism (Saikaly et al, 2005) along with fluorescence in situ hybridization (FISH) have been employed in wastewater microbiology to analyse and compare the microbial structure of activated sludge
The results showed that the composition of the bacterial community differed substantially from other WWTP previously reported, since Betaproteobacteria did not seem to be the predominant group; in contrast, other classes of Proteobacteria, such as Alpha- and Gammaproteobacteria, as well as members of Bacteroidetes and Deinoccocus-Thermus contributed in higher proportions
Summary
Activated sludge constitutes a crucial tool in the biodegradation of organic materials, transformation of toxic compounds into harmless products and nutrient removal in wastewater treatment plants (WWTPs). Ye and colleagues (2011), who analysed by pyrosequencing the bacterial composition of a slightly saline activated sludge from a laboratory-scale nitrification reactor and a WWTP from Hong Kong, found that, in addition to Proteobacteria and Bacteroidetes, the phylum Firmicutes was abundant in their samples; they obtained similar groups as in the present study, such as the Actinobacteria, Planctomycetes, Verrumicrobia, Deinococcus-Thermus, Chloroflexi and Spirochaetes, at different relative ratios, as well as different phyla not retrieved in the present work, for example the Nitrospira, Chlamydiae and TM7.
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