Study of Microbial Community Diversity

Even hypothetical considerations of cooperation in the granule demonstrate that there might be diverse microbial community containing microorganisms with different physiological functions. Additionally, the heterogeneity of microbial community may be created by spatial diversity of environmental conditions in the granule due to existence of different zones, layers, aggregates, and chemical or physical gradients in the granule. Another aspect of microbial diversity is temporal changes of diversity as a succession from flocs to pro-granules and then to young granules, following by stagnation or climax, characterized by weak temporal changes caused by degeneration of matured microbial granules.

The analysis of microbial community residing in the aerobically grown granule can provide information on the microorganisms responsible for granule formation, maintenance, and activity. This knowledge can be used to better control of aerobic granulation.

Microbial populations present in wastewater treatment plants have been studied conventionally by culturing bacterial isolates (Snaidr et al., 1997). These culture-dependent methods suffer from several limitations (Moyer et al., 1994; Amann et al., 1995; Head et al., 1998) and therefore are inadequate to represent the in situ diversity and ecophysiology for a meaningful analysis of community structure or specific organism functionality.

All microorganisms can be detected also by culture-independent methods (Amann et al., 1995, 1998). These methods usually involve the identification of 16S rRNA genes using DNA extraction from the environmental sample, then amplification of gene sequence using polymerase chain reaction (PCR), cloning or separation of the sequences and determination of nucleotide sequence (Head et al., 1998). Culture-independent techniques based on ribosomal ribonucleic acid (RNA) provide a more comprehensive, rapid, and concise characterization of bacteria taxa present in discrete habitats.

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