Application of DG-DGGE to analyze microbial community diversity and population dynamics in fermentative hydrogen-producing system

Anaerobic microflora enriched from sewage sludge produces hydrogen by using molasses wastewater as its substrate. Use has been made of the double gradient-denaturing gradient gel electrophoresis (DG-DGGE) to monitor the genetic diversity and dynamics of microbial communities in a bio-hydrogen producing reactor. Samples of the anaerobic sludge were analyzed every 7 days, and genomic DNA of the microbial community was extracted. After purification of the DNA by using the DNA gel recovery kit, the 16S rRNA genes (V2 to V3 region) were amplified by using the universal primers (F63GC and R518). The results of agarose gel (2%) electrophoresis show that the PCR products are about 450bp in length. These amplified DNA fragments were separated by parallel DGGE with the denaturant (urea and formamide) from 30% to 60%. The profile of DGGE changes when sludge is inoculated in the reactor, both the primary community dies out or increases, and a second micriobial community increases quickly. The change of the community structure is the greatest on the 15th day. As community succession increases with time, the community structure declines in complexity and a stable community structure forms. On the 29th day, the community diversity stops changing and the amount of the microbial dominant populations reach 19 OTUs. The community diversity tends to be stable after the decreasing under the competition and the cooperation of bacteria, and a climax community forms. Some kinds of populations have been existing in the community structure, they are primary communities. There are some great differences in composition and quantity of the dominant population between the primary community and the climax community. The primary community and the second community have a cooperation effect in the metabolizing process ; show the complex ecological characteristics of the microbial community. This is because different niche conditions lead to different enrichment of bacteria, and forms different microbial community structures. Only by enriching and selecting the needed dominant populations fast can produce hydrogen effectively in the reactor.