Distinguishing activity decay and cell death from bacterial decay for two types of methanogens

As bacterial decay consists of cell death and activity decay, and the corresponding information about AOB/NOB, OHO, PAOs and GAOs has been experimentally acquired, another functional type of bacteria in biological wastewater treatment, methanogens, remains to be investigated, to gather the same information, which is extremely important for such bacteria with low growth rates. With successfully selection and enrichment of both aceticlastic and hydrogenotrophic methanogens, and by means of measuring specific methane activity (SMA) and hydrogen consumption rate (HCR), a series of decay experiments and molecular techniques such as FISH verification and LIVE/DEAD staining revealed, identified and calculated the decay and death rates of both aceticlastic and hydrogenotrophic methanogens respectively. The results indicated that the decay rates of aceticlastic and hydrogenotrophic methanogens were 0.070 and 0.034 d−1 respectively, and the death rates were thus calculated at 0.022 and 0.016 d−1 respectively. For this reason, cell deaths were only responsible for 31% and 47% of the total bacterial decay of aceticlastic and hydrogenotrophic methanogens, and activity decays actually contributed significantly to the total bacterial decay, respectively at 69% and 53%.

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► Aceticlastic methanogens and hydrogenotrophic methanogens were successfully enriched.
► Activity decay of these two types of methanogens was distinguished from cell death.
► Both decay rates and death rates of the methanogens were quantitatively determined.
► Cell death is minor in decay and activity decay is a major contributor to total decay.