Sulfate reduction is performed by two major groups of SRB including incomplete oxidizers, which reduce compounds such as lactate to acetate and CO2, and complete oxidizers, which completely convert acetate to CO2 and HCO3[ 19].
However, the former are less versatile regarding their nutritional requirements (Widdel 1988); in addition, complete oxidizers have the ability to oxidize the organic compound to carbon dioxide, and incomplete oxidizers carry out the incomplete oxidation of the organic compound to acetate and CO2 which subsequently can be used by complete oxidizers further in the WSP system.
Indeed the growth kinetics for incomplete oxidizers is generally faster than the complete oxidizers.
Therefore, we cannot rule out that eventually the complete oxidizers might have become dominant under lactate-limiting conditions in R1.
Complete oxidizers typically utilize a broader range of substrates than incomplete oxidizers and may be considered as generalists compared with the more specialist incomplete oxidizers.
Incomplete oxidizers are present in the anoxic pond, while the complete oxidizers may be located in the following facultative and maturation ponds.
Given the fact that the nested amplification suggested that the numbers of the complete oxidizers were very low in the inoculum, a long period of time would have been required before such SRB would have grown to a significant number.
Representatives of both groups were identified within the WSP, complete oxidizers were represented by species of the genera Desulfobacter, Desulfococcus, Desulfonema, Desulfosarcina, and Desulfomonile (Rabus et al. 2006), while the incomplete oxidizers include representatives of the genera Desulfovibrio, Desulfomicrobium, and Desulfobulbus (Madigan and Martinko 2006).
However, the kinetics of this complete oxidation may not enable efficient competition with the incomplete lactate oxidizers.
