This is not the case when the contaminant is metabolized via secondary metabolism or co-metabolism or as a terminal electron acceptor
. If the contaminant does not serve as a source of energy, the addition of a primary substrate(s) is required.
Of relevance to nitrogen microbiology, oxygen, nitrate, and nitrite are terminal electron acceptors
. A range of reduced compounds (e.g, organic carbon, ammonium--N[H.sub.4.sup.+], or ferrous iron--Fe[II]) are electron donors.
A number of microbial populations that use PCE as the terminal electron acceptor
in dehalorespiration couple the reduction of chlorinated ethenes to the oxidation of hydrogen ([H.sub.2]).
depends on the availability of oxygen or nitrate as the terminal electron acceptor
(McHatton et at., 1996).
If the carbon concentration is sufficient, the dissolved oxygen in the water will first be used as the terminal electron acceptor
using bacteria metabolism.
Nitrate as terminal electron acceptor
in anaerobic respiration has been found in halophilic and thermophilic archaea .
The graphite in the sediment acts as the terminal electron acceptor
; thus there is a build-up of electrons on the graphite in the sediment.
In the sulfur-rich extreme environment, Thermococcus onnurineus NA1 can use elemental sulfur ([S.sup.0]) as a terminal electron acceptor
for energy via dissimilatory sulfur metabolism and produce [H.sub.2]S as a by-product.
On the other hand, in MBfR, the autohydrogenotropic bacteria could utilize N[O.sub.3.sup.-] and S[O.sub.4.sup.2-] as electron acceptors to generate energy for their growth , and several sulfate-reducing bacteria (SRB) are able to use alternative terminal electron acceptors
to reduce sulfate such as nitrate .