25SO4~ -

f 24CH2O + 50H+ [12]

formation of NO2 (Table 9.8). The O2 is the terminal electron acceptor and reacts with electrons and H+ to form water [13]. Transport of the electrons and H+ down the respiratory chain for final reaction with O2 to form water generates the proton motive force used to synthesize ATP. The H+ in excess of that used in reacting with O2 and electrons to form water is released to the environment, causing acidification [14]. Reverse transport is used to transfer e from NH + to NADH as in S0 oxidation. Large amounts of NH+ must be oxidized, and large amounts of H+ are released into the environment during N oxidation from NH+ to NO3 (nitrification) to reduce CO2 for CH2O production [15]. In contrast, H+ is not released during oxidation of NO2 to NO3 (Table 9.9, Eq. [16]). Consequently one should not conclude that all chemolithotrophic oxidation reactions release H+ into the soil environment.

As with S oxidation, it is instructive to estimate how much N must be oxidized to provide energy to synthesize microbial biomass of nitrifiers. To this end the quantities of N that would be oxidized for combined energy and C reduction by Nitrosomonas spp. are estimated in Table 9.10 and for Nitrobacter spp. in Table 9.11. From Eq. [14] there could be 270.7/75 = 3.6 mol ATP moE1 of NH+ oxidized (ATP/2e~ = 1.2). The net estimate is that 12 mol of H+ are released, and 4 mol of C are reduced for every 6 mol of NH+ oxidized to NO2 (Eq. [18]). This NO2 rarely accumulates in soil; it is further oxidized to NO3 (Eq. [19]). Less energy is obtained by oxidizing a mole of NO2 (Eq. [16]) than is obtained by oxidizing a mole of NH+ (Eq. [14]). This partly reflects the smaller number of

TABLE 9.8 NH4 Oxidation both for Energy and for Reduction of CO2in Autotrophic Chemolithotrophs such as Nitrosomonas spp.


NH+ -

Was this article helpful?

0 0
Worm Farming

Worm Farming

Do You Want To Learn More About Green Living That Can Save You Money? Discover How To Create A Worm Farm From Scratch! Recycling has caught on with a more people as the years go by. Well, now theres another way to recycle that may seem unconventional at first, but it can save you money down the road.

Get My Free Ebook

Post a comment