Pnl. Lens et al., PROPIONATE DEGRADATION BY MESOPHILIC ANAEROBIC SLUDGE - DEGRADATION PATHWAYS AND EFFECTS OF OTHER VOLATILE FATTY-ACIDS, Journal of fermentation and bioengineering, 82(4), 1996, pp. 387-391
The degradation of volatile fatty acids by flocculant mesophilic (35 /- 2 degrees C) syntrophic sludge grown in an anaerobic hybrid reactor
fed with a mixture of propionate, n-butyrate and ethanol (1:1:2 on CO
D basis) at a volumetric loading rate of 3.7 kg COD per m(3) per day w
as examined. The propionate degradation rate amounted to 1.1 mmol per
g volatile suspended solids per day. The same propionate degradation r
ate was measured in the presence of 10 mM acetate, but it decreased by
30% when 10 mM n-butyrate was added. C-13-Nuclear magnetic resonance
spectroscopy demonstrated interconversion of 1% to 10% of both the pro
pionate and butyrate pool, during their simultaneous degradation. Prop
ionate formation from [2-C-13]butyrate was not via a direct decarboxyl
ation. C-13-Propionate was converted via at least three different path
ways. The first pathway was syntrophic conversion of propionate via th
e randomising pathway, evidenced by scrambling of [3-C-13]propionate i
nto [2-C-13]propionate. Secondly, reductive carboxylation occurred, i.
e. [3-C-13]propionate and [2,3-C-13]propionate were partly (2 to 10%)
converted into [4-C-13]butyrate and [3,4-C-13]butyrate, respectively.
Reductive carboxylation probably involved a transcarboxylase, as C-13-
bicarbonate was not incorporated in the carboxyl group of butyrate. Th
irdly, propionate was converted into higher fatty acids: [2,3-C-13]pro
pionate was converted into [4,5-C-13]valerate and 2-methyl[2,3-C-13]bu
tyrate.