Complex medium enriched for production of VFAs through lactic
acid formation and consumption and is linked with lactic acid bacteria
and Megasphaera
Evaluating the pathways for the complex medium enrichment showed a best
fit when glucose was catabolised through the heterofermentative (69%)
and homofermentative (31%) pathway (Table S5). Lactate was subsequently
fermented into propionate, butyrate, valerate, H2 and
CO2. The secondary lactate fermentation was confirmed in
a batch experiment with the enrichment culture and replacing glucose
with lactate (Figure S5). The microbial community analysis revealed a
dominance of Lactobacillus , Lactococcus andMegasphaera (Figure 3B, 3C and 3E).
Lactococcus species are known homofermentative lactic acid
bacteria, while Lactobacillus and Leuconostoc species can
also be heterofermentative (Madigan and Martinko, 2006).Megasphaera elsdenii is known to produce acetate, propionate,
butyrate and valerate from lactate (Prabhu et al., 2012).Megasphaera is known to convert lactate in the intestinal tract
of cows, pigs and humans (Duncan et al., 2004) and is linked to
lactate-mediated medium-chain length carboxylate production microbiomes
(Spirito et al., 2014). Megasphaera elsdenii interestingly
prefers lactate uptake over glucose uptake, taking up limited amounts of
glucose when lactate is present (Marounek et al., 1989), which argues
for the Megasphaera species having a mainly lactate consuming
role in the community.