3.2 Efficient bioconversion of xylose into succinic acid byA. succinogenes 130Z
Previous studies have shown that A. succinogenes 130Z could
consume a broad range of substrates including C6 (e.g., glucose) and C5
sugars (e.g., xylose) (Salvachúa et al., 2016). Especially, A.
succinogenes 130Z showed comparable xylose utilization efficiency as
glucose. However,A. succinogenes 130Z could
not directly utilize xylan due to the lack of related hydrolases. As
seen in Fig 3A,A. succinogenes 130Z could
generate approximately 45.56 g/L of succinic acid from 80 g/L xylose
with yield and productivity of 0.57 g/g and 0.63 g/L/h, respectively.
The highest xylose utilization rate
reached 1.93 g/L/h, which is comparable to that using glucose as the
substrate (data not shown). When xylose concentration was further
increased to 100 g/L, succinic acid production was also decreased. It
should be noticed that succinic aid yield was decreased when xylose
concentration exceeded 40 g/L.
As mentioned, T.
thermosaccharolyticum M5 would be a good partner to achieve succinic
acid production from hemicellulosic materials owning to its
efficient xylan degradation
capability. The xylose production rate ofT. thermosaccharolyticum M5
and xylose consumption rate ofA. succinogenes 130Z were accordingly compared. As shown in
Fig 3B, the xylose consumption rate
of A. succinogenes 130Z
reached the highest 1.93 g/L/h
during the first 24 h and tends to be stabilized after 72 h. While the
xylose production rate of T. thermosaccharolyticum M5 was
basically stable at 0.60 g/L/h, suggesting that xylose was continuously
secreted. Therefore, the higher xylose consumption rate of A.
succinogenes 130Z would eliminate enzymes activities inhibition ofT. thermosaccharolyticum M5, as xylose could be simultaneously
consumed when A. succinogenes 130Z and T.
thermosaccharolyticum M5 were co-cultivated together. Indeed, xylanase
and β-xylosidase activities could maintain at 0.38-0.43 U/mL and
6.02-7.34 U/mL during the fermentation period.