Clostridium beijerinckii is a remarkable biocatalyst that can perform Acetone-Butanol-Ethanol (ABE) fermentation. Nevertheless, some C. beijerinckii strains lose the capacity to produce butanol. Here, we compare xylose fermentation in the presence of acetic acid and butyric acid by two C. beijerinckii strains: Br21 and ATCC 35702. The former strain is non-solventogenic (it lacks the adc gene for acetoacetate decarboxylase), whereas the latter is a known solventogenic strain capable of ABE fermentation. Fermentation of xylose alone and with acetic acid, butyric acid, or acetic and butyric acid supplementation revealed differences between strains Br21 and ATCC 35702 in terms of product profile. Strain Br21 consumed six times more acetic acid than strain ATCC 35702. External butyric acid addition helped strain ATCC 35702 to enhance butanol generation. However, butyric acid supplementation did not affect strain Br21, which was not able to reassimilate butyric acid to produce butanol. Expression of acidogenic enzymes revealed that acetoacetyl-CoA-acetate/butyrate-CoA-transferase was a key enzyme for butyric acid evolution by strain Br21. Besides xylose fermentation, strain Br21 was able to use acetic acid, a biomass hydrolysis derivative, to form butyric acid as the only fermentation product. Although C. beijerinckii Br21 was unable to form butanol, it is a promising biocatalyst for obtaining butyric acid through an unconventional pathway involving xylose fermentation and acetate assimilation.

拜氏梭菌是一种卓越的生物催化剂，可以进行丙酮-丁醇-乙醇 (ABE) 发酵。然而，一些C. beijerinckii菌株失去了生产丁醇的能力。在这里，我们比较了两种拜氏梭菌菌株在乙酸和丁酸存在下的木糖发酵：Br21 和 ATCC 35702。前一种菌株是非溶剂型的（它缺少adc乙酰乙酸脱羧酶基因），而后者是已知的能够进行 ABE 发酵的产溶剂菌株。木糖单独发酵以及与乙酸、丁酸或补充乙酸和丁酸一起发酵揭示了菌株 Br21 和 ATCC 35702 在产品概况方面的差异。菌株 Br21 消耗的乙酸是菌株 ATCC 35702 的六倍。外部丁酸添加有助于菌株 ATCC 35702 提高丁醇生成。然而，丁酸补充剂不影响菌株 Br21，该菌株不能重新同化丁酸以生产丁醇。产酸酶的表达表明，乙酰乙酰-CoA-乙酸/丁酸-CoA-转移酶是菌株 Br21 产生丁酸的关键酶。除了木糖发酵，菌株 Br21 还能够使用乙酸，一种生物质水解衍生物，形成丁酸作为唯一的发酵产物。虽然C. beijerinckii Br21 不能形成丁醇，它是一种很有前途的生物催化剂，可通过木糖发酵和乙酸同化等非常规途径获得丁酸。