Ali Sameh Samir, Wu Jian, Xie Rongrong, Zhou Feng, Sun Jianzhong, Huang Miao
Biofuels Institute, School of the Environment and Safety Engineering, Jiangsu University, Zhenjiang, China.
Botany Department, Faculty of Science, Tanta University, Tanta, Egypt.
PLoS One. 2017 Jul 13;12(7):e0181141. doi: 10.1371/journal.pone.0181141. eCollection 2017.
The effective fermentation of xylose remains an intractable challenge in bioethanol industry. The relevant xylanase enzyme is also in a high demand from industry for several biotechnological applications that inevitably in recent times led to many efforts for screening some novel microorganisms for better xylanase production and fermentation performance. Recently, it seems that wood-feeding termites can truly be considered as highly efficient natural bioreactors. The highly specialized gut systems of such insects are not yet fully realized, particularly, in xylose fermentation and xylanase production to advance industrial bioethanol technology as well as industrial applications of xylanases. A total of 92 strains from 18 yeast species were successfully isolated and identified from the gut of wood-feeding termite, Reticulitermes chinensis. Of these yeasts and strains, seven were identified for new species: Candida gotoi, Candida pseudorhagii, Hamamotoa lignophila, Meyerozyma guilliermondii, Sugiyamaella sp.1, Sugiyamaella sp. 2, and Sugiyamaella sp.3. Based on the phylogenetic and phenotypic characterization, the type strain of C. pseudorhagii sp. nov., which was originally designated strain SSA-1542T, was the most frequently occurred yeast from termite gut samples, showed the highly xylanolytic activity as well as D-xylose fermentation. The highest xylanase activity was recorded as 1.73 and 0.98 U/mL with xylan or D-xylose substrate, respectively, from SSA-1542T. Among xylanase-producing yeasts, four novel species were identified as D-xylose-fermenting yeasts, where the yeast, C. pseudorhagii SSA-1542T, showed the highest ethanol yield (0.31 g/g), ethanol productivity (0.31 g/L·h), and its fermentation efficiency (60.7%) in 48 h. Clearly, the symbiotic yeasts isolated from termite guts have demonstrated a competitive capability to produce xylanase and ferment xylose, suggesting that the wood-feeding termite gut is a promising reservoir for novel xylanases-producing and xylose-fermenting yeasts that are potentially valued for biorefinery industry.
木糖的有效发酵仍是生物乙醇工业中一个棘手的挑战。工业上对相关木聚糖酶也有很高需求，用于多种生物技术应用，这不可避免地促使人们近年来努力筛选一些新型微生物，以实现更好的木聚糖酶生产和发酵性能。最近，以木材为食的白蚁似乎可被视为高效的天然生物反应器。这类昆虫高度特化的肠道系统尚未得到充分认识，特别是在木糖发酵和木聚糖酶生产方面，以推动工业生物乙醇技术以及木聚糖酶的工业应用。从以木材为食的白蚁（中国散白蚁）肠道中成功分离并鉴定出了来自18个酵母物种的92株菌株。在这些酵母和菌株中，有7种被鉴定为新物种：后藤假丝酵母、假拉格假丝酵母、嗜木滨松酵母、季也蒙毕赤酵母、杉山酵母1号、杉山酵母2号和杉山酵母3号。基于系统发育和表型特征，假拉格假丝酵母新种的模式菌株最初被指定为菌株SSA - 1542T，是白蚁肠道样本中最常见的酵母，表现出高度的木聚糖分解活性以及D - 木糖发酵能力。来自SSA - 1542T的木聚糖酶活性在以木聚糖或D - 木糖为底物时分别达到最高，为1.73和0.98 U/mL。在产木聚糖酶的酵母中，有4个新物种被鉴定为能发酵D - 木糖的酵母，其中假拉格假丝酵母SSA - 1542T在48小时内的乙醇产量最高（0.31 g/g）、乙醇生产率最高（0.31 g/L·h），其发酵效率为60.7%。显然，从白蚁肠道中分离出的共生酵母已证明具有生产木聚糖酶和发酵木糖的竞争能力，这表明以木材为食的白蚁肠道是新型产木聚糖酶和木糖发酵酵母的一个有前景的来源，这些酵母对生物精炼工业可能具有潜在价值。
