Enterococcus faecium QU 50: a novel thermophilic lactic acid bacterium for high-yield l-lactic acid production from xylose

Production of optically pure lactic acid from lignocellulosic material for commercial purposes is hampered by several difficulties, including heterofermentation of pentose sugars and high energy consumption by mesophilic lactic acid bacteria. Here, we report a novel lactic acid bacterium, strain QU 50, that has the potential to produce optically pure l-lactic acid (≥99.2%) in a homofermentative manner from xylose under thermophilic conditions. Strain QU 50 was isolated from Egyptian fertile soil and identified as Enterococcus faecium QU 50 by analyzing its sugar fermentation pattern and 16S rRNA gene sequence. Enterococcus faecium QU 50 fermented xylose efficiently to produce lactic acid over wide pH (6.0–10.0) and temperature ranges (30–52°C), with a pH of 6.5 and temperature of 50°C being optimal. To our knowledge, this is the first report of homofermentative lactic acid production from xylose by a thermophilic lactic acid bacterium. A novel thermophilic l-lactic acid bacterium, Enterococcus faecium QU 50, was isolated. Strain QU 50 showed high lactic acid yield (∼1.0 g g−1) from several lignocellulose-derived sugars. QU 50 produced l-lactic acid homofermentatively (∼1.0 g g−1 yield) from low-concentration xylose. QU 50 showed efficient fermentation at 50°C. QU 50 is the only thermophilic LAB strain that utilizes hexose and pentose sugars homofermentatively.