High Improvement in Lactic Acid Productivity by New Alkaliphilic Bacterium Using Repeated Batch Fermentation Integrated with Increased Substrate Concentration.

Abstract

Optically pure lactic acid (LA) is an important chemical platform that has a wide range of industrial and biotechnological applications. Improved parameters for cost effective LA production are of great interest for industrial developments. In the present study, an alkaliphilic lactic acid bacterium, BoM 1-2, was selected among 369 newly obtained bacterial isolates. It was characterized using API 50 CHL kit and identified as Enterococcus hirae BoM 1-2 by 16S rRNA gene sequence analysis. Efficient polymer-grade L-lactic acid production was achieved at pH 9.0 and 40°C. In batch fermentation strategy using 20 g L−1 glucose, 19.6 g L−1 lactic acid was obtained with volumetric productivity of 2.18 g L−1 h−1. While using 100 g L−1 glucose, 96.0 g L−1 lactic acid was obtained with volumetric productivity of 1.07 g L−1 h−1. The highest lactic acid concentration of 180.6 g L−1 was achieved in multipulse fed batch strategy with volumetric productivity of 0.65 g L−1 h−1. To achieve higher productivity, repeated fermentation processes were applied using the two different strategies. In the first strategy, the lactic acid productivity was increased from 1.97 g L−1 h−1 to 4.48 g L−1 h−1 when the total of 10 repeated runs were carried out using 60 g L−1 glucose, but lactic acid productivity decreased to 2.95 g L−1 h−1 using 100 g L−1 glucose. In second strategy, repeated fermentation coupled with gradual increase in glucose concentration from 40 to 100 g L−1 was conducted for 24 runs. A dramatic increase in LA productivity up to 39.9 g L−1 h−1 (18-fold compared to first run) was achieved using 40 g L−1 glucose while volumetric productivity ranging between 24.8 and 29.9 g L−1 h−1 was achieved using 60–100 g L−1 glucose.