Ratio of <span style="font-variant: small-caps">l</span>-(+)- and <span style="font-variant: small-caps">d</span>-(−)-Lactic Acids Produced by <i>Enterococcus faecalis</i> Changes Depending on the Culture pH
<i>Enterococcus faecalis</i> (<i>E. faecalis</i>) has been associated with the specific production of <span style="font-variant: small-caps;">l</span>-(+)-lactic acid. However, in this study, <span style="font-variant: small-caps;">d</...
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| Main Authors: | , |
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| Format: | Article |
| Language: | English |
| Published: |
MDPI AG
2024-12-01
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| Series: | Microbiology Research |
| Subjects: | |
| Online Access: | https://www.mdpi.com/2036-7481/15/4/179 |
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| Summary: | <i>Enterococcus faecalis</i> (<i>E. faecalis</i>) has been associated with the specific production of <span style="font-variant: small-caps;">l</span>-(+)-lactic acid. However, in this study, <span style="font-variant: small-caps;">d</span>-(−)-lactic acid production by <i>E. faecalis</i> was observed under specific pH conditions. <i>E. faecalis</i> PR31 exhibited a significant amount of <span style="font-variant: small-caps;">d</span>-(−)-lactic acid under a stirring culture in MRS broth at pH 4.5, 5.8, and 6.0, and the contents of <span style="font-variant: small-caps;">d</span>-(−)-lactic acid were 45.1, 35.9, and 36.2%, respectively. When the cell suspension prepared at a pH of 6.0 was reacted with <span style="font-variant: small-caps;">l</span>-(+)- or <span style="font-variant: small-caps;">d</span>-(−)-lactic acid, <span style="font-variant: small-caps;">d</span>-(−)- or <span style="font-variant: small-caps;">l</span>-(+)-lactic acid was produced, respectively, in a time- and dose-dependent manner. Therefore, this phenomenon of <span style="font-variant: small-caps;">d</span>-(−)-lactic acid production in PR31 was suggested to be due to the activation of the <i>larA</i> gene encoding lactate racemase that is present in PR31. However, even in the <i>E. faecalis</i>-type strain NBRC 100480, which contains neither <i>larA</i> nor <i>vanH,</i> encoding <span style="font-variant: small-caps;">d</span>-(−)-lactate dehydrogenase VanH, <span style="font-variant: small-caps;">d</span>-(−)-lactic acid was also produced at specific pH values. Therefore, the production of <span style="font-variant: small-caps;">d</span>-(−)-lactic acid in NBRC 100480 was thought to occur not via the activation of <i>larA</i>. The biological significance of <span style="font-variant: small-caps;">d</span>-(−)-lactic acid production in <i>E. faecalis</i> depending on the pH and the detailed underlying mechanism, including whether it is the same in PR31 and NBRC 100480, remain to be elucidated in future studies. |
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| ISSN: | 2036-7481 |