Bench scale production of nicotinic acid using a versatile amide-hydrolysing Geobacillus subterraneus RL-2a isolated from thermal spring of Manikaran, India

• Biotransformation of nicotinamide to nicotinic acid, in 1 l scale fed batch reactor.
• This is the first reported Geobacillus subterraneus species having amidase activity.
• This is first reported broad substrate spectrum amidase from Geobacillus sp.
• Amidase with deactivation constant (kd) and enzyme t1/2 of 4.15 × 10−5 s−1 and 6 h 4 min.
• The amidase showed activity at wide range of temperature (40–90 °C) and pH (4.5–13).

A new thermostable amidase-producing isolate identified as Geobacillus subterraneus RL-2a has been studied extensively for the optimization of enzyme operational conditions in the production of nicotinic acid in fed batch mode. The amidase of G. subterraneus RL-2a is constitutive in nature, active at broad pH (pH 4.5–13.0), temperature (40–90 °C) with optimal activity at 70 °C and pH 6.5. The enzyme was fairly stable at 70 °C with a deactivation constant (kd) and enzyme half-life of 4.15 × 10−5 s−1 and 6 h 4 min. Another advantage of this enzyme was its broad substrate specificity, including aliphatic, aromatic and amino acid amides respectively. In a fed batch reaction at one litre scale using resting cells corresponding to 8 U ml−1 amidase activity (7.76 mg dcw ml−1), a total of 88.6 g nicotinic acid was produced at a rate of 2.85 g h−1 g−1 dcw. This thermostable amidase represents the first reported broad substrate spectrum amidase with exceptional thermostability from a thermophilic G. subterraneus RL-2a.

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