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Updated: Jan 28, 2026

Characterizing Extracellular Vesicles from Biological Fluids
Published on: February 28, 2025
Characterization of a novel extracellular α-amylase from Ruminococcus bromii ATCC 27255 with neopullulanase-like
Jong-Hyun Jung1, Yu-Kyung An2, Su-Yeong Son2
1Research Division for Biotechnology, Korea Atomic Energy Research Institute, Jeongeup 56212, Republic of Korea; Department of Radiation Science and Technology, University of Science and Technology, Daejeon 34113, Republic of Korea.
Abstract:
Ruminococcus is one of the keystone bacteria of the human colonic microbiota and is highly specific for utilization of resistant starch via formation of amylosomes. Here, we present the characteristics of an extracellular amylase, Rbamy5, in Ruminococcus bromii. In an in silico study, it showed low homology with any other known amylases, but it was evolutionarily classified as a GH13_36 subfamily intermediary amylase. Recombinant Rbamy5 exhibited maximum activity toward amylose (384 ± 26 U·mg-1) over soluble starch (254 ± 3 U·mg-1), amylopectin (46.1 ± 2.6 U·mg-1) and pullulan (72.5 ± 0.41 U·mg-1) at 45 °C and pH 5.0. It was also able to degrade small substrates such as maltotriose (G3), maltotetraose (G4), and maltopentaose (G5) into maltose (G2). Despite lacking a specific N-terminal domain, Rbamy5 opened the cyclodextrin ring, which resembles those of neopullulanase. Moreover, it accumulated short α-(1 → 6)-branched maltooligosaccharides from soluble starch and maltosyl-β-cyclodextrin (G2-β-CD), while panose was solely derived from pullulan. These results suggest that Rbamy5 may have a role to provide branched maltooligosaccharides to stimulate the growth of beneficial microorganisms in the human intestine.
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