Abstract
BackgroundStarch is an inexpensive and renewable raw material for numerous industrial applications. However, most starch-based products are not cost-efficient due to high-energy input needed in traditional enzymatic starch conversion processes. Therefore, α-amylase with high efficiency to directly hydrolyze high concentration raw starches at a relatively lower temperature will have a profound impact on the efficient application of starch.ResultsA novel raw starch digesting α-amylase (named AmyZ1) was screened and cloned from a deep-sea bacterium Pontibacillus sp. ZY. Phylogenetic analysis showed that AmyZ1 was a member of subfamily 5 of glycoside hydrolase family 13. When expressed in Escherichia coli, the recombinant AmyZ1 showed high activity at pH 6.0–7.5 and 25–50 °C. Its optimal pH and temperature were 7.0 and 35 °C, respectively. Similar to most α-amylases, AmyZ1 activity was enhanced (2.4-fold) by 1.0 mM Ca2+. Its half-life time at 35 °C was also extended from about 10 min to 100 min. In comparison, AmyZ1 showed a broad substrate specificity toward raw starches, including those derived from rice, corn, and wheat. The specific activity of AmyZ1 towards raw rice starch was 12,621 ± 196 U/mg, much higher than other reported raw starch hydrolases. When used in raw starch hydrolyzing process, AmyZ1 hydrolyzed 52%, 47% and 38% of 30% (w/v) rice, corn, and wheat starch after 4 h incubation. It can also hydrolyze marine raw starch derived from Chlorella pyrenoidosa, resulting in 50.9 mg/g DW (dry weight of the biomass) of reducing sugars after 4 h incubation at 35 °C. Furthermore, when hydrolyzing raw corn starch using the combination of AmyZ1 and commercial glucoamylase, the hydrolysis rate reached 75% after 4.5 h reaction, notably higher than that obtained in existing starch-processing industries.ConclusionsAs a novel raw starch-digesting α-amylase with high specific activity, AmyZ1 efficiently hydrolyzed raw starches derived from both terrestrial and marine environments at near ambient temperature, suggesting its application potential in starch-based industrial processes.
Highlights
Starch is an inexpensive and renewable raw material for numerous industrial applications
Phylogenetic analysis suggested that the 16S rRNA gene of strain ZY showed 99% sequence identity to the marine bacteria Pontibacillus halophilus JSM 076056
Pontibacillus sp., implicating “Bacillus affiliated with the marine”, was a novel genus identified for the first time in 2005 [23,24,25]
Summary
Starch is an inexpensive and renewable raw material for numerous industrial applications. Α-Amylase (EC 3.2.1.1) is one of the oldest and most important industrial enzymes used for starch processing [1]. The usage of α-amylase digesting raw starch brings about 10–20% reduction in energy consumption compared to the traditional physical/chemical processes [3, 5]. Only approximately 10% of the known α-amylases can efficiently digest raw starches directly to glucose because of their densely compacted architecture, large size, and unique surface profile [2, 3]. It is essential to explore novel α-amylases with higher specific activity toward raw starches to decrease the dosage and cost on the enzyme [15]
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