Cultivable alginate lyase-excreting bacteria associated with the Arctic brown alga Laminaria.

Sheng Dong,Mei Shi,Xiao-Yan Song,Xiu-Lan Chen,Jie Yang,Yu-Zhong Zhang,Xi-Ying Zhang

doi:10.3390/md10112481

Abstract

Although some alginate lyases have been isolated from marine bacteria, alginate lyases-excreting bacteria from the Arctic alga have not yet been investigated. Here, the diversity of the bacteria associated with the brown alga Laminaria from the Arctic Ocean was investigated for the first time. Sixty five strains belonging to nine genera were recovered from six Laminaria samples, in which Psychrobacter (33/65), Psychromonas (10/65) and Polaribacter (8/65) were the predominant groups. Moreover, 21 alginate lyase-excreting strains were further screened from these Laminaria-associated bacteria. These alginate lyase-excreting strains belong to five genera. Psychromonas (8/21), Psedoalteromonas (6/21) and Polaribacter (4/21) are the predominant genera, and Psychrobacter, Winogradskyella, Psychromonas and Polaribacter were first found to produce alginate lyases. The optimal temperatures for the growth and algiante lyase production of many strains were as low as 10–20 °C, indicating that they are psychrophilic bacteria. The alginate lyases produced by 11 strains showed the highest activity at 20–30 °C, indicating that these enzymes are cold-adapted enzymes. Some strians showed high levels of extracellular alginate lyase activity around 200 U/mL. These results suggest that these algiante lyase-excreting bacteria from the Arctic alga are good materials for studying bacterial cold-adapted alginate lyases.

Highlights

Alginate is a liner unbranched copolymer of α-L-guluronate (G) and its C5 epimer, β-D-mannuronate (M), arranged in block structures such as homopolymeric G block, M block, alternating MG (GM) block, and heteropolymeric MG (GM) block [1]
Alginate lyases are classified into three groups by their substrate specificity: the first type is specific toward G block (EC4.2.2.11), the second type is specific toward M block (EC4.2.2.3), and the third type is bifunctional for G and M block
Diversity of Bacteria Associated with the Arctic Brown Alga Laminaria

Summary

Introduction

Alginate is a liner unbranched copolymer of α-L-guluronate (G) and its C5 epimer, β-D-mannuronate (M), arranged in block structures such as homopolymeric G block, M block, alternating MG (GM) block, and heteropolymeric MG (GM) block [1]. Alginate lyases degrade alginate by a β-elimination mechanism that generate a product containing. 4-deoxy-L-erythro-hex-4-enopyranosyluronic acid as the non-reducing terminal moiety [4]. The non-reducing end groups of the products generate an increasing absorbance at 235 nm, which can be used to monitor real-time alginate lyase activity [5,6]. Alginate lyases are grouped into three classes by their molecular masses: 20–35 kDa class, ~40 kDa class, and ~60 kDa class [7]. Based on their primary structures, alginate lyases are classified into seven families (PL5, 6, 7, 14, 15, 17 and 18) [8]

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