Abstract
1,3-xylan is present in the cell walls of some red and green algae and is an important organic carbon in the ocean. However, information on its bacterial degradation is quite limited. Here, after enrichment with 1,3-xylan, the diversity of bacteria recovered from marine algae collected in Hainan, China, was analyzed with both the 16S rRNA gene amplicon sequencing and the culture-dependent method. Bacteria recovered were affiliated with more than 19 families mainly in phyla Proteobacteria and Bacteroidetes, suggesting a high bacterial diversity. Moreover, 12 strains with high 1,3-xylanase-secreting ability from genera Vibrio, Neiella, Alteromonas, and Gilvimarinus were isolated from the enrichment culture. The extracellular 1,3-xylanases secreted by Vibrio sp. EA2, Neiella sp. GA3, Alteromonas sp. CA13-2, and Gilvimarinus sp. HA3-2, which were taken as representatives due to their efficient utilization of 1,3-xylan for growth, were further characterized. The extracellular 1,3-xylanases secreted by these strains showed the highest activity at pH 6.0–7.0 and 30–40°C in 0–0.5M NaCl, exhibiting thermo-unstable and alkali-resistant characters. Their degradation products on 1,3-xylan were mainly 1,3-xylobiose and 1,3-xylotriose. This study reveals the diversity of marine bacteria involved in the degradation and utilization of 1,3-xylan, helpful in our understanding of the recycling of 1,3-xylan driven by bacteria in the ocean and the discovery of novel 1,3-xylanases.
Highlights
Marine algae generate approximately 104.9 petagram organic carbon per year that mainly deposit as polysaccharides, the most promising candidates for biomass conversion (Field et al, 1998; Hehemann et al, 2014)
We investigated the diversity of 1,3-xylan-utilizing bacteria associated with marine algae Caulerpa sp. and Chaetomorpha sp. and characterized the extracellular 1,3-xylanases secreted by several representative strains
For 1,3-xylan, the main structural constituent in the cell walls of some red and green algae (Iriki et al, 1960; Veluraja and Atkins, 1987), only 4 1,3-xylanasesecreting bacteria have been isolated from marine sources including Vibrio sp
Summary
Marine algae generate approximately 104.9 petagram organic carbon per year that mainly deposit as polysaccharides, the most promising candidates for biomass conversion (Field et al, 1998; Hehemann et al, 2014). In the cell walls of land plants, xylans are the most abundant polysaccharides secondary to cellulose. 1,3-xylanases (EC 3.2.1.32), capable of cleaving the β-1,3xylosidic linkages in 1,3-xylan, are crucial in the degradation and recycling of 1,3-xylan in the ocean They represent a vast potential for algal biomass conversion, functional xylooligosaccharides production, and protoplast preparation (Araki et al, 1994; Maeda et al, 2012; Umemoto et al, 2012). All the discovered 1,3-xylanases belong to glycoside hydrolase (GH) family 26 according to the assignment in the Carbohydrate Active Enzymes (CAZy) database (Lombard et al, 2014).1 Despite these studies, bacterial degradation on 1,3-xylan is still a largely unexplored field. The diversity of marine bacteria participating in the degradation and utilization of 1,3-xylan still lacks investigation, and more 1,3-xylanasesecreting bacteria and 1,3-xylanases await discovery and exploitation
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