Researchers have discovered two novel marine bacteria, Halosquirtibacter laminarini and Halosquirtibacter xylanolyticus, that possess remarkable abilities to break down tough polysaccharides like laminarin and xylan. These findings could have significant implications for understanding the role of marine bacteria in the global carbon cycle and exploring their potential in biotechnological applications.
The ocean is a vast, unexplored frontier, teeming with diverse and fascinating microbial life. Among these marine microbes, a group known as the Bacteroidota plays a crucial role in the global carbon cycle by degrading a wide range of polysaccharides, the complex carbohydrates that make up the structural components of marine organisms.
Researchers from the Korea Research Institute of Bioscience and Biotechnology have now discovered two novel marine bacteria, Halosquirtibacter laminarini and Halosquirtibacter xylanolyticus, that belong to the Bacteroidota phylum. These bacteria were isolated from a sea squirt, a filter-feeding marine animal, and possess remarkable abilities to degrade polysaccharides like laminarin and xylan.
Laminarin and Xylan: Tough Polysaccharides
Laminarin is a highly abundant polysaccharide found in brown algae and some microalgae, with an estimated annual production of 12-18 gigatons globally. It is a complex molecule composed of β-(1→3)-linked glucose chains with some β-(1→6)-linked side chains. Degrading laminarin is a challenging task, as it requires specialized enzymes that can cleave both the main chain and the side chains.
Xylan, on the other hand, is the most abundant form of hemicellulose found in nature, occurring in both marine and terrestrial environments. The backbone of marine xylan mainly consists of 1,3-glycoside bonds, making it even more resistant to biological degradation.
Uncovering the Secrets of Polysaccharide Degradation
The researchers conducted a comprehensive investigation, combining genome analysis and in vitro experiments, to understand how these novel marine bacteria degrade laminarin and xylan.
Genome mining revealed that the two novel isolates, Halosquirtibacter laminarini and Halosquirtibacter xylanolyticus, harbor a remarkable arsenal of carbohydrate-active enzymes (CAZymes), with a particularly high abundance of glycoside hydrolases (GHs) – the enzymes responsible for breaking down the glycosidic bonds in polysaccharides.
In vitro experiments demonstrated that Halosquirtibacter laminarini could utilize laminarin as its sole carbon source, while Halosquirtibacter xylanolyticus could degrade both laminarin and xylan. Further analysis revealed that the laminarin-degrading enzymes in both strains were cell-associated and exhibited exo-hydrolytic activity, releasing glucose as the primary product. The xylan-degrading enzymes of Halosquirtibacter xylanolyticus, on the other hand, were also cell-associated and had endo-hydrolytic activities, releasing xylotriose and xylotetraose as the main products.
Implications for Understanding Marine Carbon Cycling
The discovery of these novel marine bacteria with their exceptional polysaccharide-degrading capabilities could have significant implications for our understanding of the marine carbon cycle. As the Bacteroidota group is known to be one of the most abundant in marine ecosystems, the ability of Halosquirtibacter laminarini and Halosquirtibacter xylanolyticus to anaerobically degrade laminarin and xylan could play a crucial role in sequestering carbon within the marine environment.
Furthermore, the insights gained from this study could inform future biotechnological applications, such as the development of enzymes for the production of biofuels, biomedicine, and food supplements from renewable marine resources.
Expanding the Frontiers of Marine Microbiology
The discovery of these novel marine bacteria highlights the vast untapped potential of the ocean’s microbial diversity. By employing innovative isolation techniques and combining genomic and biochemical analyses, researchers are unveiling the secrets of how marine bacteria contribute to the global carbon cycle and unraveling their potential for various biotechnological applications.
As we continue to explore the rich and diverse microbial life in the ocean, we can expect more groundbreaking discoveries that could revolutionize our understanding of the marine ecosystem and unlock new avenues for sustainable development.
Author credit: This article is based on research by Tra T. H. Nguyen, Tien Q. Vuong, Ho Le Han, Song-Gun Kim.
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