Saccharophagus degradans 2-40
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Microbulbifer degradans has been renamed to Saccharophagus degradans 2-40. The paper is currently in press at IJSEM.

In terrestrial habitats, a specialized group of microorganisms participate in the degradation of a significant portion of the more than 52 billion tons of cellulose that accumulate yearly by producing powerful, hydrolytic structures termed cellulosomes. Cellulosomes are exo- and extracellular multienzyme arrays that organize the cellulolytic enzymes for a concerted attack on the complex carbohydrate, so that cellulose hydrolysis occurs much more efficiently. Polycellulosomal "organelles" adorn the cell surface, appearing as protuberances.

In the oceans, comprising most of the biosphere, less is known about how the annual production of the more than 25 billion tons of complex carbohydrates, especially those associated with biofilms, planktonic organisms, algal blooms and shells of benthic invertebrates, is recycled to usable carbon. Most of these complex carbohydrates are insoluble or relatively insoluble (insoluble complex polysaccharides; ICP). Like cellulose, they are generally very stable polymers. Their degradation is not governed by conventional enzymology, which deals with homogeneous, monophasic solutions.

A group of marine bacteria was recently discovered that degrades and recycles complex carbohydrates. A new species within this group of marine bacteria, Microbulbifer degradans, strain 2-40 [2-40] has been found to be capable of recycling a multitude of ICP by forming degradative surface protuberances, containing what we collectively term hydrolosomes. 2-40 protuberances morphologically resemble clostridial protuberances that contain cellulosomes and immunologically crossreact with a key cellulosomic scaffoldin protein.

We posit that the Microbulbifer group of marine bacteria utilizes cellulosome-like mechanisms to degrade ICP. We believe that 2-40 degradosomes are involved in the breakdown of many different ICP, including chitin, alginate and agarose.

The marine bacterium Microbulbifer degradans strain 2-40 was originally isolated from the salt marsh cord grass, Spartina alterniflora, in the Chesapeake Bay watershed. It is pleomorphic, Gram negative bacterium that is aerobic, rod shaped, and motile. M. degradans can degrade at least 11 relatively insoluble complex polysaccharides including agar, chitin, alginic acid, carrageenan, cellulose, B-glucan, laminarin, pectin, pullulan, starch, and xylan. In addition it synthesizes a true tyrosinase et. al. and several proteases. By 16SrRNA analysis M. degradans is a member of the gamma subclass of the phylum Proteobacteria, realted to Microbulbifer hydrolyticus and to cellulolytic nitrogen fixing bacteria that are symbionts of shipworms.

We have shown that the chitinase, agarase and alginase produced by M. degradans are not exported into the extracellular medium as freely diffusible enzymes but are, instead, localized in surface protuberances morphologically resembling protuberances synthesized by some cellulolytic clostridia. Agarase, chitinases, and alginases were each shown to be assembled into unique and distinguishable surface protuberances, which bind the substrate and presumably degrade it.

The fact that M. degradans degrades more complex carbohydrates than reported for any other bacteria makes it useful for a number of applications. As human population pressure build and more food is required, agricultural, aquacultural, and algalcultural wastes threaten to become an increasingly serious problem. The wastes are mostly recalcitrant complex carbohydrates, namely cellulose, chitin and agar. Trillions of tons of chitin (Alexander, 1977), algal slimes and agricultural waste accumulate annually in the natural environment. In many developing nations, there is also a severe shortage of feedstock. The complex carbohydrates from natural and human practices are composed of monosaccharides, many of which can provide valuable feedstock when hydrolyzed. The degradative protuberances of M. degradans may become important bioremediation tools, using them as concentrated, organized, protective enzyme packets.