What Is Flavobacterium johnsoniae and Why Is It Important?

Flavobacterium johnsoniae is a common bacterium from the phylum Bacteroidetes, found in soil and fresh water. It serves as a model for understanding specific biological functions, and its ability to move and digest complex materials makes it a focus of research into microbial processes.

Defining Flavobacterium johnsoniae

Initially known as Cytophaga johnsonae, this organism is a Gram-negative, rod-shaped bacterium. When grown in a laboratory setting on agar plates, it forms characteristic yellow-pigmented colonies. Its genome contains the genetic instructions for many enzymes that break down large biological molecules like chitin and cellulose. Chitin, a major component of insect exoskeletons and fungal cell walls, is one of the most abundant polymers on Earth.

F. johnsoniae thrives in soil and freshwater ecosystems, often on the surfaces of aquatic organisms. The bacterium’s method of digestion requires direct cell contact with these insoluble substances.

Environmental Presence and Functions

In its natural environment, Flavobacterium johnsoniae plays a part in nutrient cycling. As a decomposer, it breaks down complex organic materials like proteins and polysaccharides, releasing simpler compounds that other organisms can then use. This function is a component of the carbon cycle in the microbial communities where it resides.

The bacterium lives a saprophytic lifestyle, meaning it feeds on dead or decaying organic matter. Its motility allows it to seek out and attach to substrates like decaying plant material or chitinous remains.

This organism coexists with other microorganisms in soil and water, where its role as a decomposer influences the community structure. By breaking down complex polymers that are inaccessible to many other microbes, it helps to sustain the local food web and recycle nutrients.

The Distinctive Gliding Motility

A defining feature of Flavobacterium johnsoniae is its ability to perform gliding motility, a form of movement across surfaces that does not rely on flagella. This allows the bacterium to spread rapidly over solid and semi-solid environments, forming thin, expanding colonies. This movement enables the bacterium to actively explore its surroundings for nutrients and colonize new areas.

The molecular machinery driving this gliding is complex and involves a protein secretion system known as the Type IX Secretion System (T9SS). This system transports proteins across the cell envelope to the cell surface. One of these surface proteins is an adhesin called SprB, which functions like a track that moves along the cell body, propelling the bacterium forward. The SprB protein is moved by the energy generated from the T9SS apparatus.

This motility is directly linked to the bacterium’s ability to digest large, insoluble nutrients. Research has shown that mutants unable to glide also have defects in their ability to use chitin, suggesting that gliding is necessary to bring the cell’s digestive enzymes into close contact with their targets.

Scientific and Practical Significance

The biological systems of Flavobacterium johnsoniae make it a valuable model organism for scientific research. It is useful for studying bacterial gliding motility, the degradation of polysaccharides, and the function of the Type IX Secretion System. Genetic tools have been developed to manipulate the bacterium, allowing researchers to dissect the genes and proteins involved in these processes.

While not a threat to humans, some Flavobacterium strains are pathogenic to fish, causing conditions like bacterial gill disease. Studying F. johnsoniae can help in understanding these related pathogens and developing strategies to protect aquaculture environments.

The bacterium’s ability to produce enzymes for breaking down polymers has attracted biotechnological interest. These enzymes, such as chitinases and proteases, could be used for industrial applications, including waste treatment and the production of biofuels from plant biomass. The study of F. johnsoniae also reveals potential uses in bioremediation, where its digestive capabilities could be applied to clean up environmental pollutants.