The Myxobacteria

The myxobacteria are a group of Gram negative, rod shaped organisms.  Most, in appearance, are very long and thin.  they were taxonomically lumped together with Cytophaga and their relatives (another group of interest in my research) until G+C analysis revealed that the two groups are quite unrelated.

Habitat: Myxobacteria are generally found in areas rich in organic matter, including compost and decaying vegetable matter on forest floors. There are two general classes of myxobacteria, those that degrade primarily cellulose, and those that degrade primarily protein.  It is this latter group which is the most studied.  In decaying matter, it is often other microbes that are degraded as a food for myxobacteria rather than the vegetation.  Myxobacteria are often referred to as either prdators or scavengers.  Methods used to isolate myxobacteria from these environments include incubating tree bark (from the ground) under moist conditions and looking for the characteristic fruiting bodies (more later) or using sterilized rabbit dung pellets as bait.  Such pellets are full of dead bacteria which act as the nutrient source for the myxobacteria.

Metabolism and social behavior.  Myxobacteria are strict aerobes, requiring oxygen for growth.  Their primary nutrient source is protein or amino acids, and thus they grow well on general purpose culture media, though slowly.  There seems to be a requirement for divalent cation, otherwise autolysis occurs, so a source of magnesium is usually included in the medium.  Calcium promotes clumping which is not preferred in liquid medium.  In the wild, myxobacteria engage in what is commonly known as wolfpack feeding.  Myxobacteria live in groups called swarms, and each individual cell contributes a variety of hydrolytic enzymes which breakdown proteins, cell wall components, and nucleic acids.  An individual cell does not produce enough enzyme to support itself, but the group as a whole is capable of breaking down polymers in the area.  The low molecular weight molecules that result are taken up by the myxobacteria for food.  

Social Behavior and the Life Cycle.  Myxobacteria are in constant communication with each other through a variety of means including fimbriae, long appendages made of protein with which the cells touch each other.  They move through a process called gliding motility which remains mostly unexplained.  Cells move in a coordinated way, and individual cells seldom leave the group.  When certain amino acids become scarce, and balanced growth is no longer possible, cells begin a series of coordinated movements leading to the production of a fruiting body.  This structure, composed entirely of cells that have piled on top of each other plus the slime they have produced, is brightly colored and visible to the naked eye, about 0.1 mm or slightly larger.  Many fruiting bodies are produced by one swarm.  Many cells within the swarm undergo a shape change from a long thin rod to a shorter, plumper myxospore.  These cells do produce a cell coat which makes them somewhat resistant to heat and rather resistant to desiccation, but these myxospores do not have the incredible environmental tolerance that the typical bacterial endospore has.  When a fruiting body is transported to a new location (think of one sticking to an insect's leg bristles and being carried away), all the myxospores in the structure "germinate" and become "vegetative" cells again.  Thus, a new swarm is born; individual cells do not need to start a new swarm all by themselves.

I have several papers including review articles in my possession as well as one Master's thesis.  Also, please check out the following web site for more references, pictures, time lapse films, etc: http://www.microbiology.med.umn.edu/myxobacteria/index.html