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The bacteria Myxococcus Xanthus is a decomposer that moves and forms fruiting bodies to reproduce. These fruiting bodies are mounds that grow into mushroom cloud like bodies, where cells differentiate on the inside to form small spores that are heat and desiccation resistant. In her discussion of Myxococcus Xanthus, Dr. Hartzell addresses various complexes that make flagella-less movement possible for the bacteria. The researchers traced cell movements and found that Myxococcus Xanthus moves at a rate of 2. 5 micrometers per minute.
A rate that is slower than continental drift (3 micrometers per minute). Cell movements occur in two different forms: social (moving in groups of cells) and adventurous (individuals moving). Movement is found to be gene determined. Two genes were found to be required for any movement: mgl A and mgl B. Furthermore, there are specific genes required for social movement and specific genes required for adventurous movement. Mgl A, a magnesium dependant, is a GTP-ase (a protein that binds and cleaves GTP to GDP) like Ras.
It was found that mgl A was necessary for development of the fruiting body and for movement, but not for growth of the cell. When mgl A binds to GDP, it is inactive. However, when it binds GTP, it is active. Then mgl A was sequenced and found to have one of the Aspartine amino acids exchanged for a Threonine. If mgl A was mutated to replace Threonine with Asoartine (the way it is in most Ras proteins), no movement or formation of the fruiting body occurred. Also, induced activation of this protein (forcing GTP to bind to it) causes movement, but not development of the fruiting body.
The calcium dependent mgl B protein is also required for movement. Found right next to mgl A and transcribed at the same time, mgl B is believed to be a guano nucleotide release factor (REM for short). REMs facilitate the release of GDP from Ras type proteins (mgl A) so that it can bind more GTP, and thus get reactivated. Furthermore, even with removal of mgl A and mgl B, movement could still occur by adding SAR 1 (a yeast) and Sec 12. SAR 1 is like mgl A and Sec 12 is very similar to mgl B (40 % of the c terminus of the protein is the same).
In numerous other experiments, many other proteins were found to be directly involved with movement. These proteins are Tol protein homologs. Tol proteins are involved in secretion and movement of other organisms. Myxococcus Xanthus has two copies of the Tol homolog complex. These copies may be for front and back movements. Also, it is believed that the bacteria moves by secretion.
The activation of the Tol homolog complexes is believed to involve mgl A, however, these hypotheses are still not yet known to be true. Considering the complexity of the movement of the bacteria, it appears that mgl A and mgl B are the causes of movement in Myxococcus Xanthus. The evidence presented by Dr. Hartzell is sufficient to support and sustain the theory, and it seems appropriate to add that Tol homologs may also cause movement given what is known already about its involvement with movement in other organisms.
Bibliography: seminar by Dr. Trish Hartzell from university of idaho
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Research essay sample on Micrometers Per Minute Specific Genes Required Mgl
