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Bacillus subtilis General Description

Bacillus subtilis is one of the best understood prokaryotes, in terms of molecular biology and cell biology. Its superb genetic amenability and relatively large size have provided the powerful tools required to investigate a bacterium from all possible aspects.

Bacillus subtilis is included in the genus of Gram-positive, rod-shaped (bacillus), bacteria. Bacillus subtilis is an obligate aerobes (oxygen reliant). But more recently, it has been found to have the ability,when in the presence of nitrates or glucose, to be aerobic as well as anaerobic, making it a facultative anaerobes. Bacillus subtilis is an endospore forming bacteria, and the endospore that it forms allows it to withstand extreme temperatures as well as dry environments. Under stressful environmental conditions, the bacteria can produce oval endospores that are not true spores but which the bacteria can reduce themselves to and remain in a dormant state for very long periods. These characteristics originally defined the genus.

Bacillus subtilis is not considered pathogenic or toxic and is not a disease causing agent. B. subtilis is readily present everywhere; the air, soil and in plant compost. In this article we are focusing on Basillus subtilis as a soil microorganism. However interestingly enough, it’s main habitat is in our stomachs. Although B subtilis is commonly found in soil, more evidence suggests that it is a normal gut commensal in humans. A 2009 study compared the density of spores found in soil (~106 spores per gram) to that found in human feces (~104 spores per gram). The number of spores found in the human gut is too high to be attributed solely to consumption through food contamination. Soil simply serves as a reservoir, suggesting that B. subtilis inhabits the gut and should be considered as a normal gut commensa.

 

Bacillus subtilis | Agricultural Tool

Basillus subtilis produces an abundance of beneficial toxins and enzymes, most importantly it produces a toxin called subtilisin and a class of lipopeptide antibiotics called iturins.  Iturins has direct fungicidal activity on many pathogens, such as Rhyzoctonia Pythium, Phytophthora, Fusarium, Rhizopus, Mucor, Oidium, Botrytis, Colletotrichum, Erwinia, Pseudomonas, Xanthomonas, as well as nematodos. Iturins help B. subtilis bacteria out-compete other microorganisms by either killing them or reducing their growth rate. In this way subtilis takes up space on the roots, leaving less area or source for occupation by disease pathogens.

There is a symbiosis component to the B. subtilis-plant dynamics as well. B subtilis feeds off plant exudates, which also serve as a food source for disease pathogens. Because it consumes exudates, it deprives disease pathogens of a major food source, thereby inhibiting their ability to thrive and reproduce. The exudes feed subtilis and this allows it to protect the plant from pathogens.