GETTING TO KNOW YOUR MICROBES
healthcare, cosmetics, laundry detergent, explosives, safe disposal of radionuclide wastes and genetic engineering.
In agricultural applications, they are
used to prevent and control fungal
infections. More specifically:
• B. subtilis bacteria produce a class of
lipopeptide antibiotics called iturins.
The bacteria use the iturins to help
them out-compete other micro-organisms by either reducing their growth
rate or killing them.
• B. pumulis produces compounds
that compete with fungal diseases for
amino sugars needed to build cell
walls, which makes it impossible for
fungal cells to build and grow. It has
been shown to specifically prevent
Rhizoctonia and Fusarium spores
from germinating.
• B. licheniformis has been approved
to treat ornamental plants to protect
against fungal pathogens. It is
especially effective against fungi that
cause leafspot and blight diseases.
Its ability to produce important
extracellular enzymes and break
down complex polysaccharides also
makes it useful in nutrient cycling.
Another member of the Bacillus
family, B. thuringiensis (Bt), is a
well-known biological pesticide.
B. thuringiensis forms crystals of
proteinaceous insecticidal endotoxins
called cry proteins. These toxins are
harmful for many insects, including
caterpillars, moths, butterflies, flies,
mosquitos, beetles, wasps, bees,
ants, sawflies and nematodes. Bt has
been used, quite controversially, in
genetically engineered corn. You can
usually find Bt in the pesticide section
of your grow shop, and it is included in
most mycorrhizal products.
The Paenibacillus genus has gained
a lot of attention in the agricultural
world. Once classified as Bacillus,
it was reclassified as a separate,
although very similar, genus in 1993.
Several Paenibacillus species are
plant growth-promoting rhizobacteria
(PGPR). PGPR are competitive
colonizers of the root zone, acting as
both biofertilizers and biopesticides.
They make phosphates available
to plants, fix atmospheric nitrogen
into a form plants can use, degrade
environmental pollutants and produce
important hormones. They also
control phytopathogens by competing
for resources such as iron, amino
acids and sugars. They even produce
helpful antibiotics.
You will often find Paenibacillus
polymyxa, Paenibacillus azotofixans
and Paenibacillus durum in
store-bought mycorrhizae
products. They are all nitrogenfixing bacteria, important in the
vegetative growth stage. In 1994,
scientists recommended that P.
durum be reclassified as a species
of P. azotofixans because they
are so similar, although you will
still see both names on product
labels. Other nitrogen fixers you
will find in products from your
local hydroponics store include
Azospirillum brasilense and species
from the genus Azotobacter.
Beneficial microbes are essential
to the soil food web and should be
a mainstay in our gardens. They
protect plants growing in stressful
conditions, and help them to thrive
in ideal ones. They will even attract
the gardener to the garden by way
of a friendly bacterium that lives
in the soil called Mycobacterium
vaccae. When humans come into
contact with it while gardening,
it causes serotonin to be released
in our brains. No wonder we love
gardening so much!
“
plant growth-promoting
rhizobacteria are
competitive colonizers of
the root zone, acting
as both biofertilizers
and biopesticides.
”
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Maximum Yield USA | November 2015