Integrated Environmental Biotechnology - Environmental Biotechnology: Theory and Application - page 255

Bacteria have been found capable of encouraging this association, earning
themselves the title of 'micorrhizal helper bacteria'. Clearly, anything which
increases the efficiency of nutrient uptake by crop plants reduces the requirement
for the addition of artificial fertilisers and thus reduces the potential for

agri-chemical environmental disturbance.
The influence of microbes on the welfare of plants is not confined to the
ground and may even affect the weather. An often quoted example is that drawn
from Pseudomonas syringae which produces a protein known to act as a point of
nucleation of ice crystals. Plants which harbour this bacterium run an increased
risk of frost damage especially if their tissue is particularly susceptible as is the
case with strawberries. P. syringae has been subjected to genetic engineering
which successfully reduced the problem. A description of the project is given in
Chapter 9.
Plant-microbe interactions are becoming recognised as having an immediate
and direct importance to human health in the role they can play in reducing
the effect of 'sick buildings'. They occur principally because these buildings
are closed systems in which people work, breathing in volatile components
from plastics, paint, chemicals used in office machinery such as photocopiers
and printers and a range of other sources including furnishing manufactured
using synthetic materials. Bacteria resident in the soil of potted plants in the
office are able to degrade many of these volatiles, which include phenolics,
formaldehyde and trichloroethylene, thus improving the air quality. The plants
themselves contribute to this improvement, not only by supporting the rhizo-
sphere microbial community, but also by producing oxygen during photosynthesis
described in Chapter 2. In essence, this is root zone phytotechnology on a
small scale.
Although straying away slightly from the remit of this section, it is interesting
to point out that soil microbial activity has a major influence in the balance of
stable atmospheric gases. These include the greenhouse gases, carbon dioxide,
nitrous and nitric oxide and methane, so called because they trap heat re-emitted
by Earth from energy radiated by the sun. The atmospheric balance of less sta-
ble gases which include ammonia, hydrogen sulphide and dimethylsulphide are
also subject to microbial activity, as will be apparent from an understanding of
the foregoing chapters on metabolism. A final word on soil microbes concerns the
degradation of lignin. This is a major constituent of woody plant material and
is recalcitrant to degradation. However, filamentous fungi are responsible for its
degradation worldwide, augmented in the tropics by bacteria living in the gut of
termites. This degradation requires the presence of oxygen, hence wood residing
in anaerobic conditions is somewhat protected. Clearly, should the water table
drop exposing to air, for example the wood pilings supporting buildings, there is
a danger of invasion by filamentous fungi able to degrade lignin and thus weaken
the building structure. This also explains in part the necessity to aerate a compost
heap containing any woody plant material to allow invasion by filamentous fungi
capable of degrading lignin.