Microbial Inoculants: an Approach to Sustainable Agriculture

originally an article published here by Sunita Gaind, i thought i'd repost it, given there's a wealth of good information on the subject, which gives a broad overview:

The green revolution though made India self sufficient in food production, but at the cost of soil health. Persistent use of chemical fertilizers and low input of organic material in soil reduced its organic matter content, resulting in stagnation of food grain production by 1.5 %.

To restore the productivity of soil, efforts need to be focused on use of natural resources that can be an alternate to costly chemical fertilizers and restrict soil impoverishment. Current developments in sustainability involve the rationale exploitation of soil microbial activities and use of less available sources of plant nutrients. Nitrogen and phosphorus are the macronutrients that limit the plant growth. To meet the crop need, these are generally supplemented through chemical fertilizers. Soil inhabits microorganisms that possess the particular trait for nitrogen and phosphorus transformation. Their application to soil under crop cultivation can improve the nutrient availability; reduce the input of chemical fertilizer and a way to sustainable agriculture.

What are microbial inoculants?
Microbial inoculants are the formulations of beneficial living microorganisms that when added to soil, directly or indirectly, improve the nutrient availability to the host plant and promote plant growth. Microbial inoculants for biological nitrogen fixation are both strain and crop specific. However, phosphorus solubilization and mineralization can be mediated by potential isolates of bacteria and fungi. The latter being the key components of soil plant system can be developed as phosphate solubilizing microbial inoculants.

Fungi vs Bacteria as Phosphate solubilizeres
 Fungi maintain their P dissolving efficiency even on repeated sub culturing
 The extracellular production of phosphatase and organic acid is higher with fungi compared to bacteria. Therefore, fungi are more effective phosphate mineralizer/ solubilizers compared to bacteria.
 Their hyphae can travel long distance in soil more easily than bacteria and can prove more beneficial for solubilization of phosphorus in soil.
 They can tolerate low moisture, high temperature, heavy metals and agrochemicals.
 Their spore forming nature is an additional advantage for their survival under environmental stress.

How do microbes improve the availability of nutrients?
Soil microorganisms are involved in large number of processes that affect the P transformation and influence its availability to plant roots.
 By the excretion of hydrogen ions.
 By release of organic acids.
 By production of phosphatase enzymes that can mineralize soil organic P.
 Chelating metal ions that may be associated with complexed forms of P or may facilitate the release of adsorbed P through ligand exchange reactions.
 By displacement of sorption equilibria that results in increased net transfer of phosphate ions into soil solution or an increase in the mobility of organic forms of phosphorus.
 Growth stimulation through production of phytohormones.
 By production of siderophores.
 Phosphate dissolving fungi may also provide micronutrients for formation of polyphenol and other aspects of phenolic metabolism.
 Phosphate dissolving Trichoderma harzianum has shown the ability to accelerate the oxidative dissolution of metallic Zn.
 They also provide disease resistance to plants due to production of antibiotics and protection against soil borne pathogens.

Phosphate dissolving microorganisms used as microbial inoculants
Fungi: Aspergillus awamori, Aspergillus niger, Penicillium digitatum, Pencillium radicum, Penicillium bilaiae, Trichoderma koningii

Bacteria: Pseudomonas striata, Bacillus polymyxa, Bacillus megaterium, B.subtilis, B. circulans

Carriers: Charcoal- soil mixture, vermiculite, press mud, peat, cow dung cake powder, farm yard manure, wheat bran etc. Amendment of charcoal soil - mixture carrier with calcium alginate resulted in better retention of moisture.

living foundries - the new future with microbes?

As the name suggests, "Living Foundries" are the bacterial and fungal colonies which can produce a new generation of human resources, with a low environmental impact.

Aside from new uses in supplying phosphor and nitrogen for truly sustainable farming, one farming input which can't be solved with microbes is fuel.  Whether we like it or not, bacteria can't just eat sugars and secrete petroleum products into the tractors, combines and delivery trucks to supply us truly sustainable foods - or can they?

it seems they might just be able to.

for some time, research has been ongoing into the possibility of pressing oils from algae

but now bio-engineers in the USA are taking the idea of living foundries further - by engineering e-coli to excrete diesel directly.  A guardian interview asked Jay Keasling, a professor of bioengineering at the University of California, Berkeley and CEO of the US Department of Energy's Joint BioEnergy Institute (JBEI) about his previous successes manufacturing anti-malaria drugs using "living foundries" before asking him about his new biodiesel bugs:


How easy is it to make fuel from microbes?
About a year ago, we published a paper in Nature where we engineered E. coli to produce a diesel fuel. The beauty of it was that the E. coli took in the sugar, transformed it directly into diesel, and the diesel was secreted outside the cell. Because it's oily, the diesel floats to the top. So unlike ethanol, which you have to distil to get it pure enough to use in an engine, the diesel purifies itself. That reduces the cost and the amount of energy needed to make it.

Will your diesel be as good as the fuel at the pump?
It's as good, if not better. Fuel is incredibly complicated – it has many different components and it's optimised for different things. We can build the fuel from the most valuable molecules, so we don't have the unwanted components that existing fuels have. You get better gas mileage out of it and cleaner emissions. And we're talking about a substantial improvement for the environment. Our diesel reduces greenhouse gas emissions by 80%, which is pretty substantial.

The world uses around 90 million barrels of oil a day. How can bugs compete?
We're looking at replacing 30% of transportation fuel in, say, a 20- to 30-year period. That is a huge undertaking. We are going to develop the technology to make the fuels and license them out. In the next 10 to 20 years, we'll see a very diverse range of companies all working with different techniques to make fuels.

How will your work affect the giant oil companies?
The energy business is the biggest sector in the world, and the beauty about working in the biggest industry on the planet is that there is room for everybody. Exxon is the largest company in the US, but it has only 5% of the transportation fuel market. That alone tells you that anybody can play.

Will synthetic biology be used to make more than fuels?
As well as fuels, we are looking at everything else we produce from petroleum, including polymers and plastics, and asking: can we go in and replace those? I don't see any reason why we can't make almost any chemical we want from sugar, a renewable resource. It's a great time to be in biology and biotechnology, because we have so many more tools and it's so much more powerful than it used to be.

Jay Keasling believes he can create alternatives to diesel and jet fuel using synthetic biology.
Photograph: Roy Kaltschmidt/Lawrence Berkeley Nat'l Lab

a future-facing convention regarding living foundries is to be held soon.

in the mean-time, we wait with baited breath at what other uses bugs will be put to, in terms of the immense environmental service they can provide.