Inoculant Production & the Micro Production Unit
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Quality inoculants can be produced with a variety of methods and a range of production scales. The following photographs show small, medium and large scale mass cell production methods used around the world. One concept that NifTAL promoted was the Micro Production Unit (MPU)
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Filter sterilized air is commonly bubbled through small capacity fermentors (1-20 L) using an aquarium pump or other small capacity pump. Other designs in use in Thailand and S. Africa use cylindrical borosilicate glass vessels; a lower cost alternative to Erlenmeyer flasks. Commercial producers produce large volumes of many different types of inoculant with these small capacity fermentors by connecting a larger air pump to a manifold (frequently made from p.v.c.. pipe) with valves installed along its length. In this way many small glass fermentors can be connected and disconnected from the to the air supply at any time. Some producers do not used forced air. They simply put inoculated flasks or other glass vessels on a large rotary shaker. This approach is common in India.
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| Medium capacity fermentors |
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Medium scale fermentors commonly have 20-300 L capacity. There are two approaches to sterilizing these fermentors: 1) by autoclaving the entire unit (e.g. the FAO designed UPIL fermentor), or 2) manufacturing the fermentor with a pressure vessel equipped with pressure control/relief capability and an external heat source.
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| Large capacity fermentors. |
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Large capacity fermentors for inoculant production range from 300 L to many thousands
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The Micro Production Unit (MPU)
For a detailed description and planning guide for the MPU concept please see Joe Rourke's The Micro-Production Unit Planning Guide in the Inoculant Production Resources page.
The MPU concept was developed to facilitate the efficient production of high quality, sterile carrier based inoculants.
At the core of the approach is diluting liquid cultures of rhizobia with sterile water and injecting it into sterile carrier material. The dilution technique was developed at NifTAL by Padma Somasegaran. He showed that when cultures were diluted up to 1000 fold and then injected into sterile peat the population would grow back to densities greater than 1 X 109 cells/g peat.
The dilution technique has been used commercially by many inoculant producers around the world including Canada, Australia, UK, Thailand, India, Zambia, and Indonesia. They usually dilute cultures with water at a ratio ranging from 1:40 to 1: 100 (culture:water) The dilution technique allows inoculant producers to reduce their fermentor capacity which saves on capital investment and makes it easier to maintain. |
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Flow diagram of MPU process and physical layout of a demonstration system.
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| Mass cell Culture |
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Cultures are grown in small fermentor vessels. Producers commonly use vessels ranging in size from 1 L to 100 L.
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| MPU set-up |
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Water first flows into 5 um then 1 um sediment filters followed by activated carbon to remove color and particulate matter (three plastic cylinders at top of image). This treatment is followed by followed ultra violet sterilization (stainless steel housing below left of filtration units). The now sterilized water flows into one head of a dual head dilution pump (piston, diaphragm of peristaltic pumps work so long as either heat or chemical sterilization can by applied to the internal pump parts). Culture from the fermentor vessel is enters the other pump head and is diluted and ready for injection into the sterile carrier.
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Connection of culture vessel to pump via needle.
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100 L fermentor hooked to dilution pump in next room at Bangkok Seed Co. in Thailand
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Injecting diluted broth into sterile inoculant carrier
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| Injecting bags of carrier with diluted culture. Bottom image is injecting diluted culture made by batches in a sterile flask without a dual head pump. |
