[USCC] Vermicompost microbiology

[kuter.agresource@verizon.net]

I worked with Dr. Nelson when he was at OARDC with Dr Harry Hoitink and concur with the statements made here by Allison L.H. Jack. Our work with both bacterila and fungal communities associated with suppressive and and conducive media amended with composts showed that the there were a variety of factors associated with the establishment of suppression.  



>From: Allison L H Jack <alh54 at cornell.edu>
>Date: 2007/03/01 Thu AM 11:23:50 CST
>To: compost at composter.com
>Subject: [USCC] Vermicompost microbiology

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>>Dear Dr. Byvoz,
>
>Something interesting that has come out of previous work done in Dr. Eric 
>Nelson's lab is that there may be emergent properties involved when 
>considering compost mediated suppression of plant diseases. One of his 
>studies compared a disease suppressive and a disease conducive compost. 
>They isolated the seed-colonizing microbes at a critical time point when 
>they had observed suppression to occur. Then they looked at how each 
>individual isolate performed as a treatment protecting the seed from 
>Pythium. They didn't exhaustively sample individuals from each community, 
>but even this small study has interesting implications.
>
>What they found was that the disease conducive compost (the one that did 
>not protect the plants from disease) had many species that were suppressive 
>when tested individually, while the disease suppressive compost did not 
>have as many species that were individually suppressive. The amazing thing 
>was that when they combined the isolates together and used them as a seed 
>treatment, the community with the high proportion of individually 
>suppressive isolates was NOT suppressive. [See table 4] So the bottom line 
>is that "the whole is greater than the sum of the parts" which is a 
>prevalent concept in ecology. The ecological interactions that are taking 
>place between microbial species are so incredibly complex. There is a lot 
>going on that we do not yet understand.
>
>McKellar, M.E. and E.B. Nelson (2003) Compost-induced suppression of 
>Pythium damping-off is mediated by fatty-acid-metabolizing seed-colonizing 
>microbial communities. Applied and Environmental Microbiology, 69(1): p. 
>452-460.
>
>The implication of this and other findings is that although we are able 
>measure total numbers and possibly activity of known "beneficial" and 
>"pathogenic" microorganisms in compost, it may not actually tell us 
>anything about how that compost will perform with respect to disease 
>suppression. Merely the presence or absence of certain species does not 
>always correlate with suppression.
>
>I'm familiar with your work on Actinomycetes and I agree that they are 
>potentially major players in disease suppression because of their 
>antibiotic capability. In this same study however, they found 
>actinobacteria present on the seed surface, but they were not implicated in 
>the actual suppression and no inhibitory substances like antibiotics were 
>found. Instead a group of microbes capable of metabolizing fatty acids was 
>most likely responsible for the suppression. With this important chemical 
>signal degraded, Pythium sporangia never germinated, and were unable to 
>infect the seeds. Pythium infections happen so quickly (within 2 hours) 
>that it is unlikely the actinobacteria would have time to colonize a 
>germinating seed and switch their metabolism over to the production of 
>antibiotics, which is common in later stages of growth.
>
>So it is most likely that there are different complex mechanisms involved 
>for specific pathogens. I believe that scientists are still a long way off 
>from being able to make sound predictions of compost quality with relation 
>to disease suppression because we don't know enough about how it works. 
>Even with all the molecular methods we have available, we still need to 
>know what we're looking for and have sound data linking it to the function 
>we want to predict. I know as an industry we need to have some working 
>estimates of compost quality to use now, but I think we should also focus 
>some energy on uncovering the exact mechanisms so we can develop better 
>predictive tools in the future.
>
>I look forward to hearing more comments on this topic :-).
>
>Take care,
>Allison
>
>p.s. I'll send the pdfs to Dr. Byvoz individually, and if anyone else is 
>interested in taking a look at them, let me know and I can send them out.
>
>
>
>>Thinking about standardization of vermicompost properties, I mean those
>>microbiological parameters that correlate with its fertility and suppressive
>>activity. I partially agree with those people who consider presence (and
>>activity) of just “beneficial” and “harmful” microorganisms to be 
>>the only
>>useful properties to measure.
>>
>>
>>
>>However, we need to know who are “beneficial” and who are 
>>“harmful”? With
>>the harmful ones is more or less clear. These are phytopathogenic fungi and
>>bacteria.
>>
>>
>>
>> >From our experience, vermicomposts (just two samples we have studied)
>>contain high abundance of the fungus Aspergillus flavus and other A. spp.,
>>which are known to be phytotoxic. However, we have many other species of
>>fungi that are potentially harmful. Using luminescent microscope, we found
>>around 1000000 spores/g (!) of fungi in vermicompost (45% moisture) made of
>>cow manure, but practically no mycelium. Who are they? What will happen to
>>these spores when they come to soil?
>>
>>
>>
>>To isolate and identify them sometimes we need specific methods and
>>experience. Here we can use both dilution plate and molecular methods. The
>>latter I think is more preferable, but requires equipment and experience of
>>the personal. Using molecular technique, we can follow the population
>>dynamics of those microorganisms that are potentially important for
>>vermicomposts.
>>
>>
>>
>>Beneficial microorganisms are much less clear. Growth promoting or
>>antagonistic microbes? How can we follow them?
>>
>>
>>
>>Again form our experience, vermicomposting process promotes actinomycetes to
>>grow. Spores of some actinomycetes can proliferate during passage through
>>the earthworm digestive tract (our works in 90ths). We found more
>>actinomycete mycelium in vermicasts comparing to excrement and in
>>vermicompost vs. food substrate (Byzov et al., 1995). Actinomycetes are
>>known as producers of antibiotics. May be this is an important parameter?
>>
>>
>>
>>Therefore, we need to find a set of such SOIL microorganisms that could be
>>indicators of bad and good quality of vermicomposts. May be some of them can
>>be eliminated or introduced to compost to improve its quality. But, it is a
>>labor and time-consuming work.
>>
>>
>>
>>Integral parameters (which are easier to measure) such as BIOLOG, Degens,
>>Harris’ catabolic diversity and others, could be useful too, but we have to
>>find how they correlate with the quality of product.
>>
>>
>>
>>Regards,
>>
>>
>>
>>Boris
>>
>>
>
>**************************************************************************************
>Allison L H Jack
>Graduate Student
>Department of Plant Pathology
>Cornell University
>335 Plant Science
>Ithaca, NY 14850
>607.273.5762
>************************************************************************************* 
>
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