Date: Fri, 11 May 2001 08:18:07 -0500 Reply-To: Sustainable Agriculture Network Discussion Group Sender: Sustainable Agriculture Network Discussion Group From: "Wilson, Dale" Subject: Chitin in laymans terms Content-Type: text/plain; charset="iso-8859-1" Sanjay, > Could someone please give us an explanation in LAYMAN'S > language, as to what is Chitin? Two basic strategies for mechanical support are found among living things, bones/muscles and tough, hard shells. Plants, fungi, insects, spiders, and crustaceans (including lots of tiny, tiny soil creatures) have shells or cell walls. Most of these exoskeletons and walls are made of sugar molecules spun together to make long chains. The sugar molecules are connected by a kind of linkage or bond that is very resistant to breakdown (unlike starch, which is easily broken into sugar). The plants make cell walls mainly out of cellulose, the main constituent of cotton and wood. The animals (and most fungi) that make cell walls and exoskeletons make them out of a substance very similar to cellulose called chitin, also fiberous and hard to break down. It is almost identical chemically to cellulose, except the sugar molecules have an amino group (contains N) stuck on the side. The fact that chitin contains all this nitrogen has important implications ecologically. Nitrogen is a scarce resource in most systems (well, not if you apply 200 lb/a!), and chitin is an important source of N, and sugar in many systems. There has been great pressure for the evolution of organisms that can exploit this resource. In soils with a large currency of chitin (soils with a lot of fungi) there are also many organisms that eat chitin for breakfast. In such situations, chitin is less effective as armor plate. It so happens that nematodes use chitin as armor plate, and of course most fungi do to. Soil with a high rate of formation and breakdown of chitin is less hospitable to nematodes and fungi. Flora must spend more energy defending itself. Plants have ways of exploiting this situation at the root/soil interface. It is all wonderfully complex and, well, miraculous (also very violent on a tiny scale). Dale Date: Thu, 10 May 2001 23:58:28 -0700 Reply-To: Sustainable Agriculture Network Discussion Group Sender: Sustainable Agriculture Network Discussion Group From: Don Lotter Subject: Chitin, microbes, and soil: an addition to the discussion Content-Type: text/plain; charset="iso-8859-1"; format=flowed I've been skimming over the discussion on chitin in soil the last week or two. Rodriguez-Kabana's work on chitin in soil has been really good. Here is the first part of one of his papers. Here is the intro to a paper by him: Don Lotter Naturally-occurring nematode suppressiveness has been reported for several agricultural systems (Stirling et al., 1979; Kerry, 1982; Kluepfel et al., 1993), but suppressiveness can also be induced by crop rotation with antagonistic plants such as switchgrass (Panicum virgatum) (Kokalis-Burelle et al., 1995) and velvetbean (Mucuna deeringiana) (Vargas et al., 1994) or organic amendments including pine bark (Kokalis-Burelle et al., 1994), hemicellulose (Culbreath et al., 1985) and chitin (Mankau and Das, 1969; Spiegel et al., 1986; Rodríguez-Kábana and Morgan-Jones, 1987). A major component of the suppressiveness of chitin amendments is believed to be biotic and several reports confirm increased numbers of nematode antagonistic microorganisms associated with chitin-induced suppressive soils (Godoy et al., 1983; Rodríguez-Kábana et al., 1984). Extensive work has been done over the past years on fungi associated with chitin amendments (Godoy et al., 1983; Rodríguez-Kábana et al., 1984); however, information on bacterial community structure and the role of bacteria in chitin-induced suppressiveness is still very limited. We chose chitin amendments as a model system to study the effect of suppressiveness on bacterial diversity in the soil and endorhiza. Endophytic bacteria were included in this study because they colonize the same root tissues as sedentary plant-parasitic nematodes. This association of endophytic bacteria with nematodes throughout the nematode life cycles makes these bacteria excellent candidates for biocontrol strategies. Chitin is a structural component of some fungi, insects, various crustaceans and nematode eggs. In egg shells of tylenchoid nematodes, chitin is located between the outer vitelline layer and the inner lipid layer and may occur in association with proteins (Bird and Bird, 1991). The breakdown of this polymer by chitinases can cause premature hatch, resulting in fewer viable juveniles (Mercer et al., 1992). In the soil, chitinases are produced by some actinomycetes (Mitchell and Alexander, 1962), fungi (Mian et al., 1982) and bacteria (Ordentlich et al., 1988; Inbar and Chet, 1991), but chitinases are also released by many plants as part of their defense mechanism against various pathogens (Punja and Zhang, 1993) and plant-parasitic nematodes (Roberts et al., 1992). Chitinases depolymerize the chitin polymer into N-acetylglucosamine and chitobiose. Further microbial activity results in the deamination of the sugar and accumulation of ammonium ions and nitrates (Rodríguez-Kábana et al., 1983). Nematicidal concentrations of ammonia in association with a newly formed chitinolytic microflora are believed to cause nematode suppressiveness (Mian et al., 1982; Godoy et al., 1983). Benhamou et al. (1994) have shown that chitosan, the deacetylated derivative of chitin, induces systemic plant resistance against Fusarium oxysporum f.sp. radicis-lycopersici in tomato when applied as a seed treatment or soil amendment. This suggests that plant defense mechanisms might contribute to the overall nematode suppression. Our objective was to determine if the chitin-mediated suppression of plant parasitic nematodes is related to changes in bacterial communities in soils, rhizospheres or within cotton roots. From: Chitin-mediated changes in bacterial communities of the soil, rhizosphere and within roots of cotton in relation to nematode control Soil Biology and Biochemistry Volume 31, Issue 4 April 1999 Pages 551-560 J. Hallmann1, R. Rodríguez-Kábana and J. W. Kloepper* Biological Control Institute, Alabama Agricultural Experiment Station, Department of Plant Pathology, Auburn University, Auburn, AL 36849-5409, USA Abstract Changes in microbial communities associated with nematode control were studied by comparing population numbers of fungi and bacteria in the soil and in internal root tissues (endorhiza) in non-amended and chitin-amended soils. Addition of chitin to soil at 1% (w/w) eliminated plant-parasitic nematodes in a first planting of cotton cv. `Rowden' and significantly reduced Meloidogyne incognita infestation in a second planting, confirming long-term nematode suppressiveness induced by this organic amendment. The chitin amendment was associated with an increase in fungal and bacterial populations, especially those with chitinolytic activity. The bacterial communities of soil, rhizosphere and endorhiza were assessed by examining the taxonomic diversity of recoverable bacteria based on identification with fatty acid analysis of sample sizes of 35 soil and rhizosphere bacteria and 25 endophytic bacteria. All major bacterial species which formed at least 2% of the total population in non-amended soils and rhizospheres also occurred with chitin amendment. In contrast, chitin-amended soils and rhizospheres yielded several species which were not found without chitin amendment, including Aureobacterium testaceum, Corynebacterium aquaticum and Rathayibacter tritici. Burkholderia cepacia was recovered from both amended and non-amended soils and rhizospheres, but it was most abundant with chitin amendment at the end of the first cotton planting. Soil was probably the major source for bacterial endophytes of cotton roots, since nearly all endophytic bacteria were also found in the soil or rhizosphere. However, two dominant genera in the soil and rhizosphere, Bacillus and Arthrobacter, were not detected as endophytes. Chitin amendment exhibited a further specific influence on the endophytic bacterial community; Phyllobacterium rubiacearum was not a common endophyte following chitin amendment, even though chitin amendment stimulated its populations in non-planted soil. Burkholderia cepacia, found in similar numbers in the soil of both treatments, was the dominant endophyte in plants grown in chitin-amended soil but rarely colonized cotton roots grown in non-amended soil. These results indicate that application of an organic amendment can lead to modifications of the bacterial communities of the soil, rhizosphere and endorhiza. From "The American Heritage Dictionary of the English Language", American Heritage Publishing Co., INC. and Houghton Mifflin Company. chi-tin n. A simitransparant horny substance, primarily a mucopolysaccharide, forming the principal component of crustacean shells, insect exoskeletons, and the cell walls of certain fungi. Date: Wed, 6 Jun 2001 10:38:09 +0200 Reply-To: Wiegand@lufa-sp.vdlufa.de Sender: Sustainable Agriculture Network Discussion Group From: Klaus Wiegand Organization: Landw. U.-& Forsch.-Anstalt Speyer Subject: chitin relating to the recent discussion (raised by dale wilson) on chitin-producing fungi, i ran upon an interesting paper on that topic: Are chitinolytic rhizosphere bacteria really beneficial to plants? Wietse de Boer & J.A. van Veen Netherlands Institute of Ecology, Centre for Terrestrial Ecology, Department of Plant-Micro-organism Interactions, P.O. Box 40, 6666 ZG Heteren, The Netherlands. E-Mail: wdeboer@cto.nioo.knaw.nl The observations of mycolysis by chitinolytic bacteria have stimulated research on possible application of these bacteria for biocontrol purposes. The focus has been on rhizosphere bacteria as they should be adapted to the environment where plant-pathogenic fungi infect roots. Chitinolytic rhizosphere isolates, showing in vitro antifungal effects have therefore been tested for their ability to protect plants against infection by plant pathogens. In several cases these strains reduced disease symptoms significantly under controlled greenhouse conditions. However, application of such strains under field conditions has been far less successful, and it is not at all clear that mycolytic activities should be expected under field conditions. Before this issue can be resolved information is needed about the ecological function of bacterial chitinases including environmental conditions that might promote chitinase production and mycolytic activity. In this paper it will be argued that chitinases of rhizosphere bacteria are most likely involved in mycoparasitism and defence against lysis by fungi. Obviously, mycoparasitic growth of chitinolytic rhizosphere bacteria could be an important mechanism to control plant-pathogenic fungi. However, chitinase production in soil bacteria, including potential biocontrol strains, is repressed by small organic substrates like sugars and amino acids. This indicates that mycolytic activity does only occur when no other growth substrates are available i.e. under starvation conditions. Hence, the release of organic compounds by the root is expected to repress mycolytic activities of most chitinolytic rhizosphere bacteria. This does, however, not suggest that the search for biocontrol strains is futile, but indicates that knowledge of chitinase expression and repression must be taken into account during this process. A potential negative effect of chitinolytic bacteria may be exterted on mycorrhizal development. In fact, the starvation conditions in the bulk soil, into which mycorrhizal hyphae are extending from the root, should promote mycolytic activities. Therefore, study of interactions between chitinolytic strains and mycorrhizal fungi should be part of biocontrol studies. ----- klaus Date: Wed, 6 Jun 2001 08:42:05 -0500 Reply-To: Sustainable Agriculture Network Discussion Group Sender: Sustainable Agriculture Network Discussion Group From: "Wilson, Dale" Subject: Re: chitin Content-Type: text/plain; charset="iso-8859-1" Klaus, > i ran upon an interesting paper on that topic: This is a really interesting subject. The other day we had Gary Harman here for a little seminar. Gary is the guy who developed the rhizoplane-competent Trichoderma harzianum strain T-22. He showed nice pictures of how the Trichoderma eats little holes in the cell wall of other fungi using chitinase (among other enzyme tricks). > "application of such strains under field conditions has > been far less successful, and it is not at all clear that > mycolytic activities should be expected under field conditions. > Before this issue can be resolved information is needed about the > ecological function of bacterial chitinases including > environmental conditions that might promote chitinase production > and mycolytic activity." (de Boer and van Veen) Trichoderma too has been more consistently beneficial in the greenhouse. I think that the field soil environment is a veritable zoo, including, besides fungi, bacteria, and actinomycetes, microarthropods (and protozoa?) that feed on fungi. Greenhouse soils are probably much simpler systems. BTW, we see consistent and somewhat mysterious growth enhancement in the field from seed treatment with systemic neonicotinoid insecticides. Probably, we are suppressing some little critter in the root zone. > "chitinase production > in soil bacteria, including potential biocontrol strains, is > repressed by small organic substrates like sugars and amino > acids. This indicates that mycolytic activity does only occur > when no other growth substrates are available i.e. under > starvation conditions." (de Boer and van Veen) And this may be where plant roots come in. They leak small organic molecules onto the rhizoplane and alter the ecology. And they snap up N and P. So rhizoplane colonizers are confronted with a substrate-rich, but nutrient-poor niche, that may favor mycoparasites that can obtain N by breaking down fungi. Iron availability too may be a key player in some of these systems (thinking of some of the Pseudomonads). God this is interesting! What I think is happening (and I am going way, way out on a speculative limb here!) is that plants exploit this situation, producing a mycoparasitic environment on the rhizoplane, creating rapid N-turnover, and suck out N from the system. Gary presented evidence that colonization by his strain of Trichoderma can often greatly enhance N uptake, reducing the need for N application. I can't vouch for their data, and they ARE trying to peddle their wares, but the results looked pretty encouraging. I just did a little literature search: "(chitinase or chitinolytic) and (hyperparasitism or mycoparasitism)" All eight papers were about fungus-fungus parasitism. Also did a search on "(chitinase or chitinolytic) and biocontrol" I will send these if anyone is interested. Dale Date: Thu, 7 Jun 2001 08:02:19 +0800 Reply-To: Sustainable Agriculture Network Discussion Group Sender: Sustainable Agriculture Network Discussion Group From: David Menne Subject: Re: chitin Content-Type: text/plain; charset=us-ascii Researching references for an article "Enzymatically improving infant nutrition in developing countries [particularly KwaZulu/Natal]" (see http://www.plantsfood.com/infantenzyme.htm), I came across the interesting claims that chitinases have proven active against human pathogens such as Listeria monocytogenes, Clostridium botulinum, Bacillus cereus, Staphylococcus aureus and E coli. I have a general interest in the mechanics of what I suppose one could call health-promoting food production; and possibly a need to be aware of destructive food production processes [such as boiling the hostel cabbage to a pulp - Greytown High School boarding hostel, 1950's]; and would value any related references which might/should turn up or be in the databases of those following this thread.