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.