Bacteria nematode associations

In the second case, the dying off of cuttings begins with an intense chlorosis after the third day in the propagator. Within 10 days all the affected cuttings die out. Rotting of the base of the stem is believed to be due to nematodes and bacteria frequently associated with this condition. 

A study was conducted to determine the effects of combinations of organic amendments and benzaldehyde on plant-parasitic and non-parasitic nematode populations, soil microbial activity, and plant growth (Chavarria-Carvajal et al., 2001). Pine bark, velvetbean and kudzu were applied to soil at rates of 30 g/kg and paper waste at 40 g/kg alone and in combination with benzaldehyde (300 mul/kg), for control of plant-parasitic nematodes. Pre-plant and post-harvest soil and soybean root samples were analyzed, and the number of parasitic and non-parasitic nematodes associated with soil and roots were determined. Soil samples were taken at 0, 2, and 10 weeks after treatment to determine population densities of bacteria and fungi. Treatment... 

Nematodes that are possibly bacteriophagous also increase after the treatment (Yamanaka 1995a, 1995c), a possible reflection of increased bacterial numbers. This phenomenon has also been observed in association with decomposing pig carcasses (Carter et al., unpublished). The appearance of the possible nematode parasite Rhopalomyces elegans var. minor (see Section 4.2.2) creates a potential tripartite food web among bacteria, nematodes, and fungi, as hypothesized by Barron (1977). 

Akhurst R, Dunphy GB. Tripartite interactions between symbioti-cally associated entomopathogenic bacteria, nematodes, and their insect hosts. In Parasites and Pathogens of Insects 2. Beckage N, Thompson S, Federici B, eds. 1993. Academic Press, New York, pp. 1—23. 

As with animal systems a large amount of work has been devoted to the delineation of the involvement of the rare earths in extracellular and extra membrane pathways. These elements have been implicated in a wide range of physiological processes in plants, bacteria and nematodes associated with plants. Many of these, but by no means all, are associated with REE/Ca " interactions. 

Table 13.1 Entomopathogenic nematodes and their symbiotically associated bacteria (Reproduced...

Martens EC, Heungens K, Goodrich-Blair H. Early colonization events in the mutualistic association between Steinemema carpocapsae nematodes and Xenorhabdus nematophila bacteria. J Bacteriol. 2003 185 3147-3154. 

The nematode species of most interest for the control of crop insect pests are from the genera Steinernema and Heterorhabditis, both characterised by their association with bacteria from the genera Xenorhabdus and Photorhabdus. These nematodes invade the insect and then release their symbiotic bacteria into the insect s haemocoel. The nematodes release metabolites that repress the immune system of the insect, allowing the bacteria to develop. The bacteria then release toxins that kill the insect within two to three days and also produce antibiotics that prevent the invasion of the dead insect by other bacteria. These bacteria then invade the entire insect cadaver and the nematodes subsequently begin to consume the bacteria. 

Receptors and their ligands are numerous, varied, and essential to all forms of life. Cell-surface receptors on bacteria detect feeding attractants as well as dangerous molecules. From bacteria to humans seven-helix receptors function to detect light, odors, hormones, and other molecules. Tire numbers of different receptors are impressive. For example, the tiny nematode C. elegans has 650 seven-helix transmembrane receptors and 411 protein kinases, many of which may be associated with receptors.34 Our bodies have thousands. 

Chen, G., Dunphy, G.B. and Webster, J.M. (1994) Antifungal activity of two Xenorhab-dus species and Photorhabdus luminescens, bacteria associated with the nematodes Steinernema species and Heterorhabditis megidis. Biological Control 4, 157-162. 

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