Feeding of the Nematode Acrobeloides nanus on Bacteria.

Information on the effect of bacteria-feeding nematodes on bacterial populations in the soil is sparse. We have isolated, cultured, and microscopically examined bacteria and nematodes coexisting within an agricultural soil and have studied their feeding relationship. The bacterium Pseudomonas corrugata isolate 2140R is a biocontrol agent against the pathogenic fungus Gaeumannomyces graminis var. tritici. The nematode Acrobeloides nanus is a cosmopolitan, bacteria-feeding organism widespread in agricultural and arid soils throughout Australia. Using light and electron microscopy, we observed the ingestion and breakdown of P. corrugata in the pharynx of A. nanus and bacterial passage through the nematode intestine as well as the accumulation of fluorescent compounds from ingested and broken P. fluorescens in the lumen of the nematode's intestine. We also observed A. nanus feeding, growing, and reproducing on the Gram-positive bacterium Clavibacter toxicus, the causative agent of the disease annual ryegrass toxicity, and detected crushed bacteria in the nematode's intestine.

Morphology, Oviposition, and Embryogenesis in an Australian Population of Acrobeloides nanus.

A population of Acrobeloides nanus in Australia is described and illustrated, based on light and scanning electron microscopy. Embryogenesis from egg laying to hatching is followed over a wide range of temperatures. At 15 C, hatching occurs in about 125 hours and at 35 and 37.5 C after about 40 hours. At 40 C, egg development ceases early in cleavage. The capacity of A. nanus to develop over such a range of temperatures, and its anhydrobiotic capabilities, are discussed in relation to its survival and wide distribution in Australia.

Observations on Crystalloid Bodies in the Pseudocoelom of Eutobrilus heptapapillatus.

Eutobrilus heptapapillatus, found in a number of different sites at the mouth of the River Murray in South Australia, were examined under light and electron microscopes. The pseudocoeloms of these nematodes often contained oval crystalloid bodies containing carbohydrate, sulfur, phosphorus, and lipid. The bodies varied considerably in size up to a maximum of 10 mum long. The precise function of these crytalloids remains unknown. Nematodes having these crystalloids often also contained numerous small regular densely staining particles, about 20 nm d and occurring throughout the nematode's body.

Vital staining of glycoprotein secreted by infective third stage larvae of Haemonchus contortus prior to exsheathment.

Staining of infective third stage larvae of Haemonchus contortus prior to exsheathment shows that protein is exuded from the head region and spreads between the cuticles and that a carbohydrate-containing substance is also found between the L2 and L3 cuticles throughout, at exactly the same sites in this nematode. This glycoprotein, which is either secreted from the mouth or the amphids or both is exuded whether or not the larvae have been stimulated to exsheath. Slight staining was also sometimes detected at the secretory-excretory pore and to an even lesser extent at the anus. This glycoprotein is thought to function as a lubricant to prevent abrasion between the cuticles. It accumulates in areas where there is greatest space between the cuticles such as the head, tail and where bending of the nematode body occurs.

Studies on the surface coat (glycocalyx) of the dauer larva of Anguina agrostis.

Imprints of the surface coat (glycocalyx) from the cuticles of living second stage dauer larvae (DL2) of Anguina agrostis (syn. A. funesta) have been examined using incident light fluorescence microscopy and scanning electron microscopy. These surface coats contain residues of N-acetyl-D-glucosamine which were detected by treatment with wheat germ agglutinin labelled with either fluorescein or rhodamine. They also contain protein which was demonstrated by treatment with either pepsin or trypsin. These enzymes inhibited the attachment of the coryneform bacterium Clavibacter sp. to the surface coat, indicating that proteins play a crucial role in the adhesion of these bacteria to the nematode. This inhibition of attachment was reversed within 18 h after removal of the DL2 from the enzymes, indicating that the nematode was capable of renewing its surface proteins.

Composition of High Molecular Weight Excretions-Secretions from Infective Larvae of Meloidogyne javanica.

Infective larvae (J2) of Meloidogyne javanica were incubated in distilled water for up to 14 days, and their high molecular weight (> 1,000 daltons) excretions-secretions (ES) were isolated and partially characterized. The ES consisted of a mixture of proteins, glycoproteins, and proteoglycans or polysaccharides as revealed by differential staining on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and compositional analysis. Carbohydrate, with approximately equal amounts of neutral monosaccharides and hexosamines, was the major constituent of the ES, with only low levels of protein detected. Acidic sugar residues, including sialic acids, were not detected.

Responses of the plant parasitic nematodes Rotylenchulus reniformis, Anguina agrostis and Meloidogyne javanica to chemical attractants.

Rotylenchulus reniformis, Anguina agrostis and Meloidogyne javanica respond differently to gradients of chemical attractants. In chemotaxis assays performed on agarose plates, R. reniformis L2 larvae oriented their movement to several common inorganic salts, cyclic AMP and AMP, as well as to germinated host plant seeds. M. javanica L2 larvae were attracted to germinated seeds, but not to the salts tested, and A. agrostis dauer larvae were not strongly attracted to any of 12 different tested agents, including host root or shoot tips. Attraction of R. reniformis to salts was measured by comparing different pairwise combinations of ions at equivalent concentrations. The indicated order of attractiveness was: Cl- greater than Na+ greater than C2H3O2- greater than Mg2+, NH4+, SO4(2-). The least attractive salts, (NH4)2 SO4 and MgSO4, were weakly attractive at an orientation threshold of 1 mM, whereas the most attractive salt, MgCl2, was strongly attractive at a threshold of 0.2 mM Cl-. 3',5' cyclic AMP was strongly attractive at a threshold of 0.05 mM, whereas 5'-AMP was a weak attractant. Some of these responses may affect the distribution of R. reniformis in its natural environment.

Responses of Anguina agrostis to Detergent and Anesthetic Treatment.

The infective dauer juvenile (DJ2) of Anguina agrostis, a stage capable of surviving desiccation, is up to sixfold more resistant to the detergent sodium dodecyl sulfate than are freshly hatched juveniles or adult males, and twofold more resistant to the anesthetic phenoxypropanol. Thus, the DJ2, like dauer stages of other species, may also be more resistant to various types of environmental stress in its natural habitat. In A. agrostis, however, resistance appears to be acquired gradually during development of the second juvenile stage, rather than during a molt.

The Incorporation of Photosynthates by Meloidogyne javanica.

The root-knot nematode, Meloidogyne javanica, incorporated (1)C from its host after exposure of the plant to (1)CO. This uptake was relatively slow and was not detected in nematodes exposed to a labelled plant for periods of 2 and 4 h, but was after 24 h. Nematodes were grown in plants previously infected at weekly intervals to provide animals at various stages of growth. Plants were harvested 24 h after exposure to the label and the rate of incorporation per unit area of nematode was measured. This rate was found to be related to the nematode's physiological age and reached its peak at the time egg-laying commenced, after which it started to decline. The results support the hypothesis that the nematode functions as a metabolic sink.

Suppression of Embryogenesis and Hatching in Meloidogyne javanica by Thermal Stress.

Embryogenes is and hatching of eggs of Meloidogyne javanica were suppressed by brief heat treatment (46 C for 10 min). The period of suppression or arrested development differs according to the stage of development of the nematode when heat treatment is applied. The effect on hatching is much more pronounced than on embryogenesis.

Changes in the Ultrastructure of the Gelatinous Matrix of Meloidogyne javanica During Dehydration.

The fine structure of the gelatinous matrix of Meloidogyne javanica in both moist and dry states was studied by means of chemical fixation and thin sectioning techniques and the freeze-etch method. The matrix consists of an irregular meshwork when hydrated and a uniform granular mass of much greater density when dehydrated. The spaces in the hydrated meshwork are presumed to contain water. The change from a hydrated to a dehydrated state is accompanied by an overall shrinkage and hardening of the egg mass with a change in color from yellow to reddish-orange. The possible functions of this unusual glycoprotein are discussed.

Influence of Temperature on Embryogenesis in Meloidogyne javanica.

The optimum temperature for embryogenesis in Meloidogyne javanica lies between 25 and 30 C. Embryogenesis is slightly more rapid at 30 C (9-10 days), but more eggs complete development at 25 C (11-13 days). At temperatures of 25, 27.5, and 30 C, embryogenesis is about twice as rapid as at 20 C (23-25 days), and about four times as rapid as at 15 C (46-48 days). Time-lapse studies showed that the thermal optimum is similar throughout the different stages of embryonic development.