Gerard M. Thomas

Xenorhabdus gen. nov., a Genus of Entomopathogenic, Nematophilic Bacteria of the Family Enterobacteriaceae

A new genus, Xenorhabdus, is created to accommodate large, gram-negative, rod-shaped, facultatively anaerobic, entomopathogenic bacteria which are intimately associated with entomogenous nematodes. The normal habitat of these bacteria is the intestinal lumen of nematodes or the body cavity of host insects into which they have been introduced by the nematodes. The genus is placed in the family Enterobacteriaceae since the bacteria possess most of the important characteristics of this family. Xenorhabdus differs from other genera of Enterobacteriaceae in large cell size, failure to reduce nitrates to nitrites, intimate association with entomogenous nematodes, entomopathogenesis, and immunological characteristics. The type species is Xenorhabdus nematophilus (Poinar and Thomas) comb. nov. (synonym: Achromobacter nematophilus Poinar and Thomas). Xenorhabdus luminescens sp. nov., a bioluminescent, entomopathogenic bacterium isolated from the intestinal lumen of an entomogenous nematode, Heterorhabditis bacteriophora, is also described. In addition to their immunological differences, the two species are dissimilar in that X. luminescens is positive for bioluminescence and catalase activity, whereas X. nematophilus is not. The type strain of X. nematophilus is ATCC 19061, and that of X. luminescens is strain Hb (= ATCC 29999).

Significance of Achromobacter nematophilus Poinar and Thomas (Achromobacteraceae: Eubacteriales) in the development of the nematode, DD-136 (Neoaplectana sp. Steinernematidae).

By culturing Galleria mellonella, Neoaplectana sp. (DD-136) and Achromobacter nematophilus separately under axenic conditions in the laboratory, it was possible to study the relationship between the bacterium and nematode during nematode parasitism of the insect. The infective-stage juveniles of the nematode were able to penetrate and kill the insect host without the presence of A. nematophilus or any other bacterium. However, without accompanying bacteria the nematode was unable to reproduce. Only when A. nematophilus or a possible replacement, such as Pseudomonas aeruginosa , was added to the blood did reproduction occur. The relationship between A. nematophilus and the nematode is considered a mutualistic one, since the bacterium lives and is protected inside the intestine of the free-living stage of the nematode and is transported and released by the nematode to the haemolymph of a host insect. The nematode, in turn, is dependent on the bacterium for reproduction.

Characteristics of the Specific Bacterium Associated With Heterorhabditis Bacteriophora (Heterorhabditidae: Rhabditida)

The infective stage juveniles of Heterorhabditis bacteriophora Poinar (Heterorhabditidae: Rhabditida) carry a specific bacterium in the lumen of their pharynx and intestine. The bacterial cells are large, motile, peritrichously flagellated, gram negative, non-sporeforming rods. They are released by the infective-stage juveniles after they reach the hemolymph of susceptible insects. Additional cultural and biological characteristics of the specific bacterium are presented.

Diagnostic manual for the identification of insect pathogens.

Identification of the Groups of Insect Pathogens.- Fungi.- Taxonomic Status.- Life Cycle.- Characteristics of Infected Insects.- Methods of Examination.- Isolation and Cultivation.- Identification.- Testing for Pathogenicity.- Storage.- Literature.- Key to Common Genera.- Bacteria.- Taxonomic Status.- Life Cycle.- Characteristics of Infected Insects.- Factors Affecting Bacterial Infections.- Methods of Examination.- Isolation and Cultivation.- Identification.- Testing for Pathogenicity.- Storage.- Literature.- Key to Common Genera and Species.- Viruses.- Taxonomic Status.- Life Cycle.- Characteristics of Infected Insects.- Methods of Examination.- Isolation.- Identification.- Testing for Pathogenicity.- Storage.- Literature.- Key to Groups of Viruses.- Protozoa.- Taxonomic Status.- Life Cycle.- Characteristics of Infected Insects.- Methods of Examination.- Isolation and Cultivation.- Identification.- Testing for Pathogenicity.- Storage.- Literature.- Key to Common Genera.- Rickettsias.- Taxonomic Status.- Life Cycle.- Characteristics of Infected Insects.- Factors Affecting Natural Infections.- Methods of Examination.- Isolation and Cultivation.- Identification.- Testing for Pathogenicity.- Storage.- Literature.- Key to Genera and Species.- Techniques.- Culture Media, Differential Media, and Ringers Solution.- Bacteriological Tests.- Stains and Staining Procedures.- Miscellaneous Techniques.- Literature Cited.

The nature of Achromobacter nematophilus as an insect pathogen

Abstract The bacterium Achromobacter nematophilus, which has been isolated from two populations of nematodes belonging to the genus Neoaplectana, was found to be extremely lethal to larvae of Galleria mellonella when injected into the hemocoel. Although producing no obvious effects if fed per os, when one to three bacterial cells were introduced into the body cavity, the insects usually died. In nature, this bacterium occurs in the body of insects attacked by certain neoaplectanid nematodes and, between periods of insect infection, inside the gut of infective stage nematodes. The cells are very fastidious and appear to have a very transient existence in soil or water.

Biology and Redescription of Pheromermis Pachysoma (V. Linstow) N. Gen., N. Comb. (Nematoda: Mermithidae), a Parasite of Yellowjackets (Hymenoptera: Vespidae)

Pheromermis pachysoma (von Linstow) n. gen., n. comb., a parasite of the yellowjacket, Vespula pensylvanica (Saussure), is described from California. The genus, Pheromermis, is characterized by the presence of four submedian cephalic papillae; large anteriorly placed cup-shaped amphids; an S-shaped vagina not bent in a transverse plane to the body; six hypodermal cords; paired, short, separate spicules; cuticle with cross fibers; and eggs lacking processes. The development of P. pachysoma is unique because a paratenic or transport host is required for completion of the life cycle. The adult nematodes occur in water or saturated soil and the eggs are fully embryonated at oviposition. The eggs hatch in the gut of various insects and infective stage juveniles penetrate the gut wall and enter a quiescent state in the tissues of these paratenic hosts. Wasp larvae are probably infected when they are fed paratenic hosts captured by worker yellowjackets. Postparasitic juveniles of P. pachysoma emerge from adult wasps when the latter visit wet sites after their fall emergence from the nest. The ant parasite, Mermis myrmecophila Baylis, is transferred to the genus Pheromermis.

Growth and luminescence of the symbolic bacteria associated with the terrestrial nematode, Heterorphabditis bacteriophora

Abstract The terrestrial nematode, Heterorhabitis bacteriophora contains symbiotic terrestrial bacteria which emit low but detectable luminescence in the symbiotic state. When the nematode is ingested by caterpillar larvae (or other insects), the bacteria are released into t he hemocoel, where they grow rapidly (doubling time of 3 h or less), reach high cell numbers (109 ml−1 greater), and are brightly luminous. The enzyme that catalyzes light emission is a typical bacterial luciferase as judged by its substrate requirements and the kinetics in vitro. Bacteria grown in synthetic media emit luminescence that is nearly identical in color with that of other luminescent bacteria, while the color of light from infected caterpillar is substantially red-shifted.

A new bacterium, Achromobacter nematophilus sp.nov. (Achromobacteriaceae: Eubacteriales) associated with a nematode.

ABSTRACT Achromobacter nematophilus sp. nov., isolated from the intestinal lumen of a species of Neoaplectana (Steinernematidae: Nematoda), is described. It can be distinguished from other species of Achromobacter by its larger cell size and action on gelatin and litmus milk.

Further Characterization of Achromobacter nematophilus from American and Soviet Populations of the Nematode Neoaplectana carpocapsae Weiser

Cultural and biochemical studies showed no significant differences between a bacterium isolated from the nematode Neoaplectana carpocapsae in the Soviet Union and the bacterium, originally described as Achromobacter nematophilus, isolated from the DD-136 strain of N. carpocapsae in the United States. Further characterization of A. nematophilus is presented, but its reallocation to a more suitable genus should await the reorganization of the families Achromobacteraceae and Enterobacteriaceae now in progress.

Effect of neoaplectanid and heterorhabitid nematodes (Nematoda: Rhabditoidea) on the millipede Oxidus gracilis

Abstract At high dosages, infective-stage juveniles of Neoaplectana carpocapsae and Heterorhabditis heliothidis were able to penetrate into and kill the garden millipede. Nematode development was inhibited by host defense reactions which consisted of encapsulation and enmeshment in tracheoles and connective tissue surrounding the millipedes midgut. Foreign bacteria quickly entered the millipedes hemocoel at death and out-competed the nematodes symbiotic bacteria, Xenorhabdus sp. The dauer stages of an unidentified rhabditid nematode were associated with the living millipede. These nematodes reproduced on the millipedes cadaver.