Isolation of bacteria from the luminous organ of the fish Monocentris japonica has revealed that the organ contains a pure culture of luminous bacteria. For the four fish examined, all contained Photobacterium fischeri as their luminous bacterial symbiont. This is the first time that P. fischeri has been identified in a symbiotic association.A representative isolate (MJl) of the light organ population was selected for in vivo studies of its luminous system. Several physiological features suggest adaptation for symbiotic existence. First, MJl has been shown to produce and respond to an inducer of luciferase that could accumulate in the light organ. Secondly, the specific activity of light production was seen to be maximal under low, growth-limiting concentrations of oxygen. Thirdly, unlike another luminous species (Beneckea harveyi), synthesis of the light production system of these bacteria is not catabolite repressed by glucose—a possible source of nutrition in the light organ. Fourthly, when grown aerob...

Symbiotic association of Photobacterium fischeri with the marine luminous fish Monocentris japonica; a model of symbiosis based on bacterial studies.

The Douglas fir terpene α-pinene was shown to inhibit the growth of a variety of bacteria and a yeast. Other terpenes of the Douglas fir, including limonene, camphene, and isobornyl acetate, were also inhibitory to Bacillus thuringiensis. All terpenes were inhibitory at concentrations normally present in the fir needle diet of Douglas fir tussock moth larvae. The presence of such terpenes in the diet of these insects was found to strongly influence the infectivity of B. thuringiensis spores for the Douglas fir tussock moth larvae. The terpene α-pinene destroyed the cellular integrity and modified mitochondrial activity in certain microorganisms.

Some effects of douglas fir terpenes on certain microorganisms.

Light microscopy and scanning and transmission electron microscopy were used to examine the in situ morphology of the gut microbiota of Reticulitermes flavipes and Caoptotermes formosanus. Laboratory-maintained termites were used and, for R. flavipes, specimens were also prepared immediately after collection from a natural infestation. The latter endeavor enabled a study of different castes and developmental stages of R. flavipes and revealed differences in the microbiota of field versus laboratory specimens. The termite paunch microbiota consisted of an abundance of morphologically diverse bacteria and protozoa. Thirteen bacterial morphotypes in the paunch were described in detail: seven were observed only in R. flavipes, three were observed only in C. formosanus, and three were common to both termite species. The paunch epithelium was densely colonized by bacteria, many of which possessed holdfast elements that secured them tightly to this tissue and to other bacterial cells. Besides bacteria, the protozoan Pyrsonympha vertens adhered to the paunch epithelium of R. flavipes by means of an attachment organelle. Cuplike indentations were present on the paunch epithelial surface and were sites of bacterial aggregation. Ultrastructural features of cups suggested their involvement in ion absorption. In addition to the paunch, the midgut was also colonized by bacteria that were situated between epithelial microvilli. Results suggest that bacteria are an integral part of the gut ecosystem.

In situ morphology of the gut microbiota of wood-eating termites [Reticulitermes flavipes (Kollar) and Coptotermes formosanus Shiraki]

The number of bacteria in the intestine of 12 species of arthropods, belonging to 7 different orders, was determined to obtain information about the significance of intestinal bacteria for the digestion of food. Therefore, a simple and effective method for direct counts of 4′, 6-diamidino-2-phenylindole (DAPI) stained bacteria from the gastrointestinal tract of arthropods was developed. The intestinal bacteria could be released from the gut wall by ultrasonic treatment in the presence of sodium tetrapyrophosphate (PPi). The bacterial counts ranged between 0.2 and 3.6 × 109 (ml gut)−1 in the foregut, 0.2 and 28 × 109 (ml gut)−1 in the midgut, and 0.1 and 190 × 109 (ml gut)−1 in the hindgut. The foregut and hindgut of Hylotrupes bajules larvae were devoid of bacteria; the whole intestinal tract of Eurycanta calcarata and Schistocerca gragaria contained only low numbers of bacteria. The population of bacteria in some parts of the intestinal tract of several arthropods were high enough to suggest a potential contribution to digestive processes.

Bacteria in the Intestinal Tract of Different Species of Arthropods

Could microbial symbionts of arthropod guts contribute significantly to nitrogen fixation in terrestrial ecosystems

Scanning electron microscopy and transmission electron microscopy have been used to visualize the morphology and ultrastructure of two types of microorganisms in the hindgut of the cockroach Blaberus posticus. Both organisms, designated as either short or long rods, are attached to chitinous projections from the gut wall. Micrographs suggest that the organisms are prokaryotic with a cell wall complex characteristic of gram-negative bacteria. However, certain differences were noted between the cell wall complex of the two types. Two forms of the long-rod type were noted, with one form appearing to be a "degenerate" or "transitional" cell. In the degenerate cells, vesicles are observed that often are contiguous with the cytoplasmic membrane. There are indications that the long-rod type may divide by longitudinal fission. Neither the short- nor long-rod type has been cultivated in its respective recognizable form.

A J Markovetz

Papers

Ultrastructal morphology of some prokaryotic microorganisms associated with the hindgut of cockroaches.