Tissue damage after acute intoxication by polychlorinated biphenyls in cockroaches.

It is common knowledge that polychlorinated biphenyls (PCBs) represent a serious threat to the health of both vertebrates and invertebrates. As far as the former are concerned, especially as regards human beings, a broad literature describes the direct and indirect effects induced by the PCBs on their systems and organs. Among invertebrates, the information available is mostly related to arthropods and is, however, very scarce. The aim of this work was to evaluate the effects of polychlorinated biphenyls (PCBs) on tissues and organs of individuals belonging to a species of Blattaria (Blattella germanica) treated with various doses of this toxic material. The pathologies found became more serious as the dosage increased and were present throughout the entire digestive system, in the fat body and in the male gonads: in these areas cell and tissue breakdown and severely damaged spermiogenesis were observed. In particular, the testes, Malpighian tubules and fat body accumulated an amorphous basophilic PAS-positive substance. Furthermore, the NOS-dependent NADPH diaphorase activity pattern in the retina and optic lobes was more evident in the treated than in the control insects.

Bacteriocyte population growth in Blattella germanica.

The number of bacteriocytes with nucleus in the M or S phase was analysed in relation to their rate of increase, throughout two nymphal instars (N1 and N6) of Blattella germanica Linnaeus (Blattaria, Blattellidae). We treated the experimental specimens with colcemid in order to visualize C-metaphases, and with labelled thymidine in order to evidence DNA synthesis in these bacteria-carrying cells. In both young and old nymphs, the C-metaphases showed a similar trend: their average number was only 0.3 per 100 bacteriocytes counted throughout the entire instars. In the young nymphs, the number of bacteriocytes in the S phase was congruent with the frequencies of the C metaphases. Since the number of M or S bacteriocytes was not sufficient to account for the observed increase in number of these endosymbiotic cells during nymphal development, we hypothesize a mechanism of bacterial transmission from bacteriocytes to other fat body cells that may explain the numerical growth of the bacteriocyte population.

Some aspects of intracellular symbiosis during embryo development of Mastotermes darwiniensis (Isoptera: Mastotermitidae).

All examined species of cockroaches have been shown to harbour intracellular bacteria in specialized cells (bacteriocytes) of the fat body. In termites, bacteria in specialized cells have been observed only in Mastotermes darwiniensis (Isoptera: Mastotermitidae). All of these bacteria have been assigned to the same eubacterial lineage, with the bacteria of M. darwiniensis as the sister group to the cockroach bacteria. While the main steps of the life cycle of cockroach bacteria have been described, little is known about the bacteria of M. darwiniensis. More specifically, no data are available on their behaviour during the development of this termite. Using both optical and electron microscopy methods, we examined embryos of M. darwiniensis at different developmental stages. Our results show that the integration of bacteria during the development of M. darwiniensis is implemented in the same way as in cockroaches. In particular, we observed the aggregation of a large amount of bacteria in a single mass in the yolk sac, with vitellophage-associated bacterial lysis. In cockroaches, a similar process has been described in detail for Periplaneta americana (Blattaria: Blattidae), where the bacterial mass is referred to as the transitory mycetome. The formation of a transitory mycetome could thus be regarded as an ancestral condition for cockroaches and termites.

Occurrence of apoptosis in serosa of Periplaneta americana l. (Blattaria: blattidae): ultrastructural and biochemical features.

In 16-17-day-old embryos of Periplaneta americana, the amnion-serosa penetrates the cavity of the middle intestine, where it forms a cluster of compressed roundish cells. We demonstrated that these cells degenerate throughout apoptosis. The programmed cell death revealed by morphological and biochemical approaches showed all the apoptotic steps: chromatin fragmentation and pyknosis, cytoplasm condensation, karyorrhexis, cytoplasm cleavage. Nevertheless, some ultrastructural peculiarities (atypical heterochromatin arrangement, appearance of nuclear envelope protrusions, absence of nucleolar structures) suggest that the apoptotic expression partially depends on the biological situation (type of organism and inducing factors) in which the programmed cell death takes place. The presence of histiocytic cells internalizing cell debris, of apoptotic and non-apototic derivation, may be correlated with the importance of recycling substances useful for embryo growth.

Flavobacteria as intracellular symbionts in cockroaches.

Animal cells are the sole habitat for a variety of bacteria. Molecular sequence data have been used to position a number of these intracellular microorganisms in the overall scheme of eubacterial evolution. Most of them have been classified as proteobacteria or chlamydiae. Here we present molecular evidence placing an intracellular symbiont among the flavobacteria-bacteroides. This microorganism inhabits specialized cells in the cockroach fat body and has been described as a mutualistic endosymbiont of uncertain phylogenetic position. The small subunit ribosomal DNA of these bacteria was analysed after polymerase chain reaction amplification to investigate their phylogeny. The endosymbionts of five species of cockroaches were found to make up a coherent group with no close relatives within the eubacterial phylum defined by the flavobacteria. In addition, the relationships among the endosymbionts, as revealed by DNA sequence data, appeared to be congruent with the host taxonomic relationships. Based on the host fossil record, a tentative calibration of the nucleotide substitution rate for the cockroach flavobacteria gave results congruent with those obtained for the aphid endosymbiotic proteobacteria.

Histochemical demonstration of oxidoreductase activities in the fat body and symbionts of Blattella germanica (Blattodea) following chlortetracycline-treatment.

The metabolic apport of prokaryotic symbionts in the fat body of Blattella germanica was investigated by histoenzymatic methods, using chlortetracycline-treated and normal strains. In the experimental insects, bacteriocytes showed a decreased oxidoreductase activity, whereas the staining intensity of the other cell types was generally unchanged. Electron microscopic observations showed that some bacteria were still present in the bacteriocytes of the treated insects, but exhibited degeneration patterns to a different extent; therefore, they are not likely to carry on any enzymatic activity. Hence, chlortetracycline, an antibiotic that blocks the transovaric transmission of the symbionts, is active also on the endocellular symbionts of the fat body.

Multiple forms with glucose 6-phosphate dehydrogenase activity in Musca domestica L. as revealed by electrophoresis on cellulose acetate gel.

Single newly emerged males of Musca domestica, WHO strain, usually show five electrophoretic bands of glucose 6-phosphate dehydrogenase (G6PD) activity. Of these five molecular forms, designated with Roman numerals in order from the origin, we have considered the first three: these have been characterized with respect to their substrate and coenzyme specificity and to their sensitivity to some sulfhydryl inhibitors. The data show band III to be G6P specific, nicotinamide adenine dinucleotide phosphate dependent and to be a type I enzyme according to Kamada and Hori's classification. Bands I and II, on the other hand, show wide substrate specificity and low sensitivity to the sulfhydryl inhibitors assayed. In addition, in the absence of an exogenous substrate and in the presence of nicotinamide adenine dinucleotide as a coenzyme, fairly weak bands, which can be ascribed to the so called "nothing dehydrogenase" effect, are seen in the position I and II. Nevertheless, the data reported do not allow a clear definition of the enzymatic type corresponding to bands I and II of G6PD activity.

The in vitro conversion of a specific molecular form of glucose 6-phosphate dehydrogenase from Musca domestica L.

A nicotinamide adenine dinucleotide phosphate dependent glucose 6-phosphate dehydrogenase (G6PD), belonging to type I of Kamada and Hori's classification, is present on the zymograms of newly emerged males of Musca domestica. It is capable of undergoing tryptic degradation and being thus transformed into a different active enzymatic form, with some of its catalytic properties unchanged, but with different electrophoretic mobility. We show in this paper that this specific G6PD form of gut origin in M. domestica is not a tissue-specific enzyme, but rather a product of hydrolytic degradation by gut proteinases which act during the process of homogenization. Besides, the G6PD of type I in the housefly is shown to be sensitive to the "storage effect" and to protection by mercaptoethanol, contrary to its hydrolytic gut form which is not sensitive to these processes. In this connection, we discuss the possible reasons for these differences in behavior.