Aldo Grigolo

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.

Symbionts in the oocytes of Blattella germanica (L.) (Dictyoptera : Blattellidae): Their mode of transmission

Abstract In Blattodea, the transmission of symbionts from one generation to the next is of transovarial type. The symbionts in Blattella germanica (L.) (Dictyoptera : Blattellidae) reach the ovary inside bacteriocytes in the 5-day-old nymphal instar, and are located among the ovarioles. Between the 11th and 17th day, the symbionts leave the bacteriocytes, cross the ovariole sheath, the tunica propria, and the follicular epithelium, and reach the space between the latter and the oocyte. In 17-day-old nymphs, the symbionts are in contact with the microvilli of the oocyte, remaining in this position until the end of the vitellogenic phase, when the microvillar border is progressively reduced. At this stage, the symbionts are actively phagocytosed by the oocyte before chorion formation.

Behavior of symbionts during oogenesis and early stages of development in the German cockroach, Blattella germanica (Blattodea)

Abstract Ovarial infection by symbiotic bacteroids and the formation of bacteriocytes were studied in Blattella germanica . The ovaries of an embryo are bacteroid-free until hatching from the ootheca. At this time, bacteriocytes migrate from the fat body and gather around the ovaries, without infecting germinal cells. Then the bacteriocytes penetrate the ovarioles and adhere to the oocytes, which they infect after several days, when auxocytosis begins. Bacteriocytes are derived from cells which originate from the nuclei of the mesodermal plasmodium, and their infection occurs when the symbionts specifically migrate from the embryonic epineural sinus toward these cells.

The fate of the endocytobionts of Blattella germanica (Blattaria: Blattellidae) and periplaneta Americana (Blattaria: Blattidae) during embryo development

Abstract In this paper we describe the behaviour of the symbiotic bacteria of Blattella germanica and Periplaneta americana during embryo development using transmission and scanning electron microscopy. In Blattella germanica, the bacteria are transferred by endocytosis to the egg cell and are sited in its peripheral cytoplasm; thence they begin to internalize in the yolk, using cytoskeletic structures which are probably only synthesized at this particular phase of their migration. In the 6–7‐day‐old embryo, the bacteria are in close contact with the vitellophages scattered in the yolk, where some of them appear to be in a degenerative phase. In Periplaneta americana, after the internalization of the bacteria, there is the formation of the mycetome which appears to be made up of a syncytial envelope, probably formed by the vitellophages, that contains a ball of symbionts of considerable number. During development, there is a progressive decline in the bacterial population, caused by complex lytic processe...

Mortality and tissue damage by heavy metal contamination in the German cockroach, Blattella germanica (Blattaria, Blattellidae)

Abstract The accumulation of lead, cadmium, mercury, and chromium, supplied in the diet under experimental conditions, was studied in adult German cockroaches. Chronic heavy‐metal exposure de termined different rates of mortality, higher in males than in fe males. In both sexes, Hg, Pb, and Cr bioaccumulated in time, whereas Cd remained at constant low concentrations. Histological studies showed that in some organs and structures, such as the ovary, the testis, the alimentary canal and the fat bodies, there were profound and irreversible pathological anomalies in their tis sues. Also the embryos of some treated females suffered heavy damage during development, and the symbiotic relationships be tween bacteria and fat body cells were deeply altered.

Effects of heat treatment on the symbiotic system of Blattoidea: Morphofunctional alterations of bacteriocytes

Abstract The purpose of the research was to study the morphological alterations that were produced in the symbiotic equilibrium of individuals of Leucophaea maderae, Periplaneta americana and Nauphoeta cinerea heat‐treated at + 39° C. The bacteria localized in the bacteriophorous vacuoles in the bacteriocytes of the samples treated underwent a series of structural modifications that led to protoplast formation. This phenomenon is similar to that which occurs in free‐living bacteria. The protoplasts were then further digested into the bacteriophorous vacuoles which had become cytolysosomes, to the point that they became residual bodies. When the process of endocellular lysis involved the whole symbiotic complement, the nucleus and the cytoplasmatic organelles of the bacteriocyte began to degenerate. These alterations were irreversible and could lead to the death of the cell. As a result, the number of bacteriocytes diminished. Heat treatment, which had lethal effects on the bacteria, altered the equilibriu...

Pattern of bacteriocyte formation in Periplaneta americana (L.) (Blattaria: Blattidae)

Abstract In the embryos of Periplaneta americana (L.) (Blattaria: Blattidae), bacterial symbionts, together with vitellophages, form a mycetomic structure inside the deutoplasm; this regresses between the 15th and 16th day after deposition of the ootheca. In this article we describe the migration of bacteria across the wall of the midgut from the mycetome, and the topographic distribution of pre-bacteriocyte cells. We also report that the pre-bacteriocytes are present only on the lateral surface of the internal abdominal fat bodies. We discuss the possible embryological origin and evolution of these cells, and put forward the hypothesis that pre-bacteriocytes are derived from oenocytes activated to perform phagocytosis.

Membrane systems in endocytobiosis I. Specializations of the vacuolar membrane in bacteriocytes of Blattella germanica (L.) (Dictyoptera: Blattellidae)☆

Abstract In bacteriocytes of Blattella germanica the symbionts are enveloped by the vacuolar membrane which is produced by the eukaryotic host cell. A study of serial thin sections shows the presence of vesicles originated from a blebbing process of the vacuolar membrane. Also, the presence of close adhesion sites between the vacuolar membrane and the prokaryotic cell envelope is revealed. Freeze-fracture replicas evidence aggregates of intramembrane particles on the vacuolar membrane while no corresponding membrane differentiation is present on the symbiont cell envelope. These observations are discussed in relation to the peculiarity of the interaction which involves both eukaryotic and prokaryotic cell membranes.

Endocytobiosis in Dictyoptera: the transmission of symbiotic bacteria in Blattella germanica L. (Dictyoptera Blattellidae)

The cockroach Blattella germanica hosts symbiotic bacteria in both the fat body and the ovary. The transmission of symbionts from one generation to the next is of the transovarial type. In 2nd-instar nymphs, bacteria leave the intraovaric bacteriocytes and reach the space between the follicular epithelium and the oocyte. At the end of the vitellogenic phase, the symbionts make contact with the egg surface and are taken in the egg periplasm. During early stages of embryogenesis, cells identifiable as plasmatocytes take in symbiont bacteria, scattered in the epineural sinus, by endocytosis. These cells, that we call pre-bacteriocytes, interacting with the prokaryote symbionts, initiate a series of structural and functional modifications that lead to the differentiation of the bacteriocytes.

On the mycetome formation in Periplaneta americana (Blattaria, Blattidae)

Abstract The behaviour of the symbiont bacteria of Periplaneta americana during the different phases of embryogenesis is described. The succession of events that determine an interaction between the vitellophagic energids and the symbionts is analysed, with the successive formation of a mycetome that at first envelops the bacteria and from which they then migrate to colonize the plasmatocytes that will become bacteriocytes. We suggest that the mycetome is the primary site of symbiotic population growth.