An ultrastructural study and stereological analysis of the colon wall in the cockroach Periplaneta americana

Ultrastructural differentiation of plasma membrane and cell junctions in the hindgut cells is synchronized with key developmental transitions in Porcellio scaber

Differentiation of transporting epithelial cells during development of animal organisms includes remodelling of apical and basal plasma membranes to increase the available surface for transport and formation of occluding junctions, which maintain a paracellular diffusion barrier. This study provides a detailed ultrastructural analysis of apical and basal plasma membrane remodelling and cell junction formation in hindgut cells during late embryonic and early postembryonic development of the crustacean Porcellio scaber. Hindgut cells in late-stage embryos are columnar with flat apical and basal plasma membranes. In early-stage marsupial mancae the hindgut cells begin to acquire their characteristic dome shape, the first apical membrane folding is evident and the septate junctions expand considerably, all changes being probably associated with the onset of active feeding. In postmarsupial mancae the apical labyrinth is further elaborated and the septate junctions are expanded. This coincides with the transition to an external environment and food sources. First basal infoldings appear in the anterior chamber of early-stage marsupial mancae, but in the papillate region they are mostly formed in postmarsupial mancae. In molting late-stage marsupial mancae, the plasma membrane acquires a topology characteristic of cuticle-producing arthropod epithelia and the septate junctions are considerably reduced.

Compartmentalization of microbial communities that inhabit the hindguts of millipedes

The gut lumen of the arthropod detritivore provides hospitable and multifaceted environments for diverse assemblages of microbes. Many microbes, including trichomycetes fungi, bacteria, and archaea establish stable, adherent communities on the cuticular surface secreted by the hindgut epithelium. Regional differences in the surface topography within the hindgut of a given millipede are reflected in differing and diverse microbial assemblages. The spirostreptid millipede Cambala speobia is a detritivore found on the floors of Texas caves. This millipede species has a very circumscribed distribution in North America and a diet confined to the limited litter that accumulates on floors of these caves while the common julid millipede Cylindroiulus caeruleocinctus, an introduced European species, feeds on the diverse litter found in organic soils throughout North America. In both millipedes, the gut lumina are inhabited along their entire lengths by microbes, with the highest microbial densities in the hindguts. The anterior third of the hindgut with its distinctive six-fold symmetry is lined by cuticle having fine polarized scales, and the posterior-most third is lined by smooth cuticle. Trichomycetes only inhabit the anterior third of the hindgut, and scattered patches of filamentous bacteria along with their smaller adherent microbes occupy the posterior third. The densest populations of microbes inhabit the central region of the hindgut. Over the cuticular surface of this hindgut region, uniformly distributed indentations mark possible channels for nutrient and water exchange between the hindgut lumen and host hemolymph. Films of microbes are adherent to the cuticle that lines the hindgut while those microbes in the remainder of the gut (i.e., foregut + midgut) represent mostly unattached inhabitants.

Physiology of environmental adaptations and resource acquisition in cockroaches

Cockroaches are a group of insects that evolved early in geological time. Because of their antiquity, they for the most part display generalized behavior and physiology and accordingly have frequently been used as model insects to examine physiological and biochemical mechanisms involved with water balance, nutrition, reproduction, genetics, and insecticide resistance. As a result, a considerable amount of information on these topics is available. However, there is much more to be learned by employing new protocols, microchemical analytical techniques, and molecular biology tools to explore many unanswered questions.

The bacterial community in the gut of the Cockroach Shelfordella lateralis reflects the close evolutionary relatedness of cockroaches and termites

Termites and cockroaches are closely related, with molecular phylogenetic analyses even placing termites within the radiation of cockroaches. The intestinal tract of wood-feeding termites harbors a remarkably diverse microbial community that is essential for the digestion of lignocellulose. However, surprisingly little is known about the gut microbiota of their closest relatives, the omnivorous cockroaches. Here, we present a combined characterization of physiological parameters, metabolic activities, and bacterial microbiota in the gut of Shelfordella lateralis, a representative of the cockroach family Blattidae, the sister group of termites. We compared the bacterial communities within each gut compartment using terminal-restriction fragment length polymorphism (T-RFLP) analysis and made a 16S rRNA gene clone library of the microbiota in the colon-the dilated part of the hindgut with the highest density and diversity of bacteria. The colonic community was dominated by members of the Bacteroidetes, Firmicutes (mainly Clostridia), and some Deltaproteobacteria. Spirochaetes and Fibrobacteres, which are abundant members of termite gut communities, were conspicuously absent. Nevertheless, detailed phylogenetic analysis revealed that many of the clones from the cockroach colon clustered with sequences previously obtained from the termite gut, which indicated that the composition of the bacterial community reflects at least in part the phylogeny of the host.

Communities of microbes that inhabit the changing hindgut landscape of a subsocial beetle

Microbes that have adopted endosymbiotic life styles not only have evolved to live in specialized habitats within living organisms, but the living habitats also have evolved to accommodate them. The hindgut of the passalid beetle (Odontotaenius disjunctus) is lined with a cuticle that undergoes dramatic topographic changes during the life cycle of the beetle. This manuscript addresses the changes that have been observed in time and space for the cuticular landscape of the hindgut as well as for the microbial communities within the hindgut. Microbial identity is based on morphology, culture, and extrapolation from previously reported passalid gut inhabitants.

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

Fixed nitrogen is a limiting nutrient in most terrestrial ecosystems and has been assumed to be supplied almost entirely by free-living bacteria as well as by bacteria living in association with plants. The survival and growth of many arthropods on diets with extremely high carbon to nitrogen (C:N) ratios suggest that these arthropods are not obtaining sufficient nitrogen from their diets but must be obtaining additional nitrogen from some other source(s). Estimates of N(2) fixation have suggested that symbiotic microbes of some arthropod hindguts could be obtaining this additional nitrogen as a result of nitrogen fixation. With the recent availability of antibody and nucleic acid probes, the presence of the enzyme that reduces dinitrogen gas to ammonia (nitrogenase) as well as the presence of its transcripts can be detected and localized with great sensitivity. A preliminary survey of a few detritivores indicates that nitrogen-fixing microbes of diverse forms are widespread in arthropod hindguts. In calculating nitrogen budgets, the possible contributions of nitrogen fixation by symbionts in arthropod guts, however, has been largely ignored. N(2) fixation in arthropod guts, with rates as high as 10-40 kg/ha/year being possible, may represent a significant contribution both to the growth of arthropods and to their ecosystem functions of processing carbon and nitrogen.

Morphological specializations of the digestive tract of Zacryptocerus rohweri (Hymenoptera: Formicidae)

Light, scanning, and transmission electron microscopy are used to examine the morphology and ultrastructure of the peculiar digestive tract of the turtle ant, Zacryptocerus rohweri. The proventriculus is heavily sclerotized and covered with clusters of small spines. Narrow spine-lined channels converging at the opening to the midgut act as a fine filter of food; particles >12.5 μm are unable to pass through the proventriculus. In the midgut, ultrastructural study reveals bacteria among the microvilli of midgut epithelial cells. The hindgut of Z. rohweri consists of an enlarged, dark-colored pouch filled with masses of bacteria of three major morphotypes. A thick layer of circular muscle and deep infoldings of the epithelium greatly increase surface area for absorption. Newly emerged individuals appear to acquire these microorganisms by soliciting material from the abdomen tip of other older workers in the colony. Whether or not the hindgut bacteria are true symbionts is unknown; their acquisition and presence suggest that they may supplement the ants' limited, liquid diet by supplying essential amino acids and other nutrients. J. Morphol. 234:253-262, 1997. © 1997 Wiley-Liss, Inc.

Properties of lactate dehydrogenase in a psychrophilic marine bacterium

Lactate dehydrogenase (EC 1.1.1.27) from Vibrio marinus MP-1 was purified 15-fold and ammonium activated. The optimum pH for pyruvate reduction was 7.4. Maximum lactate dehydrogenase activity occurred at 10 to 15 degrees C, and none occurred at 40 degrees C. The crude-extract enzyme was stable between 15 and 20 degrees C and lost 50% of its activity after 60 min at 45 degrees C. The partially purified enzyme was stable between 8 and 15 degrees C and lost 50% of its activity after 60 min at 30 degrees C. The thermal stability of lactate dehydrogenase was increased by mercaptoethanol, with 50% remaining activity at 42 degrees C.

The colon of Leucophaea maderae: fine structure and physiological features

The colon of L. maderae consists of a single columnar epithelium covered with a cuticle and of a musculo-connective sheath. The apical plasma membranes form a system of leaflets with numerous mitochondria inserted in association with microfilaments. Lateral plasma membranes are linked together by junctional complexes consisting of a zonula adherens and a long convoluted septate junction of the pleated type. In the basal region of the cell, numerous membrane infolds and scattered scalariform junctions with associated mitochondria are present. These cell specializations are typical of arthropod transporting organs, being distinctive features of ion and fluid transporting epithelia. The isolated colon exhibited a transepithelial electrical potential difference (PD) of about 100 mV, lumen side positive with respect to the haemolymph side. The PD was almost abolished by metabolic inhibitors, it was reduced by acetazolamide and SITS, and it was unaffected by ouabain. These effects suggest that HCO3- and Cl- are involved in the genesis of the PD, whereas Na+ is not directly responsible of the PD. Measurements of Na+ and Cl- fluxes across the colon wall confirm that Na+ moves following the PD across the tissue, while Cl- movement occurs against an electrochemical potential difference. The electrical profile of the epithelial cells is of the well type and it suggests that the primary or secondary active step for Cl- transport across the epithelium should be located at the mucosal border of the cell.

Microbial aspects of the cockroach hindgut

The cockroach hindgut has a complex, active microbiota, a large portion of which is associated with the chitinous gut wall. It provides a different environment from that of termites and other insects which are dependent on their hindgut microbiota for the digestion of cellulose. The pH of the midgut of Eublaberus posticus was not as high as it is in insects with a primarily cellulolytic nutrition. The hindgut of E. posticus was highly methanogenic, normal adults producing typically 10-25 mumol of methane per hour. The hindgut contained large amounts of the storage products polyphosphate and poly-beta-hydroxybutyrate. Dilution series on nonselective medium yielded 100 times more obligately anaerobic colonies than facultatively anaerobic colonies. The most common facultative isolates were Klebsiella oxytoca, Citrobacter freundii and Enterobacter agglomerans. Treatment of E. posticus with metronidazole caused a dedifferentiation of the different regions of the hindgut. One region of the hindgut is characterized by its visibly black color, a unique microbiota, and electron dense deposits in electron micrographs. Chemical determinations showed high concentrations of ferrous and sulfide ions in the region. X-ray microprobe analysis showed that some of the electron dense deposits consisted of iron, sulfur and lower amounts of copper, aluminium, and chromium associated with ruthenium red staining material. Spectra of other deposits revealed only silicon, which was not associated with ruthenium red.