Fungal symbionts (Harpellales) in Norwegian aquatic insect larvae

Collections of aquatic insect larvae in Norway, over a 40 d period in May and Aug 2002, resulted in finding more than 25 species and one new genus of Harpellales (Trichomycetes). Nine new fungal symbionts are described and named: Ephemerellomyces aquilonius (a new monotypic genus), Glotzia stenospora and Legeriosimilis europaeus in mayfly nymphs (Ephemeroptera); Genistelloides amplispora and G. communis in stonefly nymphs (Plecoptera); and Smittium biforme, Sm. precipitiorum, Stachylina acutibasilaris and St. lentica in midge larvae (Diptera: Chironomidae). Two possibly new species of Smittium in Chironomidae larvae are described but not formally named. New hosts and biogeographical distributions are recorded for 14 previously described species, including the rare occurrence of Smittium simulii in mosquito larvae.     

Developmental studies of vitellogenesis in a dipteran insect, Chironomus thummi.

Vitellogenesis of developing oocytes of a Dipteran insect Chironomus thummi has been investigated. The onset of yolk deposition is marked by the differentiation of the oolemma including the formation of microvilli and endocytosis. These changes are accompanied by the appearance of small electron dense granules, similar in density to the yolk platelets, arising through the sequential accumulation of material into the matrices of the multivesicular bodies (MVBs). These latter structures are produced in the previtellogenic oocytes of the pharate pupae and early pharate adults. Often the limiting membrane of the MVBs bears bristle coats resembling those of the coated vesicles of pinocytotic origin, suggesting that it is through the fusion with the pinocytotic vesicles that the accumulation of dense material in the MVBs results. That the Mvbs transform into structures resembling yolk granules is supported by statistical analysis which indicates that the decrease in the number of electron-dense MVBs coincides with the increase in the occurrence of small dense yolk granules. In the late pharate adult stage the yolk granules are considerably larger than those of earlier stages. It is during this period that at least one type of electron-dense granule occurs at the oocyte follicle cell border, and that these apparently contribute to the formation of the vitelline envelope. The results of the present study indicate that preformed oocytic elements, the MVBs, play a strategic role in the formation and arrangement of the yolk granules in Chironomus. Since these structures account for the bulk of the ooplasm, it appears that the MVBs are at least partly responsible for the correct ordering of the cytoplasmic constituents of the oocytes, which is critical for the proper development and differentiation of the embryo.     

水生双翅目昆虫监测水体重金属污染的研究

水生双翅目昆虫是监测水体重金属污染的理想对象。文章归纳用于监测重金属污染的水生双翅目昆虫的种类,重点介绍水生双翅目昆虫在重金属污染下外部形态、内部结构、生化及分子水平的变化,以及相关生物标志物的研究,为水生双翅目昆虫用于水体重金属污染的生物监测提供科学依据。     

Molecular characterization of an insect genome: Chironomus thummi.

DNA extracted from Chironomus thummi larvae was studied by isopycnic centrifugation in CsCl, thermal denaturation and DNA-DNA reassociation techniques. The mean G+C content of the C. thummi DNA is 28-29% as indicated both by centrifugation in CsCl and thermal denaturation. According to optical reassociation analysis of total DNA and of isolated DNA fractions the C. thummi genome is composed of at least four components. About 80% of the DNA is classified as unique with a kinetic complexity of nearly 7 X 10(10) daltons. 6-8% intermediate DNA exhibits a kinetic complexity slightly above 10(8) daltons with a mean repetition frequency of 35. 11-13% fast-reassociating DNA has a kinetic complexity slightly above 10(6) daltons with a mean repetition frequency of 6000. 3-5% of the DNA cannot be properly studied by the optical reassociation technique and probably contains inverted repeats. The thermal denaturation behaviour of isolated DNA fractions indicated that most of the repetitive sequences in the C. thummi genome are tightly interspersed.     

Behavioural,developmental and morphological responses of Chironomus gr. thummi larvae (Diptera,Nematocera) to aquatic pollution

Populations of Chironomus gr. thummi larvae from two differently polluted lowland streams (Dommei, high cadmium and zinc; Ijse, medium copper and organic xenobiotics) were screened for behavioural and morphological responses to pollution. Behaviours such as locomotion (swimming and looping), respiration movements (ventilation) and inactivity were quantified with impedance conversion technique. Chironomids from the Dommel were more active than larvae from Ijse. In Ijse, deformed larvae showed less emergence, less locomotion and more ventilation than non-deformed larvae. In Dommel, deformed and normal larvae were equally fit (behaviour, emergence).     

Anaerobic and aerobic energy metabolism in the larvae (tetrathyridia) of Mesocestoides corti

The tetrathyridia of Mesocestoides corti produce lactate, succinate, acetate, and CO₂ as major carbon-containing end products during in vitro incubation with glucose as the substrate. Differences in the rate of glucose consumption and lactate production under anaerobic or aerobic conditions were observed, but their significance could not be determined. However, succinate production was greatly decreased in the presence of oxygen.The relative activities and intracellular distribution of various enzymes involved in energy-supplying metabolism of the larvae appear to conform to the pathways observed in other parasitic helminths known to produce lactate, succinate, and volatile fatty acids as metabolic end products. Some common features found in this respect are the relatively low pyruvate kinase activity, the presence of a highly active cytoplasmic phosphoenolpyruvate carboxylase and the capability of mitochondrial membrane bound fumarate reductase to reduce fumarate by means of NADH. Although a stimulatory effect of fructose-1,6-diphosphate on the reaction velocity of pyruvate kinase occurred, the absolute activity of this enzyme is very low.Nearly all the enzymes required for Krebs cycle activity are available in the tetrathyridia. Under the assay conditions employed by us, only NAD-dependent isocitrate dehydrogenase could not be demonstrated. The small amounts of ¹⁴CO₂ liberated from 6-¹⁴C-glucose suggest that the cycle in its classical form probably only functions at a very low rate. The incorporation of ¹⁴C from labeled glucose into glycogen indicates the presence of enzymes capable of glycogenesis. The incorporation rate was found to be higher in the presence of oxygen than under anaerobic conditions. On account of the very low NAD-linked glycerol-3-phosphate dehydrogenase activity the glycerolphosphate cycle may be of minor importance for the tetrathyridia.As a result of these studies a scheme for the main carbohydrate dissimilating pathways in the tetrathyridia is proposed and the significance of oxygen with respect to energy-supplying metabolism is discussed.     

Diabetic larvae and obese flies-emerging studies of metabolism in Drosophila

The past few years have seen a shift in the use of Drosophila, from studies of growth and development toward genetic characterization of carbohydrate, sterol, and lipid metabolism. This research, reviewed below, establishes a new foundation for using this simple genetic model system to define the basic regulatory mechanisms that underlie metabolic homeostasis and holds the promise of providing new insights into the causes and treatments of critical human disorders such as diabetes and obesity.     

Anaerobic metabolism in plants

Exposure to oxygen deficits is more widespread in biological systems than is commonly believed. Until recently, the general perception of anaerobic metabolism was often limited to the induction of alcoholic or lactic acid fermentation as the sole biochemical response to hypoxia/anoxia. Developments in the physiology, biochemistry, and molecular biology of anaerobic responses in invertebrates, lower plants, and higher plants have demonstrated that, depending upon the species, anaerobic metabolism may encompass much more than simple glycolytic metabolism. Here, recent progress in elucidating the mechanism(s) determining tolerance versus intolerance to anaerobic environments in higher plants is discussed, drawing most heavily on experimental systems using seeds or seedlings.     

Fatty acid composition of aquatic insect larvae Stictochironomus pictulus (Diptera: Chironomidae): evidence of feeding upon methanotrophic bacteria

Larvae of the chironomid Stictochironomus pictulus were collected from Lake Biwa, central Japan. Both the fatty acid composition of the total lipid fraction and the carbon stable isotope ratios of whole larvae were determined. Larvae showed δ¹³C values of −57.4‰ to −62.4‰, similar to the values of methane recorded from the lake sediments. A high level of monounsaturated fatty acids (MUFAs; approximately 50% of total fatty acids) and an extremely low level of n-3 series polyunsaturated fatty acids (PUFAs) in the total lipids of S. pictulus indicated a predominantly bacterial nutrition for this species. Moreover, chironomid tissues contained large amounts of the Type I methanotroph group-specific fatty acid, 16:1(n-8) (approximately 8% of total fatty acids). This is the first time such a fatty acid biomarker has been described from freshwater invertebrates. The data suggest that S. pictulus larvae directly feed upon methanotrophic bacteria.     

Anaerobic metabolism of phenol in proteobacteria and further studies of phenylphosphate carboxylase

Anaerobic phenol metabolism was studied in three facultative aerobic denitrifying bacteria, Thauera aromatica, “Aromatoleum aromaticum” strain EbN1 (Betaproteobacteria), and Magnetospirillum sp. (Alphaproteobacterium). All species formed phenylphosphate and contained phenylphosphate carboxylase but not phenol carboxylase activity. This is in contrast to direct phenol carboxylation by fermenting bacteria. Antisera raised against subunits of the Thauera phenylphosphate synthase and phenylphosphate carboxylase partly cross-reacted with the corresponding proteins in the other species. Some unsolved features of phenylphosphate carboxylase were addressed in T. aromatica. The core sub-complex of this enzyme consists of three different subunits and catalyzes the exchange of ¹⁴CO₂ with the carboxyl group of 4-hydroxybenzoate, but not phenylphosphate carboxylation. It was inactivated by oxygen or by the oxidizing agent thionin and fully reactivated under reducing conditions. The purified recombinant phosphatase subunit alone had only low phenylphosphate phosphatase activity in the absence of the other components. However, activity was strongly enhanced in the presence of the core enzyme resulting in phenylphosphate carboxylation. Hence, a tight interaction of the carboxylase subunits is required for dephosphorylation of phenylphosphate, which is coupled to the concomitant carboxylation of the produced phenolate to 4-hydroxybenzoate, thus preventing a futile cycle.