Johannes H. P. Hackstein

An anaerobic mitochondrion that produces hydrogen.

Hydrogenosomes are organelles that produce ATP and hydrogen, and are found in various unrelated eukaryotes, such as anaerobic flagellates, chytridiomycete fungi and ciliates. Although all of these organelles generate hydrogen, the hydrogenosomes from these organisms are structurally and metabolically quite different, just like mitochondria where large differences also exist. These differences have led to a continuing debate about the evolutionary origin of hydrogenosomes. Here we show that the hydrogenosomes of the anaerobic ciliate Nyctotherus ovalis, which thrives in the hindgut of cockroaches, have retained a rudimentary genome encoding components of a mitochondrial electron transport chain. Phylogenetic analyses reveal that those proteins cluster with their homologues from aerobic ciliates. In addition, several nucleus-encoded components of the mitochondrial proteome, such as pyruvate dehydrogenase and complex II, were identified. The N. ovalis hydrogenosome is sensitive to inhibitors of mitochondrial complex I and produces succinate as a major metabolic end product—biochemical traits typical of anaerobic mitochondria. The production of hydrogen, together with the presence of a genome encoding respiratory chain components, and biochemical features characteristic of anaerobic mitochondria, identify the N. ovalis organelle as a missing link between mitochondria and hydrogenosomes.

Spermatogenesis in Drosophila

Spermatogenesis is an intensively studied developmental process in Drosophila melanogaster and Drosophila hydei. Nonetheless, some phases of the development of the germ cells are still hardly understood. The main gap of information is with respect to the germ line-soma differentiation and the formation of the gonad. Our knowledge about pole cell formation and its migration to the testis anlagen is still incomplete, and nearly nothing is known about the genetic control of these processes. In addition, some of these processes may be shared by both spermatogenesis and oogenesis. Therefore, this chapter will deal mainly with later stages of spermatogenesis, i.e., with the genetic control of the spermatogenesis sensu strictu.

Bacteria in the Intestinal Tract of Different Species of Arthropods

A bstractThe 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.

FECAL METHANOGENS AND VERTEBRATE EVOLUTION

It has been assumed that the feeding habits of vertebrates predispose the variety of intestinal differentiations and the composition of the microbial biota living in their intestinal tracts. Consequently, the presence of methanogenic bacteria in the various differentiations of the large intestine and the foregut of herbivorous vertebrates had been attributed primarily to the existence of anaerobic habitats and the availability of carbon dioxide and hydrogen originating from the fermentative microbial digestion of plant‐based diets. However, Australian ratites, many murids, and several New World primates lack methanogens, despite their intestinal differentiations and their vegetarian feeding habits. Crocodiles, giant snakes, aardvarks, and ant‐eaters on the other hand release significant amounts of methane. A determination of methane emissions by 253 vertebrate species confirmed that competence for intestinal methanogenic bacteria is shared by related species and higher taxa, irrespective of different feeding habits. In “methanogenic” branches of the evolutionary tree, a variety of differentiations of the large intestine evolved and, in some cases, differentiations of the foregut. In contrast, the lack of competence for methanogens in chiropterans/insectivores and carnivores apparently has precluded the evolution of specialized fermenting differentiations of the digestive tract. Our observations reveal that the presence of intestinal methanogenic bacteria is under phylogenetic rather than dietary control: competence for intestinal methanogenic bacteria is a plesiomorphic (primitive‐shared) character among reptiles, birds, and mammals. This competence for methanogenic bacteria has been crucial for the evolution of the amniotes.

Parasitic apicomplexans harbor a chlorophyll a-D1 complex, the potential target for therapeutic triazines

Ultrastructural evidence is presented for the presence of plastid-like organelles inToxoplasma gondii, Sarcocystis muris, Babesia ovis, andPlasmodium falciparum. In addition, it was shown that merozoites ofT. gondii contain protochlorophyllidaea and traces of chlorophylla bound to the photosynthetic reaction centers I PS I and PS II. ApsbA gene was isolated from merozoites ofS. muris by the polymerase chain reaction (PCR). Partial sequencing of the PCR product revealed that the herbicide-binding region is highly conserved. Therefore, it is likely that the sensitivity of apicomplexans to the herbicide toltrazuril depends on the interaction of the herbicide with the D1 protein of the photosynthetic reaction center of the parasites organelles.

Towards an understanding of the genetics of human male infertility: lessons from flies

It has been argued that about 4-5% of male adults suffer from infertility due to a genetic causation. From studies in the fruitfly Drosophila, there is evidence that up to 1500 recessive genes contribute to male fertility in that species. Here we suggest that the control of human male fertility is of at least comparable genetic complexity. However, because of small family size, conventional positional cloning methods for identifying human genes will have little impact on the dissection of male infertility. A critical selection of well-defined infertility phenotypes in model organisms, combined with identification of the genes involved and their orthologues in man, might reveal the genes that contribute to human male infertility.

Multiple origins of hydrogenosomes : functional and phylogenetic evidence from the ADP/ATP carrier of the anaerobic chytrid Neocallimastix sp.

A mitochondrial‐type ADP/ATP carrier (AAC) has been identified in the hydrogenosomes of the anaerobic chytridiomycete fungus Neocallimastix sp. L2. Biochemical and immunocytochemical studies revealed that this ADP/ATP carrier is an integral component of hydrogenosomal membranes. Expression of the corresponding cDNA in Escherichia coli confers the ability on the bacterial host to incorporate ADP at significantly higher rates than ATP – similar to isolated mitochondria of yeast and animals. Phylogenetic analysis of this AAC gene (hdgaac) confirmed with high statistical support that the hydrogenosomal ADP/ATP carrier of Neocallimastix sp. L2 belongs to the family of veritable mitochondrial‐type AACs. Hydrogenosome‐bearing anaerobic ciliates possess clearly distinct mitochondrial‐type AACs, whereas the potential hydrogenosomal carrier Hmp31 of the anaerobic flagellate Trichomonas vaginalis and its homologue from Trichomonas gallinae do not belong to this family of proteins. Also, phylogenetic analysis of genes encoding mitochondrial‐type chaperonin 60 proteins (HSP 60) supports the conclusion that the hydrogenosomes of anaerobic chytrids and anaerobic ciliates had independent origins, although both of them arose from mitochondria.

A hydrogenosome with pyruvate formate-lyase: anaerobic chytrid fungi use an alternative route for pyruvate catabolism

The chytrid fungi Piromyces sp. E2 and Neocallimastix sp. L2 are obligatory amitochondriate anaerobes that possess hydrogenosomes. Hydrogenosomes are highly specialized organelles engaged in anaerobic carbon metabolism; they generate molecular hydrogen and ATP. Here, we show for the first time that chytrid hydrogenosomes use pyruvate formate‐lyase (PFL) and not pyruvate:ferredoxin oxidoreductase (PFO) for pyruvate catabolism, unlike all other hydrogenosomes studied to date. Chytrid PFLs are encoded by a multigene family and are abundantly expressed in Piromyces sp. E2 and Neocallimastix sp. L2. Western blotting after cellular fractionation, proteinase K protection assays and determinations of enzyme activities reveal that PFL is present in the hydrogenosomes of Piromyces sp. E2. The main route of the hydrogenosomal carbon metabolism involves PFL; the formation of equimolar amounts of formate and acetate by isolated hydrogenosomes excludes a significant contribution by PFO. Our data support the assumption that chytrid hydrogenosomes are unique and argue for a polyphyletic origin of these organelles.

Mitochondria, hydrogenosomes and mitosomes: products of evolutionary tinkering!

One hundred years ago, C. Mereschkowsky, “Privatdozent an der Kaiserlichen Universitat in Kasan (Russia)” published a notoriously ignored landmark paper: “Uber Natur und Ursprung der Chromatophoren im PXanzenreiche.” (“On the nature and origin of the chromatophores in the plant kingdom”; Mereschkowsky 1905). In spite of the fact that this paper was written in German (the lingua franca in biology at the time), its fate was similar to Mendel’s publication, which signiWed, in retrospect, the birth of genetics (Mendel 1865). Both before and after the publication of Mereschkowsky’s article there were many publications dealing with plant “chimera’s” and cytoplasmic inheritance in plants, which should have favoured the interpretation of plastids as “semi-autonomous” symbiotic entities in the cytoplasm of the eukaryotic plant cell (e.g. Braun 1873; Hildebrand 1908; Baur 1909; Renner 1922, 1924, 1934, 1936a, b; Darlington 1929; Stubbe 1959; Tilney-Basset 1963). In addition, millions of people had variegated Pelargonium and other green-and-white spotted plants in their homes, or variegated plants such as Euonymus, Hedera or Ilex aquifolius in their gardens, which could have provided comprehensive evidence for plastid inheritance to the naked eye. Therefore, it is one of the mysteries of the 20th century that an endosymbiotic origin of plastids had not been generally accepted before the 1970s and 1980s, especially after the courageous paper of Lynn Margulis (Sagan 1967) and the unequivocal demonstration of DNA in plastids (Gibor and Izawa 1963). Twenty years after Mereschkowsky’s plea for an endosymbiotic origin of plastids, Wallin (1925, 1927) postulated the “bacterial nature of mitochondria”. The reasons for this postulate were less obvious, since—in contrast to chloroplast mutations—you cannot experience the consequences of mutations in the mitochondrial genome by naked eye—you need at least a good microscope and basic experience in cytochemical staining techniques (reviewed by Ernster and Schatz 1981). Moreover, Wallin’s claim of having cultivated mitochondria in vitro turned out (of course) to be wrong, just as Portier’s fancy speculation that food-associated bacteria could fuse with mitochondria in order to rejuvenate the latter (Portier 1918). Most importantly, however, the genetic evidence for the presence of hereditary factors in mitochondria was diYcult to interpret. The reasons for these peculiarities of mitochondrial genetics are well understood today, but still notoriously ignored in many textbooks. First of all, mitochondrial DNA is usually present in multiple copies in one and the same mitochondrion and, notably, the hundreds to thousands of mitochondria in a single Communicated by R. Bock

Assessment of ciliates in the sheep rumen by DGGE

Aims:  This work was carried out to develop a rapid molecular profiling technique to screen ciliate populations in the rumen of sheep.