An enterotoxin-producing strain of Escherichia coli isolated from a case of cholera-like diarrhea (E. coli strain H-10407) was found to possess a surfaceassociated colonization factor. Colonization was manifested as the ability of small inocula (105 bacteria) to attain large (10w) populations in the infant rabbit intestine with a concomitant diarrheal response. A laboratory-passed derivative of E. coli H-10407, designated H-10407-P, failed to exhibit an increase in population in the infant rabbit and also failed to induce diarrhea. Cell-free culture supernatant fluids of E. coli H-10407 and H-10407-P produced equivalent enterotoxic responses in infant and in adult rabbits. Specific anti-colonization factor antiserum was produced by adsorbing hyperimmune anti-H-10407 serum with both heat-killed and living cells of E. coli H-10407-P. This specific adsorbed serum protected infant rabbits from challenge with living E. coli H-10407 although the serum did not possess bactericidal activity. The anti-colonization factor serum did not agglutinate a strain of E. coli K-12 possessing the K88 colonization factor peculiar to E. coli enterotoxigenic for swine. By electron microscopy it was demonstrated that E. coli H-10407, but not H-10407-P, possessed pilus-like surface structures which agglutinated with the specific adsorbed (anti-colonization factor) antiserum. E. coli H-10407 possessed three species of plasmid deoxyribonucleic acid, measuring 60 x 10X, 42 x 106, and 3.7 x 10' daltons, respectively. E. coli H-10407-P possessed only the 42 x 106and the 3.7 x 106-dalton plasmid species. Spontaneous loss of the specific H-10407 surface-associated antigen was accompanied by loss of the 60 x 106-dalton species of

Two kinds of predatory bacteria have been observed and characterized by light and electron microscopy in samples from freshwater sulfurous lakes in northeastern Spain. The first bacterium, named Vampirococcus, is Gram-negative and ovoidal (0.6 jam wide). An anaerobic epibiont, it adheres to the surface of phototrophic bacteria (Chromatium spp.) by specific attachment structures and, as it grows and divides by fission, destroys its prey. An important in situ predatory role can be inferred for Vampirococcus from direct counts in natural samples. The second bacterium, named Daptobacter, is a Gram-negative, facultatively anaerobic straight rod (0.5 x 1.5 ,um) with a single polar flagellum, which collides, penetrates, and grows inside the cytoplasm of its prey (several genera of Chromatiaceae). Considering also the well-known case of Bdellovibrio, a Gram-negative, aerobic curved rod that penetrates and divides in the periplasmic space of many chemotrophic Gram-negative bacteria, there are three types of predatory prokaryotes presently known (epibiotic, cytoplasmic, and periplasmic). Thus, we conclude that antagonistic relationships such as primary consumption, predation, and scavenging had already evolved in microbial ecosystems prior to the appearance of eukaryotes. Furthermore, because they represent methods by which prokaryotes can penetrate other prokaryotes in the absence of phagocytosis, these associations can be considered preadaptations for the origin of intracellular organelles.Although symbiotic bacteria have been extensively studied and their evolutionary importance in the origin of eukaryotic cells has been recognized (1, 2), predatory behavior in bacteria is known only for Bdellovibrio (3, 4) and Vampirovibrio (5,6). Antagonistic relationships among large organisms are considered to be properties of ecosystems and integrated into ecological theory (7); however, such behavior (e.g., primary consumption, predation, and scavenging) attributed only to animals and plants (8) MATERIALS AND METHODS Studies were conducted in Lake Estanya (420 02' N, 0O 32' E) and Lake Cis6 (420 08' N, 20 45' E) in northeastern Spain.Both lakes are sinkholes formed in karstic areas, rich in calcium sulfate as gypsum and anhydrite. They receive most of their water inputs through seepage. The water conductivity, about 1800 gS cm-l for Lake Estanya and 1300 ;LS-cm-'for Lake Cis6, is high, primarily as a consequence of dissolved salts as sulfates (siemens are reciprocal ohms; S = 1/fl). From 7 to 10 mM sulfate is present in solution in the hypolimnia of both lakes. Lake Estanya, figure-eight shaped, has two basins 12 and 20 m deep, respectively. They are separated by a 2-m-deep sill (10). Lake Cis6, an almost semispherical basin, is 9 m deep and 25 m in average diameter at the surface. Because of high production of hydrogen sulfide in the sediments, it is completely anoxic during mixing (11). Details of lake ecology and methods of study have been published (12)(13)(14). In both lakes light penetrates down to the thermocline,...

Light and electron microscope observations showed that the filamentous, segmented bacterium commonly found attached to the ileal epithelium of rats and mice undergoes a complex life cycle. Filaments comprising up to 90 segments were attached to the microvillous border of absorptive epithelial cells by a specialized terminal holdfast segment. Starting at the free end of the filament and progressing toward the attached end, undifferentiated segments were converted into reproductive or mother segments. Within each mother cell two new holdfast segments developed. As the holdfasts matured, their mother cells degenerated and released them into the intervillar space where they attached, grew, and divided to produce new segmented filaments. Alternately, in some filaments, newly formed but not yet released holdfasts were converted into endospores, which were released in the same manner as holdfasts, presumably to spread the bacterial colony to other members of the rodent population. 572 on July 31, 2020 by guest http://jb.asm.org/ Downloaded from holdfasts. Scale = 10 p.m.

The role of the mitochondrial genome in early development and differentiation was studied in mouse embryos cultured in vitro from the two to four cell stage to the blastocyst (about 100 cells) . During this period the mitochondria undergo morphological differentiation : progressive enlargement followed by an increase in matrix density, in number of cristae, and in number of mitochondrial ribosomes . Mitochondrial ribosomal and transfer RNA synthesis occurs from the 8 to 16 cell stage on and contributes to the establishment of a mitochondrial protein-synthesizing system . Inhibition of mitochondrial RNA-and proteinsynthesis by 0 .1 µg/ml of ethidium bromide or 31 .2 ug/ml of chloramphenicol permits essentially normal embryo development and cellular differentiation . Mitochondrial morphogenesis is also nearly normal except for the appearance of dilated and vesicular cristae in blastocyst mitochondria . Such blastocysts are capable of normal postimplantation development when transplanted into the uteri of foster mothers. Higher concentrations of these inhibitors have general toxic effects and arrest embryo development . It is concluded that mitochondrial differentiation in the early mouse embryo occurs through the progressive transformation of the preexisting mitochondria and is largely controlled by the nucleocytoplasmic system . Mitochondrial protein synthesis is required for the normal structural organization of the cristae in blastocyst mitochondria . Embryo development and cellular differentiation up to the blastocyst stage are not dependent on mitochondrial genetic activity .

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