Molecular cloning of, and phylogenetic analysis of, an actin in Naegleria fowleri

We cloned and sequenced an intronless actin gene from the amoebo-flagellate Naegleria fowleri, LEE strain, an opportunistic pathogen of man. Codon usage and third-position-codon nucleotide frequency were significantly different from Acanthamoeba, another amoeba genus which also includes opportunistic pathogens of man. Between the two amoebae, actin peptide sequences were 92.8% similar, while nucleotide sequences were only 70% similar. A phylogenetic reconstruction of actin amino acid sequences, using a distance method, placed Naegleria in a cluster with Plasmodium and Entamoeba.

A simple, efficient method to create a cDNA library

The simplified "All In One Tube" protocol for constructing a cDNA library combines the advantages of the "Classic method" and the Okayama-Berg method while overcoming some of their drawbacks. In this method, adding adapters, linkers or enzyme digestion steps are no longer necessary after cDNA synthesis, thus making it quicker and especially useful when dealing with small samples of mRNA.

Cloning and characterization of transcripts showing virulence-related gene expression in Naegleria fowleri

The pathogenic LEE strain of Naegleria fowleri isolated from human or mouse brain loses pathogenicity when cultured axenically in a nutrient broth. To identify genes differentially expressed in highly virulent versus weakly virulent amoebae, a cDNA library was constructed by using mRNA from amoebae recovered from a mouse brain. Two cDNA clones were isolated by differential screening of the library. The transcript homologous to clone Nf314 was preferentially expressed in highly virulent cells, whereas the transcript homologous to clone Nf435 was preferentially expressed in weakly virulent cells. Other clones showed negligible differential hybridization, but actin transcript levels were slightly elevated in the highly virulent cells. The Nf314 cDNA has an open reading frame for a 53-kDa protein 94% similar and 19% identical over 194 amino acid residues to serine carboxypeptidase from yeast cells, barley, and wheat. Southern blot analysis is consistent with a single copy of the Nf314 gene in the genome. Interestingly, the increased Nf314 transcript levels were present in cells fed on mouse brain, liver, or NIH 3T3 fibroblasts but not in cells fed on bacteria or in axenic culture. Thus, the inducer of the increased gene expression correlates with use of mammalian cells as a food source without regard to level of virulence. Since amoebae fed in culture on dissociated mouse brain were weakly virulent, as measured by their abilities to kill mice, the Nf314 gene may be required but is not sufficient for increased virulence.

Virulence-related protein synthesis in Naegleria fowleri

Protein synthesis patterns of the low-virulence Naegleria fowleri LEE strain from axenic culture, the same strain after mouse brain passage to increase virulence, and the same strain after growth on bacteria were studied. Comparisons of accumulated proteins, in vivo-synthesized proteins, and in vitro-synthesized proteins translated from poly(A)+ mRNA were made. Differences between amoebae from the different treatments were noted. After 6 months in axenic culture, pathogenic protein synthesis patterns were lost and there was a decrease in virulence. Therefore, the increase in virulence is correlated with numerous specific changes in protein synthesis.

Restriction endonuclease analysis of mitochondrial DNA as an aid in the taxonomy of Naegleria and Vahlkampfia

Using restriction enzyme analysis, mitochondrial DNA fragment patterns from seven strains of pathogenic and nonpathogenic Naegleria and one strain of Vahlkampfia were compared to estimate nucleotide sequence divergence. Significantly high levels of estimated genetic variation between strains of N. gruberi, N. fowleri, and N. jadini support the current taxonomic level of the individual Naegleria species and suggest a distinct phylogeny for each group. Naegleria lovaniensis, strain TS, was shown to have significant nucleotide sequence homology with N. gruberi, strain EGs, suggesting that the two groups share a close taxonomic relationship. The pathogenic strain MB-41 of N. fowleri exhibited distinct genetic divergence from the highly homologous, pathogenic strain Nf66 and the drug-cured strain 6088. Morphologically distinct strains EGs and 1518/la of N. gruberi exhibited significantly large sequence divergence consistent with a more distant taxonomic relationship. Amoebae from the genus Vahlkampfia expressed genetic similarity with strains of N. gruberi.

Polyphenol oxidase produced during encystation of Acanthamoeba castellanii

Acanthamoeba castellanii has a phenol oxidase activity that is believed to be a laccase. Enzyme activity was found in the outer cyst wall, in the cytoplasm of encysting amoebae and in the encystment medium. Encystment procedures were modified to promote an increase in the amount of soluble enzyme secreted during encystation. Acanthamoeba polyphenol oxidase has a pH optimum of 6.0 and a Km value of 0.21 mM with dihydroxyphenylalanine. The enzyme does not oxidize tyrosine, and it is inhibited by chloride but not by inhibitors of peroxidase. Its synthesis coincides with encystation, and known inhibitors of polyphenol oxidase prevent encystation. Polyphenol oxidase may have a role in making the cyst resistant to mechanical and chemical breakdown.

The existence of LSP-1 beta S in Drosophila melanogaster natural populations in two northern states

LSP-1 beta S is present in Michigan and Massachusetts Drosophila melanogaster natural populations. Its frequency, 10%, is significantly higher in an East Jordan, Mich. (latitude, 45.10 degrees N), population than in East Lansing, Mich. (latitude 42.44 degrees N), or Hadley, Mass. (latitude, 42.21 degrees N), populations, where it averages 3% at each location. The average frequency of LSP-2S is more comparable, 6, 5, and 7% at East Jordan, East Lansing, and Hadley, respectively. LSP-1 gamma F variants are also present. A total of 342 single third-instar larvae was scored for LSP-1 autosomal variants, and 323 for LSP-2 variants. Each larva represented a newly established isofemale line from collections at East Jordan in 1981 and 1983, East Lansing in 1982, and Hadley in 1981, 1982, and 1983. Within localities, frequencies of hemolymph protein variants did not differ significantly between years. Proteins 9, 10, 11, and 15 correspond to the LSP-1 gamma, beta, and alpha triplet and LSP-2 polypeptide in D. melanogaster. Our results together with those of Singh and Coulthart [(1982). Genetics 102:437] indicate that D. melanogaster populations in north temperate climates maintain considerable genetic heterogeneity for the larval hemolymph proteins.

Growth response of axenic Entamoeba histolytica to hydrogen, carbon dioxide, and oxygen

Entamoeba histolytica required CO2 for growth in axenic culture while growth was inhibited by H2. The organism was tolerant to 5% O2 in the gas phase and it was able to detoxify products of O2 reduction in the medium. The ameba did not require a negative oxidation-reduction potential for axenic growth. However, little or no free O2 was present in media exposed to 5% O2 in the gas phase. Growth was improved by adding yeast extract to the medium.

Hemin replaces serum as a growth requirement for Naegleria

Four strains of Naegleria gruberi were grown axenically without serum. Serum was replaced by hemin or two selected hemoproteins. Aside from the utility of eliminating serum from the culture medium, the present work shows that Naegleria does not require intact protein, and establishes a specific micronutrient requirement for this amoebo-flagellate.

Assembly of lipids into membranes in Acanthamoeba palestinensis. I. Observations on the specificity and stability of choline- 14 C and glycerol- 3 H as labels for membrane phospholipids

In order to determine the feasibility of using radioactive precursors as markers for membrane phospholipids in Acanthamoeba palestinensis, the characteristics of phospholipids labeled with choline-(14)C and glycerol-(3)H were examined. Choline-(14)C was found to be a specific label for phosphatidyl choline. There was a turnover of the radioactive moiety of phosphatidyl choline at a rate that varied with the concentration of nonradioactive choline added to the growth medium. Radioactivity was lost from labeled phosphatidyl choline into the acid-soluble intracellular pool and from the pool into the extracellular medium. This loss of radioactivity from cells leveled off and an equilibrium was reached between the label in the cells and in the medium. Radioactive choline was incorporated into phosphatidyl choline by cell-free microsomal suspensions. This incorporation leveled off with the attainment of an equilibrium between the choline-(14)C in the reaction mixture and the choline-(14)C moiety of phosphatidyl choline in the microsomal membranes. Therefore, a choline exchange reaction may occur in cell-free membranes, as well as living A. palestinensis. In contrast to choline-(14)C, the apparent turnover of glycerol-(3)H-labeled phospholipids was not affected by large concentrations of nonradioactive choline or glycerol in the medium. The radioactivity in lipids labeled with glycerol-(3)H consisted of 33% neutral lipids and 67% phospholipids. Phospholipids labeled with glycerol-(3)H turned over slowly, with a concomitant increase in the percentage of label in neutral lipids, indicating a conversion of phospholipids to neutral lipids. Because most ( approximately 96%) of the glycerol-(3)H recovered from microsomal membranes was in phospholipids, whereas only a minor component ( approximately 2%) of the glycerol-(3)H was in the phospholipids isolated from nonmembrane lipids, glycerol-(3)H was judged to be a specific marker for membrane phospholipids.

Assembly of lipids into membranes in Acanthamoeba palestinensis. II. The origin and fate of glycerol- 3 H--labeled phospholipids of cellular membranes

The membranes of Acanthamoeba palestinensis were studied by examination in fixed cells, and then by following the movements of glycerol-(3)H-labeled phospholipids by cell fractionation. Two previously undescribed structures were observed: collapsed cytoplasmic vesicles of cup shape, and plaques in food vacuole and plasma membrane similar in size to the collapsed vesicles. It appeared that the plaques formed by insertion of collapsed vesicles into membranes and/or that collapsed vesicles formed by pinching off of plaques. Fractions were isolated, enriched with nuclei, rough endoplasmic reticulum (RER), plasma membrane, Golgi-like membranes, and collapsed vesicles. The changes in specific activity of glycerol-(3)H-labeled phospholipids in these membranes during incorporation, turnover, and after pulse-labeling indicated an ordered sequence of appearances of newly synthesized phospholipids, first in nuclei and RER, then successively in Golgi membranes, collapsed vesicles, and finally, plasma membrane. In previous work we had found no large nonmembranous phospholipid pool in A. palestinensis. These observations are consistent with the hypothesis that membrane phospholipids are synthesized, perhaps as integral parts of membranes, in RER and nuclei. Subsequently, some of the newly synthesized phospholipids are transported to the Golgi complex to become integrated into the membranes of collapsed vesicles, which are precursors of the plasma membrane. Collapsed vesicles from the plasma membrane by inserting into it as plaques. When portions of the plasmalemma from food vacuoles, collapsed vesicles pinch off from their membranes and are recycled back to the cell surface.