Spirochete motility is enigmatic: It differs from the motility of most other bacteria in that the entire bacterium is involved in translocation in the absence of external appendages. Using the Lyme disease spirochete Borrelia burgdorferi (Bb) as a model system, we explore the current research on spirochete motility and chemotaxis. Bb has periplasmic flagella (PFs) subterminally attached to each end of the protoplasmic cell cylinder, and surrounding the cell is an outer membrane. These internal helically shaped PFs allow the spirochete to swim by generating backward-moving waves by rotation. Exciting advances using cryoelectron microscopy tomography are presented with respect to in situ analysis of cell, PF, and motor structure. In addition, advances in the dynamics of motility, chemotaxis, gene regulation, and the role of motility and chemotaxis in the life cycle of Bb are summarized. The results indicate that the motility paradigms of flagellated bacteria do not apply to these unique bacteria.

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The complete sequence (15,455 bp) of the mitochondrial DNA of the mosquito Anopheles quadrimaculatus species A is reported. This genome is compact and very A+T rich (77.4% A+T). It contains genes for 2 ribosomal RNAs (rRNAs), 22 transfer RNAs (tRNAs), and 13 subunits of the mitochondrial inner membrane respiratory complexes. The gene arrangement is the same as in Drosophila yakuba, except that the positions of two contiguous tRNAs are reversed and a third tRNA is transcribed from the complementary strand. Protein-coding genes, rRNAs, and most tRNAs were similar to D. yakuba. Two tRNAs had nonstandard secondary structures comparable with those of nematode mitochondrial tRNAs. The very small putative control region (625 bp) contains no sequence motifs similar to those used in vertebrates and other insects for initiation of transcription and replication.

Restriction endonucleases were used to test an hypothesis, based on cytological data, proposing the existence of two races in Anopheles nuneztovari, one Venezuelan-Colombian and the other Amazonian, and to examine variation in the mitochondrial DNA (mtDNA) of 263 individual A. nuneztovari mosquitoes from 12 sites in Bolivia, Brazil, Colombia, Suriname, and Venezuela. Cladistic analysis of the mtDNA data using three outgroups suggests that A. nuneztovari is monophyletic. However, this analysis is poorly resolved by parsimony, probably caused by extensive homoplasy. Analysis of the relationships among haplotypes, based on genetic distances, results in five haplotype lineages, three of which are in the Amazon Basin. Relationships among the 12 populations reveal distinctive lineages, one in Venezuela-Colombia and two within the Amazon Basin. Molecular variance components and F statistics (phi) among neotropical biomes, among populations/biomes, among cytotypes, among populations/cytotypes, and within populations all demonstrate significant subdivision and strongly support multiple lineages, which could be interpreted as recently evolved species, within A. nuneztovari. The Mantel analysis showed no significant correlation between genetic and geographic distances, suggesting that it is biomes and cytotypes that contribute most strongly to subdivision.Key words: mtDNA lineages, anopheline mosquito, gene flow, genetic diversity, neotropical.