The Mediterranean fruit fly in California: evidence for multiple introductions and persistent populations based on microsatellite and mitochondrial DNA variability.

Microsatellite and mitochondrial DNA (mtDNA) variability data were used to study outbreaks of Mediterranean fruit fly in California in the years 1992-94 and 1997-99. A total of 359 flies caught in monitoring traps during these years were examined at three polymorphic mtDNA restriction sites and two microsatellite loci. Composite genotypes obtained through analysis of these markers indicate at least five independent introductions of medflies into California between 1992 and 1998. Whereas the majority of specimens displayed a single mtDNA haplotype (AAA), variation of microsatellite alleles among these flies suggests at least one additional introduction in 1993 into southern California. Flies displaying the AAB haplotype sampled in 1992 both in northern and southern California shared microsatellite alleles absent in AAA flies although lacking others commonly found in AAA specimens, thus supporting the hypothesis of an independent introduction of these flies from a different source. In contrast to earlier infestations, a few specimens caught in southern California in 1993 and again in 1998 showed both mtDNA and microsatellite patterns consistent with a Hawaiian origin. Single flies collected in Santa Clara County in 1997 and in El Monte, Los Angeles County & in 1999 most likely represent a sixth and seventh distinct introduction, respectively.

Revised group classification of the genus Spiroplasma.

Significant changes have been made in the systematics of the genus Spiroplasma (class Mollicutes) since it was expanded by revision in 1987 to include 23 groups and eight sub-groups. Since that time, two additional spiroplasmas have been assigned group numbers and species names. More recently, specific epithets have been assigned to nine previously designated groups and three sub-groups. Also, taxonomic descriptions and species names have been published for six previously ungrouped spiroplasmas. These six new organisms are: Spiroplasma alleghenense (strain PLHS-1T) (group XXVI), Spiroplasma lineolae (strain TALS-2T) (group XXVII), Spiroplasma platyhelix (strain PALS-1T) (group XXVIII), Spiroplasma montanense (strain HYOS-1T) (group XXXI), Spiroplasma helicoides (strain TABS-2T) (group XXXII) and Spiroplasma tabanidicola (strain TAUS-1T) (group XXXIII). Also, group XVII, which became vacant when strain DF-1T (Spiroplasma chrysopicola) was transferred to group VIII, has been filled with strain Tab 4c. The discovery of these strains reflects continuing primary search in insect reservoirs, particularly horse flies and deer files (Diptera: Tabanidae). In the current revision, new group designations for 10 spiroplasma strains, including six recently named organisms, are proposed. Three unnamed but newly grouped spiroplasmas are strain TIUS-1 (group XXIX; ATCC 51751) from a typhiid wasp (Hymenoptera: Tiphiidae), strain BIUS-1 (group XXX; ATCC 51750) from floral surfaces of the tickseed sunflower (Bidens sp.) and strain BARC 1901 (group XXXIV; ATCC 700283). Strain BARC 2649 (ATCC 700284) from Tabanus lineola has been proposed as a new sub-group of group VIII. Strains TIUS-1 and BIUS-1 have unusual morphologies, appearing as helices at only certain stages in culture. In this revision, potentially important intergroup serological relationships observed between strain DW-1 (group II) from a neotropical Drosophila species and certain sub-group representatives of group I spiroplasmas are also reported.

Spiroplasma lineolae sp. nov., from the horsefly Tabanus lineola (Diptera: Tabanidae).

Spiroplasma strain TALS-2T from the viscera of the striped horsefly, Tabanus lineola, collected in Georgia was serologically distinct from other Spiroplasma species, groups, putative groups, and subgroups. Light and electron microscopy of cells of strain TALS-2T revealed helical motile cells surrounded only by a single cytoplasmic membrane. The organism grew in M1D and SP-4 liquid media. Growth also occurred in 1% serum fraction medium and in conventional horse serum medium. Growth in liquid media was serum dependent. The strain passed through 220-nm filter pores, but was retained in filters with 100-nm pores. The optimum temperature for growth was 30 degrees C. Multiplication occurred at temperatures from 20 to 37 degrees C, with a doubling time at the optimum temperature of 5.6 h in M1D broth. Strain TALS-2T catabolized glucose but hydrolyzed neither arginine nor urea. The guanine-plus-cytosine content of the DNA was 25 +/- 1 mol%. The genome size was 1,390 kbp. Six isolates serologically similar to strain TALS-2T were obtained from the same host in coastal Georgia. Three strains closely related to strain TALS-2T were isolated from the horsefly Poeciloderas quadripunctatus in Costa Rica. Strain TALS-2T (= ATCC 51749), a representative of group XXVII, is designated the type strain of a new species, Spiroplasma lineolae (Mollicutes: Entomoplasmatales).

Spiroplasma corruscae sp. nov., from a firefly beetle (Coleoptera: Lampyridae) and tabanid flies (Diptera: Tabanidae).

Spiroplasma strain EC-1T (T = type strain), which was isolated from the gut of a lampyrid beetle (Ellychnia corrusca) in Maryland, was serologically distinct from other spiroplasma species and groups. Similar strains were obtained from other E. corrusca specimens, and, later, numerous isolates of similar or partially related strains were obtained from several species of tabanid files. Cells of strain EC-1T were helical, motile filaments that were bound by a single cytoplasmic membrane, and there was no evidence of a cell wall. The cells were filterable through 220-nm-pore-size membrane filters but not through 100-nm-pore-size membrane filters. The organism was absolutely resistant to penicillin (1,000 U/ml) and required sterol for growth. Strain EC-1T grew well in M1D and SP-4 liquid media and could be cultivated in the Edward formulation of conventional mycoplasma medium and in 1% serum fraction medium. Optimal growth occurred at 32 degrees C (doubling time, 1.5 h). Strain EC-1T multiplied at 10 to 41 degrees C, but not at 5 or 43 degrees C. This organism produced acid from glucose, but did not hydrolyze arginine or utilize urea. The guanine-plus-cytosine content of the DNA was determined to be 26.3 mol% by the melting temperature method and 27.0 mol% by the buoyant density method. As a result of our studies, strain EC-1 (= ATCC 43212) is designated the type strain of a new species, Spiroplasma corruscae.

Improved cultivation systems for isolation of the colorado potato beetle spiroplasma.

In North America, the Colorado potato beetle, Leptinotarsa decemlineata, is often infected with the host-specific, gut-inhabiting Colorado potato beetle spiroplasma (CPBS). CPBS is apparently a commensal, but it may be useful in biocontrol if it can be transformed to express an insect-lethal gene. Difficulty in cultivating the organism, however, has hindered the development of a suitable transformation system. In this study, we eliminated the need for coculturing CPBS with insect cells. CPBS was reliably isolated with the BBL Anaerobic GasPak Jar system (low redox, enhanced CO(inf2)), which was easier to use and less expensive than insect cell coculture methods. A further advantage is a reduction in contaminating insect cell components. Use of anaerobiosis should facilitate early-passage screening of isolates for extrachromosomal elements, for use in gene vector constructs. The unique spiral (decreasing amplitude of coils) morphology of CPBS was preserved by anaerobiosis. The use of low-pH (6.0 to 6.5) media allowed aerobic adaptation of CPBS to M1D and SP-4 broth media. These formulations permitted the first cultivation of CPBS on solid media, an accomplishment that will simplify the selection of molecular transformants. Potato beetles collected at four sites in Poland yielded CPBS strains similar to those previously obtained from populations in North America.

Spiroplasma syrphidicola sp. nov., from a syrphid fly (Diptera: Syrphidae).

Spiroplasma sp. strain EA-1(T) (T = type strain) (subgroup VIII-1), which was isolated from the syrphid fly Eristalis arbustorum, was serologically distinct from other spiroplasma species, groups, and subgroups, The cells of this strain, as revealed by dark-field light microscopy, were short, helical, and motile. An electron microscopic examination revealed wall-less cells delimited by a single membrane. The unusually short cells passed through 220-nm filter pores with no reduction in titer. The organisms grew well in SM-1, M1D, and SP-4 liquid media. Growth also occurred in conventional horse serum medium and 1% serum fraction medium. Strain EA-1(T) grew at temperatures between 10 and 41 degrees C, and optimum growth occurred at 32 degrees C. The doubling time at the optimal temperature was 1.0 h. The strain catabolized glucose and hydrolyzed arginine but did not hydrolyze urea. The guanine-plus-cytosine content of the DNA was 30 +/- 1 mol%. The genome size was about 1,230 kbp. Strain Ea-1 (= ATCC 33826), which represents subgroup VIII-1, is designated the type strain of a new species, Spiroplasma syrphidicola.

Analysis of mitochondrial DNA and development of PCR-based diagnostic molecular markers for Mediterranean fruit fly (Ceratitis capitata) populations.

A 2.99 kb mtDNA fragment containing two variable restriction endonuclease sites (EcoRV and XbaI) was subcloned and sequenced from the Mediterranean fruit fly (Ceratitis capitata). This fragment represents approximately one-fifth of the entire mitochondrial sequence. The sequence was aligned with the comparable region from Drosophila yakuba and Anopheles gambiae, resulting in 81.8% and 76.7% identity at the nucleotide level, and 77% and 67.7% identity, respectively, at the amino acid level. The sequenced region includes the complete genes for NADH dehydrogenase 4, NADH dehydrogenase 4L, NADH dehydrogenase 6, and transfer RNAs for proline, threonine and histidine, and part of the genes for NADH dehydrogenase 5 and cytochrome b. Oligonucleotide primers were designed to asymmetrically bracket each of two variable restriction endonuclease sites to allow PCR amplification and subsequent restriction endonuclease analysis of individual fly samples.

Characterization of a cryptic extrachromosomal element isolated from the mollicute Spiroplasma taiwanense.

Characterization of an extrachromosomal element from an organism in the genus Spiroplasma is likely to be an essential step in the development of cloning vectors which replicate in these organisms. A restriction map for an 11-kb element, designated pCT-1, isolated from Spiroplasma taiwanese strain CT-1 (ATCC 43302) has been constructed using the restriction enzymes Bg/II, EcoRI, HincII, HindIII, HpaI, PstI, and XbaI. This element is distinct from any previously characterized spiroplasma virus or plasmid. pCT-1 has been cloned into the Escherichia coli vector pBR322 as a step in the development of a biphasic shuttle vector system.

Mitochondrial DNA restriction map for the Mediterranean fruit fly, Ceratitis capitata.

Molecular genetic research on the Mediterranean fruit fly, Ceratitis capitata, will provide tools to permit determination of source populations for new pest infestations. Restriction fragment length polymorphism (RFLP) of mitochondrial DNA provides some interpopulation discrimination. A restriction map, including the informative variable EcoRV and XbaI restriction sites, is constructed for the Mediterranean fruit fly, and several restriction sites are associated with specific gene regions based on polymerase chain reaction-RFLP and sequence analyses. A partial sequence of the mitochondrial 16S ribosomal RNA gene is reported.

Optimization of methods for transfecting Spiroplasma citri strain R8A2 HP with the spiroplasma virus SpV1 replicative form.

Seven methods for the transfection of bacteria were compared and optimized for use in Spiroplasma citri strain HP using the spiroplasma virus SpV1 R8A2 B replicative form (RF). These methods included both chemical-mediated protocols [CaCl2, RbCl/CaCl2, polyethylene glycol (PEG)], liposome-mediated transfection, electroporation, freeze/thaw cycling, and natural competence. The best protocols were those which utilized PEG or electroporation, yielding transfection frequencies of 1.4 x 10(-4) and 9.1 x 10(-4) transfectants/colony-forming unit (CFU), respectively. For both of these protocols, transfection frequencies were higher using CsCl-purified, covalently closed, circular DNA. In the PEG-mediated protocol, Sigma 8000 brand PEG at a final concentration of 44%, and the presence of carrier DNA proved to be optimal with a PEG exposure time of 2 min. Using electroporation, a 1-2 ms pulse of a 6.5 kV/cm electric field was best; washing the host cell pellet prior to electroporation enhanced efficiencies by 50%. Linearization of the DNA resulted in lower transfection efficiencies by either method.

Occurrence of extrachromosomal deoxyribonucleic acids in spiroplasmas associated with plants, insects, and ticks.

Several spiroplasmas (helical, motile mollicutes) were previously shown to contain extrachromosomal DNA (E-DNA) elements in the form of viruses (double-stranded viruses or the replicative form of single-stranded viruses) or plasmids. These elements are now being investigated as potential vectors for use in spiroplasma transformation systems. Described herein is the first extensive survey of spiroplasma E-DNA in 23 spiroplasma groups (30 strains), a study facilitated by improvements in protocols for E-DNA extraction. E-DNA elements were found in spiroplasmas associated with leafhoppers/plants (spiroplasma subgroups I-1, I-3, and I-8), other insects (subgroups I-2, I-5, I-6, and I-7 and groups IV and XXII), and ticks (subgroup I-4 and groups V and VI). Elements, maintained by passage with their host spiroplasmas, were often lost after extended passage. Whether the current distribution of E-DNA elements is indicative of historical or proximate factors is not known. Many elements (about 75%) from group I spiroplasmas hybridized with Spiroplasma citri viruses SpV1 or SpV3. Of the elements associated with other spiroplasma groups, none hybridized with either virus. These include Spiroplasma apis strains B31 (18 kb) and L89 (18 and 20 kb), S. mirum strains SMCA (20 kb) and Anderson (16 and 20 kb), group VI strain Y32 (7, 9, 10, and 16 kb), and group XXII strain CT-1 (8 kb). Several of these elements will be characterized and examined for their suitability as spiroplasma cloning vectors.

The cpcE and cpcF genes of Synechococcus sp. PCC 7002. Construction and phenotypic characterization of interposon mutants.

The 3' region of the cpc operon of Synechococcus sp. PCC 7002 has been sequenced, transcriptionally characterized, and analyzed by interposon mutagenesis. The cpc operon contains six genes, 5' cpcB-cpcA-cpcC-cpcD-cpcE-cpcF 3', and gives rise to at least eight (more likely ten) discrete mRNA transcripts. The steady-state levels of transcripts for the cpcE and cpcF genes are very low and are estimated to represent only about 1-2% of the total transcripts arising from the cpc locus. The cpcE gene predicts a protein of 268 amino acid residues, whereas the cpcF gene predicts a protein of 205 amino acid residues. The deduced amino acid sequences of these proteins are about 50% identical and 70% similar to the predicted products of homologous genes which have been identified in other cyanobacterial cpc operons. Interposon insertion mutations were constructed in the cpcE and cpcF genes, and an interposon deletion mutation affecting both genes was constructed. The phenotypes of all mutant strains were similar. These strains were yellow-green in color, had doubling times approximately twice that of the wild-type strain, and failed to accumulate normal levels of phycocyanin. Further analyses indicated that these strains contained substantial amounts of apparently normal phycocyanin beta subunits; however the majority of the phycocyanin alpha subunit (about 90%) did not carry a phycocyanobilin chromophore. During serial subculturing of the mutant strains, suppressor mutations, which allowed cells to regain the ability to synthesize phycocyanin, arose at significant frequency. Based upon the results reported here, as well as those presented in the accompanying paper (Swanson, R. V., Zhou, J., Leary, J. A., Williams, T., de Lorimier, R., Bryant, D. A., and Glazer, A. N. (1992) J. Biol. Chem. 267, 16146-16154), we propose that the CpcE and CpcF polypeptides are the two subunits of a phycocyanobilin lyase specifically required for chromophorylation of the phycocyanin alpha subunit.

The psaC genes of Synechococcus sp. PCC7002 and Cyanophora paradoxa: cloning and sequence analysis.

The psaC genes of the cyanobacterium, Synechococcus sp. PCC7002, and of the cyanelle genome of the phylogenetically ambiguous biflagellate, Cyanophora paradoxa, were cloned, mapped and sequenced. The PsaC proteins of both species exhibit high degrees (approx. 95%) of sequence similarity to the PsaC proteins of other cyanobacteria as well as the chloroplast-encoded proteins of green algae and higher plants. The Synechococcus sp. PCC7002 psaC gene is transcribed as a monocistronic mRNA of approx. 350-400 nt, and transcription is initiated 51 nt upstream from the translational start codon. As found for the chloroplasts of higher plants, the C. paradoxa psaC gene is encoded within the small single-copy region of the cyanelle genome. In contrast to results obtained for chloroplasts and for the cyanobacterium Synechocystis sp. PCC6803, neither psaC gene is flanked by genes encoding components of the NAD(P)H dehydrogenase complex.

Nucleotide sequence and further characterization of the Synechococcus sp. strain PCC 7002 recA gene: complementation of a cyanobacterial recA mutation by the Escherichia coli recA gene.

The nucleotide sequence and transcript initiation site of the Synechococcus sp. strain PCC 7002 recA gene have been determined. The deduced amino acid sequence of the RecA protein of this cyanobacterium is 56% identical and 73% similar to the Escherichia coli RecA protein. Northern (RNA) blot analysis indicates that the Synechococcus strain PCC 7002 recA gene is transcribed as a monocistronic transcript 1,200 bases in length. The 5' endpoint of the recA mRNA was mapped by primer extension by using synthetic oligonucleotides of 17 and 27 nucleotides as primers. The nucleotide sequence 5' to the mapped endpoint contained sequence motifs bearing a striking resemblance to the heat shock (sigma 32-specific) promoters of E. coli but did not contain sequences similar to the E. coli SOS operator recognized by the LexA repressor. An insertion mutation introduced into the recA locus of Synechococcus strain PCC 7002 via homologous recombination resulted in the formation of diploids carrying both mutant and wild-type recA alleles. A variety of growth regimens and transformation procedures failed to produce a recA Synechococcus strain PCC 7002 mutant. However, introduction into these diploid cells of the E. coli recA gene in trans on a biphasic shuttle vector resulted in segregation of the cyanobacterial recA alleles, indicating that the E. coli recA gene was able to provide a function required for growth of recA Synechococcus strain PCC 7002 cells. This interpretation is supported by the observation that the E. coli recA gene is maintained in these cells when antibiotic selection for the shuttle vector is removed.

Nucleotide sequence and expression of the two genes encoding D2 protein and the single gene encoding the CP43 protein of Photosystem II in the cyanobacterium synechococcus sp. PCC 7002.

The unicellular photoheterotrophic cyanobacterium Synechococcus sp. PCC 7002 was shown to encode two genes for the Photosystem II reaction center core protein D2 and one gene for the reaction center chlorophyhll-binding protein CP43. These three genes were cloned and their DNA sequences determined along with their flanking DNA sequences. Northern hybridization experiments show that both genes which encode D2, psbD1 and psbD2, are expressed at roughly equivalent levels. For each of the two psbD genes, there are 18 nucleotide differences among the 1059 nucleotides which are translated. The DNA sequences surrounding the coding sequences are nearly 70% divergent. Despite the DNA sequence differences in the genes, the proteins encoded by the two genes are predicted to be identical. The proteins encoded by psbD1 and psbD2 are ∼92% homologous to other sequenced cyanobacterial psbD genes and ∼86% homologous to sequenced chloroplast-encoded psbD genes.The single gene for CP43, psbC, overlaps the 3' end of psbD1 and is co-transcribed with it. Results from previous sequencing of psbC genes encoded by chloroplasts suggest that the 5' end of the psbC gene overlaps the 3' end of the coding sequence of psbD by ∼50 nucleotides. In Synechococcus sp. PCC 7002, the methionine codon previously proposed to be the start codon for psbC is replaced by an ACG (threonine) codon. We propose an alternative start for the psbC gene at a GTG codon 36 nucleotides downstream from the threonine codon. This GTG codon is preceded by a consensus E. coli-like ribosome binding sequence. Both the GTG start codon and its preceding ribosome binding sequence are conserved in all psbC genes sequenced from cyanobacteria and chloroplasts. This suggests that all psbC genes start at this alternative GTG codon. Based on this alternative start codon, the gene product is ∼85% identical to other cyanobacterial psbC gene products and ∼77% identical to eucaryotic chloroplast-encoded psbC gene products.