Potential of an indigenous strain of the entomopathogenic fungus Beauveria bassiana as a biological control agent against the Red Palm Weevil, Rhynchophorus ferrugineus

The potential of a strain of Beauveria bassiana (Ascomycota: Clavicipitaceae) obtained from a naturally infected Rhynchophorus ferrugineus (Coleoptera: Curculionidae) pupa as a biological control agent against this weevil was evaluated both in the laboratory and in semi-field assays. Laboratory results indicate that this strain of B. bassiana can infect eggs, larvae and adults of R. ferrugineus (LC₅₀ from 6.3 × 10⁷ to 3.0 × 10⁹ conidia per ml). However, mortality was not the only indicator of treatment efficacy because adults of either sex inoculated with the fungus efficiently transmitted the disease to untreated adults of the opposite sex, with male-to-female and female-to-male rates of transmission of 55% and 60%, respectively. In addition, treatment with B. bassiana significantly reduced fecundity (up to 62.6%) and egg hatching (32.8%) in pairing combinations with fungus-challenged males, females or both sexes. Likewise, 30-35% increase in larval mortality was observed in larvae obtained from eggs from fungus-challenged females or from untreated females coupled with inoculated males, resulting in an overall 78% progeny reduction. Semi-field preventive assays on potted 5-year old Phoenix canariensis palms, with efficacies up to 85.7%, confirmed the potential of this strain as a biological control agent against R. ferrugineus.     

Modelling contact spread of infection in host-parasitoid systems: Vertical transmission of pathogens can cause chaos

All animals and plants are, to some extent, susceptible to disease caused by varying combinations of parasites, viruses and bacteria. In this paper, we develop a mathematical model of contact spread infection to investigate the effect of introducing a parasitoid-vectored infection into a one-host-two-parasitoid competition model. We use a system of ordinary differential equations to investigate the separate influences of horizontal and vertical pathogen transmission on a model system appropriate for a variety of competitive situations. Computational simulations and steady-state analysis show that the transient and long-term dynamics exhibited under contact spread infection are highly complex. Horizontal pathogen transmission has a stabilising effect on the system whilst vertical transmission can destabilise it to the point of chaotic fluctuations in population levels. This has implications when considering the introduction of host pathogens for the control of insect vectored diseases such as bovine tuberculosis or yellow fever.     

Bacterial mercury resistance from atoms to ecosystems

Bacterial resistance to inorganic and organic mercury compounds (HgR) is one of the most widely observed phenotypes in eubacteria. Loci conferring HgR in Gram-positive or Gram-negative bacteria typically have at minimum a mercuric reductase enzyme (MerA) that reduces reactive ionic Hg(II) to volatile, relatively inert, monoatomic Hg(0) vapor and a membrane-bound protein (MerT) for uptake of Hg(II) arranged in an operon under control of MerR, a novel metal-responsive regulator. Many HgR loci encode an additional enzyme, MerB, that degrades organomercurials by protonolysis, and one or more additional proteins apparently involved in transport. Genes conferring HgR occur on chromosomes, plasmids, and transposons and their operon arrangements can be quite diverse, frequently involving duplications of the above noted structural genes, several of which are modular themselves. How this very mobile and plastic suite of proteins protects host cells from this pervasive toxic metal, what roles it has in the biogeochemical cycling of Hg, and how it has been employed in ameliorating environmental contamination are the subjects of this review.     

High phylogenetic diversity of transconjugants carrying plasmid pJP4 in an activated sludge-derived microbial community

Transconjugants of plasmid pJP4, originating from an agar plate mating of a Pseudomonas putida donor with an activated sludge-derived microbial community, were isolated and identified by partial 16S rDNA sequencing. The transconjugant strains belonged to a variety of genera of the alpha-, beta-, gamabeta- and gamma-classes of the Proteobacteria, mostly to the families Rhizobiaceae and Comamonadaceae and the genus Stenotrophomonas. Only P. putida and Delftia spp. strains were able to grow on 2,4-D as the sole carbon source.     

Approaches to investigating the ecology of plasmids in marine bacterial communities

To better understand prokaryotic gene flux in marine ecosystems and to determine whether or not environmental parameters can effect the composition and structure of plasmid populations in marine bacterial communities, information on the distribution, diversity, and ecological traits of marine plasmids is necessary. This mini-review highlights recent insights gained into the molecular diversity and ecology of plasmids occurring in marine microbial communities.     

Molecular Evolution of P Transposable Elements in the Genus Drosophila. II. The obscura Species Group

A phylogenetic analysis of P transposable elements in the Drosophila obscura species group is described. Multiple P sequences from each of 10 species were obtained using PCR primers that flank a conserved region of exon 2 of the transposase gene. In general, the P element phylogeny is congruent with the species phylogeny, indicating that the dominant mode of transmission has been vertical, from generation to generation. One manifestation of this is the distinction of P elements from the Old World obscura and subobscura subgroups from those of the New World affinis subgroup. However, the overall distribution of elements within the obscura species group is not congruent with the phylogenetic relationships of the species themselves. There are at least four distinct subfamilies of P elements, which differ in sequence from each other by as much as 34%, and some individual species carry sequences belonging to different subfamilies. P sequences from D. bifasciata are particularly interesting. These sequences belong to two subfamilies and both are distinct from all other P elements identified in this survey. Several mechanisms are postulated to be involved in determining phylogenetic relationships among P elements in the obscura group. In addition to vertical transmission, these include retention of ancestral polymorphisms and horizontal transfer by an unknown mating-independent mechanism.     

Gypsy homologous sequences inDrosophila subobscura (gypsyDS)

Summary Characterization of sequences homologous to theDrosophila melanogaster gypsy transposable element was carried out inDrosophila subobscura (gypsyDS). They were found to be widely distributed among natural populations of this species. From Southern blot and in situ analyses, these sequences appear to be mobile in this species.GypsyDS sequences are located in both euchromatic and heterochromatic regions. A completegypsyDS sequence was isolated from aD. subobscura genomic library, and a 1.3-kb fragment which aligns with the ORF2 of theD. melanogaster gypsy element was sequenced. Comparisons of this sequence in three species (D. subobscura, D. melanogaster, and D. virilis) indicate that there is greater similarity between theD. subobscura-D. virilis sequences than betweenD. subobscura andD. melanogaster. Molecular divergence ofgypsy sequences betweenD. virilis andD. subobscura is estimated at 16 MY, whereas the most likely divergence time of these two species is more than 60 MY. These data strongly suggest thatgypsy sequences have been horizontally transferred between these species.Offprint requests to: T.M. Alberola     

Evolutionary origin of the class A and class C β-lactamases

Summary The protein sequences of 18 class A -lactamases and 2 class C -lactamases were analyzed to produce a rooted phylogenetic tree using the DD peptidase of Streptomyces R61 as an outgroup. This tree supports the penicillin-binding proteins as the most likely candidate for the ancestoral origin of the class A and class C -lactamases, these proteins diverging from a common evolutionary origin close to the DD peptidase. The actinomycetes are clearly shown as the origin of the class A -lactamases found in other non-actinomycete species. The tree also divides the -lactamases from the Streptomyces into two subgroups. One subgroup is closer to the DD peptidase root. The other Streptomyces subgroup shares a common branch point with the rest of the class A -lactamases, showing this subgroup as the origin of the non-actinomycete class A -lactamases. The non-actinomycete class A -lactamase phylogenetic tree suggests a spread of these -lactamases by horizontal transfer from the Streptomyces into the non-actinomycete gram-positive bacteria and thence into the gram-negative bacteria. The phylogenetic tree of the Streptomyces class A -lactamases supports the possibility that horizontal transfer of class A -lactamases occurred within the Streptomyces.     

A classification scheme for mobilization regions of bacterial plasmids

Transmissible plasmids can be classified according to their mobilization ability, as being conjugative (self-transmissible) or mobilizable (transmissible only in the presence of additional conjugative functions). Naturally occurring mobilizable plasmids carry the genetic information necessary for relaxosome formation and processing, but lack the functions required for mating pair formation. Mobilizable plasmids have a tremendous impact in horizontal gene transfer in nature, including the spread of antibiotic resistance. However, analysis of their promiscuity and diversity has attracted less attention than that of conjugative plasmids. This review will focus on the analysis of the diversity of mobilizable plasmids. For this purpose, we primarily compared the amino acid sequences of their relaxases and, when pertinent, we compared these enzymes with conjugative plasmid relaxases. In this way, we established phylogenetic relationships among the members of each superfamily. We conducted a database and literature analysis that led us to propose a classification system for small mobilizable plasmids in families and superfamilies according to their mobilization regions. This review outlines the genetic organization of each family of mobilization regions, as well as the most relevant properties and relationships among their constituent encoded proteins. In this respect, the present review constitutes a first approach to the characterization of the global gene pool of mobilization regions of small mobilizable plasmids.