title: VapC Toxins from Mycobacterium tuberculosis are ribonucleases that differentially inhibit growth and are neutralized by cognate VapB antitoxins

authors: Ahidjo, Bintou Ahmadou

subjects: Mycobacterium tuberculosis

abstract: The chromosome of Mycobacterium tuberculosis (Mtb) encodes forty seven toxin-antitoxin modules belonging to the VapBC family. The role of these modules in the physiology of Mtb and the function(s) served by their expansion are unknown. We investigated ten vapBC modules from Mtb and the single vapBC from M. smegmatis. Of the Mtb vapCs assessed, only Rv0549c, Rv0595c, Rv2549c and Rv2829c were toxic when expressed from a tetracycline-regulated promoter in M. smegmatis. The same genes displayed toxicity when conditionally expressed in Mtb. Toxicity of Rv2549c in M. smegmatis correlated with the level of protein expressed, suggesting that the VapC level must exceed a threshold for toxicity to be observed. In addition, the level of Rv2456 protein induced in M. smegmatis was markedly lower than Rv2549c, which may account for the lack of toxicity of this and other VapCs scored as ‘non-toxic’. The growth inhibitory effects of toxic VapCs were neutralized by expression of the cognate VapB as part of a vapBC operon or from a different chromosomal locus, while that of non-cognate antitoxins did not. These results demonstrated a specificity of interaction between VapCs and their cognate VapBs, a finding corroborated by yeast two-hybrid analyses. Deletion of selected vapC or vapBC genes did not affect mycobacterial growth in vitro, but rendered the organisms more susceptible to growth inhibition following toxic VapC expression. However, toxicity of ‘non-toxic’ VapCs was not unveiled in deletion mutant strains, even when the mutation eliminated the corresponding cognate VapB, presumably due to insufficient levels of VapC protein. Together with the ribonuclease (RNase) activity demonstrated for Rv0065 and Rv0617 – VapC proteins with similarity to Rv0549c and Rv3320c, respectively – these results suggest that the VapBC family potentially provides an abundant source of RNase activity in Mtb, which may profoundly impact the physiology of the organism.

text: VapC Toxins from Mycobacterium tuberculosis are ribonucleases that differentially inhibit growth and are neutralized by cognate VapB antitoxins The chromosome of Mycobacterium tuberculosis (Mtb) encodes forty seven toxin-antitoxin modules belonging to the VapBC family. The role of these modules in the physiology of Mtb and the function(s) served by their expansion are unknown. We investigated ten vapBC modules from Mtb and the single vapBC from M. smegmatis. Of the Mtb vapCs assessed, only Rv0549c, Rv0595c, Rv2549c and Rv2829c were toxic when expressed from a tetracycline-regulated promoter in M. smegmatis. The same genes displayed toxicity when conditionally expressed in Mtb. Toxicity of Rv2549c in M. smegmatis correlated with the level of protein expressed, suggesting that the VapC level must exceed a threshold for toxicity to be observed. In addition, the level of Rv2456 protein induced in M. smegmatis was markedly lower than Rv2549c, which may account for the lack of toxicity of this and other VapCs scored as ‘non-toxic’. The growth inhibitory effects of toxic VapCs were neutralized by expression of the cognate VapB as part of a vapBC operon or from a different chromosomal locus, while that of non-cognate antitoxins did not. These results demonstrated a specificity of interaction between VapCs and their cognate VapBs, a finding corroborated by yeast two-hybrid analyses. Deletion of selected vapC or vapBC genes did not affect mycobacterial growth in vitro, but rendered the organisms more susceptible to growth inhibition following toxic VapC expression. However, toxicity of ‘non-toxic’ VapCs was not unveiled in deletion mutant strains, even when the mutation eliminated the corresponding cognate VapB, presumably due to insufficient levels of VapC protein. Together with the ribonuclease (RNase) activity demonstrated for Rv0065 and Rv0617 – VapC proteins with similarity to Rv0549c and Rv3320c, respectively – these results suggest that the VapBC family potentially provides an abundant source of RNase activity in Mtb, which may profoundly impact the physiology of the organism.

year: 2011

title: Macrophyte architecture affects the abundance and diversity of littoral microfauna

authors: Lucena-Moya, Paloma

subjects: zooplankton

abstract: We tested the hypothesis that structural complexity is an important factor influencing the abundance and taxon richness of microfauna (e.g., rotifers, copepods, cladocerans) in littoral habitats. Research on littoral microfauna has to date focused mainly on field observations, which commonly show microfauna have preference for some macrophytes over others. However, while such studies commonly conclude that macrophyte architecture is a major determinant of these variations, independent factors may also be responsible (e.g., differences in macrophyte ages, differences in macrophyte bed densities and the depth of the respective macrophyte beds sampled). We used artificial macrophytes with three levels of complexity to keep the surface area and mass of the substrate sampled constant, and to control for confounding factors not related to the complexity of the plants. Our results support the hypothesis that structural complexity is an important factor influencing abundance and taxon richness, independent of other potential confounding factors. Microfaunal (mainly rotifer) abundance and richness were generally greater on more complex artificial macrophytes, likely a result of more complex substrates (1) providing a greater variety of habitat, (2) supporting a greater concentration or variety of food and/or (3) affording greater protection against predators. Less mobile surface-associated (i.e., benthic/periphytic) taxa were found to discriminate among substrates, whereas the abundance and richness of planktonic species were not affected by complexity level. Relatively low abundances and taxon richness of microfauna recorded in control samples, which did not contain artificial macrophytes, supports the contention that vegetated areas sustain a higher abundance and variety of species than non-vegetated areas.

text: Macrophyte architecture affects the abundance and diversity of littoral microfauna We tested the hypothesis that structural complexity is an important factor influencing the abundance and taxon richness of microfauna (e.g., rotifers, copepods, cladocerans) in littoral habitats. Research on littoral microfauna has to date focused mainly on field observations, which commonly show microfauna have preference for some macrophytes over others. However, while such studies commonly conclude that macrophyte architecture is a major determinant of these variations, independent factors may also be responsible (e.g., differences in macrophyte ages, differences in macrophyte bed densities and the depth of the respective macrophyte beds sampled). We used artificial macrophytes with three levels of complexity to keep the surface area and mass of the substrate sampled constant, and to control for confounding factors not related to the complexity of the plants. Our results support the hypothesis that structural complexity is an important factor influencing abundance and taxon richness, independent of other potential confounding factors. Microfaunal (mainly rotifer) abundance and richness were generally greater on more complex artificial macrophytes, likely a result of more complex substrates (1) providing a greater variety of habitat, (2) supporting a greater concentration or variety of food and/or (3) affording greater protection against predators. Less mobile surface-associated (i.e., benthic/periphytic) taxa were found to discriminate among substrates, whereas the abundance and richness of planktonic species were not affected by complexity level. Relatively low abundances and taxon richness of microfauna recorded in control samples, which did not contain artificial macrophytes, supports the contention that vegetated areas sustain a higher abundance and variety of species than non-vegetated areas.

year: 2011

title: Composition Portfolio

authors: Ulenberg, Phillippa

subjects: composition portfolio

abstract: The music written for this portfolio offers creative answers to some of the challenges facing contemporary New Zealand composition, including multiculturalism.This has involved in-depth research using a variety of methods. Engagement was undertaken with linguists and musicians from Malaysia and Korea, who not only assisted with texts, but also spoke knowledgeably about their cultural traditions and past and present musical genres. The inclusion of Chinese gu-zheng in several of the works was made possible with the assistance given by Chen Xi Yao, an excellent performer who comes from a long lineage of musicians. Attending concerts given by performers of the instruments that have been used in the portfolio was essential to understanding the sounds and uses of the instruments. In addition, on-line sources include many examples of the sounds. Attendance at workshops on Māori taonga pūoro also brought the additional honour, benefits and experience of making and playing the instruments, and the opportunities to meet and work with leading makers and performers of these musical treasures. Sources of Western classical music that have been particularly influential during the writing of the portfolio are orchestral works by Igor Stravinsky, Samuel Barber and Param Vir, and the song cycles of Alban Berg and Benjamin Britten. Luciano Berio’s virtuosic piece for solo bassoon was also instructive. Experiences of composition, reflection and scholarly research underpin the portfolio and have have informed the composition of each work.

text: Composition Portfolio The music written for this portfolio offers creative answers to some of the challenges facing contemporary New Zealand composition, including multiculturalism.This has involved in-depth research using a variety of methods. Engagement was undertaken with linguists and musicians from Malaysia and Korea, who not only assisted with texts, but also spoke knowledgeably about their cultural traditions and past and present musical genres. The inclusion of Chinese gu-zheng in several of the works was made possible with the assistance given by Chen Xi Yao, an excellent performer who comes from a long lineage of musicians. Attending concerts given by performers of the instruments that have been used in the portfolio was essential to understanding the sounds and uses of the instruments. In addition, on-line sources include many examples of the sounds. Attendance at workshops on Māori taonga pūoro also brought the additional honour, benefits and experience of making and playing the instruments, and the opportunities to meet and work with leading makers and performers of these musical treasures. Sources of Western classical music that have been particularly influential during the writing of the portfolio are orchestral works by Igor Stravinsky, Samuel Barber and Param Vir, and the song cycles of Alban Berg and Benjamin Britten. Luciano Berio’s virtuosic piece for solo bassoon was also instructive. Experiences of composition, reflection and scholarly research underpin the portfolio and have have informed the composition of each work.

year: 2011