A novel class of CoA-transferase involved in short-chain fatty acid metabolism in butyrate-producing human colonic bacteria

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Conspecific pollen loads on insects visiting female flowers on parasitic \u3ci\u3ePhoradendron californicum\u3c/i\u3e (Viscaceae)

Desert mistletoe, Phoradendron californicum (Viscaceae), is a dioecious parasitic plant that grows on woody legumes in the Mojave and Sonoran Deserts, produces minute flowers during winter, and is dispersed by birds defecating fruits. Pollination of desert mistletoe has not been examined despite the species’ reliance on insects for transporting pollen from male to female plants. I investigated the pollination of P. californicum parasitizing Acacia greggii (Fabaceae) shrubs at 3 sites at different elevations in the Mojave Desert of southern Nevada during February 2015. I examined pollen from male flowers, aspirated insects landing on female flowers, and counted pollen grains in insect pollen loads. Desert mistletoe’s tricolpate pollen differed from a previous description by being oblate instead of subprolate in equatorial view. Female flowers were visited by 13 species of Diptera in 10 genera and 6 families and 3 species of Hymenoptera in 3 families. Almost all (98.5%) of the pollen carried by insects was from desert mistletoe. Five species of phytophagous fruit flies in Tephritidae were frequently found on flowers, comprising 53% of the insects collected, but carried low amounts of P. californicum pollen. Two species of blow flies in Calliphoridae, both larval decomposers of animals, were also relatively abundant on flowers and carried moderate to high pollen loads. Flies in Syrphidae, 2 predators and 1 plant-decomposer, carried varying amounts of conspecific pollen. Conspecific pollen loads also varied on a species of native bee in Halictidae and on naturalized honey bees in Apidae. Desert mistletoe appears to be pollinated mostly by tephritids, due to their abundance on female flowers, and by calliphorids. Blow flies would be more likely than fruit flies to carry pollen between male and female plants on different host shrubs due to their larger size and stronger flight. Parasitic, dioecious P. californicum plants appear to rely on a web of mutualism between fruit-eating birds and flower-fertilizing insects.El muérdago del desierto, Phoradendron californicum (Viscaceae), es una planta parásita dioica que crece en leguminosas leñosas en los Desiertos de Mojave y de Sonora. Esta planta produce flores diminutas durante el invierno y son dispersadas por aves que defecan las semillas. La polinización del muérdago del desierto no ha sido estudiada, a pesar de la dependencia a los insectos para transportar polen de plantas macho a plantas hembras. Estudié la polinización de P. californicum que parasita los arbustosAcacia greggii (Fabaceae) en tres sitios a diferentes elevaciones en el Desierto de Mojave al sur de Nevada, durante febrero del 2015. Examiné el polen de flores macho, insectos succionados al aterrizar en flores hembras y conté los granos de polen en las cargas de polen de los insectos. El polen tricolpado del muérdago del desierto difirió de una descripción anterior por ser achatado en lugar de subprolado en vista ecuatorial. Las flores hembra fueron visitadas por 13 especies de dípteros (Diptera) en 10 géneros y 6 familias, y 3 especies de himenópteros (Hymenoptera) en 3 familias. Casi todo el polen (98.5%) llevado por los insectos pertenecía al muérdago del desierto. Encontré con frecuencia cinco especies de moscas de la fruta fitófagas en las flores, comprendiendo el 53% de los insectos colectados, pero llevaban cantidades bajas de polen de P. californicum. Dos especies de moscas verdes Calliphoridae, ambas descomponedoras de animales en etapa larval, fueron relativamente abundantes en las flores y transportaron tanto cargas moderadas como cargas grandes de polen. Las moscas Syrphidae, dos depredadoras y una descomponedora de plantas, transportaron cantidades variables de polen conespecífico. Las cargas de polen conespecífico también variaron en una especie de abeja nativa Halictidae y en abejas melíferas Apidae. El muérdago del desierto parece ser polinizado principalmente por los tefrítidos, debido a su abundancia en flores hembras y califóridos. Las moscas verdes serían más propensas, que las moscas de la fruta, a transportar el polen entre plantas macho y plantas hembras en diferentes arbustos de refugio debido a su tamaño mayor y a su vuelo más firme. Las plantas parasitas dioicas P. californicum, parecen depender de una red de mutualismo entre aves que se alimentan de frutas e insectos fertilizadores de flores

Conspecific pollen loads on insects from \u3ci\u3ePrunus fasciculata\u3c/i\u3e (Rosaceae) female flowers in southern Nevada

Desert almond, Prunus fasciculata (Rosaceae), is a Mojave Desert shrub that primarily produces male and female flowers on different plants. I investigated the plant’s pollination by examining pollen loads on insects aspirated from female flowers on 3 dioecious shrubs, growing near male-flowering shrubs, at one locality in southern Nevada during March 2014. Pollen loads were analyzed on 9 species of Diptera in Bombyliidae, Syrphidae, Calliphoridae, and Tachinidae and 4 species of Hymenoptera in Andrenidae (all female Andrena). All but 4 of the 65 flies and 38 bees aspirated carriedP. fasciculata pollen grains, recognized by their tricolpate shape in polar view and oblate shape in equatorial view. Two species of syrphid flies in Copestylum were frequently aspirated and carried high P. fasciculata pollen loads and moderate proportions of conspecific pollen. High conspecific pollen loads on the tachinidChaetogaedia also indicated potential for pollinating P. fasciculata. Three of the 4 species of Andrena bees carried large amounts of P. fasciculata pollen. Conspecific pollen also comprised most of the pollen load on Andrena bees, suggesting high flower constancies to the plant. Pollinators of P. fasciculata would vary over the plant’s range, and likely between years, because of the localized populations or narrow larval diets of many of the insects collected from flowers. The female desert almond shrubs examined in southern Nevada during 2014 appeared to be pollinated by a variety of native flies and bees, especially syrphid flies in Copestylum and andrenid bees in Andrena.Las almendras del desierto, Prunus fasciculata (Rosaceae), es un arbusto del desierto de Mojave, que produce flores masculinas y femeninas en diferentes plantas. Investigué la polinización de la planta examinando la carga de polen aspirada en insectos de flores femeninas en tres arbustos deciduos, creciendo cerca de arbustos de floración masculina, en una localidad al sur de Nevada durante marzo del 2014. Las cargas de polen fueron analizados en 9 especies de dípteros en Bombyliidae, Syrphidae, Calliphoridae y Tachinidae y 4 especies de himenópteros en Andrenidae (todas hembrasAndrena). Todos menos 4 de las 65 moscas y 38 abejas llevaron de polen de P. fasciculata, reconocido por su forma tricolpado en vista polar y su forma achatada en vista ecuatorial. Dos especies de sírfidos en Copestylum aspiraron frecuentemente polen de P. fasciculata y proporciones moderadas de polen de conespecíficos. Altas cargas de polen conspecífico en Chaetogaedia indicaron un potencial polinizador de P. fasciculata. Tres de las 4 especies de abejas Andrena lleva a grandes cantidades de polen de P. fasciculata. El polen conespecífico también compone la mayor parte de la carga de polen de las abejas Andrena, sugiriendo constancia de flores en la planta. Los polinizadores de P. fasciculata varían a lo largo de la planta, y es probable que entre años, debido a las poblaciones localizadas o a la estrecha dieta de larvas de muchos de los insectos encontrados en las flores. Las hembras, de los arbustos examinadas en el sur de Nevada en 2014 parecían ser polinizadas por una variedad de moscas y abejas nativas, especialmente los sírfidos Copestylum y abejas Andrena

Coenzyme A-transferase-independent butyrate re-assimilation in Clostridium acetobutylicum - evidence from a mathematical model

The hetero-dimeric CoA-transferase CtfA/B is believed to be crucial for the metabolic transition from acidogenesis to solventogenesis in Clostridium acetobutylicum as part of the industrial-relevant acetone-butanol-ethanol (ABE) fermentation. Here, the enzyme is assumed to mediate re-assimilation of acetate and butyrate during a pH-induced metabolic shift and to faciliate the first step of acetone formation from acetoacetyl-CoA. However, recent investigations using phosphate-limited continuous cultures have questioned this common dogma. To address the emerging experimental discrepancies, we investigated the mutant strain Cac-ctfA398s::CT using chemostat cultures. As a consequence of this mutation, the cells are unable to express functional ctfA and are thus lacking CoA-transferase activity. A mathematical model of the pH-induced metabolic shift, which was recently developed for the wild type, is used to analyse the observed behaviour of the mutant strain with a focus on re-assimilation activities for the two produced acids. Our theoretical analysis reveals that the ctfA mutant still re-assimilates butyrate, but not acetate. Based upon this finding, we conclude that C. acetobutylicum possesses a CoA-tranferase-independent butyrate uptake mechanism that is activated by decreasing pH levels. Furthermore, we observe that butanol formation is not inhibited under our experimental conditions, as suggested by previous batch culture experiments. In concordance with recent batch experiments, acetone formation is abolished in chemostat cultures using the ctfa mutant

Redox-switch regulatory mechanism of thiolase from Clostridium acetobutylicum

Thiolase is the first enzyme catalysing the condensation of two acetyl-coenzyme A (CoA) molecules to form acetoacetyl-CoA in a dedicated pathway towards the biosynthesis of n-butanol, an important solvent and biofuel. Here we elucidate the crystal structure of Clostridium acetobutylicum thiolase (CaTHL) in its reduced/oxidized states. CaTHL, unlike those from other aerobic bacteria such as Escherichia coli and Zoogloea ramegera, is regulated by the redox-switch modulation through reversible disulfide bond formation between two catalytic cysteine residues, Cys88 and Cys378. When CaTHL is overexpressed in wild-type C. acetobutylicum, butanol production is reduced due to the disturbance of acidogenic to solventogenic shift. The CaTHLV77Q/N153Y/A286K mutant, which is not able to form disulfide bonds, exhibits higher activity than wild-type CaTHL, and enhances butanol production upon overexpression. On the basis of these results, we suggest that CaTHL functions as a key enzyme in the regulation of the main metabolism of C. acetobutylicum through a redox-switch regulatory mechanism.close0

Mathematical modelling of clostridial acetone-butanol-ethanol fermentation

Clostridial acetone-butanol-ethanol (ABE) fermentation features a remarkable shift in the cellular metabolic activity from acid formation, acidogenesis, to the production of industrial-relevant solvents, solventogensis. In recent decades, mathematical models have been employed to elucidate the complex interlinked regulation and conditions that determine these two distinct metabolic states and govern the transition between them. In this review, we discuss these models with a focus on the mechanisms controlling intra- and extracellular changes between acidogenesis and solventogenesis. In particular, we critically evaluate underlying model assumptions and predictions in the light of current experimental knowledge. Towards this end, we briefly introduce key ideas and assumptions applied in the discussed modelling approaches, but waive a comprehensive mathematical presentation. We distinguish between structural and dynamical models, which will be discussed in their chronological order to illustrate how new biological information facilitates the ‘evolution’ of mathematical models. Mathematical models and their analysis have significantly contributed to our knowledge of ABE fermentation and the underlying regulatory network which spans all levels of biological organization. However, the ties between the different levels of cellular regulation are not well understood. Furthermore, contradictory experimental and theoretical results challenge our current notion of ABE metabolic network structure. Thus, clostridial ABE fermentation still poses theoretical as well as experimental challenges which are best approached in close collaboration between modellers and experimentalists

Factors influencing citrus fruit scarring caused by Pezothrips kellyanus

[EN] Kelly s citrus thrips (KCT) Pezothrips kellyanus (Bagnall) (Thysanoptera: Thripidae) is a recently recorded cosmopolitan citrus pest, causing fruit scarring that results in downgrading of fruit. Due to the detrimental effects caused on fruits by KCT, we wanted to study some of the factors influencing fruit scarring. Specifically, the objectives were: (1) to determine the fruit development stage when citrus fruits are damaged by KCT and the population structure of KCT during this period, (2) to study the influence of temperature on intensity of damage, and finally, (3) to identify alternative host plants. KCT populations on flowers and fruitlets and alternate plant hosts were sampled in four citrus orchards from 2008 to 2010. The percentage of damaged fruits was also recorded. The exotic vine Araujia sericifera (Apocynaceae) was recorded as a new host for KCT. Thrips scarring started to increase at 350 650 degree-days (DD) above 10.2 C, coinciding with a peak abundance of the second instar larval stages over all 3 years of the study. The maximum percentage of larval stages of KCT was observed in the 3 years at about 500 DD, a period which corresponds to the end of May or early June. Variation in the severity of fruit scarring appeared to be related to air temperature. Temperature likely affects the synchronisation between the peak in abundance of KCT larvae, and the period when fruitlets are susceptible to thrips damage. Temperature can also influence the survival and development of KCT populations in citrus and other host plants in the citrus agro-ecosystem.The authors thank Alejandro Tena for his valuable suggestions and two anonymous referees for their careful review and helpful comments. We also extend our thanks to the owners of the commercial orchards for giving us permission to use their citrus orchards. The first author was awarded an FPI fellowship from the Polytechnic University of Valencia to obtain her PhD degree.Navarro Campos, C.; Pekas, A.; Aguilar Martí, MA.; Garcia Marí, F. (2013). Factors influencing citrus fruit scarring caused by Pezothrips kellyanus. Journal of Pest Science. (86):459-467. doi:10.1007/s10340-013-0489-7S45946786Baker GJ (2006) Kelly citrus thrips management. Fact sheet. Government of South Australia, primary industries and resources SA. http://www.sardi.sa.gov.au/__data/assets/pdf_file/0010/44875/kctfact_sheet.pdf . Accessed 16 July 2012Baker GJ, Jackman DJ, Keller M, MacGregor A, Purvis S (2002) Development of an integrated pest management system for thrips in Citrus. HAL Final Report CT97007. http://www.sardi.sa.gov.au/pestsdiseases/horticulture/horticultural_pests/kelly_citrus_thrips/research_report_1997-2000 . Accessed 16 July 2012Bedford ECG (1998) Thrips, wind and other blemishes. Citrus pests in the Republic of South Africa. 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Comparative genomic and transcriptomic analysis revealed genetic characteristics related to solvent formation and xylose utilization in Clostridium acetobutylicum EA 2018

<p>Abstract</p> <p>Background</p> <p><it>Clostridium acetobutylicum</it>, a gram-positive and spore-forming anaerobe, is a major strain for the fermentative production of acetone, butanol and ethanol. But a previously isolated hyper-butanol producing strain <it>C. acetobutylicum </it>EA 2018 does not produce spores and has greater capability of solvent production, especially for butanol, than the type strain <it>C. acetobutylicum </it>ATCC 824.</p> <p>Results</p> <p>Complete genome of <it>C. acetobutylicum </it>EA 2018 was sequenced using Roche 454 pyrosequencing. Genomic comparison with ATCC 824 identified many variations which may contribute to the hyper-butanol producing characteristics in the EA 2018 strain, including a total of 46 deletion sites and 26 insertion sites. In addition, transcriptomic profiling of gene expression in EA 2018 relative to that of ATCC824 revealed expression-level changes of several key genes related to solvent formation. For example, <it>spo0A </it>and <it>adhEII </it>have higher expression level, and most of the acid formation related genes have lower expression level in EA 2018. Interestingly, the results also showed that the variation in CEA_G2622 (CAC2613 in ATCC 824), a putative transcriptional regulator involved in xylose utilization, might accelerate utilization of substrate xylose.</p> <p>Conclusions</p> <p>Comparative analysis of <it>C. acetobutylicum </it>hyper-butanol producing strain EA 2018 and type strain ATCC 824 at both genomic and transcriptomic levels, for the first time, provides molecular-level understanding of non-sporulation, higher solvent production and enhanced xylose utilization in the mutant EA 2018. The information could be valuable for further genetic modification of <it>C. acetobutylicum </it>for more effective butanol production.</p