In situ substrate conversion and assimilation by nitrifying bacteria in a model biofilm

Local nitrification and carbon assimilation activities were studied in situ in a model biofilm to investigate carbon yields and contribution of distinct populations to these activities. Immobilized microcolonies (related to Nitrosomonas europaea/eutropha, Nitrosomonas oligotropha, Nitrospira sp., and to other Bacteria) were incubated with [14C]-bicarbonate under different experimental conditions. Nitrifying activity was measured concomitantly with microsensors (oxygen, ammonium, nitrite, nitrate). Biofilm thin sections were subjected to fluorescence in situ hybridization (FISH), microautoradiography (MAR), and local quantification of [14C]-bicarbonate uptake (beta microimaging). Nitrifying activity and tracer assimilation were restricted to a surface layer of different thickness in the various experiments (substrate or oxygen limitation). Excess oxygen uptake under all conditions revealed heterotrophic activity fuelled by decay or excretion products during active nitrification. Depth limits and intensity of tracer incorporation profiles were in agreement with ammonia-oxidation activity (measured with microsensors), and distribution of incorporated tracer (detected with MAR). Microautoradiography revealed a sharp individual response of distinct populations in terms of in-/activity depending on the (local) environmental conditions within the biofilm. Net in situ carbon yields on N, expressed as e- equivalent ratios, varied between 0.005 and 0.018, and, thus, were in the lower range of data reported for pure cultures of nitrifiers.     

Brood Ball-Mediated Transmission of Microbiome Members in the Dung Beetle,Onthophagus taurus (Coleoptera: Scarabaeidae)

Insects feeding on plant sap, blood, and other nutritionally incomplete diets are typically associated with mutualistic bacteria that supplement missing nutrients. Herbivorous mammal dung contains more than 86% cellulose and lacks amino acids essential for insect development and reproduction. Yet one of the most ecologically necessary and evolutionarily successful groups of beetles, the dung beetles (Scarabaeinae) feeds primarily, or exclusively, on dung. These associations suggest that dung beetles may benefit from mutualistic bacteria that provide nutrients missing from dung. The nesting behaviors of the female parent and the feeding behaviors of the larvae suggest that a microbiome could be vertically transmitted from the parental female to her offspring through the brood ball. Using sterile rearing and a combination of molecular and culture-based techniques, we examine transmission of the microbiome in the bull-headed dung beetle, Onthophagus taurus. Beetles were reared on autoclaved dung and the microbiome was characterized across development. A ~1425 bp region of the 16S rRNA identified Pseudomonadaceae, Enterobacteriaceae, and Comamonadaceae as the most common bacterial families across all life stages and populations, including cultured isolates from the 3^rd instar digestive system. Finer level phylotyping analyses based on lepA and gyrB amplicons of cultured isolates placed the isolates closest to Enterobacter cloacae, Providencia stuartii, Pusillimonas sp., Pedobacter heparinus, and Lysinibacillus sphaericus. Scanning electron micrographs of brood balls constructed from sterile dung reveals secretions and microbes only in the chamber the female prepares for the egg. The use of autoclaved dung for rearing, the presence of microbes in the brood ball and offspring, and identical 16S rRNA sequences in both parent and offspring suggests that the O. taurus female parent transmits specific microbiome members to her offspring through the brood chamber. The transmission of the dung beetle microbiome highlights the maintenance and likely importance of this newly-characterized bacterial community.     

Ein Beitrag zur Selbstfertilität beim Weißklee

Zusammenfassung Es wurden aus einer lettischen Weißkleepopulation selbstfertile Formen ausgelesen und im Verlaufe von 7 Jahren geprüft. Dabei wurde festgestellt, daß die bei den fremdbestäubten Weißklee-Populationen in der Praxis beobachteten Schwankungen im Samenertrag auch bei den selbstfertilen Formen zu beobachten sind, obwohl diese vom Bienenflug nicht mehr unbedingt abhängig sind. Als Ursache dieser Schwankungen konnte die Witterungsgestaltung während der Vorund Hochsommermonate ermittelt werden. Allerdings scheinen die Witterungsbedingungen nicht unmittelbar, sondern mittelbar über die negative Korrelation zwischen der Ausbildung vegetativer und generativer Pflanzenmasse auf die Selbstfertilität einzuwirken. Neben der starken Variabilität der Selbstfertilität traten aber auch erblich bedingte Selbstfertilitätsunterschiede auf, die sich von den Umweltbedingungen nicht verwischen ließen. Daraus wird die Möglichkeit abgeleitet, durch weitere züchterische Bearbeitung die noch sehr labil ausgebildete Selbstfertilität bei den ausgelesenen Pflanzen zu verbessern und zu festigen.Mit 9 Textabbildungen     

Citrate oscillates in liver and pancreatic beta cell mitochondria and in INS-1 insulinoma cells

Oscillations in citric acid cycle intermediates have never been previously reported in any type of cell. Here we show that adding pyruvate to isolated mitochondria from liver, pancreatic islets, and INS-1 insulinoma cells or adding glucose to intact INS-1 cells causes sustained oscillations in citrate levels. Other citric acid cycle intermediates measured either did not oscillate or possibly oscillated with a low amplitude. In INS-1 mitochondria citrate oscillations are in phase with NAD(P) oscillations, and in intact INS-1 cells citrate oscillations parallel oscillations in ATP, suggesting that these processes are co-regulated. Oscillations have been extensively studied in the pancreatic beta cell where oscillations in glycolysis, NAD(P)/NAD(P)H and ATP/ADP ratios, plasma membrane electrical activity, calcium levels, and insulin secretion have been well documented. Because the mitochondrion is the major site of ATP synthesis and NADH oxidation and the only site of citrate synthesis, mitochondria need to be synchronized for these factors to oscillate. In suspensions of mitochondria from various organs, most of the citrate is exported from the mitochondria. In addition, citrate inhibits its own synthesis. We propose that this enables citrate itself to act as one of the cellular messengers that synchronizes mitochondria. Furthermore, because citrate is a potent inhibitor of the glycolytic enzyme phosphofructokinase, the pacemaker of glycolytic oscillations, citrate may act as a metabolic link between mitochondria and glycolysis. Citrate oscillations may coordinate oscillations in mitochondrial energy production and anaplerosis with glycolytic oscillations, which in the beta cell are known to parallel oscillations in insulin secretion.     

Molecular structure of a novel cholesterol-responsive A subclass ABC transporter,ABCA9

We recently identified a novel ABC A subclass transporter, ABCA6, in human macrophages. Here, we report the molecular cloning of an additional ABC A subfamily transporter from macrophages denoted ABCA9. The identified coding sequence is 4.9 kb in size and codes for a 1624 amino acid protein product. In accordance with the proposed nomenclature, the novel transporter was designated ABCA9. The putative full-length ABC transporter polypeptide consists of two transmembrane domains and two nucleotide binding folds and thus conforms to the group of full-size ABC transporters. We identified alternative ABCA9 mRNA variants in human macrophages that predict the existence of three truncated forms of the novel transporter. Among the human ABC A subfamily transporters, ABCA9 exhibits the highest amino acid sequence homology with ABCA8 (72%) and ABCA6 (60%), respectively. The striking amino acid sequence similarity between these transporter molecules supports the notion that they represent an evolutionary more recently emerged subgroup within the family of ABC A transporters, which we refer to as "ABCA6-like transporters." ABCA9 mRNA is ubiquitously expressed with the highest mRNA levels in heart, brain, and fetal tissues. Analysis of the genomic structure revealed that the ABCA9 gene consists of 39 exons that are located within a genomic region of approximately 85 kb size on chromosome 17q24.2. In human macrophages, ABCA9 mRNA is induced during monocyte differentiation into macrophages and suppressed by cholesterol import indicating that ABCA9, like other known ABC A subfamily transporters, is a cholesterol-responsive gene. Based on this information, ABCA9 is likely involved in monocyte differentiation and macrophage lipid homeostasis.     

Pupal remodeling and the evolution and development of alternative male morphologies in horned beetles

Background  

How novel morphological traits originate and diversify represents a major frontier in evolutionary biology. Horned beetles are emerging as an increasingly popular model system to explore the genetic, developmental, and ecological mechanisms, as well as the interplay between them, in the genesis of novelty and diversity. The horns of beetles originate during a rapid growth phase during the prepupal stage of larval development. Differential growth during this period is either implicitly or explicitly assumed to be the sole mechanism underlying differences in horn expression within and between species. Here I focus on male horn dimorphisms, a phenomenon at the center of many studies in behavioral ecology and evolutionary development, and quantify the relative contributions of a previously ignored developmental process, pupal remodeling, to the expression of male dimorphism in three horned beetle species.