Effects of limited aeration and of the ArcAB system on intermediary pyruvate catabolism in Escherichia coli

The capacity of Escherichia coli to adapt its catabolism to prevailing redox conditions resides mainly in three catabolic branch points involving (i) pyruvate formate-lyase (PFL) and the pyruvate dehydrogenase complex (PDHc), (ii) the exclusively fermentative enzymes and those of the Krebs cycle, and (iii) the alternative terminal cytochrome bd and cytochrome bo oxidases. A quantitative analysis of the relative catabolic fluxes through these pathways is presented for steady-state glucose-limited chemostat cultures with controlled oxygen availability ranging from full aerobiosis to complete anaerobiosis. Remarkably, PFL contributed significantly to the catabolic flux under microaerobic conditions and was found to be active simultaneously with PDHc and cytochrome bd oxidase-dependent respiration. The synthesis of PFL and cytochrome bd oxidase was found to be maximal in the lower microaerobic range but not in a delta ArcA mutant, and we conclude that the Arc system is more active with respect to regulation of these two positively regulated operons during microaerobiosis than during anaerobiosis.     

Effect of target gene CpG content on spontaneous mutation in transgenic mice

Transgenic mutation assays utilizing bacterial target genes display a high frequency of spontaneous mutation at CpG sequences. This is believed to result from the fact that: (1) the prokaryotic genes currently being used as transgenic mutation targets have a high CpG content and (2) these sequences are methylated by mammalian cells to produce 5-methylcytosine (5MC), a known promutagenic base. To study the effect of CpG content on the frequency and type of spontaneous mutation, we have synthesized an analogue of the bacterial lacI target gene (mrkII) that contains a reduced number of CpG sequences. This gene was inserted into a lambda vector and used to construct trangenic mice that undergo vector rescue from genomic DNA upon in vitro packaging. Results on spontaneous mutation frequency and spectrum have been collected and compared to those observed at the lacI gene in Big Blue™ transgenic mice. Spontaneous mutations at the mrkII gene occurred at a frequency in the mid-10⁻⁵ range and were predominantly base pair substitutions, similar to results seen in Big Blue™. However, mrkII mutations were distributed toward the carboxyl end of the gene instead of the bias toward the amino terminus seen in lacI. Unexpectedly, 23% of the spontaneous mrkII mutations were GC → AT transitions at CpG sequences (compared to 32% in lacI), despite the reduction in CpG number from 95 in lacI to only 13 in mrkII. Nine of the CpG bases undergoing transition mutations in mrkII have not been recorded previously as spontaneous sites in Big Blue™. Therefore, substantial reduction of the number of CpG sequences in the lacI transgene did not significantly reduce the rate of spontaneous mutation or alter the contribution of CpG-related events. This suggests that other factors are also operating to establish frequency and composition of spontaneous mutations in transgenic targets.     

Initial events in the photocycle of photoactive yellow protein

The light-induced isomerization of a double bond is the key event that allows the conversion of light energy into a structural change in photoactive proteins for many light-mediated biological processes, such as vision, photosynthesis, photomorphogenesis, and photo movement. Cofactors such as retinals, linear tetrapyrroles, and 4-hydroxy-cinnamic acid have been selected by nature that provide the essential double bond to transduce the light signal into a conformational change and eventually, a physiological response. Here we report the first events after light excitation of the latter chromophore, containing a single ethylene double bond, in a low temperature crystallographic study of the photoactive yellow protein. We measured experimental phases to overcome possible model bias, corrected for minimized radiation damage, and measured absorption spectra of crystals to analyze the photoproducts formed. The data show a mechanism for the light activation of photoactive yellow protein, where the energy to drive the remainder of the conformational changes is stored in a slightly strained but fully cis-chromophore configuration. In addition, our data indicate a role for backbone rearrangements during the very early structural events.     

Binding of juvenile hormone III to lipophorin from the american cockroach Periplaneta americana

Whole hemolymph from the American cockroach, Periplaneta americana, efficiently binds juvenile hormone (JH) III and to a lesser extent JH-I and 10, 11-epoxyfarnesyl diazoacetate (EFDA). The dissociation constants for racemic JH-III and EFDA are 30 ± 2 nM and 1.0 μM, respectively. Isolated lipophorin also binds [³H]JH-III and to a lesser extent JH-I. Other proteins from the hemolymph do not bind JH-III. Binding of JH-III to lipophorin is enantioselective. The dissociation constant, measured with a 92% 10R and 8% 10S mixture, is 21 ± 2 nM. Each lipophorin molecule contains one specific binding site for JH-III. It is concluded that lipophorin is the JH-III-specific transport protein in the hemolymph of the American cockroach. By a combination of photoaffinity labelling and gradient electrophoresis with sodium dodecyl sulphate on polyacrylamide gel, we showed that the JH-III-specific binding site is probably located on apolipophorin I.     

Molecular evidence places the swallow bug genus Oeciacus Stål within the bat and bed bug genus Cimex Linnaeus (Heteroptera: Cimicidae)

The genera Cimex Linnaeus and Oeciacus Stål (Heteroptera: Cimicidae) are common haematophagous ectoparasites of bats or birds in the Holarctic region. Both their phylogenetic relationship and the systematics of the entire family previously were based on data from morphology and host relationships. Relationships among nine species of the genus Cimex and three species of the genus Oeciacus were analysed here using two mitochondrial and three nuclear genes. Cimex was shown to be paraphyletic with respect to Oeciacus. Oeciacus is thus proposed as a synonym of Cimex. The characteristic phenotype of Oeciacus results from the specific host association with different species of swallows (Hirundinidae). The morphological characters that have been used as diagnostic for the genera were shown to be valid and can be further used for determination at species level. The present analyses recovered the four traditional morphologically defined species groups of the genus Cimex. However, their relationships were poorly resolved – only the C. hemipterus group showed a well‐supported relationship to the C. pipistrelli group. The molecular differentiation within the Palaearctic C. pipistrelli and the Nearctic C. pilosellus species groups correlates with their karyotype differentiation. Furthermore, the analyses suggest poly‐ or paraphyly of the former genus Oeciacus. Either way this indicates there is a large amount of host‐associated phenotypic convergence in either bat‐ or bird‐associated groups of species. The probability of host choice and subsequent switch in Cimicidae are discussed and possible scenarios of the evolution of host association in species of Cimex are suggested.     

Palaeoenvironment and taphonomy of a Late Jurassic (Late Tithonian) Lagerstätte from central Poland

A rich assemblage of exceptionally preserved marine and terrestrial fossils occurs in fine‐grained limestones in the upper part of the Late Tithonian (Middle Volgian) shallowing upward carbonate sequence in Central Poland. The richest horizon, a deposit known locally as the Corbulomima horizon, is named after the shallow burrowing suspension feeding bivalve Corbulomima obscura, moulds of which occur in densities of up to 500 per square metre on some bedding planes. The fauna in this bed also includes organic and phosphatic remains of a wide range of other creatures including the exuviae of limulids and decapods, disarticulated fish skeletons and rare isolated pterosaur bones and teeth. There are also perfectly preserved dragonfly wings and beetle exoskeletons. The average stable carbon and oxygen isotope values for ostracod shells and fine‐grained sediment from this horizon suggest precipitation of the calcium carbonate from warm seawater of normal marine salinity. The carbonate sediments overlying the fossiliferous horizon have been interpreted as nearshore to shoreface facies. These pass abruptly into coarse reworked intraclastic sediments interpreted as possible tsunami or storm surge over‐wash deposits. The clasts in this deposit have more positive oxygen isotope values than those in the underlying limestone, which may indicate that they were lithified in a slightly more evaporative, perhaps intertidal, setting. The succession terminates with silicified fine‐grained limestones likely to have formed in extremely shallow lagoonal environments. In contrast with the Solnhofen limestones of Lower Tithonian age in south‐central Germany the Corbulomima horizon is interpreted as a transitional deposit formed in a shallow marine setting by rapid burial with elements of both Konservat‐ and Konzentrat‐Lagerstätte preservation. □Konzentrat and Konservat‐Lagerstätte, Taphonomy, Palaeoenvironment, Paleogeography, Late Jurassic, Poland.     

Comparison of acoustic and traditional point count methods to assess bird diversity and composition in the Aberdare National Park,Kenya

Afromontane forests, like those in the Aberdare National Park (ANP) in Kenya, sustain unique avifaunal assemblages. There is a growing need for biodiversity inventories for Afromontane forests, especially through the utilisation of unskilled observers. Acoustic surveys are a potential aid to this, but more comparisons of this technique with that of traditional point counts are needed. We conducted a systematic survey of the ANP avifauna, assessing whether acoustic and traditional surveys resulted in different species richness scores, and whether this varied with habitat and species characteristics. We also investigated the role of habitat and elevation in driving variation in species richness. The ANP provides habitat types including scrub, moorland, montane, hagenia and bamboo forests. Overall, the surveys yielded 101 identified species. The acoustic method resulted in higher species richness scores compared to the traditional method across all habitats, and the relative performance of the two methods did not vary with habitat type or visibility. The methods detected different species, suggesting that they should be used together to maximise the range of species recorded. We found that habitat type was the primary driver of variation in species richness, with scrub and montane forest having higher species richness scores than other habitats.     

Trill consistency is an age-related assessment signal in banded wrens

Older males tend to have a competitive advantage over younger males in sexual selection. Therefore, it is expected that signals used in sexual selection change with age. Although song repertoire size in songbirds is often mentioned as an age-related trait, many species, including the banded wren (Thryothorus pleurostictus), do not increase their repertoires after the first year. Here, we show that banded wrens reproduce the trill notes in their songs with less variability between them (i.e. more consistently) when they grow older. In a playback experiment, we also show that banded wrens discriminate between younger and older birds based on structural aspects of their song. In a second experiment, banded wrens also respond differentially to natural songs versus songs with artificially enhanced consistency. We argue that consistency in trill note reproduction may be achieved through practice. Sexual selection in the form of male–male competition may therefore operate on a phenotypic trait, the expression of which is enhanced by practice.