Impact of changes in environmental parameters (pH and elevated CO2) on soil microbial communities involved in N-cycling

Microorganisms involved in the nitrogen (N)-cycle in soils are the major drivers of N-transformation changes and the main source of the potent greenhouse gas nitrous oxide (N2O) from soil, which has a global warming potential of 298 times that of carbon dioxide (CO2). Accordingly, it is of great interest to explore shifts in the rates, balances and reactions of the N-cycle impacted by climate changes, in order to offer more accurate predictions. Particularly, since increases in CO2 concentrations or changes in the pH of agricultural fields due to anthropogenic influences often lead to changes in the N-transformation rates, along with an increase of N2O emissions. However, the N-cycle and its corresponding pathways are very complex and the response to different environmental changes is difficult to predict. Many of the interactions between microorganisms and their contribution to N-transformation rates as well as N2O emission are not well understood, controversially discussed and plenty of important interactions remain puzzling. Therefore, the main objective of this thesis was to shed light on the interaction of the overall and active microbial communities involved in the N-cycle in response to pH shifts or elevated atmospheric CO2 concentrations in soils, two variables known to influence N2O fluxes from soils. In the first part we studied the influence of an acidic pH on a denitrifier community from an initial neutral pH. We followed the abundance and composition of an overall and active denitrifier community extracted from soil (pH = 7.1) when exposed to pH 5.4 and drifting back to pH 6.6. When exposed to pH 5.4, the denitrifier community was able to actively grow, but only reduced N2O to N2 after a near neutral pH was reestablished by the alkalizing metabolic activity of an acid-tolerant part of the community. The genotypes proliferating under these conditions differed from those dominant at neutral pH. Denitrifiers of the nirS-type appeared to be severely suppressed by low pH whereas nirK-type and nosZ-containing denitrifiers showed strongly reduced transcriptional activity and growth, even after restoration of neutral pH. Our study suggests that low pH episodes alter transcriptionally active populations which shape denitrifier communities and determine their gas kinetics. The second part of this thesis analyses the effect of elevated CO2 (eCO2) on the N-cycle to reveal the underlying microbial mechanisms and process inside the N-cycle causing the enhanced emission of N2O. To gain a better understanding of the impact of eCO2 on soil microbial communities, we applied a molecular approach targeting several microbial groups involved in soil N-cycling (N-fixers, denitrifiers, archaeal and bacterial ammonia oxidizers, and dissimilatory nitrate reducers to ammonia) at the Gießen Free Air Carbon dioxide Enrichment (GiFACE) site. Remarkably, soil parameters, overall microbial community abundance and composition in the top soil under eCO2 differed only slightly from soil under ambient CO2. We concluded that +20% eCO2 had little to no effect on the overall microbial community involved in N-cycling. Based on these findings, in a third part we conducted a comprehensive study monitoring N-transformation rates, nutrient fluxes, and gaseous emission, while analyzing the dynamics in microbial communities involved in N-cycling under eCO2 accompanied with simultaneous addition of N-fertilizer. We could show that long-term fumigation with eCO2 influences the response of the soil microbial communities to N inputs via fertilization. Compared to aCO2 distinct parts of the community were transcriptionally activated. Here, nirS-type denitrifiers showed the greatest positive feedback to eCO2, which correlated with increasing N2O emissions. This stimulation may be an effect of higher labile C input in the rhizosphere by increased photosynthesis. However, the input of N by fertilization rather seems to exert short term effects on the expression of functional marker genes with consequences for N-transformations which do not translate into the development of distinct communities under eCO2 in the long-term. In conclusion this thesis provides evidence that already small changes in abundance and composition of the microbial community involved in N-cycling are sufficient to strongly influence emission of N2O from soil under changing environmental parameters such as pH and elevated CO2

A Khoekhoegowab Dictionary with an English–Khoekhoegowab Index

Wilfrid H.G. Haacke and Eliphas Eiseb. A Khoekhoegowab Dictionary with an English–Khoekhoegowab Index. 2002, xiv + 740 pp. ISBN 99916- 0-401-4. Windhoek: Gamsberg Macmillan. Price: N$175.00 (Hard-cover), N$150.00 (Soft-cover)

Dynamics in bacterial flagellar systems

Bacterial cells are highly organized with respect to their shape, structure or function. In particular flagellar motility and chemotaxis of many bacteria require a precise spatiotemporal regulation of the corresponding components to avoid wasting energy. Despite the tight regulation, flagellar motility and chemotaxis are also targets of adaptation in response to extra- and intracellular cues. The balance between tight regulation and flexible adaptation allows bacteria to efficiently thrive in changing and potentially nutrient limiting environments. This thesis focuses on the adaptation of the flagella-mediated motility of the γ-proteobacterium Shewanella oneidensis MR 1 by dynamically exchanging one of its motor components and a system in Shewanella putrefaciens CN-32 that ensures proper polar localization of several proteins, among them the chemotaxis system. S. oneidensis MR-1 possesses a single polar flagellar system but harbors two types of ion-channels, the so-called stators, that power flagellar rotation. The second chapter demonstrates that both stators, the native Na+-dependent PomAB and putatively acquired H+-dependent MotAB complex, are solely sufficient to drive motility in liquid environments and may interact with the flagellar rotor in varying configurations depending on sodium-ion concentrations, likely forming a hybrid motor. The principal environmental cue that can be integrated and reacted to by PomAB/MotAB stator swapping is the external Na+ concentration. Functionality of MotAB on the other hand seems to be tied to the membrane potential and load on the flagellum. Some limitations of MotAB can be overcome by small point mutations in the plug domain of MotB, likely by changing the MotAB channel properties and/or its mechanosensing capability. The second system studied was a landmark protein that serves as an organizational platform involved in different cellular processes including chemotaxis. This transmembrane protein was identified as the functional orthologue of Vibrio cholerae HubP. In S. putrefaciens CN-32 it is required for polar localization and possibly the correct function of the chemotaxis components, but not for placement of the flagellum which depends on the GTPase FlhF. Localization of HubP itself may be dependent on its LysM peptidoglycan-binding domain. Since the swimming speed was decreased when hubP was deleted, a so far unidentified modulator of flagellar motility might require HubP for proper function. In addition, deletion of hubP caused an impairment in twitching motility and affected proper localization of the chromosome partitioning system. Due to its structural similarity to Pseudomonas aeruginosa FimV and partially matching phenotypes upon deletion, the group of HubP/FimV homologs, characterized by a rather conserved N-terminal periplasmic section and a highly variable acidic cytoplasmic part, may serve as polar markers in various bacterial species with respect to different cellular functions. Thus, two separate systems target the flagellum and chemotaxis system to the cell pole

Origin and significance of two pairs of head tentacles in the radiation of euthyneuran sea slugs and land snails

The gastropod infraclass Euthyneura comprises at least 30,000 species of snails and slugs, including nudibranch sea slugs, sea hares and garden snails, that flourish in various environments on earth. A unique morphological feature of Euthyneura is the presence of two pairs of sensory head tentacles with different shapes and functions: the anterior labial tentacles and the posterior rhinophores or eyestalks. Here we combine molecular phylogenetic and microanatomical evidence that suggests the two pairs of head tentacles have originated by splitting of the original single tentacle pair (with two parallel nerve cords in each tentacle) as seen in many other gastropods. Minute deep-sea snails of Tjaernoeia and Parvaplustrum, which in our phylogeny belonged to the euthyneurans' sister group (new infraclass Mesoneura), have tentacles that are split along much of their lengths but associated nerves and epidermal sense organs are not as specialized as in Euthyneura. We suggest that further elaboration of cephalic sense organs in Euthyneura closely coincided with their ecological radiation and drastic modification of body plans. The monotypic family Parvaplustridae nov., superfamily Tjaernoeioidea nov. (Tjaernoeiidae + Parvaplustridae), and new major clade Tetratentaculata nov. (Mesoneura nov. + Euthyneura) are also proposed based on their phylogenetic relationships and shared morphological traits

At the limits of a successful body plan-3D microanatomy, histology and evolution of Helminthope (Mollusca: Heterobranchia: Rhodopemorpha), the most worm-like gastropod

Background: Gastropods are among the most diverse animal clades, and have successfully colonized special habitats such as the marine sand interstitial. Specialized meiofaunal snails and slugs are tiny and worm-shaped. They combine regressive features - argued to be due to progenetic tendencies - with convergent adaptations. Microscopic size and concerted convergences make morphological examination non-trivial and hamper phylogenetic reconstructions. The enigmatic turbellarian-like Rhodopemorpha are a small group that has puzzled systematists for over a century. A preliminary molecular framework places the group far closer to the root of Heterobranchia - one of the major gastropod groups - than previously suggested. The poorly known meiofaunal Helminthope psammobionta Salvini-Plawen, 1991 from Bermuda is the most worm-shaped free-living gastropod and shows apparently aberrant aspects of anatomy. Its study may give important clues to understand the evolution of rhodopemorphs among basal heterobranchs versus their previously thought origin among `higher' euthyneuran taxa. Results: We describe the 3D-microanatomy of H. psammobionta using three-dimensional digital reconstruction based on serial semithin histological sections. The new dataset expands upon the original description and corrects several aspects. Helminthope shows a set of typical adaptations and regressive characters present in other mesopsammic slugs (called `meiofaunal syndrome' herein). The taxonomically important presence of five separate visceral loop ganglia is confirmed, but considerable further detail of the complex nervous system are corrected and revealed. The digestive and reproductive systems are simple and modified to the thread-like morphology of the animal; the anus is far posterior. There is no heart; the kidney resembles a protonephridium. Data on all organ systems are compiled and compared to Rhodope. Conclusions: Helminthope is related to Rhodope sharing unique apomorphies. We argue that the peculiar kidney, configuration of the visceral loop and simplicity or lack of other organs in Rhodopemorpha are results of progenesis. The posterior shift of the anus in Helminthope is interpreted as a peramorphy, i.e. hypertrophy of body length early in ontogeny. Our review of morphological and molecular evidence is consistent with an origin of Rhodopemorpha slugs among shelled `lower Heterobranchia'. Previously thought shared `diagnostic' features such as five visceral ganglia are either plesiomorphic or convergent, while euthyneury and a double-rooted cerebral nerve likely evolved independently in Rhodopemorpha and Euthyneura

The Vanishing of Nonconformist Concepts : Personal Names and Naming of Animals in Khwe

Khwe is a Central Khoisan language spoken by former hunter-gatherers in Southern Africa. While that language is still the everyday medium of communication for most members of the community, genuine concepts underlying the language are fading out. In our investigation of this transformation, we will restrict ourselves to examining two domains, the underlying principles for naming animals and persons. No hierarchical taxonomies of any type exist in Khwe, neither in the naming of the fauna nor the flora. With the exception of a very few collective terms, only individual animal species are named. The practice of naming Khwe individuals with exclusive personal names reflects the same underlying principle, that is, any hierarchical classification is avoided. There exists no pool of Khwe names from which parents and others may choose. Each Khwe lexeme could become the personal name of an individual who would then be the owner of the name. Formal education is among the main forces in transforming traditional views of the world. Despite the omnipresent external influences and subsequent changes, the Khwe language still allows scholars to analyse some of the underlying hunter-gatherer concepts. They reveal a high appreciation of and respect for individuals and items, no matter if these are humans, animals or even inanimate objects. A substantial share of the present variation in language use among the different generations and on the individual level is due to the shift from the former hunter-gatherer concepts to those of the global culture

Eleven Official Languages and More: Legislation and Language Policies in South Africa

The South African Constitution of 1996 recognises eleven official languages on an equal footing without affording English or any of the other ten languages any special status. For half a century, the white ruling class divided people according to their mother tongues in an Apartheid state. The non-white majority was forced to live in separate self-governing administrative units in which their respective home languages became the “official” languages of these so-called “independent states”. The Constitution and language policies of the new South Africa intend to foster the transformation of a previously “bilingual nation” –with Afrikaans and English as the official languages– into a new South African state in which the majority languages of its African citizens are uplifted to the same level. The legal provisions and the language policies introduced over the last twenty years have, however, had little promoting impact on the actual use of languages other than English and Afrikaans in official spheres. This chapter discusses the challenges experienced in the execution of the language provisions made in the Constitution. African languages, which are the key for the improvement of the living conditions of the black majorities, do not receive the attention and support from the government that would be required to make a difference for a better future for their speakers