Bacteria and archaea exhibit tactical behavior and can move up and down chemical gradients. This tactical behavior relies on a motility structure, which is guided by a chemosensory system. Environmental signals are sensed by membrane-inserted chemosensory receptors that are organized in large ordered arrays. While the cellular positioning of the chemotaxis machinery and that of the flagellum have been studied in detail in bacteria, we have little knowledge about the localization of such macromolecular assemblies in archaea. Although the archaeal motility structure, the archaellum, is fundamentally different from the flagellum, archaea have received the chemosensory machinery from bacteria and have connected this system with the archaellum. Here, we applied a combination of time-lapse imaging and fluorescence and electron microscopy using the model euryarchaeon Haloferax volcanii and found that archaella were specifically present at the cell poles of actively dividing rod-shaped cells. The chemosensory arrays also had a polar preference, but in addition, several smaller arrays moved freely in the lateral membranes. In the stationary phase, rod-shaped cells became round and chemosensory arrays were disassembled. The positioning of archaella and that of chemosensory arrays are not interdependent and likely require an independent form of positioning machinery. This work showed that, in the rod-shaped haloarchaeal cells, the positioning of the archaellum and of the chemosensory arrays is regulated in time and in space. These insights into the cellular organization of H. volcanii suggest the presence of an active mechanism responsible for the positioning of macromolecular protein complexes in archaea. IMPORTANCE Archaea are ubiquitous single cellular microorganisms that play important ecological roles in nature. The intracellular organization of archaeal cells is among the unresolved mysteries of archaeal biology. With this work, we show that cells of haloarchaea are polarized. The cellular positioning of proteins involved in chemotaxis and motility is spatially and temporally organized in these cells. This suggests the presence of a specific mechanism responsible for the positioning of macromolecular protein complexes in archaea.

It is shown from molecular statistical considerations that a demixing instability exists in the moment space of a microbial protein expression profile. Although avoidance of demixing is generally requisite for biological function, a comparison with proteomic and genomic data suggests that many microbes lie close to the onset of this instability. Over evolutionary time scales, straying too close or into the immiscible domain may be associated with intracellular compartmentalization. DOI: 10.1103/PhysRevLett.94.178105 PACS numbers: 87.16.-b Molecular statistical approaches to demixing thermodynamics have long focused on industrially important contexts such as polymer blends, colloids and crude oil [1]. Similar avenues might also present useful insights into the intracellular thermodynamics of microbial organisms. Odijk [2] for example, proposes an equilibrium thermodynamic view of the bacterial nucleoid according to which, under conditions of excess salt, DNA tends to reversibly collapse and demix from the cytosol proteome.The proteome itself features only as a secondary focus in Odijk's particular analysis, but it is also of interest to examine how from a statistical mechanical perspective microbes apparently manage to avoid a similar intraproteomic demixing effect [3]. Expressed proteins of course do not disperse in perfectly miscible souplike fashion, but we can reasonably suppose that they must remain essentially miscible in respect of their macroscopic phase behavior. It is known for molecular mixtures in general that miscibility is sensitive to low moments of the size distribution [4], so we might anticipate that microbial intracellular stability depends analogously on moments of the proteomic expression level profile with respect to sequence length. Our principal objective here is to demonstrate this more explicitly within a model framework.Consider a crude molecular statistical formulation of the Helmholtz free energy F U ÿ TS describing the expressed protein ensemble, where U and S denote, respectively, internal energy and entropy at temperature T. We assume a continuous distribution l over length l in amino acid residues. With the total protein number density, l dl is the concentration in the cytosol having length between l and l dl. Assuming proteins with the same l can be considered indistinguishable with respect to their mutual interactions, we can then write for the entropy density over volume V of the cytosolwhere k B is Boltzmann's constant.Next we assume that the dominant contribution to the internal energy U comes from nonspecific adhesive interaction between proteins. For a system of monodisperse adhesive well particles U=V ' ÿ 2 2 ad 2 , where d is the particle diameter, a is the well width, and is its depth. In this spirit, we writewhere h. . .i denotes the distribution-averaged moment.Here we have identified a with the amino acid length scale, and set d al 1=3 to represent a compact protein comprising l residues. To look for a miscibility gap in the parameter space of this description, we...

The role of cyclic nucleotides as second messengers for intracellular signal transduction has been well described in bacteria. One recently discovered bacterial second messenger is cyclic di‐adenylate monophosphate (c‐di‐AMP), which has been demonstrated to be essential in bacteria. Compared to bacteria, significantly less is known about second messengers in archaea. This study presents the first evidence of in vivo presence of c‐di‐AMP in an archaeon. The model organism Haloferax volcanii was demonstrated to produce c‐di‐AMP. Its genome encodes one diadenylate cyclase (DacZ) which was shown to produce c‐di‐AMP in vitro. Similar to bacteria, the dacZ gene is essential and homologous overexpression of DacZ leads to cell death, suggesting the need for tight regulation of c‐di‐AMP levels. Such tight regulation often indicates the control of important regulatory processes. A central target of c‐di‐AMP signaling in bacteria is cellular osmohomeostasis. The results presented here suggest a comparable function in H. volcanii. A strain with decreased c‐di‐AMP levels exhibited an increased cell area in hypo‐salt medium, implying impaired osmoregulation. In summary, this study expands the field of research on c‐di‐AMP and its physiological function to archaea and indicates that osmoregulation is likely to be a common function of c‐di‐AMP in bacteria and archaea.

Nematic liquid-crystal wetting at a solid interface presents particularly interesting features when the nematic director orientation at the solid interface is antagonistic to that favoured by the emerging nematic - isotropic interface. We have used the Landau - de Gennes theory of an inhomogeneous liquid crystal to make a quantitative study of this phenomenon, for the case when the solid surface favours homeotropic anchoring but the nematic - isotropic surface favours planar anchoring. By generalizing the theory of Sheng to allow spatial variation of the director, we find a richer surface phase diagram exhibiting a prewetting line or boundary transition shifted from that discussed by Sheng, as well as a transition between two nematic wetting phases, at which the wetting layer director profile changes from a homeotropic to a distorted texture.

Research on nucleotide-based second messengers began in 1956 with the discovery of cyclic adenosine monophosphate (3′,5′-cAMP) by Earl Wilbur Sutherland and his co-workers. Since then, a broad variety of different signaling molecules composed of nucleotides has been discovered. These molecules fulfill crucial tasks in the context of intracellular signal transduction. The vast majority of the currently available knowledge about nucleotide-based second messengers originates from model organisms belonging either to the domain of eukaryotes or to the domain of bacteria, while the archaeal domain is significantly underrepresented in the field of nucleotide-based second messenger research. For several well-stablished eukaryotic and/or bacterial nucleotide-based second messengers, it is currently not clear whether these signaling molecules are present in archaea. In order to shed some light on this issue, this study analyzed cell extracts of two major archaeal model organisms, the euryarchaeon Haloferax volcanii and the crenarchaeon Sulfolobus acidocaldarius, using a modern mass spectrometry method to detect a broad variety of currently known nucleotide-based second messengers. The nucleotides 3′,5′-cAMP, cyclic guanosine monophosphate (3′,5′-cGMP), 5′-phosphoadenylyl-3′,5′-adenosine (5′-pApA), diadenosine tetraphosphate (Ap4A) as well as the 2′,3′-cyclic isomers of all four RNA building blocks (2′,3′-cNMPs) were present in both species. In addition, H. volcanii cell extracts also contain cyclic cytosine monophosphate (3′,5′-cCMP), cyclic uridine monophosphate (3′,5′-cUMP) and cyclic diadenosine monophosphate (3′,5′-c-di-AMP). The widely distributed bacterial second messengers cyclic diguanosine monophosphate (3′,5′-c-di-GMP) and guanosine (penta-)/tetraphosphate [(p)ppGpp] could not be detected. In summary, this study gives a comprehensive overview on the presence of a large set of currently established or putative nucleotide-based second messengers in an eury- and a crenarchaeal model organism.

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This paper describes the identification of compounds, which stimulate the activity of the protein phosphatase PPH-5 and addresses the influence of the identified compounds on the enzymatic properties and the potential mechanism of their action.

We discuss spinodal dewetting of a nematic film destabilized by Van der Waals forces, focusing on the case of non-antagonistic anchoring conditions. Using physical parameters pertinent to low-molecular-weight thermotropic liquid crystals, we predict a small damping effect. In the presence of an antagonistic applied magnetic field, the anchoring conditions become more significant, and can influence the shape and dynamics of the unstable modes.