Four signalling domains in the hybrid histidine protein kinase RodK of Myxococcus xanthus are required for activity

In prokaryotes, the principal signal transduction systems operating at the level of protein phosphorylation are the two-component systems. A number of hybrid histidine protein kinases in these systems contain several receiver domains, however, the function of these receiver domains is unknown. The RodK kinase in Myxococcus xanthus has an unconventional domain composition with a putative N-terminal sensor domain followed by a histidine kinase domain and three receiver domains. RodK is essential for the spatial coupling of the two morphogenetic events underlying fruiting body formation in M. xanthus, aggregation of cells into nascent fruiting bodies and the subsequent sporulation of these cells. RodK kinase activity is indispensable for RodK activity. By systematically substituting the conserved, phosphorylatable aspartate residues in the three receiver domains, genetic evidence is provided that each receiver domain is important for RodK function and that each receiver domain has a distinct function, which depends on phosphorylation. Biochemical analyses provided indirect evidence for phosphotransfer from the RodK kinase domain to the third receiver domain. This is the first example of a hybrid histidine protein kinase in which four signalling domains have been shown to be required for full activity.     

Variable responses within epiphytic and benthic microalgal communities to nutrient enrichment

We evaluated how changes in nutrient supply altered the composition of epiphytic and benthic microalgal communities in a Thalassia testudinum (turtle grass) bed in Florida Bay. We established study plots at four sites in the bay and added nitrogen (N) and phosphorus (P) to the sediments in a factorial design. After 18, 24, and 30 months of fertilization we measured the pigment concentrations in the epiphytic and benthic microalgal assemblages using high performance liquid chromatography. Overall, the epiphytic assemblage was P-limited in the eastern portion of the bay, but each phototrophic group displayed unique spatial and temporal responses to N and P addition. Epiphytic chlorophyll a, an indicator of total microalgal load, and epiphytic fucoxanthin, an indicator of diatoms, increased in response to P addition at one eastern bay site, decreased at another eastern bay site, and were not affected by P or N addition at two western bay sites. Epiphytic zeaxanthin, an indicator of the cyanobacterial/coralline red algae complex, and epiphytic chlorophyll b, an indicator of green algae, generally increased in response to P addition at both eastern bay sites but did not respond to P or N addition in the western bay. Benthic chlorophyll a, chlorophyll b, fucoxanthin, and zeaxanthin showed complex responses to N and P addition in the eastern bay, suggesting that the benthic assemblage is limited by both N and P. Benthic assemblages in the western bay were variable over time and displayed few responses to N or P addition. The contrasting nutrient limitation patterns between the epiphytic and benthic communities in the eastern bay suggest that altering nutrient input to the bay, as might occur during Everglades restoration, can shift microalgal community structure, which may subsequently alter food web support for upper trophic levels.     

Differential localization of Mre proteins with PBP2 in Rhodobacter sphaeroides

In Rhodobacter sphaeroides, MreB, MreC, MreD, PBP2, and RodA are encoded at the same locus. The localizations of PBP2, MreB, and MreC, which have all been implicated in the synthesis of the peptidoglycan layer, were investigated under different growth conditions to gain insight into the relationships between these proteins. Immunofluorescence microscopy showed that PBP2 localized to specific sites at the midcell of elongating cells under both aerobic and photoheterotrophic conditions. Visualizing PBP2 at different stages of the cell cycle showed that in elongating cells, PBP2 was found predominately at the midcell, with asymmetric foci and bands across the cell. PBP2 remained at midcell until the start of septation, after which it moved to midcell of the daughter cells. Deconvolution and three-dimensional reconstructions suggested that PBP2 forms a partial ring at the midcell of newly divided cells and elongated cells, while in septating cells, partial PBP2 rings were present at one-quarter and three-quarter positions. Due to the diffraction limits of light microscopy, these partial rings could represent unresolved helices. Colocalization studies showed that MreC always colocalized with PBP2, while MreB colocalized with PBP2 only during elongation; during septation, MreB remained at the septation site, whereas PBP2 relocalized to the one-quarter and three-quarter positions. These results suggest that PBP2 and MreC are involved in peptidoglycan synthesis during elongation and that this occurs at specific sites close to midcell in R. sphaeroides.     

Dim light melatonin onset in alcohol-dependent men and women compared with healthy controls

Sleep disturbances in alcohol-dependent (AD) individuals may persist despite abstinence from alcohol and can influence the course of the disorder. Although the mechanisms of sleep disturbances of AD are not well understood and some evidence suggests dysregulation of circadian rhythms, dim light melatonin onset (DLMO) has not previously been assessed in AD versus healthy control (HC) individuals in a sample that varied by sex and race. The authors assessed 52 AD participants (mean?±?SD age: 36.0?±?11.0 yrs of age, 10 women) who were 3-12 wks since their last drink (abstinence: 57.9?±?19.3 d) and 19 age- and sex-matched HCs (34.4?±?10.6 yrs, 5 women). Following a 23:00-06:00?h at-home sleep schedule for at least 5 d and screening/baseline nights in the sleep laboratory, participants underwent a 3-h extension of wakefulness (02:00?h bedtime) during which salivary melatonin samples were collected every 30?min beginning at 19:30?h. The time of DLMO was the primary measure of circadian physiology and was assessed with two commonly used methodologies. There was a slower rate of rise and lower maximal amplitude of the melatonin rhythm in the AD group. DLMO varied by the method used to derive it. Using 3 pg/mL as threshold, no significant differences were found between the AD and HC groups. Using 2 standard deviations above the mean of the first three samples, the DLMO in AD occurred significantly later, 21:02?±?00:41?h, than in HC, 20:44?±?00:21?h (t?=?-2.4, p?=?.02). Although melatonin in the AD group appears to have a slower rate of rise, using well-established criteria to assess the salivary DLMO did not reveal differences between AD and HC participants. Only when capturing melatonin when it is already rising was DLMO found to be significantly delayed by a mean 18?min in AD participants. Future circadian analyses on alcoholics should account for these methodological caveats.     

Flagellar hook flexibility is essential for bundle formation in swimming Escherichia coli cells

Swimming Escherichia coli cells are propelled by the rotary motion of their flagellar filaments. In the normal swimming pattern, filaments positioned randomly over the cell form a bundle at the posterior pole. It has long been assumed that the hook functions as a universal joint, transmitting rotation on the motor axis through up to ～90° to the filament in the bundle. Structural models of the hook have revealed how its flexibility is expected to arise from dynamic changes in the distance between monomers in the helical lattice. In particular, each of the 11 protofilaments that comprise the hook is predicted to cycle between short and long forms, corresponding to the inside and outside of the curved hook, once each revolution of the motor when the hook is acting as a universal joint. To test this, we genetically modified the hook so that it could be stiffened by binding streptavidin to biotinylated monomers, impeding their motion relative to each other. We found that impeding the action of the universal joint resulted in atypical swimming behavior as a consequence of disrupted bundle formation, in agreement with the universal joint model.     

Nitrogen deposition enhances moss growth,but leads to an overall decline in habitat condition of mountain moss‐sedge heath

Ecosystems are subject to multiple, natural and anthropogenic environmental influences, including nitrogen (N) deposition, land use and climate. Assessment of the relative importance of these influences on biodiversity and ecosystem functioning is crucial for guiding policy and management decisions to mitigate global change; yet, few studies consider multiple drivers. In the UK, ongoing loss of the internationally important arctic/alpine moss‐sedge community, Racomitrium heath, has been linked to elevated N deposition, high grazing pressures and their combination; however, the relative importance of these drivers remains unclear. We used environmental gradients across the habitat's European distribution (UK, Faroes, Norway and Iceland) to investigate the relative impact of N deposition and grazing pressure, as well as climate, on the condition of the dominant moss species, Racomitrium lanuginosum. Key variables including tissue chemistry, growth and cover were measured at 36 sites, and multiple linear regressions were used to examine the relative importance of the drivers across sites. Our results clearly show that regional variation in the condition of R. lanuginosum across Europe is primarily associated with the impacts of N deposition, with climate (air temperature) and grazing pressure playing secondary roles. In contrast to previous experimental studies, we found moss growth to be stimulated by elevated N deposition; this apparent discrepancy may result from the use of artificially high N concentrations in many experiments. Despite increased growth rates, we found that moss mat depth and cover declined in response to N deposition. Our results suggest that this is due to increased decomposition of material in the moss mat, which ultimately leads to loss of moss cover and habitat degradation. This study clearly demonstrates both the key role of N deposition in degradation of Racomitrium heath and the importance of observational studies along natural gradients for testing predictions from experimental studies in the real world.     

White adipocytes: more than just fat depots

Globally 30% of adults are overweight or obese. The white adipocyte is a major component of adipose tissue, and as the obesity epidemic increases it is critically important to understand the factors determining adipocyte development and function. Adipogenesis has two distinct phases; determination of the adipocyte from a multipotent stem cell, and terminal differentiation of a pre-adipocyte into a mature adipocyte. The environment encountered in early life can alter adipocyte number and size and potentially impact upon adipocyte endocrine function in adulthood. These alterations may contribute to the pathophysiology of chronic diseases and thus targeted therapy of the adipocyte has great potential for treating the current obesity epidemic.     

Evidence of a robust resident bacteriophage population revealed through analysis of the human salivary virome

Viruses are the most abundant known infectious agents on the planet and are significant drivers of diversity in a variety of ecosystems. Although there have been numerous studies of viral communities, few have focused on viruses within the indigenous human microbiota. We analyzed 2 267 695 virome reads from viral particles and compared them with 263 516 bacterial 16S rRNA gene sequences from the saliva of five healthy human subjects over a 2- to 3-month period, in order to improve our understanding of the role viruses have in the complex oral ecosystem. Our data reveal viral communities in human saliva dominated by bacteriophages whose constituents are temporally distinct. The preponderance of shared homologs between the salivary viral communities in two unrelated subjects in the same household suggests that environmental factors are determinants of community membership. When comparing salivary viromes to those from human stool and the respiratory tract, each group was distinct, further indicating that habitat is of substantial importance in shaping human viromes. Compared with coexisting bacteria, there was concordance among certain predicted host–virus pairings such as Veillonella and Streptococcus, whereas there was discordance among others such as Actinomyces. We identified 122 728 virulence factor homologs, suggesting that salivary viruses may serve as reservoirs for pathogenic gene function in the oral environment. That the vast majority of human oral viruses are bacteriophages whose putative gene function signifies some have a prominent role in lysogeny, suggests these viruses may have an important role in helping shape the microbial diversity in the human oral cavity.