Initiation of Swarming Motility by Proteus mirabilis Occurs in Response to Specific Cues Present in Urine and Requires Excess l-Glutamine

Proteus mirabilis, a leading cause of catheter-associated urinary tract infection (CaUTI), differentiates into swarm cells that migrate across catheter surfaces and medium solidified with 1.5% agar. While many genes and nutrient requirements involved in the swarming process have been identified, few studies have addressed the signals that promote initiation of swarming following initial contact with a surface. In this study, we show that P. mirabilis CaUTI isolates initiate swarming in response to specific nutrients and environmental cues. Thirty-three compounds, including amino acids, polyamines, fatty acids, and tricarboxylic acid (TCA) cycle intermediates, were tested for the ability to promote swarming when added to normally nonpermissive media. l-Arginine, l-glutamine, dl-histidine, malate, and dl-ornithine promoted swarming on several types of media without enhancing swimming motility or growth rate. Testing of isogenic mutants revealed that swarming in response to the cues required putrescine biosynthesis and pathways involved in amino acid metabolism. Furthermore, excess glutamine was found to be a strict requirement for swarming on normal swarm agar in addition to being a swarming cue under normally nonpermissive conditions. We thus conclude that initiation of swarming occurs in response to specific cues and that manipulating concentrations of key nutrient cues can signal whether or not a particular environment is permissive for swarming.     

Motor Adaptations to Pain during a Bilateral Plantarflexion Task: Does the Cost of Using the Non-Painful Limb Matter?

During a force-matched bilateral task, when pain is induced in one limb, a shift of load to the non-painful leg is classically observed. This study aimed to test the hypothesis that this adaptation to pain depends on the mechanical efficiency of the non-painful leg. We studied a bilateral plantarflexion task that allowed flexibility in the relative force produced with each leg, but constrained the sum of forces from both legs to match a target. We manipulated the mechanical efficiency of the non-painful leg by imposing scaling factors: 1, 0.75, or 0.25 to decrease mechanical efficiency (Decreased efficiency experiment: 18 participants); and 1, 1.33 or 4 to increase mechanical efficiency (Increased efficiency experiment: 17 participants). Participants performed multiple sets of three submaximal bilateral isometric plantarflexions with each scaling factor during two conditions (Baseline and Pain). Pain was induced by injection of hypertonic saline into the soleus. Force was equally distributed between legs during the Baseline contractions (laterality index was close to 1; Decreased efficiency experiment: 1.16±0.33; Increased efficiency experiment: 1.11±0.32), with no significant effect of Scaling factor. The laterality index was affected by Pain such that the painful leg contributed less than the non-painful leg to the total force (Decreased efficiency experiment: 0.90±0.41, P<0.001; Increased efficiency experiment: 0.75±0.32, P<0.001), regardless of the efficiency (scaling factor) of the non-painful leg. When compared to the force produced during Baseline of the corresponding scaling condition, a decrease in force produced by the painful leg was observed for all conditions, except for scaling 0.25. This decrease in force was correlated with a decrease in drive to the soleus muscle. These data highlight that regardless of the overall mechanical cost, the nervous system appears to prefer to alter force sharing between limbs such that force produced by the painful leg is reduced relative to the non-painful leg.     

Conservation of regional gene expression in mouse and human brain

Many neurodegenerative diseases have a hallmark regional and cellular pathology. Gene expression analysis of healthy tissues may provide clues to the differences that distinguish resistant and sensitive tissues and cell types. Comparative analysis of gene expression in healthy mouse and human brain provides a framework to explore the ability of mice to model diseases of the human brain. It may also aid in understanding brain evolution and the basis for higher order cognitive abilities. Here we compare gene expression profiles of human motor cortex, caudate nucleus, and cerebellum to one another and identify genes that are more highly expressed in one region relative to another. We separately perform identical analysis on corresponding brain regions from mice. Within each species, we find that the different brain regions have distinctly different expression profiles. Contrasting between the two species shows that regionally enriched genes in one species are generally regionally enriched genes in the other species. Thus, even when considering thousands of genes, the expression ratios in two regions from one species are significantly correlated with expression ratios in the other species. Finally, genes whose expression is higher in one area of the brain relative to the other areas, in other words genes with patterned expression, tend to have greater conservation of nucleotide sequence than more widely expressed genes. Together these observations suggest that region-specific genes have been conserved in the mammalian brain at both the sequence and gene expression levels. Given the general similarity between patterns of gene expression in healthy human and mouse brains, we believe it is reasonable to expect a high degree of concordance between microarray phenotypes of human neurodegenerative diseases and their mouse models. Finally, these data on very divergent species provide context for studies in more closely related species that address questions such as the origins of cognitive differences.     

Bucking the trend: the African Black Oystercatcher as a recent conservation success story

The African Black Oystercatcher Haematopus moquini is a charismatic, southern African near-endemic, wader species, that is often seen as a flagship species for coastal bird conservation, as it was recently down-listed regionally to Least Concern on the IUCN Red List of Threatened Species. To celebrate this rare conservation success story, BirdLife South Africa named it the 2018 Bird of the Year and ran a year-long programme in collaboration with the Nature’s Valley Trust highlighting aspects of the species’ biology, current threats, and conservation success. We used data collected by the Southern African Bird Atlas Project (SABAP1 and SABAP2) to examine changes in the species’ range and relative abundance, both in the records between the two projects, as well as trends within the SABAP2 sampling period (2008–2017). This case study enabled us to assess whether such metrics can accurately reflect abundance and distributional changes in a species. We found increases in the reported range and the reporting rates between the two Atlas projects, and that the SABAP2 reporting rate was stable. Regionally, across four coastal categories, the reporting rate was lowest in KwaZulu-Natal, though this region also showed an increase in the probability of reporting during the SABAP2 period. While corroborating the recent change in the species’ conservation status, we also provide good evidence that the long-term SABAP data can be used successfully to assess population trends and range changes over time.     

Solution structure of the C-terminal antiparallel coiled-coil domain from Escherichia coli osmosensor ProP

Bacteria respond to increasing medium osmolality by accumulating organic solutes that are compatible with cellular functions. Transporter ProP of Escherichia coli, a proton symporter and a member of the major facilitator superfamily, senses osmotic shifts and responds by importing osmolytes such as glycine betaine. ProP contains a cytoplasmic, C-terminal extension that is essential for its activity. A peptide corresponding to the C-terminal extension of ProP forms a homodimeric alpha-helical coiled-coil even though some of its heptad a positions are not occupied by hydrophobic amino acid residues. Unexpectedly, amino acid replacement R488I, occurring at a heptad a position, destabilized the coiled-coil formed by the ProP peptide and attenuated the response of the intact transporter to osmotic upshifts in vivo. Thus, ProP was proposed to dimerize via an antiparallel coiled-coil. We used nuclear magnetic resonance (NMR) spectroscopy to determine the structure of the synthetic peptide corresponding to residues 468-497 of ProP. This region did form an antiparallel coil-coil in which critical residue R488 specifies the antiparallel coiled-coil orientation by forming stabilizing salt-bridges. Charged residues (both acidic and basic) are clustered on the c/g surface of the coiled-coil whereas polar residues are distributed on the b/e surface. This causes the structure to be bent, in contrast to other known antiparallel coiled-coils (those from the hepatitis delta antigen (PDB ID code 1A92) and the bovine F(1) ATPase inhibitor protein (PDB ID code 1HF9)). The coiled-coil and its possible importance for osmosensing are discussed.     

Identification of a novel transporter for dicarboxylates and tricarboxylates in plant mitochondria. Bacterial expression, reconstitution, functional characterization, and tissue distribution

A cDNA from Arabidopsis thaliana and four related cDNAs from Nicotiana tabacum that we have isolated encode hitherto unidentified members of the mitochondrial carrier family. These proteins have been overexpressed in bacteria and reconstituted into phospholipid vesicles. Their transport properties demonstrate that they are orthologs/isoforms of a novel mitochondrial carrier capable of transporting both dicarboxylates (such as malate, oxaloacetate, oxoglutarate, and maleate) and tricarboxylates (such as citrate, isocitrate, cis-aconitate, and trans-aconitate). The newly identified dicarboxylate-tricarboxylate carrier accepts only the single protonated form of citrate (H-citrate2-) and the unprotonated form of malate (malate2-) and catalyzes obligatory, electroneutral exchanges. Oxoglutarate, citrate, and malate are mutually competitive inhibitors, showing K(i) close to the respective K(m). The carrier is expressed in all plant tissues examined and is largely spread in the plant kingdom. Furthermore, nitrate supply to nitrogen-starved tobacco plants leads to an increase in its mRNA in roots and leaves. The dicarboxylate-tricarboxylate carrier may play a role in important plant metabolic functions requiring organic acid flux to or from the mitochondria, such as nitrogen assimilation, export of reducing equivalents from the mitochondria, and fatty acid elongation.     

A differential scanning calorimetric and 31P NMR spectroscopic study of the effect of transmembrane alpha-helical peptides on the lamellar-reversed hexagonal phase transition of phosphatidylethanolamine model membranes

We have investigated the effects of the model alpha-helical transmembrane peptide Ac-K(2)L(24)K(2)-amide (L(24)) on the thermotropic phase behavior of aqueous dispersions of 1,2-dielaidoylphosphatidylethanolamine (DEPE) to understand better the interactions between lipid bilayers and the membrane-spanning segments of integral membrane proteins. We studied in particular the effect of L(24) and three derivatives thereof on the liquid-crystalline lamellar (L(alpha))-reversed hexagonal (H(II)) phase transition of DEPE model membranes by differential scanning calorimetry and (31)P nuclear magnetic resonance spectroscopy. We found that the incorporation of L(24) progressively decreases the temperature, enthalpy, and cooperativity of the L(alpha)-H(II) phase transition, as well as induces the formation of an inverted cubic phase, indicating that this transmembrane peptide promotes the formation of inverted nonlamellar phases, despite the fact that the hydrophobic length of this peptide exceeds the hydrophobic thickness of the host lipid bilayer. These characteristic effects are not altered by truncation of the side chains of the terminal lysine residues or by replacing each of the leucine residues at the end of the polyleucine core of L(24) with a tryptophan residue. Thus, the characteristic effects of these transmembrane peptides on DEPE thermotropic phase behavior are independent of their detailed chemical structure. Importantly, significantly shortening the polyleucine core of L(24) results in a smaller decrease in the L(alpha)-H(II) phase transition temperature of the DEPE matrix into which it is incorporated, and reducing the thickness of the host phosphatidylethanolamine bilayer results in a larger reduction in the L(alpha)-H(II) phase transition temperature. These results are not those predicted by hydrophobic mismatch considerations or reported in previous studies of other transmembrane alpha-helical peptides containing a core of an alternating sequence of leucine and alanine residues. We thus conclude that the hydrophobicity and conformational flexibility of transmembrane peptides can affect their propensity to induce the formation of inverted nonlamellar phases by mechanisms not primarily dependent on lipid-peptide hydrophobic mismatch.     

A procedure for regenerating Japonica and Indica varieties of rice from protoplasts

Fertile rice plants have been regenerated from protoplasts of two japonica rice varieties (Radon and Baldo) using a protocol initially developed for plant regeneration from protoplasts of an indica rice. Embryogenic calli were developed from immature embryos of Radon and Baldo rice on a callus induction medium, and then used to establish cell suspensions. Protoplasts were isolated from the cell suspensions, and cultured on a Millipore filter placed on a Kao/agarose medium that contained cell clusters from suspensions of IR52 or IR45. The protoplasts grew vigorously on Kao medium and developed into embryogenic calli within two to three weeks. Somatic embryo development occurred during a subsequent transfer of the calli to an LS medium for two to three weeks. The calli were then transferred to MS or N6 plant regeneration medium, and within one to three weeks, plants regenerated from 21 to 32% of the Radon calli, and 33 to 35% of the Baldo calli. Based upon these results and the previous success in regenerating an indica variety from protoplasts, this procedure has great promise for regenerating a range of rice varieties, and probably for regeneration of other monocotyledonous plants from protoplasts     

Mepiquat chloride (PIX)-induced changes in photosynthesis and growth of cotton

Mepiquat chloride (N, N-dimethylpiperidinium chloride), well known as PIX, is a potential systemic plant growth regulator. The effects of PIX on plant height, stem elongation, leaf area, net photosynthetic rates, chlorophyll content, sucrose and starch levels, and RuBP carboxylase activity in cotton (Gossypium hirsutum L. cv. DES 119) plants were measured. PIX was sprayed (0, 7.65, 15.3, 30.6 or 61.2 g active ingredient ha^–1) on the plants at first square (25 days after emergence) and measurements were made at frequent intervals. Plant height was clearly reduced by PIX. The total length of vegetative branches and fruiting branches was 40% and 50% less than the control. Total leaf area in PIX treated plants was 16% less than the control. Net photosynthetic rates were 25% less in PIX-treated leaves. PIX treated leaves had more chlorophyll content. The activity of RuBP carboxylase was decreased in PIX treated plants. Starch accumulation was noticed in PIX treated leaves while sucrose content was not changed. The data reported here suggest that reduced growth responses induced by PIX results in partial loss of photosynthetic capacity in cotton at least up to 20 days after application of the growth regulator.