Altering the Sex Pheromone Cyclo(l-Pro-l-Pro) of the Diatom Seminavis robusta towards a Chemical Probe

As a major group of algae, diatoms are responsible for a substantial part of the primary production on the planet. Pennate diatoms have a predominantly benthic lifestyle and are the most species-rich diatom group, with members of the raphid clades being motile and generally having heterothallic sexual reproduction. It was recently shown that the model species Seminavis robusta uses multiple sexual cues during mating, including cyclo(l-Pro-l-Pro) as an attraction pheromone. Elaboration of the pheromone-detection system is a key aspect in elucidating pennate diatom life-cycle regulation that could yield novel fundamental insights into diatom speciation. This study reports the synthesis and bio-evaluation of seven novel pheromone analogs containing small structural alterations to the cyclo(l-Pro-l-Pro) pheromone. Toxicity, attraction, and interference assays were applied to assess their potential activity as a pheromone. Most of our analogs show a moderate-to-good bioactivity and low-to-no phytotoxicity. The pheromone activity of azide- and diazirine-containing analogs was unaffected and induced a similar mating behavior as the natural pheromone. These results demonstrate that the introduction of confined structural modifications can be used to develop a chemical probe based on the diazirine- and/or azide-containing analogs to study the pheromone-detection system of S. robusta.

News from the Western Front: Guidelines for the excavation of casualties of the First and Second World War (Flanders, Belgium)

In cooperation with many other actors, the Flanders Heritage Agency (Flemish Government) set up a guideline with procedures how to act when human remains are found in the soil of Flanders (the northern part of Belgium). The basic principle is that human remains with an archaeological value always must be excavated by archaeologists and physical anthropologists, according to the Flemish legislation on archaeology. This also applies for casualties of the First and Second World War: excavating using archaeological techniques does not conflict at all with the principles of the Geneva Convention, on the contrary: this way of working guarantees a qualitative research that increases the chance of identification and delivers more details about the battle and war: a win-win.

The Seminavis robusta genome provides insights into the evolutionary adaptations of benthic diatoms

Benthic diatoms are the main primary producers in shallow freshwater and coastal environments, fulfilling important ecological functions such as nutrient cycling and sediment stabilization. However, little is known about their evolutionary adaptations to these highly structured but heterogeneous environments. Here, we report a reference genome for the marine biofilm-forming diatom Seminavis robusta, showing that gene family expansions are responsible for a quarter of all 36,254 protein-coding genes. Tandem duplications play a key role in extending the repertoire of specific gene functions, including light and oxygen sensing, which are probably central for its adaptation to benthic habitats. Genes differentially expressed during interactions with bacteria are strongly conserved in other benthic diatoms while many species-specific genes are strongly upregulated during sexual reproduction. Combined with re-sequencing data from 48 strains, our results offer insights into the genetic diversity and gene functions in benthic diatoms.

Distinctive Growth and Transcriptional Changes of the Diatom Seminavis robusta in Response to Quorum Sensing Related Compounds

In aquatic habitats, diatoms are frequently found in association with Proteobacteria, many members of which employ cell-to-cell communication via N-acyl homoserine lactones (AHLs). It has been suggested that diatoms could distinguish between beneficial and algicidal bacteria in their surroundings by sensing AHLs. Although some microalgae can interfere with AHL signaling, e.g., by releasing AHL mimics or degrading them, molecular responses to AHLs in microalgae are still unclear. Therefore, we tested the effects of short-chained AHLs, i.e., N-hexanoyl homoserine lactone (C6-HSL), N-3-hydroxyhexanoyl homoserine lactone (OH-C6-HSL), and N-3-oxohexanoyl homoserine lactone (oxo-C6-HSL) and long-chained AHLs, i.e., N-tetradecanoyl homoserine lactone (C14-HSL), N-3-hydroxytetradecanoyl homoserine lactone (OH-C14-HSL), and N-3-oxotetradecanoyl homoserine lactone (oxo-C14-HSL), on growth of the benthic diatom Seminavis robusta. All tested short-chained AHLs did not affect diatom growth, while long-chained AHLs promoted (C14-HSL) or inhibited (OH-C14-HSL and oxo-C14-HSL) growth. To investigate the physiological effects of these long-chained AHLs in more detail, an RNA-seq experiment was performed during which S. robusta was treated with the growth-promoting C14-HSL and the growth-inhibiting oxo-C14-HSL. One tetramic acid was also tested (TA14), a structural rearrangement product of oxo-C14-HSL, which also induced growth inhibition in S. robusta. After 3 days of treatment, analysis revealed that 3,410 genes were differentially expressed in response to at least one of the compounds. In the treatment with the growth-promoting C14-HSL many genes involved in intracellular signaling were upregulated. On the other hand, exposure to growth-inhibiting oxo-C14-HSL and TA14 triggered a switch in lipid metabolism towards increased fatty acid degradation. In addition, oxo-C14-HSL led to downregulation of cell cycle genes, which is in agreement with the stagnation of cell growth in this treatment. Combined, our results indicate that bacterial signaling molecules with high structural similarity induce contrasting physiological responses in S. robusta.

Associated Bacteria Affect Sexual Reproduction by Altering Gene Expression and Metabolic Processes in a Biofilm Inhabiting Diatom

Diatoms are unicellular algae with a fundamental role in global biogeochemical cycles as major primary producers at the base of aquatic food webs. In recent years, chemical communication between diatoms and associated bacteria has emerged as a key factor in diatom ecology, spurred by conceptual and technological advancements to study the mechanisms underlying these interactions. Here, we use a combination of physiological, transcriptomic, and metabolomic approaches to study the influence of naturally co-existing bacteria, Maribacter sp. and Roseovarius sp., on the sexual reproduction of the biofilm inhabiting marine pennate diatom Seminavis robusta. While Maribacter sp. severely reduces the reproductive success of S. robusta cultures, Roseovarius sp. slightly enhances it. Contrary to our expectation, we demonstrate that the effect of the bacterial exudates is not caused by altered cell-cycle regulation prior to the switch to meiosis. Instead, Maribacter sp. exudates cause a reduced production of diproline, the sexual attraction pheromone of S. robusta. Transcriptomic analyses show that this is likely an indirect consequence of altered intracellular metabolic fluxes in the diatom, especially those related to amino acid biosynthesis, oxidative stress response, and biosynthesis of defense molecules. This study provides the first insights into the influence of bacteria on diatom sexual reproduction and adds a new dimension to the complexity of a still understudied phenomenon in natural diatom populations.

Attraction Pheromone of The Benthic Diatom Seminavis robusta: Studies on Structure-Activity Relationships

Recently the first pheromone of a marine diatom was identified to be the diketopiperazine (S,S)-diproline. This compound facilitates attraction between mating partners in the benthic diatom Seminavis robusta. Interestingly, sexualized S. robusta cells are attracted to both the natural pheromone (S,S)-diproline as well as to its enantiomer (R,R)-diproline. Usually stereospecificity is a prerequisite for successful substrate-receptor interactions, and especially pheromone perception is often highly enantioselective. Here we introduce a structure-activity relationship study, to learn more about the principles of pheromone reception in diatoms. We analyzed the activity of nine different diketopiperazines in attraction and interference assays. The pheromone diproline itself, as well as a pipecolic acid derived diketopiperazine with two expanded aliphatic ring systems, showed the highest attractivity. Hydroxylatoin of the aliphatic rings abolished any bioactivity. Diketopiperazines derived from acyclic amino acids were not attrative as well. All stereoisomers of both the diproline and the pipecolic acid derived diketopiperazine were purified by enantioselective high-performance liquid chromatography, and application in bioactivity tests confirmed that attraction pheromone perception in this diatom is indeed not stereospecific. However, the lack of activity of diketopiperazines derived from acyclic amino acids suggests a specificity that prevents misguidance to sources of other naturally occurring diketopiperazines.

Expanding the toolbox for cryopreservation of marine and freshwater diatoms

Diatoms constitute the most diverse group of microalgae and have long been recognised for their large biotechnological potential. In the wake of growing research interest in new model species and development of commercial applications, there is a pressing need for long-term preservation of diatom strains. While cryopreservation using dimethylsulfoxide (DMSO) as a cryoprotective agent is the preferred method for long-term strain preservation, many diatom species cannot be successfully cryopreserved using DMSO. Therefore, in this study, we studied cryopreservation success in six different diatom species, representing the major morphological and ecological diatom groups, using a range of DMSO concentrations and Plant Vitrification Solution 2 (PVS2) as an alternative cryoprotectant to DMSO. In addition, we tested whether suppressing bacterial growth by antibiotics accelerates the post-thaw recovery process. Our results show that the effects of cryoprotectant choice, its concentration and the addition of antibiotics are highly species specific. In addition, we showed that PVS2 and antibiotics are useful agents to optimize cryopreservation of algae that cannot survive the traditional cryopreservation protocol using DMSO. We conclude that a species-specific approach will remain necessary to develop protocols for diatom cryopreservation and to increase their representation in public culture collections.

Self-perceived needs of primary caregivers of home-hospice clients

The purpose of this study was to assess the self-perceived needs of primary caregivers of terminally ill home-hospice clients. A home interview was conducted using an instrument based on the Neuman Systems Model. Data were analyzed in relation to intrapersonal stressors (within the individual), interpersonal stressors (between the individual and others), and extrapersonal stressors (between the individual and the environment). Five community nursing diagnoses (Porter, 1987) were identified: (a) Population at risk for health problems, (b) population at risk for role constriction/role fatigue, (c) population at risk for insufficient support, (d) population at potential risk for lack of information, and (e) population at potential risk for lack of service coordination. Early attention to limiting the impact of stressors on the caregiver can improve the caregiver's ability to care for the hospice client.

Functional health pattern assessment: a seasonal migrant farmworker community

A broad-based needs assessment of a migrant farmworker community was conducted using the community functional health pattern tool (Gikow & Kucharski, 1987) and Porter's (1987) factor-isolating theory of population group diagnosis. Data analysis revealed numerous health needs in all 10 functional health patterns and an urgent need for accessible primary prevention programs. A mobile outreach program to the migrant camps was seen as the most effective way to provide education, screening, and health care.

Community as client: appropriate baccalaureate- and graduate-level preparation

This article focuses on the theoretical concept of community as client and its application in community health nursing education and practice. Although the concept of community as client has been widely accepted, it was observed that care to individuals and families within community settings constitutes the bulk of current community health nursing practice. The argument is made that undergraduate nursing students should be prepared as generalists to provide care within community settings. Undergraduate nursing students should be introduced to the concept of community as client, with an emphasis on understanding the relationship between individual or family needs and community needs. It is also argued that graduate nursing students should be prepared at the specialist level, focusing primarily on providing care to the community as client. An example of undergraduate and graduate levels of preparation in one university nursing program is described.

Determinants of well-being in primary caregivers of spinal cord injured persons

A study of well-being in middle-aged and elderly spinal cord injured persons (Decker & Schulz, 1985) found that long-term coping was facilitated by the presence of a primary support person or caregiver. The purpose of this study was to identify the determinants of life satisfaction and depression in 67 primary caregivers of middle-aged and elderly spinal cord injured persons. The study revealed that the availability of social support and feelings of control over one's life were important determinants of caregivers' well-being. In addition, those caregivers spending more time each day assisting the disabled person and feeling burdened by these responsibilities experienced more depression and less life satisfaction. In working with spinal cord injured persons, rehabilitation nurses must consider the well-being of the spinal cord injured person/primary caregiver dyad as an important focus of nursing assessment and intervention.

Correlates of life satisfaction and depression in middle-aged and elderly spinal cord-injured persons

Advances in health care science allow more people with spinal cord injuries to live to old age. The purpose of this study was to determine those factors that contribute to the well-being of middle-aged and elderly spinal cord-injured people. One hundred spinal cord-injured people, ranging in age from 40 to 73 years, completed an extensive structured interview. In general, respondents reported a degree of well-being on the same measures of satisfaction and depression that was slightly lower than that of similarly aged nondisabled people. Pearson correlations indicated that people experiencing high levels of well-being reported high levels of perceived control, had higher levels of social support, and judged their health status to be good. These people also viewed their disability more favorably, tended to have higher incomes and more education, were employed, and were more religious than those indicating lower levels of well-being. The severity of the spinal cord injury was not correlated highly with subjective well-being, although there was a tendency for those with greater disability to report lower levels of well-being. People who were younger, who incurred their disability at a younger age, and who blamed themselves and felt they could have avoided the injury also tended to report higher levels of well-being.

Baccalaureate nursing students' identification with the women's movement

To determine if nursing and nonnursing students changed their attitudes about themselves and the "typical nurse" in relation to feminist movement goals, results of 291 questionnaires were studied. A significant difference was found in the view of self and typical nurse for female nursing students, the nurses showing more feminist leanings as they progressed in school. Male nurses, nonnurses, and females in typical and atypical female majors rated themselves lower than female nurses on the feminist scale.