Sibling Rivalry in Myxococcus xanthus Is Mediated by Kin Recognition and a Polyploid Prophage.

UNLABELLED: Myxobacteria form complex social communities that elicit multicellular behaviors. One such behavior is kin recognition, in which cells identify siblings via their polymorphic TraA cell surface receptor, to transiently fuse outer membranes and exchange their contents. In addition, outer membrane exchange (OME) regulates behaviors, such as inhibition of wild-type Myxococcus xanthus (DK1622) from swarming. Here we monitored the fate of motile cells and surprisingly found they were killed by nonmotile siblings. The kill phenotype required OME (i.e., was TraA dependent). The genetic basis of killing was traced to ancestral strains used to construct DK1622. Specifically, the kill phenotype mapped to a large "polyploid prophage," Mx alpha. Sensitive strains contained a 200-kb deletion that removed two of three Mx alpha units. To explain these results, we suggest that Mx alpha expresses a toxin-antitoxin cassette that uses the OME machinery of M. xanthus to transfer a toxin that makes the population "addicted" to Mx alpha. Thus, siblings that lost Mx alpha units (no immunity) are killed by cells that harbor the element. To test this, an Mx alpha-harboring laboratory strain was engineered (by traA allele swap) to recognize a closely related species, Myxococcus fulvus. As a result, M. fulvus, which lacks Mx alpha, was killed. These TraA-mediated antagonisms provide an explanation for how kin recognition specificity might have evolved in myxobacteria. That is, recognition specificity is determined by polymorphisms in traA, which we hypothesize were selected for because OME with non-kin leads to lethal outcomes. IMPORTANCE: The transition from single cell to multicellular life is considered a major evolutionary event. Myxobacteria have successfully made this transition. For example, in response to starvation, individual cells aggregate into multicellular fruiting bodies wherein cells differentiate into spores. To build fruits, cells need to recognize their siblings, and in part, this is mediated by the TraA cell surface receptor. Surprisingly, we report that TraA recognition can also involve sibling killing. We show that killing originates from a prophage-like element that has apparently hijacked the TraA system to deliver a toxin to kin. We hypothesize that this killing system has imposed selective pressures on kin recognition, which in turn has resulted in TraA polymorphisms and hence many different recognition groups.

Molecular recognition by a polymorphic cell surface receptor governs cooperative behaviors in bacteria.

Cell-cell recognition is a fundamental process that allows cells to coordinate multicellular behaviors. Some microbes, such as myxobacteria, build multicellular fruiting bodies from free-living cells. However, how bacterial cells recognize each other by contact is poorly understood. Here we show that myxobacteria engage in recognition through interactions between TraA cell surface receptors, which leads to the fusion and exchange of outer membrane (OM) components. OM exchange is shown to be selective among 17 environmental isolates, as exchange partners parsed into five major recognition groups. TraA is the determinant of molecular specificity because: (i) exchange partners correlated with sequence conservation within its polymorphic PA14-like domain and (ii) traA allele replacements predictably changed partner specificity. Swapping traA alleles also reprogrammed social interactions among strains, including the regulation of motility and conferred immunity from inter-strain killing. We suggest that TraA helps guide the transition of single cells into a coherent bacterial community, by a proposed mechanism that is analogous to mitochondrial fusion and fission cycling that mixes contents to establish a homogenous population. In evolutionary terms, traA functions as a rare greenbeard gene that recognizes others that bear the same allele to confer beneficial treatment.

A genetic screen in Myxococcus xanthus identifies mutants that uncouple outer membrane exchange from a downstream cellular response.

Upon physical contact with sibling cells, myxobacteria transiently fuse their outer membranes (OMs) and exchange OM proteins and lipids. From previous work, TraA and TraB were identified to be essential factors for OM exchange (OME) in donor and recipient cells. To define the genetic complexity of OME, we carried out a comprehensive forward genetic screen. The screen was based on the observation that Myxococcus xanthus nonmotile cells, by a Tra-dependent mechanism, block swarm expansion of motile cells when mixed. Thus, mutants defective in OME or a downstream responsive pathway were readily identified as escape flares from mixed inocula seeded on agar. This screen was surprisingly powerful, as we found >50 mutants defective in OME. Importantly, all of the mutations mapped to the traAB operon, suggesting that there may be few, if any, proteins besides TraA and TraB directly required for OME. We also found a second and phenotypically different class of mutants that exhibited wild-type OME but were defective in a responsive pathway. This pathway is postulated to control inner membrane homeostasis by covalently attaching amino acids to phospholipids. The identified proteins are homologous to the Staphylococcus aureus MprF protein, which is involved in membrane adaptation and antibiotic resistance. Interestingly, we also found that a small number of nonmotile cells were sufficient to block the swarming behavior of a large gliding-proficient population. This result suggests that an OME-derived signal could be amplified from a few nonmotile producers to act on many responder cells.

A Mobile Health Behavior Change Intervention for Women With Coronary Heart Disease: A RANDOMIZED CONTROLLED PILOT STUDY.

PURPOSE: The aim of this study was to evaluate the effects of a mobile health (mHealth) intervention, HerBeat, compared with educational usual care (E-UC) for improving exercise capacity (EC) and other patient-reported outcomes at 3 mo among women with coronary heart disease. METHODS: Women were randomized to the HerBeat group (n = 23), a behavior change mHealth intervention with a smartphone, smartwatch, and health coach or to the E-UC group (n = 24) who received a standardized cardiac rehabilitation workbook. The primary endpoint was EC measured with the 6-min walk test (6MWT). Secondary outcomes included cardiovascular disease risk factors and psychosocial well-being. RESULTS: A total of 47 women (age 61.2 ± 9.1 yr) underwent randomization. The HerBeat group significantly improved on the 6MWT from baseline to 3 mo ( P = .016, d = .558) while the E-UC group did not ( P = .894, d =-0.030). The between-group difference of 38 m at 3 mo was not statistically significant. From baseline to 3 mo, the HerBeat group improved in anxiety ( P = .021), eating habits confidence ( P = .028), self-efficacy for managing chronic disease ( P = .001), diastolic blood pressure ( P = .03), general health perceptions ( P = .047), perceived bodily pain ( P = .02), and waist circumference ( P = .008) while the E-UC group showed no improvement on any outcomes. CONCLUSIONS: The mHealth intervention led to improvements in EC and several secondary outcomes from baseline to 3 mo while the E-UC intervention did not. A larger study is required to detect small differences between groups. The implementation and outcomes evaluation of the HerBeat intervention was feasible and acceptable with minimal attrition.

A Mobile Health Intervention System for Women With Coronary Heart Disease: Usability Study.

BACKGROUND: Coronary heart disease (CHD) is the leading cause of death and disability among American women. The prevalence of CHD is expected to increase by more than 40% by 2035. In 2015, the estimated cost of caring for patients with CHD was US $182 billion in the United States; hospitalizations accounted for more than half of the costs. Compared with men, women with CHD or those who have undergone coronary revascularization have up to 30% more rehospitalizations within 30 days and up to 1 year. Center-based cardiac rehabilitation is the gold standard of care after an acute coronary event, but few women attend these valuable programs. Effective home-based interventions for improving cardiovascular health among women with CHD are vital for addressing this gap in care. OBJECTIVE: The ubiquity of mobile phones has made mobile health (mHealth) behavioral interventions a viable option to improve healthy behaviors of both women and men with CHD. First, this study aimed to examine the usability of a prototypic mHealth intervention designed specifically for women with CHD (herein referred to as HerBeat). Second, we examined the influence of HerBeat on selected health behaviors (self-efficacy for diet, exercise, and managing chronic illness) and psychological (perceived stress and depressive symptoms) characteristics of the participants. METHODS: Using a single-group, pretest, posttest design, 10 women participated in the 12-week usability study. Participants were provided a smartphone and a smartwatch on which the HerBeat app was installed. Using a web portal dashboard, a health coach monitored participants' ecological momentary assessment data, their behavioral data, and their heart rate and step count. Participants then completed a 12-week follow-up assessment. RESULTS: All 10 women (age: mean 64.4 years, SD 6.3 years) completed the study. The usability and acceptability of HerBeat were good, with a mean system usability score of 83.60 (SD 16.3). The participants demonstrated statistically significant improvements in waist circumference (P=.048), weight (P=.02), and BMI (P=.01). Furthermore, depressive symptoms, measured with the Patient Health Questionnaire-9, significantly improved from baseline (P=.04). CONCLUSIONS: The mHealth prototype was feasible and usable for women with CHD. Participants provided data that were useful for further development of HerBeat. The mHealth intervention is expected to help women with CHD self-manage their health behaviors. A randomized controlled trial is needed to further verify the findings.

An undergraduate laboratory module that uses the CRISPR/Cas9 system to generate frameshift mutations in yeast.

The CRISPR/Cas9 system is a powerful tool for gene editing and it has become increasingly important for biology students to understand this emerging technique. Most CRISPR laboratory teaching modules use complex metazoan systems or mammalian cell culture which can be expensive. Here, we present a lab module that engages students in learning the fundamentals of CRISPR/Cas9 methodology using the simple and inexpensive model system, Saccharomyces cerevisiae. Students use CRISPR/Cas9 and nonhomologous end joining to generate frameshift insertion and deletion mutations in the CAN1 gene, which are easily selected for using media plates that have canavanine. DNA sequencing is also performed to determine what type of mutation occurred in gene-edited cells. This easy to implement set of experiments has been run as both a 5-week and a shorter 3-week lab module. Learning assessments demonstrate increased understanding in CRISPR-related concepts as well as increased confidence using molecular techniques. Thus, this CRISPR/Cas9 lab module can be added to an existing Genetics, Microbiology, or Molecular Biology lab course to help undergraduate students learn current gene editing techniques with limited effort and cost. © 2019 International Union of Biochemistry and Molecular Biology, 47(5):573-580, 2019.

How Myxobacteria Cooperate.

Prokaryotes often reside in groups where a high degree of relatedness has allowed the evolution of cooperative behaviors. However, very few bacteria or archaea have made the successful transition from unicellular to obligate multicellular life. A notable exception is the myxobacteria, in which cells cooperate to perform group functions highlighted by fruiting body development, an obligate multicellular function. Like all multicellular organisms, myxobacteria face challenges in how to organize and maintain multicellularity. These challenges include maintaining population homeostasis, carrying out tissue repair and regulating the behavior of non-cooperators. Here, we describe the major cooperative behaviors that myxobacteria use: motility, predation and development. In addition, this review emphasizes recent discoveries in the social behavior of outer membrane exchange, wherein kin share outer membrane contents. Finally, we review evidence that outer membrane exchange may be involved in regulating population homeostasis, thus serving as a social tool for myxobacteria to make the cyclic transitions from unicellular to multicellular states.

Vibrational spectroscopy and ionic conductivity of polyethylene oxide-NaClO4-CuO nanocomposite.

Structure, morphology and thermal properties of polyethylene oxide (PEO) with sodium perchlorate (NaClO(4)) as electrolytic salt have been investigated by incorporating cupric monoxide (CuO) nanoparticles. Monoclinic CuO affects melting and glass transition temperatures of PEO-NaClO(4). Crystallinity and free ion concentration change with the variation of CuO concentration. The maximum ionic conductivity is observed for 10 wt.% CuO. Ionic conductivity follows Arrhenius type behavior as a function of temperature.

Mixed protonic-electronic conduction and dielectric response in layered vanadyl phosphate nanocomposites.

The layered vanadyl phosphate, VOPO(4)2H(2)O, is employed to prepare nanosized conducting polypyrrole by redox intercalation method. Transport and dielectric properties of various compositions have been investigated by impedance technique over a temperature range of 300-120 K. Grain boundary conductivity is larger than the bulk conductivity. The conductivity reveals a discontinuity at about 212-235 K. The conductivity is predominantly ionic at high temperature and electronic at low temperature. The dielectric spectra reveal a peak in the frequency range up to 2 MHz for higher concentration of intercalated polypyrrole. The activation energy of conductivity relaxation is different from that of total conductivity derived from the impedance plot.