Characterization of swimming motility in a marine unicellular cyanobacterium

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution April 1988The structural mechanism, behavior, energetics and functional significance of the unique swimming motility displayed by some oceanic isolates of the cyanobacterium Synechococcus was investigated. A variety of analytical techniques confirmed that these strains swam through liquids without flagella or flagellar-like appendages. No extracellular structures were observed in a broad range of cell preparations examined by transmission electron microscopy (TEM), or by high-intensity dark field microscopy. The possibility that a structure might be present that eluded visualization was eliminated by the lack of motility-dependent amplitude spectra, the absence of discrete circulation of microspheres around the cell body and the inability of shearing forces to arrest motility. TEM and gel electrophoretic analysis of spheroplasts, cell wall-enriched fractions from motile and nonmotile strains, and cell material collected following the application of a flagellar hook-basal body complex isolation technique to a motile Synechococcus strain provided no further evidence of a structure or protein unique to motile strains. The motile Synechococcus strains represent the only cyanobacterium reported to date capable of swimming rather than gliding motility. Swimming behavior was characterized by several features: between 50 - 80% of cells were actively motile during loyarithmic phase of growth, with speeds that ranged from 5 - 40 um s-1 the average speed was 13 um s-1. Swimming patterns were entirely random, consistent with the absence of bacterial flagella. Synechococcus motility resembled flagellar-mediated motility in that thrust (forward motion) was accompanied by torque (cell rotation) as demonstrated by i) dividing cells which swam with the daughter cells at an angle, ii) individual cells that were sometimes seen to rotate end over end at a rate of 3 to 5 rev s-1, iii) polystyrene beads attached to the cell body served as a point of reference as the cell rotated concomitant with translocation and iv) cells attached to the coverslip or slide spun about one pole at an average rate of 1 rev s-1. When observed in the same plane of focus, 50% of the cells spun clockwise and 50% spun counterclockwise, but unlike flagellated cells, Synechococcus was never seen to change direction of rotation, as would be predicted if the cell body were rotating as a single unit and the motility apparatus were incapable of reversing direction of rotation. This motility apparatus appeared to operate at a constant torque, as indicated by the relationship between swimming speeds and the fluidity of the surrounding medium. Investigation of the energetics of motility in Synechococcus WH8ll3 demonstrated that swimming was sodium coupled. There was a specific sodium requirement such that cells were immotile at external sodium concentrations below 10 mM, with speeds increasing with increasing sodium to a maximum speed at 150 to 250mM sodium, pH 8.0 to 8.5. The sodium motive force increased similarly, but other energetic parameters including proton motive force, electrical potential, and the proton and sodium diffusion gradients lacked correlation to levels of motility. When components of the sodium motive force were diminished by monensin or carbonyl cyanide m-chlorophenyl-hydrazone, motility was arrested. Motility was independent of the magnitude of internal ATP pools, which were depleted to 2% of control values without affecting cell motility. These results suggest that the direct source of energy for Synechococcus motility is a sodium motive force, and that the devise driving motility is located in the cytoplasmic membrane, as is the case for flagellated bacteria. The ecological role of Synechococcus motility was explored and several lines of evidence indicated that cells lacked behavioral photoresponses but were able to detect and respond to very low concentrations of simple nitrogenous compounds. When 23 compounds were tested in spatial gradients established in blind well chemotaxis chambers, cells displayed positive chemoresponses only when placed in gradients of NH4Cl, NaN03, urea, glycine and alanine. Cells also failed to respond in chambers which lacked gradients due to the presence of only seawater or an equal distribution of chemoeffector, demonstrating that a gradient was required to elicit a response. The apparent threshold levels of 10-10 M - 10-9 M for Synechococcus chemoresponses are 4 to 5 orders of magnitude lower than those for most other bacteria and place them in the range of ecological significance. The presence of chemotaxis in this oceanic cyanobacterium may help support the notion that nutrient enriched microaggregates may play an important role in picoplankton nutrient dynamics

Estimates of Burden and Consequences of Infants Born Small for Gestational Age in Low and Middle Income Countries with INTERGROWTH-21(st) Standard: Analysis of CHERG Datasets.

Objectives To estimate small for gestational age birth prevalence and attributable neonatal mortality in low and middle income countries with the INTERGROWTH-21st birth weight standard. Design Secondary analysis of data from the Child Health Epidemiology Reference Group (CHERG), including 14 birth cohorts with gestational age, birth weight, and neonatal follow-up. Small for gestational age was defined as infants weighing less than the 10th centile birth weight for gestational age and sex with the multiethnic, INTERGROWTH-21st birth weight standard. Prevalence of small for gestational age and neonatal mortality risk ratios were calculated and pooled among these datasets at the regional level. With available national level data, prevalence of small for gestational age and population attributable fractions of neonatal mortality attributable to small for gestational age were estimated. Setting CHERG birth cohorts from 14 population based sites in low and middle income countries. Main outcome measures In low and middle income countries in the year 2012, the number and proportion of infants born small for gestational age; number and proportion of neonatal deaths attributable to small for gestational age; the number and proportion of neonatal deaths that could be prevented by reducing the prevalence of small for gestational age to 10%. Results In 2012, an estimated 23.3 million infants (uncertainty range 17.6 to 31.9; 19.3% of live births) were born small for gestational age in low and middle income countries. Among these, 11.2 million (0.8 to 15.8) were term and not low birth weight (≥2500 g), 10.7 million (7.6 to 15.0) were term and low birth weight (\u3c2500 g) and 1.5 million (0.9 to 2.6) were preterm. In low and middle income countries, an estimated 606 500 (495 000 to 773 000) neonatal deaths were attributable to infants born small for gestational age, 21.9% of all neonatal deaths. The largest burden was in South Asia, where the prevalence was the highest (34%); about 26% of neonatal deaths were attributable to infants born small for gestational age. Reduction of the prevalence of small for gestational age from 19.3% to 10.0% in these countries could reduce neonatal deaths by 9.2% (254 600 neonatal deaths; 164 800 to 449 700). Conclusions In low and middle income countries, about one in five infants are born small for gestational age, and one in four neonatal deaths are among such infants. Increased efforts are required to improve the quality of care for and survival of these high risk infants in low and middle income countrie

Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead

Minimum Information about a Biosynthetic Gene cluster

A wide variety of enzymatic pathways that produce specialized metabolites in bacteria, fungi and plants are known to be encoded in biosynthetic gene clusters. Information about these clusters, pathways and metabolites is currently dispersed throughout the literature, making it difficult to exploit. To facilitate consistent and systematic deposition and retrieval of data on biosynthetic gene clusters, we propose the Minimum Information about a Biosynthetic Gene cluster (MIBiG) data standard.Chemistry and Chemical Biolog

Prescott, harley, and klein s microbiology, 7th ed./ Willey

xx, 1088 hal.: ill.; 26 cm

Prescott, harley, and klein s microbiology, 7th ed./ Willey

xx, 1088 hal.: ill.; 26 cm

Prescott's microbiology

The author team of Prescott's Microbiology continues the tradition of past editions by providing a balanced, comprehensive introduction to all major areas of microbiology. This balance makes Microbiology appropriate for microbiology majors and mixed majors courses. The authors have introduced a number of pedagogical elements designed to facilitate student learning. They also remain focused on readability, artwork, and the integration of several key themes (including evolution, ecology and diversity) throughout the text, making an already superior text even better

Interactions between Streptomyces coelicolor and Bacillus subtilis: Role of Surfactants in Raising Aerial Structures

Using mixed-species cultures, we have undertaken a study of interactions between two common spore-forming soil bacteria, Bacillus subtilis and Streptomyces coelicolor. Our experiments demonstrate that the development of aerial hyphae and spores by S. coelicolor is inhibited by surfactin, a lipopeptide surfactant produced by B. subtilis. Current models of aerial development by sporulating bacteria and fungi postulate a role for surfactants in reducing surface tension at air-liquid interfaces, thereby removing the major barrier to aerial growth. S. coelicolor produces SapB, an amphipathic peptide that is surface active and required for aerial growth on certain media. Loss of aerial hyphae in developmental mutants can be rescued by addition of purified SapB. While a surfactant from a fungus can substitute for SapB in a mutant that lacks aerial hyphae, not all surfactants have this effect. We show that surfactin is required for formation of aerial structures on the surface of B. subtilis colonies. However, in contrast to this positive role, our experiments reveal that surfactin acts antagonistically by arresting S. coelicolor aerial development and causing altered expression of developmental genes. Our observations support the idea that surfactants function specifically for a given organism regardless of their shared ability to reduce surface tension. Production of surfactants with antagonistic activity could provide a powerful competitive advantage during surface colonization and in competition for resources