Bacterial Motility Patterns Reveal Importance of Exploitation over Exploration in Marine Microhabitats. Part I: Theory

Bacteria use different motility patterns to navigate and explore natural habitats. However, how these motility patterns are selected, and what their benefits may be, are not understood. In this article, we analyze the effect of motility patterns on a cell’s ability to migrate in a chemical gradient and to localize at the top of the gradient, the two most important characteristics of bacterial chemotaxis. We will focus on two motility patterns, run-tumble and run-reverse-flick, that are observed and characterized in enteric bacterium Escherichia coli and marine bacterium Vibrio alginolyticus, respectively. To make an objective comparison, master equations are developed on the basis of microscopic motions of the bacteria. An unexpected yet significant result is that by adopting the run-reverse-flick motility pattern, a bacterium can reduce its diffusivity without compromising its drift in the chemical gradient. This finding is biologically important as it suggests that the motility pattern can improve a microorganism’s ability to sequester nutrients in a competitive environment.     

Regulation of Sperm Motility in Starfish. I. Initiation of Movement

Starfish seminal plasma has such characteristics as higher concentration of potassium ions, higher osmolality, and lower pH compared with those of sea water. These factors independently inhibited the movement of spermatozoa. Sperm movement was recorded by taking photographs of the swimming paths under a dark field microscope. Spermatozoa either did not move or swam with decreased beat frequency in isolated seminal plasma or in the presence of certain fractions of seminal plasma obtained by gel-filtration or by partitions. In normal sea water (containing calcium ions), a low pH of less than 6 resulted in a decrease in the number (%) of swimming spermatozoa, though the speed of propulsion and the beat frequency was not affected. On the other hand, in a calcium-free sea water, a large proportion of spermatozoa moved in both low and high pH conditions, but in low pH the speed of propulsion was reduced and many spermatozoa (31 %) swam in smaller circles.     

Microbial Symbiosis: Patterns of Diversity in the Marine Environment

SYNOPSIS. Symbiotic associations expand both the diversity ofpotential ecological niches and metabolic capabilities of thehost—symbiont combinations. Symbioses can also be consideredto have evolutionary potential in that the partnership can resultin a "new organism." Associations between chemoautotrophic bacteriaand marine invertebrates, discovered only 10 years ago, arenow found widely in nature, in habitats ranging from deep-seahydrothermal vents to coastal sediments. Here I review chemoautotroph—invertebrateassociations and discuss the benefits inferred for both partnerswith regard to the diversity of these symbioses in nature.     

Maternal nutrition in pregnancy. Part I: a review.

Maternal undernutrition may result in a greater deprivation of the fetus than has previously been believed. The infant not only may be "light for dates" but also has an increased risk of perinatal disability or death secondary to gross neurologic and developmental abnormalities. This article reviews current knowledge of the energy, protein, iron, vitamin, sodium and calcium requirements in pregnancy, with special reference to the management of the underweight and overweight pregnant women.     

Picosecond spectroscopy: applications in biochemistry. Part I: Techniques

A number of sources of picosecond optical pulses and the means by which they may be used to investigate fast molecular processes have been described. In addition, it should be pointed out that most of these techniques can be extended to take advantage of other properties of the laser pulses; in particular, the polarization is of use in measuring time-dependent antisotropy. The state of the art is now the generation of 30fs pulses; it seems likely that this is all the time resolution that one is likely to need for investigating biological and other molecular processes as at such short times the uncertainty principle leads to a considerable loss of spectral resolution.     

Nitrogen Turnover in Marine and Brackish Habitats: I. Nitrogen Fixation

Potential nitrogen-fixing genera were found to be abundant intwo natural populations of blue-green algae, one from a rockycoast and the other from a sand-dune slack. ¹⁵N studies confirmedthat these populations fixed nitrogen in the laboratory andin the field. Preliminary quantitative data on Fixation in thefield suggest that the algae contribute appreciable quantitiesof fixed nitrogen to the environments in which they occur.     

Bacterial Biofilm in Seawater: Cell Surface Properties of Early-attached Marine Bacteria

The development of antifouling strategies in seawater requires knowledge of the physico-chemical properties of the cell surfaces of early adherent bacteria. The hydrophilic, electrostatic and the Lewis acid-base cell surface properties of eleven marine bacteria were characterized. Although these bacteria adhered to a hydrophilic support immersed for 3 and 6?h, they presented various physico-chemical properties. Eleven strains possessed a hydrophilic surface and five a hydrophobic surface. Although the majority of the bacteria presented an electron-donating character, some could not generate Lewis acid-base interactions with the support. On the other hand, all strains possessed an isoelectric point ranging from 2.2 to 3.4 and were negatively charged at the pH of seawater. Hydrophilicity was a preponderant property among these bacteria, but other properties should not be ignored. The development of new antifouling paints must take account all the possible interaction levels used by the bacteria to adhere to an immersed surface.     

Electrical Sizing of Particles in Suspensions: I. Theory

The processes involved during the passage of a suspended particle through a small cylindrical orifice across which exists an electric field are considered in detail. Expressions are derived for the resulting change in current in terms of the ratios of particle to orifice volume and particle to suspending fluid resistivity, and particle shape. Graphs are presented of the electric field and of the fluid velocity as functions of position within the orifice, and of the shape factor of spheroids as a function of their axial ratio and orientation in the electric field. The effects of the electric and hydrodynamic fields on the orientation of nonspherical particles and on the deformation of nonrigid spheres is treated, and the migration of particles towards the orifice axis is discussed. Oscillograms of current pulses produced by rigid, nonconducting spheres in various orifices are shown and compared with the theoretical predictions.