The role of the stretch reflex in the gastrocnemius muscle during human locomotion at various speeds.

In the present study, the fascicle length (L(fa)) of the human medial gastrocnemius (MG) muscle was monitored to evaluate possible input from the short-latency stretch reflex (SLR) during the stance phase of running and to examine its timing at various running speeds. Eight subjects ran at 2.0, 3.5, 5.0, and 6.5 m/s. The L(fa) was measured with the high-speed ultrasound fascicle scanning together with kinematics and myoelectrical activities. The amplitudes and onset latency of SLR activities were determined. During ground contact, the sudden MG fascicle stretch occurred during the early contact at all running speeds. This was followed by the fascicle shortening. The timing of fascicle stretch depended on running speed and type of foot contact. In slower speed conditions (2.0, 3.5, 5 m/s), the MG fascicle stretch and the corresponding SLR activities occurred during the middle of the braking phase. In fast-speed running (6.5 m/s), however, the MG fascicle stretch occurred later compared with the lower speed. The corresponding SLR activities occurred significantly later at the end of the braking phase. In addition to the clear demonstration of the different timings of SLR in MG during ground contact of running, the results imply that the role of the MG SLR during the stance phase of running can be different between fast- and slow-speed running conditions.     

The shifting balance of littoral predator-prey interaction in regimes of hydrodynamic stress

Above lowshore levels of wave-beaten rocky shores, desiccation from tidal exposure and hydrodynamics stresses from wave action are thought to create refuges from predation, allowing concentrations of sedentary prey such as mussel beds. Underwater time-lapse photography on rocky shores in Southern California revealed that dense aggregations of spiny lobsters prey on mussels during nocturnal high tides. In contradiction of the refuge hypothesis, the densest aggregations occurred on midshore levels of the most wave-exposed site, a semi-protected site showed intermediate densities, and a protected site showed only sparse numbers of lobsters. On wave-beaten shores, the lobsters' high mobility and rapid prey handling allowed them to exploit intertidal prey in the brief period at extreme high tide, when both desiccation and hydrodynamic stresses were at a minimum. The spatial differences in lobster densities were, however, positively related to the recruitment rates of juvenile mussels, the preferred prey. A field experiment demonstrated that predation by lobsters within a mussel bed affects the age/size structure of the bed without changing primary percent coverage. Therefore, concentrations of adult prey on some wave-swept sites appear to result from elevated rates of prey recruitment that surpass rates of predation, rather than absolute refuges from predation.     

The interaction pattern of murine serum ficolin-A with microorganisms

The ficolins are soluble pattern recognition molecules in the lectin pathway of complement, but the spectrum and mode of interaction with pathogens are largely unknown. In this study, we investigated the binding properties of the murine serum ficolin-A towards a panel of different clinical relevant microorganisms (N = 45) and compared the binding profile with human serum ficolin-2 and ficolin-3. Ficolin-A was able to bind Gram-positive bacteria strains including E. faecalis, L. monocytogenes and some S. aureus strains, but not to the investigated S. agalactiae (Group B streptococcus) strains. Regarding Gram-negative bacteria ficolin-A was able to bind to some E. coli and P. aeruginosa strains, but not to the investigated Salmonella strains. Of particular interest ficolin-A bound strongly to the pathogenic E. coli, O157:H7 and O149 strains, but it did not bind to the non-pathogenic E. coli, ATCC 25922 strain. Additionally, ficolin-A was able to bind purified LPS from these pathogenic strains. Furthermore, ficolin-A bound to a clinical isolate of the fungus A. fumigatus. In general ficolin-2 showed similar selective binding spectrum towards pathogenic microorganisms as observed for ficolin-A indicating specific pathophysiological roles of these molecules in host defence. In contrast, ficolin-3 did not bind to any of the investigated microorganisms and the anti-microbial role of ficolin-3 still remains elusive.     

The role of tendon elasticity in the locomotion of the camel (Camelus dromedarius)

Several ofthe distal leg muscles ofcamels have very short or even rudimentary muscle fibres. This makes it possible to calculate the elastic extensions of tendons that occur in running, from the leg positions observed in films. A series of experiments have been performed for this purpose on the dissected legs of a camel. The initial conclusions derived from them are modified in the light of estimates of the forces that act on the tendons, and of measurements of the elastic properties of one tendon. Evidence for movement at the intertarsal and tarso-metatarsal joints. and the corresponding joints of the fore leg, is examined. The importance of the various tendons as elastic energy stores in running is assessed.     

Specificity in the genetic code. The role of nucleotide base-amino acid interaction

The mechanism of the unique and specific association of a given amino acid to its t-RNA is investigated by theoretical methods. Several possible schemes are proposed to explain specificity. The physical forces which act within these mechanisms are illustrated by the computer simulation of probable interactions between glycine and nucleotide bases and base pairs. It is demonstrated that glycine has direct and selective affinities for the nucleotide bases and that these interactions are principally determined by the polar groups. Energies have been calculated for the interaction of glycine with several base pairs. From these, the possibility that specificity arises through direct complexing of an amino acid with its anticodon is evaluated.     

Central program of hind limb interaction during locomotion in cats

The central program for interaction between the hind limbs, expressed as the time structure of motor discharges in the nerves to the various muscles, was studied in immobilized decerebrate spinal cats during fictitious locomotion. The program of hind limb interaction (alternating or inphase) in the decerebrate cats was shown to be determined by the relations between the flexor hemicenters. The activity of the latter is either antiphased or cophased. The character of activity of the extensor hemicenters is determined secondarily on account of alternating interaction of each of them with the ipsilateral flexor hemicenter. After injection of dopa into the animals the cophased program of hind limb interaction may be determined by the cophased working of the extensor center.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 11, No. 1, pp. 65–73, January–February, 1979.     

Ecological role of energy taxis in microorganisms

Motile microorganisms rapidly respond to changes in various physico-chemical gradients by directing their motility to more favorable surroundings. Energy generation is one of the most important parameters for the survival of microorganisms in their environment. Therefore it is not surprising that microorganisms are able to monitor changes in the cellular energy generating processes. The signal for this behavioral response, which is called energy taxis, originates within the electron transport system. By coupling energy metabolism and behavior, energy taxis is fine-tuned to the environment a cell finds itself in and allows efficient adaptation to changing conditions that affect cellular energy levels. Thus, energy taxis provides cells with a versatile sensory system that enables them to navigate to niches where energy generation is optimized. This behavior is likely to govern vertical species stratification and the active migration of motile cells in response to shifting gradients of electron donors and/or acceptors which are observed within microbial mats, sediments and soil pores. Energy taxis has been characterized in several species and might be widespread in the microbial world. Genome sequencing revealed that many microorganisms from aquatic and soil environments possess large numbers of chemoreceptors and are likely to be capable of energy taxis. In contrast, species that have a fewer number of chemoreceptors are often found in specific, confined environments, where relatively constant environmental conditions are expected. Future studies focusing on characterizing behavioral responses in species that are adapted to diverse environmental conditions should unravel the molecular mechanisms underlying sensory behavior in general and energy taxis in particular. Such knowledge is critical to a better understanding of the ecological role of energy taxis.     

The unique role of natural killer T cells in the response to microorganisms

Natural killer T (NKT) cells combine features of the innate and adaptive immune systems. Recently, it has become evident that these T cells have crucial roles in the response to infectious agents. The antigen receptor expressed by NKT cells directly recognizes unusual glycolipids that are part of the membrane of certain Gram-negative bacteria and spirochetes. Moreover, even in the absence of microbial glycolipid antigens, these T cells respond to innate cytokines produced by dendritic cells that have been activated by microbes. This indirect sensing of infection, by responding to cytokines from activated dendritic cells, allows NKT cells to react to a broad range of infectious agents.     

The role of different microorganisms in the genesis of tubal-peritoneal infertility and in immunity

The character of microflora, directly causing inflammatory process in tuboperitoneal infertility, was studied. The study revealed the prevalence of microbial associations, Chlamydia infection was detected in half of the women, and in 17% of the patients this infection was for the first time detected in the upper section of their reproductive apparatus, which was indicative of the role of Chlamydia infection in the occlusion of the uterine tubes. Opportunistic microflora persisting in persons with defective antimicrobial protection was found. The study of local protective factors in peritoneal fluid revealed the absence of T-cell activity, which was manifested by a low level of sIL-2R and the absence of a significant rise in the level of IL-2 in peritoneal fluid in comparison with that in healthy women. In addition, a decrease in the total complement activity and in the activity of component C3 of the complement was established.     

The role of siderophores in iron acquisition by photosynthetic marine microorganisms

The photosynthetic picocyanobacteria and eukaryotic microorganisms that inhabit the open ocean must be able to supply iron for their photosynthetic and respiratory needs from the subnanomolar concentrations available in seawater. Neither group appears to produce siderophores, although some coastal cyanobacteria do. This is interpreted as an adaptation to the dilute oceanic environment rather than a phylogenetic constraint, since there are cases in which related taxa from different environments have the capacity to produce siderophores. Most photosynthetic marine microorganisms are presumably, however, capable of accessing iron from strong chelates since the majority of dissolved iron in seawater is complexed by organic ligands, including siderophores. Rather than direct internalization of siderophores and other iron chelates, marine organisms primarily appear to use uptake pathways that involve a reduction step to free bound iron, closely coupled with transport into the cell.     

The role of teichoic acids in the regulation of biochemical processes in microorganisms]

The role of cell wall teichoic and lipoteichoic acids in the regulation of activity of some autolytic enzymes and in ion exchange, the role of lipoteichoic acids in biosynthesis of cell wall teichoic acids and some other functional features of these compounds in the bacterial cell are discussed.     

The role of microorganisms in mobilization and fixation of phosphorus in sediments

Cycling of phosphorus (P) at the sediment/water interface is generally considered to be an abiotic process. Sediment bacteria are assumed to play only an indirect role by accelerating the transfer of electron from electron donors to electron acceptors, thus providing the necessary conditions for redox-and pH-dependent, abiotic sorption/desorption or precipitation/dissolution reactions. Results summarized in this review suggest that

1. in eutrophic lakes, sediment bacteria contain as much P as settles with organic detritus during one year
2. in oligotrophic lakes, P incorporated in benthic bacterial biomass may exceed the yearly deposition of bioavailable P several times
3. storage and release of P by sediment bacteria are redox-dependent processes
4. an appreciable amount of P buried in the sediment is associated with the organic fraction
5. sediment bacteria not only regenerate PO₄, they also contribute to the production of refractory, organic P compounds, and
6. in oligotrophic lakes, a larger fraction of the P settled with organic detritus is converted to refractory organic compounds by benthic microorganisms than in eutrophic lakes.

From this we conclude that benthic bacteria do more than just mineralize organic P compounds. Especially in oligotrophic lakes, they also may regulate the flux of P across the sediment/water interface and contribute to its terminal burial by the production of refractory organic P compounds.     

Hydrodynamic interaction of two unsteady model microorganisms

The study of pair-wise interactions between swimming microorganisms is fundamental to the understanding of the rheological and transport properties of semi-dilute suspensions. In this paper, the hydrodynamic interaction of two ciliated microorganisms is investigated numerically using a boundary-element method, and the microorganisms are modeled as spherical squirmers that swim by time-dependent surface deformations. The results show that the inclusion of the unsteady terms in the ciliary propulsion model has a large impact on the trajectories of the interacting cells, and causes a significant change in scattering angles with potential important consequences on the diffusion properties of semi-dilute suspensions. Furthermore, the analysis of the shear stress acting on the surface of the microorganisms revealed that the duration and the intensity of the near-field interaction are significantly modified by the presence of unsteadiness. This observation may account for the hydrodynamic nature of randomness in some biological reactions, and supersedes the distinction between intrinsic randomness and hydrodynamic interactions, adding a further element to the understanding and modeling of interacting microorganisms.