Culture and Motion Analysis of Diatom Bacillaria paradoxa on a Microfluidic Platform

We proved the feasibility of using a microfluidic chip to culture diatom Bacillaria paradoxa, and analyzed the gliding characteristics of its self-organized colony in detail. The optimal cultivation parameters of B. paradoxa for the designed chip made with polydimethylsiloxane are as follows: the preferable cells injecting rate for keeping the cells alive is 0.2 mL/h, the initial cell density for fast reproduction is 5.5 × 10⁴ cells/mL, and the optimal replacement period of culture medium is 4 days. B. paradoxa tends to form a colony during their growth, and the colony can glide with a steady period of 29 ± 3 s along its axial direction in a constant stream, the amplitude of the colony will not decay (e.g., 24 μm of two-cell colony at 1.1 mm/s flow rate), and the colony rapidly adjusts its direction of gliding to the direction of water flow. The successful culture of diatoms on a microfluidic platform may be used for biosensing chips and the creation of gasoline-producing diatom solar panels.     

Collective colony growth is optimized by branching pattern formation in Pseudomonas aeruginosa

Branching pattern formation is common in many microbes. Extensive studies have focused on addressing how such patterns emerge from local cell–cell and cell–environment interactions. However, little is known about whether and to what extent these patterns play a physiological role. Here, we consider the colonization of bacteria as an optimization problem to find the colony patterns that maximize colony growth efficiency under different environmental conditions. We demonstrate that Pseudomonas aeruginosa colonies develop branching patterns with characteristics comparable to the prediction of modeling; for example, colonies form thin branches in a nutrient‐poor environment. Hence, the formation of branching patterns represents an optimal strategy for the growth of Pseudomonas aeruginosa colonies. The quantitative relationship between colony patterns and growth conditions enables us to develop a coarse‐grained model to predict diverse colony patterns under more complex conditions, which we validated experimentally. Our results offer new insights into branching pattern formation as a problem‐solving social behavior in microbes and enable fast and accurate predictions of complex spatial patterns in branching colonies.     

Wachstums- und Knospungsstrategie vonGrammothoa filifera Voigt & Hillmer (Bryozoa,Cheilostomata, Ob. Kreide)

The genusGrammothoa, growing on the interior walls ofThalassinoides burrows in the Maastrichtian Chalk-tuff, has developed a special growth strategy for spatial competition with other encrusting species which has not been previously recorded in bryozoans. The zoarium consists of auto-zooecia, gynozooecia and chains of smaller zooeciules, the latter forming stolon-like outgrowths from the distal edge of the colony. New areas of substratum are explored and colonized by the growth of these zooeciules. At the branching points of the zooeciules, autozooecia and gynozooecia are budded and may coalesce to form the main part of the colony.     

The role of parasitoids in regulation of Polistes wasp population (Hymenoptera, Vespidae: Polistinae)

The study conducted in 2005–2010 analyzes the behavioral response of the parasitoids Latibulus argiolus (Rossi) (Hymenoptera, Ichneumonidae) and Elasmus schmitti Ruschka (Hymenoptera, Eulophidae) to the distribution of their host, Polistes wasps (Hymenoptera, Vespidae). Various conditions of the parasitoid-host system and conditions of regulation of the host abundance are discussed. The parasitoid females are more active in wasp colony clusters and tend to infest larger nests. If the parasitoids are abundant, infestation of host colonies starts earlier, sometimes before the worker emergence; therefore, density-dependent behavioral response of parasitoids is caused primarily by the impact of the aggregation component. Thus, the host population density factor appears to be mediated not only by the non-uniform development rates of colonies and their spatial distribution, but also by the seasonal (temporal) aspect of their development. Low density of the host population, at which the parasitoids regulate the wasp abundance, corresponds to a certain phase of the seasonal colony development, namely to the period before the emergence of workers. On the whole, we are dealing with a host-parasitoid system in which the spatial and temporal factors are closely interrelated.     

Development of a novel cryogenic microscope with numerical aperture of 0.9 and its application to photosynthesis research

A novel cryogenic optical-microscope system was developed in which the objective lens is set inside of the cryostat adiabatic vacuum space. Being isolated from the sample when it was cooled, the objective lens was maintained at room temperature during the cryogenic measurement. Therefore, the authors were able to use a color-aberration corrected objective lens with a numerical aperture of 0.9. The lens is equipped with an air vent for compatibility to the vacuum. The theoretically expected spatial resolutions of 0.39 μm along the lateral direction and 1.3 μm along the axial direction were achieved by the developed system. The system was applied to the observations of non-uniform distributions of the photosystems in the cells of a green alga, Chlamydomonas reinhardtii, at 94 K. Gaussian decomposition analysis of the fluorescence spectra at all the pixels clearly demonstrated a non-uniform distribution of the two photosystems, as reflected in the variable ratios of the fluorescence intensities assigned to photosystem II and to those assigned to photosystem I. The system was also applied to the fluorescence spectroscopy of single isolated photosystem I complexes at 90 K. The fluorescence, assigned to be emitted from a single photosystem I trimer, showed an intermittent fluctuation called blinking, which is typical for a fluorescence signal from a single molecule. The vibronic fluorescence bands at around 790 nm were observed for single photosystem I trimers, suggesting that the color aberration is not serious up to the 800 nm spectral region.     

Spatiotemporal dynamics of growth and death within spherical bacterial colonies

Bacterial growth within colonies and biofilms is heterogeneous. Local reduction of growth rates has been associated with tolerance against various antibiotics. However, spatial gradients of growth rates are poorly characterized in three-dimensional bacterial colonies. Here, we report two spatially resolved methods for measuring growth rates in bacterial colonies. As bacteria grow and divide, they generate a velocity field that is directly related to the growth rates. We derive profiles of growth rates from the velocity field and show that they are consistent with the profiles obtained by single-cell-counting. Using these methods, we reveal that even small colonies initiated with a few thousand cells of the human pathogen Neisseria gonorrhoeae develop a steep gradient of growth rates within two generations. Furthermore, we show that stringent response decelerates growth inhibition at the colony center. Based on our results, we suggest that aggregation-related growth inhibition can protect gonococci from external stresses even at early biofilm stages.     

Probabilistic transition from unstable predator-prey interaction to stable coexistence of Dictyostelium discoideum and Escherichia coli

Predator-prey interactions have been found at all levels within ecosystems. Despite their ecological ubiquity and importance, the process of transition to a stable coexistent state has been poorly verified experimentally. To investigate the stabilization process of predator-prey interactions, we previously constructed a reproducible experimental predator-prey system between Dictyostelium discoideum and Escherichia coli, and showed that the phenotypically changed E. coli contributed to stabilization of the system. In the present study, we focused on the transition to stable coexistence of both species after the phenotypic change in E. coli. Analysis of E. coli cells isolated from co-culture plates as single colony enabled us to readily identify the appearance of phenotypically changed E. coli that differed in colony morphology and growth rate. It was also demonstrated that two types of viscous colony, i.e., the dense-type and sparse-type, differing in spatial distribution of both species emerged probabilistically and all of the viscous colonies maintained stably were of the sparse-type. These results suggest that the phenotypically changed E. coli may produce two types of viscous colonies probabilistically. The difference in spatial distribution would affect localized interactions between both species and then cause probabilistic stabilization of predator-prey interactions.     

Genetic Drift Suppresses Bacterial Conjugation in Spatially Structured Populations

Conjugation is the primary mechanism of horizontal gene transfer that spreads antibiotic resistance among bacteria. Although conjugation normally occurs in surface-associated growth (e.g., biofilms), it has been traditionally studied in well-mixed liquid cultures lacking spatial structure, which is known to affect many evolutionary and ecological processes. Here we visualize spatial patterns of gene transfer mediated by F plasmid conjugation in a colony of Escherichia coli growing on solid agar, and we develop a quantitative understanding by spatial extension of traditional mass-action models. We found that spatial structure suppresses conjugation in surface-associated growth because strong genetic drift leads to spatial isolation of donor and recipient cells, restricting conjugation to rare boundaries between donor and recipient strains. These results suggest that ecological strategies, such as enforcement of spatial structure and enhancement of genetic drift, could complement molecular strategies in slowing the spread of antibiotic resistance genes.     

Genetic Drift Suppresses Bacterial Conjugation in Spatially Structured Populations

Conjugation is the primary mechanism of horizontal gene transfer that spreads antibiotic resistance among bacteria. Although conjugation normally occurs in surface-associated growth (e.g., biofilms), it has been traditionally studied in well-mixed liquid cultures lacking spatial structure, which is known to affect many evolutionary and ecological processes. Here we visualize spatial patterns of gene transfer mediated by F plasmid conjugation in a colony of Escherichia coli growing on solid agar, and we develop a quantitative understanding by spatial extension of traditional mass-action models. We found that spatial structure suppresses conjugation in surface-associated growth because strong genetic drift leads to spatial isolation of donor and recipient cells, restricting conjugation to rare boundaries between donor and recipient strains. These results suggest that ecological strategies, such as enforcement of spatial structure and enhancement of genetic drift, could complement molecular strategies in slowing the spread of antibiotic resistance genes.     

The amoebal cell of Physarum polycephalum: colony formation and growth.

Two stages of colony growth were observed during microscopic studies of Physarum polycephalum amoebae. During the first stage, “spreading growth,” the colony is composed of dispersed single cells. During the second stage, “aggregate growth,” most of the active cells in a colony are aggregated in a ring at the colony boundary. Measurements of cell movement as a function of bacterial concentration indicate that, during both spreading and aggregate growth, cell movements are not affected by changes in bacterial concentration but that the transition from spreading to aggregate growth occurs earlier on plates with lower bacterial concentrations. These results indicate that autonomous characteristics of the amoebae are more important for the determination of colony form than local variations in the concentrations of nutrients.The genetic determination of colony form is demonstrated by the existence of mutants that display specific alterations in colony morphology. Because the aggregate rings of these mutants move at an increased rate, mutant clones appear as variant sectors of wild-type colonies. The increased rate of mutant ring movement suggests that this selection method may be a useful technique for isolating mutant myxamoebae with defects in movement and behavior.     

Appearance of new phage types and new lysogenic strains after adaptation of lysogenic B. megatherium to ammonium sulfate culture medium

1. Lysogenic B. megatherium 899a was adapted to growth in a minimal ammonium sulfate medium (ASCM). 2. Adaptation took place slowly and the following changes in the culture occurred: (a) The growth rate increased from 0.5 to 1.5–2.0/hr. (b) The culture changed from diffuse to mucoid. (c) The total phage titer, and the gelatinase concentration decreased to 1/100 or less. (d) The types of phage produced changed from >99 per cent T (wild type) to 30 to 60 per cent miscellaneous clear types. The original T phage was replaced by a different smaller t, never observed in the original 899a culture. (e) Several new colony types also appeared, but the colony morphology was not correlated with the phage types produced. None of the colony types was stable on repeated transfer either in peptone or ASCM, but continued to disassociate into different colony types (cf. Ivánovics, 1955). 3. Control experiments showed that these changes in phage production and colony types could not be brought about by growing sensitive B. megatherium in the presence of the various new phages, in ASCM. It is therefore unlikely that the changes observed in adapted culture were due to infection of a sensitive cell with phage. 4. Continued growth of the ASCM-adapted strain in peptone resulted in increasing the total phage titer, and also the gelatinase concentration. The growth rate returned to its original value and the ability to grow rapidly in ASCM was soon lost. The phage types, however, remained the same as in the ASCM. 5. An improved cell for steady state growth is described.     

Friends and foes from an ant brain's point of view--neuronal correlates of colony odors in a social insect

Background

Successful cooperation depends on reliable identification of friends and foes. Social insects discriminate colony members (nestmates/friends) from foreign workers (non-nestmates/foes) by colony-specific, multi-component colony odors. Traditionally, complex processing in the brain has been regarded as crucial for colony recognition. Odor information is represented as spatial patterns of activity and processed in the primary olfactory neuropile, the antennal lobe (AL) of insects, which is analogous to the vertebrate olfactory bulb. Correlative evidence indicates that the spatial activity patterns reflect odor-quality, i.e., how an odor is perceived. For colony odors, alternatively, a sensory filter in the peripheral nervous system was suggested, causing specific anosmia to nestmate colony odors. Here, we investigate neuronal correlates of colony odors in the brain of a social insect to directly test whether they are anosmic to nestmate colony odors and whether spatial activity patterns in the AL can predict how odor qualities like “friend” and “foe” are attributed to colony odors.

Methodology/Principal Findings

Using ant dummies that mimic natural conditions, we presented colony odors and investigated their neuronal representation in the ant Camponotus floridanus. Nestmate and non-nestmate colony odors elicited neuronal activity: In the periphery, we recorded sensory responses of olfactory receptor neurons (electroantennography), and in the brain, we measured colony odor specific spatial activity patterns in the AL (calcium imaging). Surprisingly, upon repeated stimulation with the same colony odor, spatial activity patterns were variable, and as variable as activity patterns elicited by different colony odors.

Conclusions

Ants are not anosmic to nestmate colony odors. However, spatial activity patterns in the AL alone do not provide sufficient information for colony odor discrimination and this finding challenges the current notion of how odor quality is coded. Our result illustrates the enormous challenge for the nervous system to classify multi-component odors and indicates that other neuronal parameters, e.g., precise timing of neuronal activity, are likely necessary for attribution of odor quality to multi-component odors.     

Colony-size effects on task organization in the harvester ant Pogonomyrmex californicus

Colony size is a fundamental attribute of insect societies that appears to play an important role in their organization of work. In the harvester ant Pogonomyrmex californicus, division of labor increases with colony size during colony ontogeny and among unmanipulated colonies of the same age. However, the mechanism(s) integrating individual task specialization and colony size is unknown. To test whether the scaling of division of labor is an emergent epiphenomenon, as predicted by self-organizational models of task performance, we manipulated colony size in P. californicus and quantified short-term behavioral responses of individuals and colonies. Variation in colony size failed to elicit a change in division of labor, suggesting that colony-size effects on task specialization are mediated by slower developmental processes and/or correlates of colony size that were missing from our experiment. In contrast, the proportional allocation of workers to tasks shifted with colony size, suggesting that task needs or priorities depend, in part, on colony size alone. Finally, although task allocation was flexible, colony members differed consistently in task performance and spatial tendency across colony size treatments. Sources of interindividual behavioral variability include worker age and genotype (matriline).     

Orientiertes Wachstum beiMillepora dichotoma (Hydrozoa)

The orientation of fans ofMillepora dichotoma was investigated on the west coast of the Gulf of Akabah. Three transects were sampled by measuring equal areas in three different depths. The total depth range of the transect was determined in each case by the occurrence of the milleporids. Orientation of fans was determined by compass and the deviation from north for each colony noted. In all cases the orientation was uniform in the lower two thirds of the transect. The upper third shows a different orientation. Orientation is correlated with the prevailing direction of water movement and the plane of the fans grows perpendicular to the water current. Broken-off colonies lying flat on the bottom orient their new growth again perpendicular to the prevailing current. Further evidence for perpendicular fan orientation to the prevailing current is reported. Some fans exhibit two planes of orientation thus suggesting a high sensitivity to local deflection of reef current from the main direction of water movement.     

What determines the growth of individual castes in social trematodes?

Phenotypic diversification among colony members often leads to formation of physical castes which are morphologically specialised for particular tasks within the colony. The relative abundance of these castes and their body sizes represent two key aspects of the demography of a colony that may reflect the colony’s needs and conditions, and ultimately influence its survival and reproductive success. In a recently discovered social trematode, Philophthalmus sp., which exhibits a reproductive division of labour, the role of competition and colony composition in shaping reproductive success and behaviour of colony members has been documented. As body size variation within physical castes often influences colony efficiency, we investigated how the growth of reproductive and non-reproductive morphs of Philophthalmus sp. responds to competitive pressure, and to other attributes of colony demography such as colony size and composition. Our survey of a natural population and in vitro experiments demonstrate that the growth of reproductive colony members reflects the interaction between colony composition and the presence of a competitor, while the non-reproductive members simply grow larger in the presence of the intra-host competitor, Maritrema novaezealandensis. Furthermore, the close association between the volume and reproductive capacity of the reproductive members corroborates an adaptive value of colony member size in determining the fitness of the trematode colony as a whole. The present study is the first to demonstrate a fitness consequence, and identify the determinants, of the growth of colony members in social trematodes.     

Uptake of Glucose and Phosphorus by Growing Colonies of Fusarium oxysporum as Quantified by Image Analysis

Olsson, S. 1994. Uptake of glucose and phosphorus by growing colonies of Fusarium oxysporum as quantified by image analysis. Experimental Mycology 18, 33-47. The simplest of all heterogeneous environments for fungal colony growth is the petri dish with an agar medium. As the colony grows there will be a depression of nutrient concentrations under the colony caused by the uptake of nutrients by the growing colony. Image analysis methods have been developed for measuring medium concentrations of glucose and phosphorus with simultaneous biomass density determinations in agar systems. Maps of the concentrations in the agar medium under the colony and of colony biomass density were produced. A new method for weighing fungal colonies grown on agar is also presented. For Fusarium oxysporum phosphorus and glucose uptake from the medium was the same irrespective of the C/mineral ratios in the medium within the measured range of ratios. Even the concentration profiles of the nutrients under the colony were the same irrespective of nutrient ratios. Distribution of biomass density was affected by differences in glucose concentrations, being highest at the colony margin at the lower concentrations. The results indicate that the fungal colony is able to take up nutrients at the margin in excess of the local needs.     

Cloning of B cells from autoimmune MRL-lpr/lpr and MRL.xid mice

The relationship between colony formation (cloning) of B cells and their activation in murine autoimmunity was investigated in MRL-lpr/lpr and MRL.xid mice. Cells from MRL-lpr/lpr mice showed similar requirements for in vitro growth as normal CBA/J and BALB/c cells, with maximal colony formation in the presence of the supporting factors lipopolysaccharide and sheep red blood cells. The frequency of colony-forming cells from MRL-lpr/lpr spleens or hapten-specific B-cell preparations was slightly greater than the two normal control strains, with this difference significant only for a comparison of BALB/c and MRL-lpr/lpr spleens. In contrast, MRL-lpr/lpr mice bearing the xid gene for B-cell immunodeficiency (MRL.xid) had markedly reduced B-cell colony formation. These mice nevertheless expressed anti-DNA antibodies, although at levels reduced from that of MRL-lpr/lpr controls. These results indicate that enhanced in vitro colony formation need not accompany B-cell hyperactivity in murine autoimmune disease and that autoantibody production can occur in mice with impairment in this growth property.     

Density of founder cells affects spatial pattern formation and cooperation in Bacillus subtilis biofilms

In nature, most bacteria live in surface-attached sedentary communities known as biofilms. Biofilms are often studied with respect to bacterial interactions. Many cells inhabiting biofilms are assumed to express ‘cooperative traits'', like the secretion of extracellular polysaccharides (EPS). These traits can enhance biofilm-related properties, such as stress resilience or colony expansion, while being costly to the cells that express them. In well-mixed populations cooperation is difficult to achieve, because non-cooperative individuals can reap the benefits of cooperation without having to pay the costs. The physical process of biofilm growth can, however, result in the spatial segregation of cooperative from non-cooperative individuals. This segregation can prevent non-cooperative cells from exploiting cooperative neighbors. Here we examine the interaction between spatial pattern formation and cooperation in Bacillus subtilis biofilms. We show, experimentally and by mathematical modeling, that the density of cells at the onset of biofilm growth affects pattern formation during biofilm growth. At low initial cell densities, co-cultured strains strongly segregate in space, whereas spatial segregation does not occur at high initial cell densities. As a consequence, EPS-producing cells have a competitive advantage over non-cooperative mutants when biofilms are initiated at a low density of founder cells, whereas EPS-deficient cells have an advantage at high cell densities. These results underline the importance of spatial pattern formation for competition among bacterial strains and the evolution of microbial cooperation.     

Effect of starving and dowex 50 treatment on growth of normal and x-irradiated yeast

1. Effects of starvation or treatment with a cation exchange resin, dowex 50, parallel in some respects those seen earlier on the respiration and fermentation of bakers' yeast receiving 90,000 r of 250 kv. x-rays. Starvation increased the radiosensitivity of cell division processes whether measured by colony formation or by turbidimetric determination of growth in a liquid medium. The dowex 50 enhanced the radiation effect by the latter measure but appeared to increase colony formation of irradiated yeast. 2. The effects on growth differ from those on respiration and fermentation in that the exchange resin treatment did not inhibit colony formation further, and neither starvation nor resin appreciably altered the growth of non-irradiated yeast. 3. Two effects of radiation are seen in these experiments: (a) a permanent inhibition of growth, and (b) a temporary inhibition of the remaining cells resulting in delay of growth. 4. The irradiated cell is more dependent on certain aspects of its environment in terms of growth responses as well as in terms of metabolism (i.e. respiration and fermentation). Whether or not potassium plays a role in the growth response as it does in the metabolic response cannot be ascertained from the present data.     

Variability of polar scurvygrass Cochlearia groenlandica individual traits along a seabird influenced gradient across Spitsbergen tundra

In the resource-limited Arctic environment, vegetation developing near seabird colonies is exceptionally luxuriant. Nevertheless, there are very few detailed quantitative studies of any specific plant species responses to ornithogenic manuring. Therefore, we studied variability of polar scurvygrass Cochlearia groe nlandica individual biomass and leaf width along a seabird influenced gradient determining environmental conditions for vegetation in south-west Spitsbergen. We found seabird colony effect being a paramount factor responsible for augmented growth of C. groenlandica. The species predominated close to the colony and reached the highest mean values of individual biomass (1.4 g) and leaf width (26.6 mm) 10 m below the colony. Its abundance and size declined towards the coast. Both C. groenlandica individual traits significantly decreased with distance from the colony, soil water and organic matter content and increased with guano deposition, soil δ ¹⁵N, conductivity, acidity and nitrate, phosphate and potassium ion content. Our study supports the hypothesis that seabirds have fundamental importance for vegetation growth in poor Arctic environment. Highly plastic species such as C. groenlandica may be a useful instrument in detecting habitat condition changes, for instance resulting from climate change.