Methods and measures for investigating microscale motility

Motility is an essential factor for an organism's survival and diversification. With the advent of novel single-cell technologies, analytical frameworks and theoretical methods, we can begin to probe the complex lives of microscopic motile organisms and answer the intertwining biological and physical questions of how these diverse lifeforms navigate their surroundings. Herein, we give an overview of different experimental, analytical, and mathematical methods used to study a suite of microscale motility mechanisms across different scales encompassing molecular-, individual- to population-level. We identify transferable techniques, pressing challenges, and future directions in the field. This review can serve as a starting point for researchers who are interested in exploring and quantifying the movements of organisms in the microscale world.Comment: 24 pages, 2 figure

Biological system development for GraviSat: A new platform for studying photosynthesis and microalgae in space

Microalgae have great potential to be used as part of a regenerative life support system and to facilitate in-situ resource utilization (ISRU) on long-duration human space missions. Little is currently known, however, about microalgal responses to the space environment over long (months) or even short (hours to days) time scales. We describe here the development of biological support subsystems for a prototype “3U” (i.e., three conjoined 10-cm cubes) nanosatellite, called GraviSat, designed to experimentally elucidate the effects of space microgravity and the radiation environment on microalgae and other microorganisms. The GraviSat project comprises the co-development of biological handling-and-support technologies with implementation of integrated measurement hardware for photosynthetic efficiency and physiological activity in support of long-duration (3–12 months) space missions. It supports sample replication in a fully autonomous system that will grow and analyze microalgal cultures in 120μL wells around the circumference of a microfluidic polymer disc; the cultures will be launched while in stasis, then grown in orbit. The disc spins at different rotational velocities to generate a range of artificial gravity levels in space, from microgravity to multiples of Earth gravity. Development of the biological support technologies for GraviSat comprised the screening of more than twenty microalgal strains for various physical, metabolic and biochemical attributes that support prolonged growth in a microfluidic disc, as well as the capacity for reversible metabolic stasis. Hardware development included that necessary to facilitate accurate and precise measurements of physical parameters by optical methods (pulse amplitude modulated fluorometry) and electrochemical sensors (ion-sensitive microelectrodes). Nearly all microalgal strains were biocompatible with nanosatellite materials; however, microalgal growth was rapidly inhibited (~1 week) within sealed microwells that did not include dissolved bicarbonate due to CO2 starvation. Additionally, oxygen production by some microalgae resulted in bubble formation within the wells, which interfered with sensor measurements. Our research achieved prolonged growth periods (\u3e10months) without excess oxygen production using two microalgal strains, Chlorella vulgaris UTEX 29 and Dunaliella bardawil 30.861, by lowering light intensities (2–10μmol photons m−2s−1) and temperature (4–12˚C). Although the experiments described here were performed to develop the GraviSat platform, the results of this study should be useful for the incorporation of microalgae in other satellite payloads with low-volume microfluidic systems

Structural mechanics and collective self-organisation in filamentous cyanobacteria

Filamentous cyanobacteria, one of the earliest types of organisms to have evolved on Earth, are photoautotrophs made of single cells joined together in long filaments. They are ubiquitous, living in water, soil, rocks and extreme environments like hot springs. Their oxygen production is believed to have led to the evolution of oxygen-dependent organisms like us. They live in colonies forming biomats, and are associated with stromatolites, which are important for understanding the evolution of early life. Commercially, filamentous cyanobacteria are used for biofuel production, food supplements, cosmetics and medicines. In order to maximise the usage of these microorganisms, we must understand how individual filaments interact and form collective structures. This thesis, therefore, focuses on quantifying the mechanical properties and collective organisation of filamentous cyanobacteria. First, the structural and mechanical properties of the filaments, such as the bending stiffness, are quantified. The mechanical properties are linked to their shapes, to predict the magnitude of internally generated active forces. These results can be used to model cyanobacteria motion and self-organisation. Next, this thesis looks at the behaviour of filaments in isolation and when interacting with other filaments or walls. These results provide parameters such as filament speed, angular drift and curvature that are then used by collaborators for modelling and predicting the collective behaviour of the cyanobacteria. The last part of this thesis provides experimental evidence of how self-organisation occurs for filamentous cyanobacteria in an open space and in confinement. A density-dependent phase transition was found, between disordered and nematically ordered patterns of filamentous cyanobacteria. Finally, in confinement studies, it was observed that certain chamber geometries, e.g. circular, promote unequal filament distribution. The results here are applicable in areas such as the study of stromatolites and the evolution of early life, and in the production of algae-based biofuels

Strategies to enhance extracellular electron transfer rates in wild-type cyanobacterium Synechococcus elongatus PCC7942 for photo-bioelectricity generation

The aim of this thesis is to enhance the extracellular electron transfer rates (exoelectrogenesis) in cyanobacteria, to be utilised for photo-bioelectricity generation in biophotovoltaics (electrochemical cell). An initial cross comparison of the cyanobacterium Synechococcus elongatus PCC7942 against other exoelectrogenic cultures showed a hindered exoelectrogenic capacity. Nonetheless, in mediatorless biophotovoltaics, it outperformed the microalgae Chlorella vulgaris. Furthermore, the performance of S. elongatus PCC7942 was improved by constructing a more efficient design (lower internal resistance), which was fabricated with carbon fibres and nitrocellulose membrane, both inexpensive materials. To strategically obtain higher exoelectrogenic rates, S. elongatus PCC7942 was conditioned by iron limitation and CO2 enrichment. Both strategies are novel in improving cyanobacteria exoelectrogenesis. Iron limitation induced unprecedented rates of extracellular ferricyanide reduction (24-fold), with the reaction occurring favourably around neutral pH, different to the cultural alkaline pH. Iron limited cultures grown in 5% and 20% CO2 showed increased exoelectrogenic rates in an earlier stage of growth in comparison to air grown cultures. Conveniently, the cultural pH under enriched CO2 was around neutral pH. Enhanced photo-bioelectricity generation in ferricyanide mediated biophotovoltaics was demonstrated. Power generation was six times higher with iron limited cultures at neutral pH than with iron sufficient cultures at alkaline pH. The enhanced performance was also observed in mediatorless biophotovoltaics, especially in the dark phase. Exoelectrogenesis was mainly driven by photosynthetic activity. However, rates in the dark were also improved and in the long term it appeared that the exoelectrogenic activity under illumination tended to that seen in the dark. Proteins participating in iron uptake by an alleged reductive mechanism were overexpressed (2-fold). However, oxidoreductases in the outer membrane remain to be identified. Furthermore, electroactive regions in biofilms of S. elongatus PCC7942 were established using cyclic voltammetry. Double step potential chronoamperometry was also successfully tested in the biofilms. Thus, the electrochemical characterisation of S. elongatus PCC7942 was demonstrated, implying that the strategies presented in this thesis could be used to screen for cyanobacteria and/or electrode materials to further develop systems for photo-bioelectricity generation.Becas Chile Conicyt - Cambridge Trus

Polymer Micro Photosynthetic Power Cell: Design, Fabrication, Parametric Study and Testing

Polymer Micro Photosynthetic Power Cell: Design, Fabrication, Parametric Study and Testing Energy and its importance are undoubtedly some unquestionable topics of all times. Not only the environmental impact of our main energy source – fossil fuels – but also their limited quantity made the human-kind find alternate sources of energy. Moreover, in the recent years there has been lots of attention on green energy. The challenge however, is finding suitable energy sources and developing appropriate energy harvesting devices. Photosynthesis is among the most frequent and vital processes occurring all over the planet and recently, it has been found to be a potential promising energy source. The challenge still remains developing an appropriate energy harvesting device. Micro Electro Mechanical Systems (MEMS) enables fabrication of devices that the human-kind was not able to produce before. So far there has been a vast research and investment on solar cells and fuel cells. However, the potential energy source mentioned earlier (photosynthesis) has not received as much attention. This work is an attempt to develop a device capable of harvesting energy from photosynthesis using nontraditional materials and processes used in MEMS. A Micro Photosynthetic Power Cell (μPSC) was fabricated and tested for performance. Then, using no-load performance optimal fabrication parameters were suggested. Some environmental and operational parameters were studied and properties such as voltage-current characteristics and long-term behavior were studied. The results and outputs of the μPSC developed in this study were presented in forms of power and current densities for comparison purposes and eventually, some points were suggested for future studies. Open circuit voltage of more than 900 mV was measured. The measured current varied from zero (open circuit) to 840 μA (short circuit). At the peak power generation of 175 μW, approximate voltage and current correspond to 400 mV and 400 μA. These results correspond to a noticeable power generation of 36.1 μW/cm2 which is comparable to that of μPSCs fabricated previously by other groups

Solar Power

A wide variety of detail regarding genuine and proprietary research from distinguished authors is presented, ranging from new means of evaluation of the local solar irradiance to the manufacturing technology of photovoltaic cells. Also included is the topic of biotechnology based on solar energy and electricity generation onboard space vehicles in an optimised manner with possible transfer to the Earth. The graphical material supports the presentation, transforming the reading into a pleasant and instructive labor for any interested specialist or student

Second Symposium on Chemical Evolution and the Origin of Life

Recent findings by NASA Exobiology investigators are reported. Scientific papers are presented in the following areas: cosmic evolution of biogenic compounds, prebiotic evolution (planetary and molecular), early evolution of life (biological and geochemical), evolution of advanced life, solar system exploration, and the Search for Extraterrestrial Intelligence (SETI)