Time-series lipidomic analysis of the oleaginous green microalga species Ettlia oleoabundans under nutrient stress.

BACKGROUND: Microalgae are uniquely advantageous organisms cultured and harvested for several value-added biochemicals. A majority of these compounds are lipid-based, such as triacylglycerols (TAGs), which can be used for biofuel production, and their accumulation is most affected under nutrient stress conditions. As such, the balance between cellular homeostasis and lipid metabolism becomes more intricate to achieve efficiency in bioproduct synthesis. Lipidomics studies in microalgae are of great importance as biochemical diversity also plays a major role in lipid regulation among oleaginous species. METHODS: The aim of this study was to analyze time-series changes in lipid families produced by microalga under different nutrient conditions and growth phases to gain comprehensive information at the cellular level. For this purpose, we worked with a highly adaptable, oleaginous, non-model green microalga species, Ettlia oleoabundans (a.k.a. Neochloris oleoabundans). Using a mass spectrometry-based untargeted and targeted metabolomics' approach, we analyzed the changes in major lipid families under both replete and deplete nitrogen and phosphorus conditions at four different time points covering exponential and stationary growth phases. RESULTS: Comprehensive analysis of the lipid metabolism highlighted the accumulation of TAGs, which can be utilized for the production of biodiesel via transesterification, and depletion of chlorophylls and certain structural lipids required for photosynthesis, under nutrient deprived conditions. We also found a correlation between the depletion of digalactosyldiacylglycerols (DGDGs) and sulfoquinovosyldiacylglycerols (SQDGs) under nutrient deprivation. CONCLUSIONS: High accumulation of TAGs under nutrient limitation as well as a depletion of other lipids of interest such as phosphatidylglycerols (PGs), DGDGs, SQDGs, and chlorophylls seem to be interconnected and related to the microalgal photosynthetic efficiency. Overall, our results provided key biochemical information on the lipid regulation and physiology of a non-model green microalga, along with optimization potential for biodiesel and other value-added product synthesis.

Identifying the role of flagella in the transport of motile and nonmotile Salmonella enterica serovars.

The influence of bacterial flagella on cell transport has been examined using three Salmonella enterica serovars with different motility phenotypes. Both a packed bed (PB) column and radial stagnation point flow system (RSPF) were employed to investigate bacterial deposition kinetics onto quartz over a range of conditions. The aim of this study was to better understand the role of motility on the deposition behavior of Salmonella, an important food- and waterborne pathogen. In both the PB column and RSPF systems, flagellated strains showed higher deposition, indicating the nonmotile cells can be transported further than the motile. At late-exponential growth phase, the deposition of the functional flagellated motile strain was enhanced, much more so than the dysfunctionally flagellated nonmotile and nonflagellated strains, highlighting the role of flagellar motion in cellular deposition and retention through available pore spaces and irregularities on quartz surfaces.

Relative transport behavior of Escherichia coli O157:H7 and Salmonella enterica serovar pullorum in packed bed column systems: influence of solution chemistry and cell concentration.

The influence of solution chemistry and cell concentration on bacterial transport has been examined using Salmonella pullorum SA1685 and Escherichia coli O157:H7. A column was employed to determine the transport behavior and deposition kinetics with aquifer sand over a range of ionic strengths and cell concentrations. O157:H7 was found to be more adhesive than SA1685, with calculated deposition rate coefficients higher than those of SA1685. Comprehensive cell surface characterization techniques including size, surface charge density, extracellular polymeric substance content, electrophoretic mobility, and hydrophobicity analyses were conducted to explain observed transporttrends. The pathogens' size and hydrophobicity were not significantly different, whereas they varied in acidity, for which O157:H7 had 19 times higher surface charge density than SA1685. Electrophoretic mobilities, in general agreement with titration analysis and column experiments, revealed SA1685 to be more negative than O157:H7. This combination of column and characterization experiments indicates that SA1685 can be transported to a greater extent than O157:H7 in groundwater environments. This study is the first comprehensive work comparing the transport behavior of two important pathogens in aquifer systems.

Diversity in cell properties and transport behavior among 12 different environmental Escherichia coli isolates.

Escherichia coli is a commonly used indicator organism for detecting the presence of fecal-borne pathogenic microorganisms in water supplies. The importance of E. coli as an indicator organism has led to numerous studies looking at cell properties and transport behavior of this microorganism. In many of these studies, however, only a single strain of E. coli was used even though research has shown that significant genetic variability exists among different strains of E. coli. If this genetic diversity results in differences in cell properties that affect transport, different strains of E. coli may exhibit different rates of transport in the environment. Therefore, the objectives of our study were to investigate the variability in surface characteristics and transport behavior of E. coli isolates obtained from six different sources: beef cattle, dairy cattle, horse, human, poultry, and wildlife. Cell properties such as electrophoretic mobility, cell size and shape, hydrophobicity, charge density, and extracellular polymeric substance composition were measured for each isolate. In addition, the transport behavior of each isolate was assessed by measuring transport through 10-cm packed beds of clean quartz sand. Our results show a large diversity in cell properties and transport behavior for the different E. coli isolates. This diversity in transport behavior must be taken into account when making assessments of the suitability of using E. coli as an indicator organism for specific pathogenic microorganisms in groundwater environments as well as modeling the movement of E. coli in the subsurface.

The transport of Mycobacterium avium subsp. paratuberculosis through saturated aquifer materials.

AIMS: To investigate the processes controlling the transport of Mycobacterium avium subsp. paratuberculosis (Map) through aquifer materials. METHODS AND RESULTS: We measured two important surface characteristics known to affect bacterial attachment to sediment surfaces: surface charge and hydrophobicity. We then measured the transport of Map through laboratory columns packed with aquifer sand with varying ionic strength solutions and sediment surface charge. We found that Map has a strong negative charge and is highly hydrophobic and that the transport of Map through positively charged Fe-coated sands was reduced compared with transport through negatively charged clean quartz sand, although Map transport for all treatments was low compared with the transport behaviour reported in the literature for other bacteria. CONCLUSIONS: Our results suggest that the potential for groundwater contamination by Map is low; however, the organism may remain bound to the soil near the surface where it can be ingested by grazing animals or be released during run off events. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first study looking at the surface characteristics and transport behaviour of Map through aquifer materials and therefore provides important information for understanding the movement of Map in the environment.

The role of starvation on Escherichia coli adhesion and transport in saturated porous media.

The influence of bacterial starvation on cell transport has been examined using two Escherichia coli isolates: one from human (HU) and one from dairy cattle (DC). To better understand the fate of starved bacteria, experiments were conducted in a packed bed column using cells that had been incubating at room temperature without nutrients for 6, 12, and 18h, as well as cells, which had not been starved (referred to as time zero). Complimentary cell characterization techniques were conducted to evaluate the hydrophobicity, mobility, size, and surface charge density of the cells at the conditions considered. It was observed that non-starved HU cells were more adhesive than starved HU cells. This behavior is attributed to the relatively high hydrophobicity of the starved cells, which resulted from greater extracellular polymeric substance (EPS) presence. Non-starved DC cells were also the most adhesive whereas 18h starved cells were the least adhesive, although cell characterization results did not correlate to transport trends like HU cells. For both isolates, the cells after 6h of starvation showed high levels of sugar relative to protein in the EPS. Additionally, following 6h of starvation, the cells did not follow expected transport trends as anticipated from the cellular characterization. Our results suggest transport behavior of environmental E. coli isolates differs in terms of isolate host and starvation conditions. Possible mechanisms responsible for this are changes in key cell surface characteristics and synthesis of starvation-induced proteins. This study highlights the importance of consistency in bacterial preparation for experimental studies and has considerable implications for future evaluation and prediction of E. coli fate in subsurface environments.