Biology subjects

Bakhtiari, L.

Publications and source records attributed to Bakhtiari, L..

3 recordsLinked to original sources

bioRxiv2019

Assaying how the success of phagocytosis depends on the mechanics of a large viscoelastic target

The state of the art does not provide a method for determining how the success of phagocytosis depends on the mechanics of a target that is much larger than the phagocytosing cell. We have developed such a method. We vary the elastic moduli of millimeter-sized abiotic gels that contain fluorescent beads to act as tracers for phagocytosis. We isolate human neutrophils, expose them to gels for one hour, and then measure what percentage of neutrophils contain beads - this is our metric for successful phagocytosis. Both increased polymer concentration in agarose gels and increased crosslinking density in alginate gels are associated with decreased success of phagocytosis. When we plot the percentage of neutrophils containing beads as a function of the gel elastic modulus, we find that data from both alginate and agarose gels collapse onto the same curve. This demonstrates the utility of our method as a way of measuring how the viscoelastic mechanics of a large target impact the success of phagocytosis.

biophysics↗

bioRxiv2018

Increased production of the extracellular polysaccharide Psl can give a growth advantage to Pseudomonas aeruginosa in low-iron conditions

In infections, biofilm formation is associated with a number of fitness advantages, such as resistance to antibiotics and to clearance by the immune system. Biofilm formation has also been linked to fitness advantages in environments other than in vivo infections; primarily, biofilms are thought to help constituent organisms evade predation and to promote intercellular signaling. The opportunistic human pathogen Pseudomonas aeruginosa forms biofilm infections in lungs, wounds, and on implants and medical devices. However, the tendency toward biofilm formation originated in this bacteriums native environment, primarily plants and soil. Such environments are polymicrobial and often resource-limited. Other researchers have recently shown that the P. aeruginosa extracellular polysaccharide Psl can bind iron. For the lab strain PA01, Psl is also the dominant adhesive and cohesive \"glue\" holding together multicellular aggregates and biofilms. Here, we perform quantitative time-lapse confocal microscopy and image analysis of early biofilm growth by PA01. We find that aggregates of P. aeruginosa have a growth advantage over single cells of P. aeruginosa in the presence of Staphylococcus aureus in low-iron environments. Our results suggest the growth advantage of aggregates is linked to their high Psl content and to the production of an active factor by S. aureus. We posit that the ability of Psl to promote iron acquisition may have been linked to the evolutionary development of the strong biofilm-forming tendencies of P. aeruginosa.

microbiology↗

bioRxiv2018

Temporal and spatial factors that influence magnetotaxis in C. elegans

Many animals can orient using the earths magnetic field. In a recent study, we performed three distinct behavioral assays providing evidence that the nematode Caenorhabditis elegans orients to earth-strength magnetic fields (Vidal-Gadea et al., 2015). In addition to these behavioral assays, we found that magnetic orientation in C. elegans depends on the AFD sensory neurons and conducted subsequent physiological experiments showing that AFD neurons respond to earth-strength magnetic fields. A new behavioral study by Landler et al. (2017) suggested that C. elegans does not orient to magnetic fields and raises issues that cast doubt on our study. Here we reanalyze Lander et al.s data to show how they appear to have missed observing positive results, and we highlight differences in experimental methods and interpretations that may explain our different results and conclusions. Moreover, we present new data from our labs together with replication by an independent lab to show how temporal and spatial factors influence the unique spatiotemporal trajectory that worms make during magnetotaxis. Together, these findings provide guidance on how to achieve robust magnetotaxis and reinforce our original finding that C. elegans is a suitable model system to study magnetoreception.

neuroscience↗