Clostridium pasteurianum ATCC 6013 achieves high n-butanol production when glycerol is used as the sole carbon source. In this study, the homeoviscous membrane response of C. pasteurianum ATCC 6013 has been examined through n-butanol challenge experiments. Homeoviscous response is a critical aspect of n-butanol tolerance and has not been examined in detail for C. pasteurianum. Lipid membrane compositions were examined for glycerol fermentations with n-butanol production, and during cell growth in the absence of n-butanol production, using gas chromatography-mass spectrometry (GC-MS) and proton nuclear magnetic resonance ((1)H-NMR). Membrane stabilization due to homeoviscous response was further examined by surface pressure-area (π-A) analysis of membrane extract monolayers. C. pasteurianum was found to exert a homeoviscous response that was comprised of an increase lipid tail length and a decrease in the percentage of unsaturated fatty acids with increasing n-butanol challenge. This led to a more rigid or stable membrane that counteracted n-butanol fluidization. This is the first report on the changes in the membrane lipid composition during n-butanol production by C. pasteurianum ATCC 6013, which is a versatile microorganism that has the potential to be engineered as an industrial n-butanol producer using crude glycerol.
Studies indicate a crucial cell membrane role in the
antibiotic
resistance of Staphylococcus aureus. To simulate its membrane structure and dynamics, a complex molecular-scale
computational representation of the S. aureus lipid bilayer was developed. Phospholipid types and their amounts
were optimized by reverse Monte Carlo to represent characterization
data from the literature, leading to 19 different phospholipid types
that combine three headgroups [phosphatidylglycerol, lysyl-phosphatidylglycerol
(LPG), and cardiolipin] and 10 tails, including iso- and anteiso-branched
saturated chains. The averaged lipid bilayer thickness was 36.7 Å,
and area per headgroup was 67.8 Å2. Phosphorus and
nitrogen density profiles showed that LPG headgroups tended to be
bent and oriented more parallel to the bilayer plane. The water density
profile showed that small amounts reached the membrane center. Carbon
density profiles indicated hydrophobic interactions for all lipids
in the middle of the bilayer. Bond vector order parameters along each
tail demonstrated different C–H ordering even within distinct
lipids of the same type; however, all tails followed similar trends
in average order parameter. These complex simulations further revealed
bilayer insights beyond those attainable with monodisperse, unbranched
lipids. Longer tails often extended into the opposite leaflet. Carbon
at and beyond a branch showed significantly decreased ordering compared
to carbon in unbranched tails; this feature arose in every branched
lipid. Diverse tail lengths distributed these disordered methyl groups
throughout the middle third of the bilayer. Distributions in mobility
and ordering reveal diverse properties that cannot be obtained with
monodisperse lipids.
Type I, bovine skin collagen was allowed to gel in the presence of various concentrations of a carbon nanotube material covered with a polystyrene/polyaniline copolymer, called a carbon nanobrush, CNB. The rate of collagen gelation was enhanced by the presence of the CNB in a dose dependent manner. The extent of collagen gelation was due to the concentration of collagen and not the amount of CNB. Collagen D-periodicity, and average fibril diameter were unchanged by the CNB material as seen in transmission electron micrographs. Gel tensile strength was reduced by the presence of the the CNB in a dose related manner. The collagen-CNB mixture may have a role in the repair and reconstruction of wounds or degenerated connective tissue.
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