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1. A tripartite model system for Southern Ocean diatom-bacterial interactions reveals the coexistence of competing symbiotic strategies

   https://doi.org/10.1038/s43705-022-00181-w  

   Andrew, Sarah ; Wilson, Travis ; Smith, Stephanie ; Marchetti, Adrian ; Septer, Alecia N. ( October 2022 , ISME Communications)

   Southern Ocean (SO) diatoms play an important role in global carbon flux, and their influence on carbon export is directly linked to interactions with epiphytic bacteria. Bacterial symbionts that increase diatom growth promote atmospheric carbon uptake, while bacterial degraders divert diatom biomass into the microbial loop where it can then be released as carbon dioxide through respiration. To further explore SO diatom-bacterial associations, a natural model system is needed that is representative of these diverse and important interactions. Here, we use concurrent cultivation to isolate a species of the ecologically-important SO diatom,Pseudo-nitzschia subcurvata, and its co-occurring bacteria. Although vitamin-depleted, axenicPseudo-nitzschiagrew poorly in culture, addition of a co-isolated Roseobacter promoted diatom growth, while addition of a co-isolated Flavobacterium negatively impacted diatom growth. Microscopy revealed both bacterial isolates are physically associated with diatom cells and genome sequencing identified important predicted functions including vitamin synthesis, motility, cell attachment mechanisms, and diverse antimicrobial weapons that could be used for interbacterial competition. These findings revealed the natural coexistence of competing symbiotic strategies of diatom-associated bacteria in the SO, and the utility of this tripartite system, composed of a diatom and two bacterial strains, as a co-culture model to probe ecological-relevant interactions between diatoms andmore »the bacteria that compete for access to the phycosphere.

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2. Visible Light-Activated Carbon Dots for Inhibiting Biofilm Formation and Inactivating Biofilm-Associated Bacterial Cells

   https://doi.org/10.3389/fbioe.2021.786077  

   Dong, Xiuli ; Overton, Christopher M. ; Tang, Yongan ; Darby, Jasmine P. ; Sun, Ya-Ping ; Yang, Liju ( November 2021 , Frontiers in Bioengineering and Biotechnology)

   This study aimed to address the significant problems of bacterial biofilms found in medical fields and many industries. It explores the potential of classic photoactive carbon dots (CDots), with 2,2′-(ethylenedioxy)bis (ethylamine) (EDA) for dot surface functionalization (thus, EDA-CDots) for their inhibitory effect on B. subtilis biofilm formation and the inactivation of B. subtilis cells within established biofilm. The EDA-CDots were synthesized by chemical functionalization of selected small carbon nanoparticles with EDA molecules in amidation reactions. The inhibitory efficacy of CDots with visible light against biofilm formation was dependent significantly on the time point when CDots were added; the earlier the CDots were added, the better the inhibitory effect on the biofilm formation. The evaluation of antibacterial action of light-activated EDA-CDots against planktonic B. subtilis cells versus the cells in biofilm indicate that CDots are highly effective for inactivating planktonic cells but barely inactivate cells in established biofilms. However, when coupling with chelating agents (e.g., EDTA) to target the biofilm architecture by breaking or weakening the EPS protection, much enhanced photoinactivation of biofilm-associated cells by CDots was achieved. The study demonstrates the potential of CDots to prevent the initiation of biofilm formation and to inhibit biofilm growth at an early stage.more »Strategic combination treatment could enhance the effectiveness of photoinactivation by CDots to biofilm-associated cells.« less
3. Carbon dots for highly effective photodynamic inactivation of multidrug-resistant bacteria

   https://doi.org/10.1039/D0MA00078G  

   Abu Rabe, Dina I. ; Mohammed, Oluwayemisi O. ; Dong, Xiuli ; Patel, Amankumar K. ; Overton, Christopher M. ; Tang, Yongan ; Kathariou, Sophia ; Sun, Ya-Ping ; Yang, Liju ( January 2020 , Materials Advances)

   For addressing the ever increasing challenge of multidrug-resistant (MDR) bacterial infections, specifically designed and prepared carbon dots (CDots) of small carbon nanoparticles with surface functionalization–passivation by oligomeric polyethylenimine were found to be readily activated by visible light to effectively and efficiently inactivate MDR bacterial strains. The inactivation was evaluated under various combinations of experimental conditions (dot concentrations, light intensities, and treatment times), with the results collectively suggesting CDots as a new class of promising agents for combating MDR bacteria. Mechanistic origins and implications of the observed strong antibacterial actions as relevant to the photoexcited state processes in CDots and the photodynamically induced cellular damages leading to the death of the bacterial cells were explored, with the results discussed.
4. Carbon dot incorporated multi-walled carbon nanotube coated filters for bacterial removal and inactivation

   https://doi.org/10.1039/c8ra00333e  

   Dong, Xiuli ; Al Awak, Mohamad ; Wang, Ping ; Sun, Ya-Ping ; Yang, Liju ( January 2018 , RSC Advances)

   Multi-walled carbon nanotube (MWCNT) filters incorporated with carbon quantum dots (CDots) or single-walled carbon nanotubes (SWCNTs) were produced for bacteria removal from aqueous solutions and also for inactivating the captured bacteria. TMTP Millipore membranes were used as the base of these filters. The results showed that filters with higher MWCNT loading had higher bacterial removal efficiencies. Filters with a MWCNT loading of 4.5 mg were highly effective at removing bacteria from aqueous solution, resulting in a log reduction of 6.41, 6.41, and 5.41 of E. coli cell numbers in filtrates compared to MWCNT filters without coating, MWCNTs filters with 0.15 mg CDot coating, and MWCNTs filters with 0.15 mg SWCNT coating, respectively. Ionic strength played an important role in bacteria removal. A higher NaCl concentration resulted in higher bacteria removal efficiencies of the filters. Both CDot coatings and SWCNT coatings did not significantly affect the MWCNT filter effects ( P > 0.05). The coatings, especially CDot coatings, significantly inhibited the activities of bacteria retained on the filter surfaces ( P < 0.05). The inhibitory rates were 94.21% or 73.17% on the MWCNT filter surfaces coated with 0.2 mg CDots or SWCNTs, respectively. These results demonstrated that MWCNT filters with CDotmore »coatings were highly effective to remove bacteria from water and to inhibit the activities of the captured bacteria on filter surfaces.« less
5. Porous marine snow differentially benefits chemotactic, motile, and nonmotile bacteria

   https://doi.org/10.1093/pnasnexus/pgac311  

   Borer, Benedict ; Zhang, Irene H ; Baker, Amy E ; O'Toole, George A ; Babbin, Andrew R ( February 2023 , PNAS Nexus)

   Dupont, Christopher (Ed.)

   Abstract Particulate organic carbon settling through the marine water column is a key process that regulates the global climate by sequestering atmospheric carbon. The initial colonization of marine particles by heterotrophic bacteria represents the first step in recycling this carbon back to inorganic constituents—setting the magnitude of vertical carbon transport to the abyss. Here, we demonstrate experimentally using millifluidic devices that, although bacterial motility is essential for effective colonization of a particle leaking organic nutrients into the water column, chemotaxis specifically benefits at intermediate and higher settling velocities to navigate the particle boundary layer during the brief window of opportunity provided by a passing particle. We develop an individual-based model that simulates the encounter and attachment of bacterial cells with leaking marine particles to systematically evaluate the role of different parameters associated with bacterial run-and-tumble motility. We further use this model to explore the role of particle microstructure on the colonization efficiency of bacteria with different motility traits. We find that the porous microstructure facilitates additional colonization by chemotactic and motile bacteria, and fundamentally alters the way nonmotile cells interact with particles due to streamlines intersecting with the particle surface.