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1. Bacterial multispecies interaction mechanisms dictate biogeographic arrangement between the oral commensals Corynebacterium matruchotii and Streptococcus mitis

   https://doi.org/10.1128/msystems.00115-23  

   Almeida, Eric ; Puri, Surendra ; Labossiere, Alex ; Elangovan, Subashini ; Kim, Jiyeon ; Ramsey, Matthew ( October 2023 , mSystems)

   Traxler, Matthew F. (Ed.)

   Polymicrobial biofilms are present in many environments particularly in the human oral cavity where they can prevent or facilitate the onset of disease. While recent advances have provided a clear picture of both the constituents and their biogeographic arrangement, it is still unclear what mechanisms of interaction occur between individual species in close proximity within these communities. In this study, we investigated two mechanisms of interaction between the highly abundant supragingival plaque (SUPP) commensalCorynebacterium matruchotiiandStreptococcus mitiswhich are directly adjacent/attachedin vivo. We discovered thatC. matruchotiienhanced the fitness of streptococci dependent on its ability to detoxify streptococcal-produced hydrogen peroxide and its ability to oxidize lactate also produced by streptococci. We demonstrate that the fitness of adjacent streptococci was linked to that ofC. matruchotiiand that these mechanisms support the previously described “corncob” arrangement between these species but that this is favorable only in aerobic conditions. Furthermore, we utilized scanning electrochemical microscopy to quantify lactate production and consumption between individual bacterial cells for the first time, revealing that lactate oxidation provides a fitness benefit toS. mitisnot due to pH mitigation. This study describes mechanistic interactions between two highly abundant human commensals that can explain their observedin vivospatial arrangements and suggest a way by which they may help preserve a healthy oral bacterial community.

   As the microbiome era matures, the need for mechanistic interaction data between species is crucial to understand how stable microbiomes are preserved, especially in healthy conditions where the microbiota could help resist opportunistic or exogenous pathogens. Here we reveal multiple mechanisms of interaction between two commensals that dictate their biogeographic relationship to each other in previously described structures in human supragingival plaque. Using a novel variation for chemical detection, we observed metabolite exchange between individual bacterial cells in real time validating the ability of these organisms to carry out metabolic crossfeeding at distal and temporal scales observedin vivo. These findings reveal one way by which these interactions are both favorable to the interacting commensals and potentially the host.

    

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2. Cytochemical Localization of Polyphenol Oxidase Activity in K2‐Bodies of Saprolegnia ferax Secondary Zoospores

   https://doi.org/10.1111/jeu.12682  

   Lehnen, Jr, Larry P. ; Powell, Martha J. ; Letcher, Peter M. ( August 2018 , Journal of Eukaryotic Microbiology)

   Zoospores of the oomyceteSaprolegnia feraxrelease adhesive material from K‐bodies at the onset of attachment to substrates. To understand more fully how K‐bodies function in adhesion, enzyme activity was investigated cytochemically in secondary zoospores. Presence of catalase, a marker enzyme for microbodies, was explored in the diaminobenzidine (DAB) reaction. Although pH 9.2 DAB‐staining characteristic of catalase activity was detected in the granular matrix regions of K‐bodies, reaction controls indicated that the reaction was due to oxidative enzyme activity other than catalase. Because polyphenol oxidase (PPO) is another metal‐containing enzyme capable of oxidizing DAB, activity of this enzyme was tested with a more specific substrate, dihydroxyphenylalanine (DOPA). In the DOPA procedure, reaction product was exclusively localized within K‐bodies, indicating the presence of PPO. Results with three methods of reaction controls (elimination of substrate, addition of a PPO enzyme inhibitor, and heat‐inactivation of enzymes) all supported the presence of PPO in K‐bodies. This study highlights potential roles for K‐body PPO in stabilization of adhesion bodies by: cross‐linking matrix phenolic proteins or glycoproteins as K‐bodies discharge adhesives onto substrates, or polymerizing phenolics protective against microbial attacks of the adhesion pad.

    

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3. Hydrogen peroxide disproportionation with manganese macrocyclic complexes of cyclen and pyclen

   https://doi.org/10.1039/c9qi01509d  

   Freire, David M. ; Beeri, Debora ; Pota, Kristof ; Johnston, Hannah M. ; Palacios, Philip ; Pierce, Brad S. ; Sherman, Benjamin D. ; Green, Kayla N. ( March 2020 , Inorganic Chemistry Frontiers)

   null (Ed.)

   The catalase family of enzymes, which include a variety with a binuclear manganese active site, mitigate the risk from reactive oxygen species by facilitating the disproportionation of hydrogen peroxide into molecular oxygen and water. In this work, hydrogen peroxide disproportionation using complexes formed between manganese and cyclen or pyclen were investigated due to the spectroscopic similarities with the native MnCAT enzyme. Potentiometric titrations were used to construct speciation diagrams that identify the manganese complex compositions at different pH values. Each complex behaves as a functional mimic of catalase enzymes. UV-visible spectroscopic investigations of the H 2 O 2 decomposition reaction yielded information about the structure of the initial catalyst and intermediates that include monomeric and dimeric species. The results indicate that rigidity imparted by the pyridine ring of pyclen is a key factor in increased TON and TOF values measured compared to cyclen. 

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4. Manganese transporters regulate the resumption of replication in hydrogen peroxide-stressed Escherichia coli

   https://doi.org/10.1007/s10534-023-00523-8  

   Wang, Natalie E. ; Courcelle, Eleanor J. ; Coltman, Samantha M. ; Spolek, Raymond L. ; Courcelle, Justin ; Courcelle, Charmain T. ( July 2023 , BioMetals)

   Following hydrogen peroxide treatment, ferrous iron (Fe2+) is oxidized to its ferric form (Fe3+), stripping it from and inactivating iron-containing proteins. Many mononuclear iron enzymes can be remetallated by manganese to restore function, while other enzymes specifically utilize manganese as a cofactor, having redundant activities that compensate for iron-depleted counterparts. DNA replication relies on one or more iron-dependent protein(s) as synthesis abates in the presence of hydrogen peroxide and requires manganese in the medium to resume. Here, we show that manganese transporters regulate the ability to resume replication following oxidative challenge in Escherichia coli. The absence of the primary manganese importer, MntH, impairs the ability to resume replication; whereas deleting the manganese exporter, MntP, or transporter regulator, MntR, dramatically increases the rate of recovery. Unregulated manganese import promoted recovery even in the absence of Fur, which maintains iron homeostasis. Similarly, replication was not restored in oxyR mutants, which cannot upregulate manganese import following hydrogen peroxide stress. Taken together, the results define a central role for manganese transport in restoring replication following oxidative stress. 

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5. Catalase protects against nonenzymatic decarboxylations during photorespiration in Arabidopsis thaliana

   https://doi.org/10.1002/pld3.366  

   Bao, Han ; Morency, Matt ; Rianti, Winda ; Saeheng, Sompop ; Roje, Sanja ; Weber, Andreas P. M. ; Walker, Berkley James ( December 2021 , Plant Direct)

   Photorespiration recovers carbon that would be otherwise lost following the oxygenation reaction of rubisco and production of glycolate. Photorespiration is essential in plants and recycles glycolate into usable metabolic products through reactions spanning the chloroplast, mitochondrion, and peroxisome. Catalase in peroxisomes plays an important role in this process by disproportionating H₂O₂resulting from glycolate oxidation into O₂and water. We hypothesize that catalase in the peroxisome also protects against nonenzymatic decarboxylations between hydrogen peroxide and photorespiratory intermediates (glyoxylate and/or hydroxypyruvate). We test this hypothesis by detailed gas exchange and biochemical analysis ofArabidopsis thalianamutants lacking peroxisomal catalase. Our results strongly support this hypothesis, with catalase mutants showing gas exchange evidence for an increased stoichiometry of CO₂release from photorespiration, specifically an increase in the CO₂compensation point, a photorespiratory‐dependent decrease in the quantum efficiency of CO₂assimilation, increase in the¹²CO₂released in a¹³CO₂background, and an increase in the postillumination CO₂burst. Further metabolic evidence suggests this excess CO₂release occurred via the nonenzymatic decarboxylation of hydroxypyruvate. Specifically, the catalase mutant showed an accumulation of photorespiratory intermediates during a transient increase in rubisco oxygenation consistent with this hypothesis. Additionally, end products of alternative hypotheses explaining this excess release were similar between wild type and catalase mutants. Furthermore, the calculated rate of hydroxypyruvate decarboxylation in catalase mutant is much higher than that of glyoxylate decarboxylation. This work provides evidence that these nonenzymatic decarboxylation reactions, predominately hydroxypyruvate decarboxylation, can occur in vivo when photorespiratory metabolism is genetically disrupted.

    

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