Chlorophylls (Chls) and bacteriochlorophylls (BChls) in photosynthetic organisms are embedded in pigment-protein complexes, mostly through the coordination of peptidyl residues to their central metal atoms. An asymmetry occurs at the axially coordinated metal centers of (B)Chls. The stereochemistry of the ligand coordination toward 42 molecules of Chls-c, the fully π-conjugated porphyrin pigments lacking C17- and C18-chiralities and a long ester chain in the C17-substituent, was surveyed across 21 pigment-protein complexes registered in the Protein Data Bank. It was found that 24 of 42 Chl-c molecules in these complexes were coordinated from the β-side of the macrocyclic π-plane, revealing a tendency opposite to the preferential α-ligation observed for the structurally different (B)Chls with a (bacterio)chlorin π-system in other proteins (129/163 surveyed sites). The most common binding sites for Chl-c molecules in the proteins correspond to the a603 and a612 sites in Chl-a/b-binding light-harvesting complex II (LHCII), both of which accommodate β-epimers. In some cases, a carotenoid molecule contacts Chl-c to occupy the space where the C17[2]-ester group of the Chl-a/b molecule is situated at the corresponding sites in LHCII, and its position of the carotenoid molecule is related to the macrocycle side of the axial ligand coordination of Chl-c. The absence or presence of chirality and bulky substituents at the C17-position of (B)Chls may be concerned with the stereochemistry of the axial coordination and the formation of these pigment-protein complexes.

Microbial populations strongly shape their environment, which can re-route adaptation toward organism-generated fitness optima. However, the conditions that promote these eco-evolutionary feedbacks are unclear. Here, we used experimental evolution to test whether high population density, by strengthening niche construction, drives eco-evolutionary feedbacks in the bacterial pathogen Pseudomonas aeruginosa (Pa) MPAO1. We tested for adaptation to organism-modified environments by measuring the relative performance of ancestral and endpoint populations in filtrate generated by each evolutionary line sampled across generations. Contrary to expectations, we found that endpoint populations had higher performance than the ancestral strain in filtrate across nearly all evolutionary lines regardless of population density. This was caused by the emergence of hyperactive filamentous bacterio(phage) mutants during experimental passaging that inhibited the ancestral strain but not endpoint populations in modified media. Hyperactive phages emerged from one of two avirulent prophages in MPAO1's genome (Pf4 or Pf6). Hyperactive phages drove the evolution of phage resistance in bacterial populations via mutations in the type IV pilus (TIVP), the phage's binding receptor. In a follow-up experiment, we showed that these TIVP mutations pleiotropically reduced motility and conferred resistance to a TIVP-targeting virulent phage, both of which are important traits for Pa infection and treatment. Overall, this work suggests that filamentous phage evolution can drive eco-evolutionary feedbacks in bacterial populations, causing phenotypic and genetic changes that would not be anticipated from adaptation to the extrinsic environment alone.

Photosynthesis, the foundation of most life, begins when sunlight is captured by (bacterio)chlorophyll ((B)Chl) and carotenoid (Crt) pigments. These molecules are arranged so that captured energy migrates rapidly to reaction centres, where it is stored as a charge separation. The complementary absorption of Crt and (B)Chl pigments, and rapid energy transfer between them, underpins solar harvesting. Here we report a Crt-to-BChl energy transfer mechanism mediated by singlet fission, in which a high-energy singlet exciton (with spin quantum number S = 0) is converted into two low-energy triplet (S = 1) excitons. In purple photosynthetic bacteria, the Crt S2 singlet exciton splits into Crt and BChl triplet excitons on adjacent sites. Once formed, the triplets transfer cooperatively to BChl and onwards to reaction centres. Energy is transferred from a singlet Crt state, via the spin-protected long-lived triplet pair, to a singlet BChl state. Thus, this singlet fission-mediated mechanism augments solar energy harvesting for photosynthesis.

Transcription initiation is regulated by transcription factors (TFs). Though TFs determine phenotype, they are nonessential for minimal cellular life. Given this and the idea that it is a certain level of organism "complexity" that calls for transcription regulation, we traced the evolution of TF repertoire on a bacterio-archaeal phylogeny using a dataset of ∼500,000 TFs. The most ancestral prokaryotes probably encoded multiple TFs. These, based on functions of extant relatives, possibly regulated sugar-fermentation metabolism, sensed overall metabolic state and redox, responded to DNA damage or bound metals; many of which are consistent with some reconstructions of ancestral gene pools and physiologies. The number of TFs and their superfamily-level diversity, through evolutionary history, are similar to those in extant bacteria. These suggest pre-LUCA diversification of TF families. Emergence of new TFs along the phylogeny shows innovation early in prokaryote evolution, in contrast to eukaryotes, in which many TF families emerged in bursts at multicellular lineages. Gains of TFs late in prokaryotic evolution appear to be products of horizontal acquisition of proteins discovered earlier along some other lineage. We speculate on the difference between the evolutionary trajectory of prokaryotic and eukaryotic TF repertoire and how this might be explained by how complexity is envisioned in these two different kingdoms.

In November 2020, an alert for a "mysterious disease" among fishermen was issued. Fishermen are particularly subjected to dermatoses due to their constant contact with seawater, fish, crustaceans, and fishing equipment that may contain harmful agents. The study aimed to examine the alert, identify the causative agent and suggest preventive and control measures. This was a cross-sectional study of dermatoses in Dakar (Senegal) from October 11 to November 30, 2020, using quantitative and qualitative methods within a 'One Health' approach." The investigation included bacterio-virological, anatomopathological and toxicological examinations. Data were analyzed using Epi info and QGIS (case mapping), We observed all confidentiality measures during the study. A total of 555 cases were diagnosed with an attack rate of 5.4% among fishermen and no deaths were reported. There was a delay in epidemic detection and notification. The epidemic was most prevalent among people from coastal areas. Average age of cases was 22 ± 9 years, and all were male and artisanal fishermen by profession. Patients presented with fever (16%), cutaneous pain (100%) and mucocutaneous lesions (100%) consisting of vesicles, papules and ulcerations localized on exposed areas of the body, external genitalia and oral mucosa, with severe cases (8%). Toxicology revealed the presence of a toxic alga (V. rugosum) in marine equipments. The notion of a sea trip in the 24-48 hours before the onset of the disease was found in 92%. Majority of cases (74%) did not have full personal protective equipment (PPE). The proportion of people without full protection was 83% among those who developed severe forms. People without full protection were more exposed to severe forms than those with full PPE; (OR = 1.818; 95% CI [0.829 - 3.988]). The investigation has linked the epidemic to a probable algal origin. We need to promote the use of personal protective equipment and improve the early warning and notification system.

The first forms of photosynthetic life date back to more than 3.2-3.5 billion years ago. They performed photosynthesis in an anoxic world of the early earth and formed large mass accumulations on any kind of surface and in shallow waters. During evolution they diverged into several major phyla with differences in structure and function of the photosynthetic machinery including two different types of photosynthetic reaction centers. The combination of both of these types eventually led to the establishment of oxygenic photosynthesis present in cyanobacteria and chloroplast-containing plants. Common to all photosynthetic life is the presence of phylogenetically related reaction center proteins and of various chlorophyll molecules as mediators of light energy transformation into biochemical forms of energy. Therefore, we used phylogenetic analyses of reaction center proteins and representative enzymes of (bacterio)chlorophyll biosynthesis in addition to synteny of genome organization to unravel early divergencies of all known phyla of photosynthetic prokaryotes: Cyanobacteria, Chloroflexi, Chlorobi, Heliobacteria, Chloracidobacteria, and phototrophic purple Proteobacteria including Gemmatimonas. It was concluded that photosynthesis evolved only once, and all known forms diverged by various mechanisms from one primordial principal ancestor with properties resembling an ancestral cyanobacterium driving anoxygenic photosynthesis with a Type I photosystem and reduced inorganic electron donors.

Skunavirus is the most frequently encountered Lactococcus-infecting (bacterio)phage genus in dairy fermentations and may cause milk acidification failure or inefficiencies. During phage infection, DNA packaging into the phage prohead is a crucial step for the successful maturation of phage progeny. In the Skunavirus genus of lactococcal phages, a predicted HNH endonuclease-encoding gene adjacent to two putative DNA packaging genes is highly conserved. In the current study, we show that this gene, designated here as hrdP (HNH endonuclease related to DNA packaging), is essential for the production of infective Skunavirus sk1 virions. HrdP exhibits non-specific endonuclease activity, while deletion of hrdP from the sk1 genome results in loss of plaque-forming ability without hindering its DNA replication or protein production. Transmission electron microscopy analysis showed that the hrdP deletion mutant in sk1 is unable to produce intact virions. However, the proheads in this mutant displayed conformational changes associated with capsid expansion, suggesting that DNA packaging had initiated and progressed to a certain extent. This study provides valuable insights into the specific role of HrdP in Skunavirus members, highlighting it as a potential target for developing anti-phage strategies to enhance starter culture robustness.

Carotenoids extend the absorption range of photosynthesis and transfer excitation energy to (bacterio-)chlorophylls with remarkable efficiency, yet the microscopic mechanism of this process, especially the role of the S X intermediate, remains unresolved. Here, we use femtosecond stimulated Raman spectroscopy, whose high vibrational frequency and temporal resolutions enable direct tracking of excited-state intermediates and their symmetry characteristics. By probing spheroidene in both solution and the light-harvesting 2 complex of Rhodobacter sphaeroides, we reveal structural change in the S2 (1Bu [+]) state that forms distorted S X and S1 (2Ag [-]) intermediates. The S X state is assigned to optically forbidden 3Ag [-] configuration rather than the earlier 1Bu [-] or Ag [+] proposals and is identified as an efficient pathway for energy transfer to bacteriochlorophylls. The spheroidene-to-bacteriochlorophyll energy transfer efficiencies are quantified as 32% via the S X state, combined with 50% from the S2 state and 12% from the S1 state, yielding an overall transfer efficiency of 94%, in excellent agreement with previous reports. We propose that the observed structural distortions of spheroidene dynamically enhance coulombic coupling with surrounding bacteriochlorophylls, which may underlie the remarkably high efficiency of excitation energy transfer.

Tryptophan is the strongest UV chromophore in proteins, and its biosynthesis is the most energy-consuming among all amino acids. In the transmembrane region of purple bacterial photosynthetic reaction centers (PbRC), tryptophan residues are densely concentrated near the inactive electron-transfer branch in subunit M, forming part of the carotenoid binding site. We investigated the redox potentials (E m) of tryptophan residues in PbRC and O2-evolving photosystem II (PSII) by solving the linear Poisson-Boltzmann equation, considering equilibrium with all titratable sites in the entire protein. The tryptophan mediating superexchange electron transfer between the active (bacterio)pheophytin and primary quinone exhibits the highest E m value in both PbRC and PSII. In contrast, in PSII, D1-Trp14, oxidized under strong light to trigger the degradation of photodamaged D1 protein, has the lowest E m value. In PbRC, a chain of tryptophan residues near the inactive branch forms an E m cascade. Quantum mechanical/molecular mechanical calculations suggest that this chain enables electron hole hopping toward the carotenoid, effectively dissipating harmful UV energy. This mechanism likely reflects the photoprotective strategy of PbRC, focusing on UV tolerance rather than oxidative stress.

Photosynthesis in bacteria, algae, and plants begins with the absorption of light energy by (bacterio)chlorophyll molecules, part of which is then converted into heat, leading to a transient change in molecular temperature. We investigated this phenomenon in reaction centers (RCs) of the purple bacterium Rhodobacter (Rba.) sphaeroides using picosecond fluorescence spectroscopy. Exclusion of charge separation processes using the VR(L157) mutation allowed us to record the spectral dynamics of fluorescence of monomeric BChl a molecules. We found that excitation of RCs into the Soret band results in significant heating of BChl a by ~160 K with subsequent vibrational cooling, which manifests itself in a dynamic narrowing of the BChl a fluorescence spectrum with two characteristic times of 5 and 16 ps. The weaker heating by ~65 K and cooling with a characteristic time of 7.5 ps are observed upon excitation of RCs into the Qx band. Excitation into the Qу band does not result in any noticeable heating of BChl a. Difference absorption spectroscopy of tryptophan in the 280 nm region showed that the observed dynamics of the BChl a fluorescence spectrum are not associated with the dielectric rearrangement of the RCs protein matrix. Analysis of the obtained data using the phenomenological model of vibrational cooling led to the conclusion that during heat diffusion from excited BChl a, several amino acid residues from the immediate environment of BChl a act as the first solvation shell (FSS). At the first, faster stage, heat is transferred from BChl a to FSS, and at the second stage, FSS transfers heat to the protein matrix of RCs. Our work has shown the importance of taking into account vibrational cooling when studying the primary processes of photosynthesis.

Low-temperature (77 K) absorption and fluorescence spectra of 12 naturally occurring photosynthetic tetrapyrrole macrocycles have been recorded in a frozen glass (2-methyltetrahydrofuran). The compounds encompass distinct chromophore classes: porphyrin, chlorophyll c2; chlorin, chlorophylls a, b, d, f and bacteriochlorophylls c, d, e, f; and bacteriochlorin, bacteriochlorophylls a, b, g. The spectra are compared with those of the same pigment in liquid solution (predominantly 2-methyltetrahydrofuran) at room temperature (293 K). The measured Stokes shifts at 77 K across the 12 macrocycles range from ~30 to 300 cm[-1]. The spectral data in digital form are made available as part of the PhotochemCAD databases. Literature searches have revealed extensive published data for Chl a (often in biological matrices) but at best rather limited data for less common macrocycles. The availability of a systematic collection of curated spectral data collected at low temperature should be useful for a variety of assessments, including reconstruction of absorption spectra of (bacterio)chlorophyll-containing protein complexes, vibrational analysis of absorption and fluorescence spectra, and calculations where knowledge of energy levels is important.

Klaus Möbius, Professor at the Free University of Berlin, was an outstanding physical chemist and biophysicist. He was a pioneer in the development of high-field/high-frequency EPR spectroscopy methods and their application in the study of photosynthesis. Among the most essential are the applications in studying the charge transfer kinetics and properties of the ion-radical pairs in photosynthetic reaction centers (RC). Under his leadership and with his direct participation a unique setup allowing registration of the kinetics of the electron transfer between the (bacterio)chlorophyll dimer and quinone in the bacterial photosynthetic RC and plant photosystem I (PSI) was created. This setup also allowed precise determining of the distance between separated charges based on measuring the frequencies of the Electron Spin Echo Envelope Modulation (ESEEM). This setup made it possible to prove that electron transfer in PSI occurs mainly along the A branch of redox cofactors. The kinetics of backward electron transfer reaction (reoxidation of the phyllosemiquinone anion A1[-] and reduction of the photooxidized chlorophyll dimer P700[+]) in PSI were measured under the same conditions. The essential data on the bioprotective effect of the disaccharide trehalose on the kinetics of forward and backward electron transfer in PSI complexes were obtained. A significant slowdown in the kinetics of electron transfer due to the restriction of protein conformational mobility, as well as long-term maintaining of functional activity of PSI dried in a vitreous trehalose matrix at room temperature (i.e., subjected to a reversible anhydrobiosis) was demonstrated. These results obtained in collaboration with Prof. Möbius and Prof. Venturoli (Bologna) allowed elucidating the role of hydrogen bond network and the conformational mobility of the protein subunits in facilitating electron transfer in the photosynthetic RC.

Pseudomonas aeruginosa and Staphylococcus aureus are opportunistic pathogens commonly found in biofilm-associated polymicrobial respiratory infections that are challenging to control. Studies performed in laboratory standard conditions suggest that bacterio(phages) and antibiotic combinations are more active against bacterial communities and biofilms than each agent alone. The purpose of this work was to study the antibacterial efficacy of phage-antibiotic combinations using an in vivo-like three-dimensional lung epithelial model that mimics aspects of the parental tissue, colonized by a mixed bacterial community of P. aeruginosa and S. aureus. The bacterial population was targeted by phages specific to P. aeruginosa and/or gentamicin and ciprofloxacin. The results showed that P. aeruginosa was eradicated from the dual-species community when phage treatment was followed by gentamicin and was significantly reduced when followed by ciprofloxacin. Moreover, applying phages first followed by antibiotics demonstrated superior antibacterial activity compared to simultaneous treatment or treatments with the reverse order of application. This approach also reduced the S. aureus population but not as significant as the P. aeruginosa population. Using an in vivo-like model we demonstrated that phages and antibiotics are effective against dual-species bacterial communities, particularly targeting the P. aeruginosa population. However, but the sequence in which these antimicrobials are applied significantly in fluences the effectiveness of bacterial killing.

Photosynthesis by (bacterio)chlorophyll-producing organisms ("chlorophototrophy") sustains virtually all life on Earth, providing the biosphere with food and energy. The oxygenic process carried out by plants, algae and cyanobacteria also generates the oxygen we breathe, and ancient cyanobacteria were responsible for oxygenating the atmosphere, creating the conditions that allowed the evolution of complex life. Cyanobacteria were also the endosymbiotic progenitors of chloroplasts, play major roles in biogeochemical cycles and as primary producers in aquatic ecosystems, and act as genetically tractable model organisms for studying oxygenic photosynthesis. In addition to the Cyanobacteriota, eight other bacterial phyla, namely Proteobacteria/Pseudomonadota, Chlorobiota, Chloroflexota, Bacillota, Acidobacteriota, Gemmatimonadota, Vulcanimicrobiota and Myxococcota contain at least one putative chlorophototrophic species, all of which perform a variant of anoxygenic photosynthesis, which does not yield oxygen as a by-product. These chlorophototrophic organisms display incredible diversity in the habitats that they colonise, and in their biochemistry, physiology and metabolism, with variation in the light-harvesting complexes and pigments they produce to utilise solar energy. Whilst some are very well understood, such as the proteobacterial 'purple bacteria', others have only been identified in the last few years and therefore relatively little is known about them - especially those that have not yet been isolated and cultured. In this chapter, we aim to summarise and compare the photosynthetic physiology and central metabolic processes of chlorophototrophic members from the nine phyla in which they are found, giving both a short historical perspective and highlighting gaps in our understanding.