Light energy absorption and transfer are very important processes in photosynthesis. In green sulfur bacteria light is absorbed primarily by the chlorosomes and its energy is transferred via the Fenna–Matthews–Olson (FMO) proteins to a homodimeric reaction center (RC). Here, we report the cryogenic electron microscopic structure of the intact FMO-RC apparatus from Chlorobaculum tepidum at 2.5 Å resolution. The FMO-RC apparatus presents an asymmetric architecture and contains two FMO trimers that show different interaction patterns with the RC core. Furthermore, the two permanently bound transmembrane subunits PscC, which donate electrons to the special pair, interact only with the two large PscA subunits. This structure fills an important gap in our understanding of the transfer of energy from antenna to the electron transport chain of this RC and the transfer of electrons from reduced sulfur compounds to the special pair.

The degradation of aromatic compounds comprises an important step in the removal of pollutants and re‐utilization of plastics and other non‐biological polymers. Here, Pseudomonas sp. strain phDV1, a gram‐negative bacterium that is selected for its ability to degrade aromatic compounds is studied. In order to understand how the aromatic compounds and their degradation products are reintroduced in the metabolism of the bacteria and the systematic/metabolic response of the bacterium to the new carbon source, the proteome of this strain is analyzed in the presence of succinate, phenol, and o‐, m‐, and p‐cresol as the sole carbon source. As a reference proteome, the bacteria are grown in succinate and then compared with the respective proteomes of bacteria grown on phenol and different cresols. In total, 2295 proteins are identified; 1908 proteins are used for quantification between different growth conditions. The carbon source affects the synthesis of enzymes related to aromatic compound degradation and in particular the enzyme involved in the meta‐pathway of monocyclic aromatic compounds degradation. In addition, proteins involved in the production of polyhydroxyalkanoate (PHA), an attractive biomaterial, show higher abundance in the presence of monocyclic aromatic compounds. The results provide, for the first time, comprehensive information on the proteome response of this strain to monocyclic aromatic compounds.

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Teaching the concept of pH buffers is considered to be important both in the final high-school years and at the early undergraduate level. Here, we propose the use of pH−log C diagrams to investigate the properties of pH buffers. This graphical approach is extremely simple to employ because it only requires drawing a simple square that can then be used to determine relevant pH-buffer parameters. This square is based on the Henderson−Hasselbalch equation with the length of each of its sides equal to abs(pH − pK a ) and abs(log C b − log C a ). In addition, the "buffer square", as we propose naming it, can be used by instructors as a pedagogical tool to introduce the concept of buffer capacity, to help determine pH change upon the addition of an acid or base, and to easily calculate the required concentrations for preparing a pH buffer with specific properties. Finally, we consider this approach to be especially powerful for helping students visualize the location of a buffer system on a full pH−log C diagram and, thus, help them evaluate if the Henderson−Hasselbalch equation is valid for accurate pH determination as an alternative to the more complex cubic or quadratic equations that are needed to describe acid−base equilibria more precisely in some cases.

Cyanobacteria are oxygenic photosynthetic prokaryotes and play a crucial role in the Earth's carbon and nitrogen cycles. The photoautotrophic cyanobacterium Anabaena sp. PCC 7120 has the ability to fix atmospheric nitrogen in heterocysts and produce hydrogen as a byproduct through a nitrogenase. In order to improve hydrogen production, mutants from Anabaena sp. PCC 7120 are constructed by inactivation of the uptake hydrogenase (ΔhupL) and the bidirectional hydrogenase (ΔhoxH) in previous studies. Here the proteomic differences of enriched heterocysts between these mutants cultured in N2‐fixing conditions are investigated. Using a label‐free quantitative proteomics approach, a total of 2728 proteins are identified and it is found that 79 proteins are differentially expressed in the ΔhupL and 117 proteins in the ΔhoxH variant. The results provide for the first time comprehensive information on proteome regulation of the uptake hydrogenase and the bidirectional hydrogenase, as well as systematic data on the hydrogen related metabolism in Anabaena sp. PCC 7120.