On the evolutionary ecology of symbioses between chemosynthetic bacteria and bivalves

Mutualistic associations between bacteria and eukaryotes occur ubiquitously in nature, forming the basis for key ecological and evolutionary innovations. Some of the most prominent examples of these symbioses are chemosynthetic bacteria and marine invertebrates living in the absence of sunlight at deep-sea hydrothermal vents and in sediments rich in reduced sulfur compounds. Here, chemosynthetic bacteria living in close association with their hosts convert CO2 or CH4 into organic compounds and provide the host with necessary nutrients. The dominant macrofauna of hydrothermal vent and cold seep ecosystems all depend on the metabolic activity of chemosynthetic bacteria, which accounts for almost all primary production in these complex ecosystems. Many of these enigmatic mutualistic associations are found within the molluscan class Bivalvia. Currently, chemosynthetic symbioses have been reported from five distinct bivalve families (Lucinidae, Mytilidae, Solemyidae, Thyasiridae, and Vesicomyidae). This brief review aims to provide an overview of the diverse physiological and genetic adaptations of symbiotic chemosynthetic bacteria and their bivalve hosts

Geometric and electronic structures of the His–Fe(IV)=O and His–Fe(IV)–Tyr hemes of MauG

Biosynthesis of the tryptophan tryptophylquinone (TTQ) cofactor activates the enzyme methylamine dehydrogenase. The diheme enzyme MauG catalyzes O-atom insertion and cross-linking of two Trp residues to complete TTQ synthesis. Solution optical and Mössbauer spectroscopic studies have indicated that the reactive form of MauG during turnover is an unusual bisFe(IV) intermediate, which has been formulated as a His-ligated ferryl heme [Fe(IV)=O] (heme A), and an Fe(IV) heme with an atypical His/Tyr ligation (heme B). In this study, Fe K-edge X-ray absorption spectroscopy and extended X-ray absorption fine structure studies have been combined with density functional theory (DFT) and time-dependent DFT methods to solve the geometric and electronic structures of each heme site in the MauG bisFe(IV) redox state. The ferryl heme site (heme A) is compared with the well-characterized compound I intermediate of cytochrome c peroxidase. Heme B is unprecedented in biology, and is shown to have a six-coordinate, S = 1 environment, with a short (1.85-Å) Fe–O(Tyr) bond. Experimentally calibrated DFT calculations are used to reveal a strong covalent interaction between the Fe and the O(Tyr) ligand of heme B in the high-valence form. A large change in the Fe–O(Tyr) bond distance on going from Fe(II) (2.02 Å) to Fe(III) (1.89 Å) to Fe(IV) (1.85 Å) signifies increasing localization of spin density on the tyrosinate ligand upon sequential oxidation of heme B to Fe(IV). As such, O(Tyr) plays an active role in attaining and stabilizing the MauG bisFe(IV) redox state

Perceived organizational climate and whistleblowing intention in academic organizations: evidence from Selçuk University (Turkey)

This paper investigates the relationship between organizational climate drivers and whistleblowing intention through a cross-sectional study in Selcuk University in Turkey. Contrary to our expectations, the findings do not fully support the existing literature and the hypotheses underpinning this research. While the work environment in faculties and institutes of Selcuk University seems to portray an overall positive organizational climate, lecturers, researchers, and research assistants have expressed a deep reluctance in the likelihood to sound the alarm in case they witness wrongdoings and malpractices committed by their supervisors and fellow colleagues. The investigation reveals that some organizational climate drivers such as organizational justice, morale, leader credibility and mobbing are consistently associated with informal whistleblowing intention while only individual autonomy is bound with formal whistleblowing intention. Nevertheless, the outputs highlight individual autonomy and morale to have negative impact on whistleblowing intention which is opposite to our expectation. Furthermore, the findings do not support the assumption relating to the mediating role of trust and safety climate in the relationship between organizational climate drivers and whistleblowing intention