Bacterial chemotaxis: introverted or extroverted? A comparison of the advantages and disadvantages of basic forms of metabolism-based and metabolism-independent behavior using a computational model

Annotation of chemotaxis gene clusters and proteins involved in chemotaxis of Bacillus subtilis strain MB378 capable of biodecolorizing different dyes

This study explores the chemotactic potential of Bacillus subtilis MB378 against industrial dyes. Initial screening with swim plate assay showed significant movement of Bacillus subtilis MB378 towards test compounds. According to quantitative capillary assay, B. subtilis MB378 exhibited high chemotaxis potential towards Acid Orange 52 (CI: 9.52), followed by Direct Red 28 (CI: 8.39) and Basic Green 4 (CI: 5.21) in glucose-supplemented medium. Sequencing and gene annotation results evidently showed presence of chemotaxis genes and flagellar motor proteins in Bacillus subtilis draft genome. Methyl-accepting proteins (involved in chemotaxis regulation) belonged to pfam00672, pfam00072, and pfam00015 protein families. Annotated chemotaxis machinery of MB378 comprised 8 Che genes, 5 chemoreceptor genes, associated flagellar proteins, and rotary motors. Chemotaxis genes of B. subtilis MB378 were compared with genes of closely related Bacillus strains (168, WK1, and HTA426), depicting highly conserved regions showing evolutionary relation between them. Considering results of present study, it can be speculated that test compounds triggered chemotactic genes, which made these compounds bioavailable to the bacterium. Hence, the bacterium recognized and approached these compounds and facilitated biodegradation and detoxification of these compounds.

Finding novel chemoreceptors that specifically sense and trigger chemotaxis toward polycyclic aromatic hydrocarbons in Novosphingobium pentaromativorans US6-1

Bacterial chemotaxis can improve the efficiency of aromatic compound degradation, however, knowledge of how bacteria sense high-molecular-weight polycyclic aromatic hydrocarbons (HMW-PAHs), is limited. Here, the chemotactic responses of Novosphingobium pentaromativorans US6-1 to 9 aromatic compounds were investigated. The results showed that US6-1 chemotactically responded to phenanthrene (PHE), pyrene (PYR), benzo[a]pyrene (BaP) and their six metabolites. Six methyl-accepting chemotaxis proteins (MCPs) were annotated from US6-1 genome, four of which contained putative ligand-binding domains (LBDs). To confirm whether these four MCPs were involved in triggering chemotaxis toward PAHs, the MCP mutants were constructed. Observations showed a loss of the chemotactic responses to benzoate, phthalate, PHE and BaP only in the mutant ∆mcp03030. Surface plasmon resonance (SPR) assays further confirmed that MCP03030LBD specifically bound phthalate, PHE, PYR and BaP, while MCP18870LBD bound only PYR. The mutant ∆mcp03030-∆mcp18870 was then constructed and was shown to have lost the chemotactic response to 5 aromatic compounds. Combined with the effects of outer membrane transporter deletion on chemotaxis and MCP deletion on the PAH degradation, our study demonstrated that the chemoreceptors MCP03030 and MCP18870 can recognize PAHs and their metabolites in the periplasm, triggering metabolism-dependent and metabolism-independent chemotaxis, and be linked with HMW-PAH biodegradation.

The Evolution of Soundscape Appraisal Through Enactive Cognition

We propose a framework based on evolutionary principles and the theory of enactive cognition ("being by doing"), that addresses the foundation of key results and central questions of soundscape research. We hypothesize that the two main descriptors (measures of how people perceive the acoustic environment) of soundscape appraisal ('pleasantness' and 'eventfulness'), reflect evolutionarily old motivational and affective systems that promote survival through preferences for certain environments and avoidance of others. Survival is aimed at ending or avoiding existential threats and protecting viability in a deficient environment. On the other hand, flourishing occurs whenever survival is not an immediate concern and aims to improve the agent's viability and by co-creating ever better conditions for existence. As such, survival is experienced as unpleasant, and deals with immediate problems to be ended or avoided, while flourishing is enjoyable, and therefore to be aimed for and maintained. Therefore, the simplest, safety-relevant meaning attributable to soundscapes (audible safety) should be key to understanding soundscape appraisal. To strengthen this, we show that the auditory nervous system is intimately connected to the parts of our brains associated with arousal and emotions. Furthermore, our theory demonstrates that 'complexity' and 'affordance content' of the perceived environment are important underlying soundscape indicators (measures used to predict the value of a soundscape descriptor). Consideration of these indicators allows the same soundscape to be viewed from a second perspective; one driven more by meaning attribution characteristics than merely emotional appraisal. The synthesis of both perspectives of the same person-environment interaction thus consolidates the affective, informational, and even the activity related perspectives on soundscape appraisal. Furthermore, we hypothesize that our current habitats are not well matched to our, evolutionarily old, auditory warning systems, and that we consequently have difficulty establishing audible safety. This leads to more negative and aroused moods and emotions, with stress-related symptoms as a result.