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Pathogen avoidance behaviour has been observed across animal taxa as a vital host-microbe interaction mechanism. The nematode Caenorhabditis elegans has evolved multiple diverse mechanisms for pathogen avoidance under natural selection pressure. We summarise the current knowledge of the stimuli that trigger pathogen avoidance, including alterations in aerotaxis, intestinal bloating, and metabolites. We then survey the neural circuits involved in pathogen avoidance, transgenerational epigenetic inheritance of pathogen avoidance, signalling crosstalk between pathogen avoidance and innate immunity, and C. elegans avoidance of non-Pseudomonas bacteria. In this review, we highlight the latest advances in understanding host-microbe interactions and the gutbrain axis. [ABSTRACT FROM AUTHOR]

Agrobacterium tumefaciens is a soil-borne pathogenic bacterium that causes crown gall disease in many plants. Chemotaxis offers A. tumefaciens the ability to find its host and establish infection. Being an aerobic bacterium, A. tumefaciens possesses one chemotaxis system with multiple potential chemoreceptors. Chemoreceptors play an important role in perceiving and responding to environmental signals. However, the studies of chemoreceptors in A. tumefaciens remain relatively restricted. Here, we characterized a cytoplasmic chemoreceptor of A. tumefaciens C58 that contains an N-terminal globin domain. The chemoreceptor was designated as Atu1027. The deletion of Atu1027 not only eliminated the aerotactic response of A. tumefaciens to atmospheric air but also resulted in a weakened chemotactic response to multiple carbon sources. Subsequent site-directed mutagenesis and phenotypic analysis showed that the conserved residue His100 in Atu1027 is essential for the globin domain's function in both chemotaxis and aerotaxis. Furthermore, deleting Atu1027 impaired the biofilm formation and pathogenicity of A. tumefaciens. Collectively, our findings demonstrated that Atu1027 functions as an aerotaxis receptor that affects agrobacterial chemotaxis and the invasion of A. tumefaciens into its host. [ABSTRACT FROM AUTHOR]

Microorganisms often actively respond to multiple external stimuli to navigate toward their preferred niches. For example, unicellular magnetotactic bacteria integrate both oxygen sensory information and the Earth's geomagnetic field to help them locate anoxic conditions in a process known as magneto-aerotaxis. However, for multicellular magnetotactic prokaryotes (MMPs), the colonial structure of 4-16 cells places fundamental constraints on collective sensing, colony motility and directed swimming. To investigate how colonies navigate environments with multiple stimuli, we performed microfluidic experiments of MMPs with opposing magnetic fields and oxygen gradients. These experiments reveal unusual back-and-forth excursions called 'escape motility', in which colonies shuttle along magnetic field lines, punctuated by abrupt-yet highly coordinated-changes in collective ciliary beating. Through cell tracking and numerical simulations, we demonstrate that escape motility can arise through a simple magneto-aerotaxis mechanism, which includes the effect of magnetic torques and chemical sensing. At sufficiently high densities of MMPs, we observe the formation of dynamic crystal structures, whose stability is governed by the magnetic field strength and near-field hydrodynamic interactions. The results shed light on how some of the earliest multicellular organisms navigate complex physico-chemical landscapes.

Pathogen avoidance behaviour has been observed across animal taxa as a vital host-microbe interaction mechanism. The nematode Caenorhabditis elegans has evolved multiple diverse mechanisms for pathogen avoidance under natural selection pressure. We summarise the current knowledge of the stimuli that trigger pathogen avoidance, including alterations in aerotaxis, intestinal bloating, and metabolites. We then survey the neural circuits involved in pathogen avoidance, transgenerational epigenetic inheritance of pathogen avoidance, signalling crosstalk between pathogen avoidance and innate immunity, and C. elegans avoidance of non- Pseudomonas bacteria. In this review, we highlight the latest advances in understanding host-microbe interactions and the gut-brain axis., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Lei, Tan, Tu and Tan.)

Agrobacterium tumefaciens is a soil-borne pathogenic bacterium that causes crown gall disease in many plants. Chemotaxis offers A. tumefaciens the ability to find its host and establish infection. Being an aerobic bacterium, A. tumefaciens possesses one chemotaxis system with multiple potential chemoreceptors. Chemoreceptors play an important role in perceiving and responding to environmental signals. However, the studies of chemoreceptors in A. tumefaciens remain relatively restricted. Here, we characterized a cytoplasmic chemoreceptor of A. tumefaciens C58 that contains an N-terminal globin domain. The chemoreceptor was designated as Atu1027. The deletion of Atu1027 not only eliminated the aerotactic response of A. tumefaciens to atmospheric air but also resulted in a weakened chemotactic response to multiple carbon sources. Subsequent site-directed mutagenesis and phenotypic analysis showed that the conserved residue His100 in Atu1027 is essential for the globin domain's function in both chemotaxis and aerotaxis. Furthermore, deleting Atu1027 impaired the biofilm formation and pathogenicity of A. tumefaciens . Collectively, our findings demonstrated that Atu1027 functions as an aerotaxis receptor that affects agrobacterial chemotaxis and the invasion of A. tumefaciens into its host., Competing Interests: The authors declare there are no competing interests., (©2024 Huang et al.)