This paper reports on the use of scanning ion conductance microscopy (SICM) to locally map the ionic properties and charge environment of two live bacterial strains: the Gram-negative Escherichia coli and the Gram-positive Bacillus subtilis. SICM results find heterogeneities across the bacterial surface and significant differences among the Gram-positive and Gram-negative bacteria. The bioelectrical environment of the B. subtilis was found to be considerably more negatively charged compared to E. coli. SICM measurements, fitted to a simplified finite element method (FEM) model, revealed surface charge values of −80 to −140 mC m −2 for the Gram-negative E. coli. The Gram-positive B. subtilis show a much higher conductivity around the cell wall, and surface charge values between −350 and −450 mC m −2 were found using the same simplified model. SICM was also able to detect regions of high negative charge near B. subtilis, not detected in the topographical SICM response and attributed to the extracellular polymeric substance. To further explore how the B. subtilis cell wall structure can influence the SICM current response, a more comprehensive FEM model, accounting for the physical properties of the Gram-positive cell wall, was developed. The new model provides a more realistic description of the cell wall and allows investigation of the relation between its key properties and SICM currents, building foundations to further investigate and improve understanding of the Gram-positive cellular microenvironment.
Cyanobacterial granules and aggregates can readily form in aquatic environments. The microbial communities found within and around these structures can be referred to as the cyanosphere, and can enable collective metabolic activities relevant to biogeochemical cycles. Cyanosphere communities are suggested to have different composition to that in the surrounding environment, but studies to date are mostly based on single time point samples. Here, we retrieved samples containing cyanobacterial granules from a freshwater reservoir and maintained a culture through sub-culture passages under laboratory conditions for over a year. We show that cyanobacteria-dominated granules form readily and repeatedly in this system over passages, and that this structure formation process seems to be associated with cyanobacterial motility. Performing longitudinal short-read sequencing over several culture passages, we identified a cyanosphere community comprising of 17 species with maintained population structure. Using long-read sequencing from two different time point samples, we have re-constructed full, circular genomes for 15 of these species and annotated metabolic functions within. This predicts several metabolic interactions among community members, including sulfur cycling and carbon and vitamin exchange. Using three individual species isolated from this cyanosphere, we provide experimental support for growth on carbon sources predicted to be secreted by the cyanobacterium in the system. These findings reinforce the view that the cyanosphere can recruit and maintain a specific microbial community with specific functionalities embedded in a spatially-organised microenvironment. The presented community will act as a key model system for further understanding the formation of the structured cyanosphere, its function and stability, and its metabolic contribution to biogeochemical cycles.
This paper reports on the use of scanning ion conductance microscopy (SICM) to locally map the ionic properties and charge environment of two live bacterial strains: the gramnegative Escherichia coli and the gram-positive Bacillus subtilis. SICM results find heterogeneities across the bacterial surface, and significant differences among the grampositive and -negative bacteria. The bioelectrical environment of the B. subtilis was found to be considerably more negatively charged compared to E. coli. SICM measurements, fitted to a simplified finite element method (FEM) model, revealed surface charge values of −80 to −140 mC m−2 for the gram-negative E. coli. The gram-positive B. subtilis show a much higher conductivity around the cell wall, and surface charge values between −350 and −450 mC m−2 were found using the same simplified model. SICM was also able to detect regions of high negative charge near B. subtilis, not detected in the topographical SICM response and attributed to extracellular polymeric substance. To further explore how the B. subtilis cell wall structure can influence the SICM current response, a more comprehensive FEM model, accounting for the physical properties of the gram-positive cell wall, was developed. The new model provides a more realistic description of the cell wall and allowed investigation of the relation between its key properties and SICM currents, building foundations to further investigate and improve understanding of the gram-positive cellular microenvironment.Abstract Figure
Spatial organization is the norm rather than the exception in the microbial world. While the study of microbial physiology has been dominated by studies in well-mixed cultures, there is now increasing interest in understanding the role of spatial organization in microbial physiology, coexistence and evolution. Where studied, spatial organization has been shown to influence all three of these aspects. In this mini review and perspective article, we emphasize that the dynamics within spatially organized microbial systems (SOMS) are governed by feedbacks between local physico-chemical conditions, cell physiology and movement, and evolution. These feedbacks can give rise to emergent dynamics, which need to be studied through a combination of spatio-temporal measurements and mathematical models. We highlight the initial formation of SOMS and their emergent dynamics as two open areas of investigation for future studies. These studies will benefit from the development of model systems that can mimic natural ones in terms of species composition and spatial structure.
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