Atomic Force Microscopy (AFM) has proven itself over recent years as an essential tool for the analysis of microbial systems. This article will review how AFM has been used to study microbial systems to provide unique insight into their behavior and relationship with their environment. Immobilization of live cells has enabled AFM imaging and force measurement to provide understanding of the structure and function of numerous microbial cells. At the macromolecular level AFM investigation into the properties of surface macromolecules and the energies associated with their mechanical conformation and functionality has helped unravel the complex interactions of microbial cells. At the level of the whole cell AFM has provided an integrated analysis of how the microbial cell exploits its environment through its selective, adaptable interface, the cell surface. In addition to these areas of study the AFM investigation of microbial biofilms has been vital for industrial and medical process analysis. There exists a tremendous potential for the future application of AFM to microbial systems and this has been strengthened by the trend to use AFM in combination with other characterization methods, such as confocal microscopy and Raman spectroscopy, to elucidate dynamic cellular processes.

The interaction of microbes and subsequent development of biofilms at surfaces has far-reaching consequences in bioprocess engineering, agriculture, medicine and dentistry. Thus, the microbial surface has been the focus of wide scientific investigation. However, only recently has technology permitted quantitative study of the molecular interactions that govern the interactions of microbes. One such technology is atomic force microscopy (AFM) that not only permits the high resolution imaging of microbial surfaces but also the direct measurement of molecular forces and physical properties found at the microbial surface. This review highlights the current development of AFM force measurements and how these may be applied to microbial cell surfaces. The refinement of the AFM force measurement technique for characterising microbial surfaces will be discussed with reference to selected studies from the author's laboratory and key results from other research teams. The review will demonstrate how the application of the AFM techniques of single-molecule force spectroscopy, functionalised tips, cell probes and lateral force measurement to microbial surfaces has provided exciting and unique insights into the microbial surface and its interactions.

We examined the rabbit retinal pigment epithelium (RPE) for Na transport properties which would allow it to buffer undesirable changes in Na concentrations in the interphotoreceptor matrix (IPM) during light and dark cycles. The RPE is selectivity permeable to sodium. Open and short circuit transport studies with RPE indicate a circulating (choroid to retina and back) Na current which does not compromise the electrical integrity of the blood brain barrier but together with the Na permselectivity is of sufficient magnitude to buffer both upwards and downwards movements of IPM [Na] during light or dark responses.

Cell surface changes that accompany the complex life cycle of Streptomyces coelicolor were monitored by atomic force microscopy (AFM) of living cells. Images were obtained using tapping mode to reveal that young, branching vegetative hyphae have a relatively smooth surface and are attached to an inert silica surface by means of a secreted extracellular matrix. Older hyphae, representing a transition between substrate and aerial growth, are sparsely decorated with fibers. Previously, a well-organized stable mosaic of fibers, called the rodlet layer, coating the surface of spores has been observed using electron microscopy. AFM revealed that aerial hyphae, prior to sporulation, possess a relatively unstable dense heterogeneous fibrous layer. Material from this layer is shed as the hyphae mature, revealing a more tightly organized fibrous mosaic layer typical of spores. The aerial hyphae are also characterized by the absence of the secreted extracellular matrix. The formation of sporulation septa is accompanied by modification to the surface layer, which undergoes localized temporary disruption at the sites of cell division. The characteristics of the hyphal surfaces of mutants show how various chaplin and rodlin proteins contribute to the formation of fibrous layers of differing stabilities. Finally, older spores with a compact rodlet layer develop surface concavities that are attributed to a reduction of intracellular turgor pressure as metabolic activity slows.The model organism Streptomyces coelicolor represents a group of soil-dwelling filamentous bacteria responsible for synthesis of a wide range of bioactive secondary metabolites, in particular, antibiotics. A good understanding of streptomycete biology has been established, based on extensive studies of S. coelicolor over many years and, more recently, availability of this bacterium's complete genome sequence (1). Of particular interest is the complex streptomycete life cycle. After spore germination, vegetative growth leads to formation of a mycelium consisting of a ramifying network of syncytial hyphae that penetrate a moist substrate by extension of hyphal tips and subapical branching. Subsequent reproductive growth often coincides with the onset of antibiotic production and proceeds with the formation of filamentous aerial hyphae that eventually undergo differentiation into chains of unigenomic spores. Several genes that are critical to various stages of this morphological differentiation have been described in S. coelicolor (5, 15), including bld genes, required for the initial growth of aerial hyphae, and whi genes, needed for the subsequent development of spore chains. Growth into the air is accompanied by a change in cell surface properties: vegetative hyphae growing in moist substrates have hydrophilic cell surfaces, whereas the aerial hyphae and spores are hydrophobic.