Membrane vesicles (MVs) are nanoparticles composed of lipid membranes that are produced by both Gram-negative and Gram-positive bacteria. MVs have been assigned diverse biological functions, and they show great potential for applications in various fields. However, the mechanisms underlying their functions and biogenesis are not completely understood. Accumulating evidence shows that MVs are heterogenous, and different types of MVs with different compositions are released from the same species. To understand the origin and function of these MVs, determining the biochemical properties of MVs is important. In this review, we will discuss recent progress in understanding the biochemical composition and properties of MVs.

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Biofilms are communities of bacteria encased in selfsecreted extracellular polymeric substances (EPS) that adhere stubbornly to submerged surfaces. Once established, these communities can cause serious chronic illnesses in medical settings, while they can promote corrosion and biofouling in industrial settings. Due to the difficulty of their removal, strongly oxidizing chemicals and detergents can be used to degrade and remove biofilms by killing the cells and degrading the matrix; however, the choice of compounds is limited in delicate environments due to the potential damage they may cause. In the case of detergents, most are synthesized from nonrenewable petrochemicals that have a degree of aquatic toxicity. There is a growing need to identify and characterize alternatives to synthetic surfactants. Biosurfactants, which are surfactants produced by microorganisms, are a promising alternative since they can be synthesized from renewable resources, have low environmental toxicity, and have been shown to have higher degrees of specificity in the mechanism of action. Sophorolipids are a class of glycolipid surfactants produced by yeast that have demonstrated great promise due to large yields from renewable feedstocks and for antimicrobial properties; however, the effect of the application of sophorolipids to Gramnegative bacterial biofilms has not been well studied. We investigate the antibiofilm properties of sophorolipids by demonstrating its ability to cause the catastrophic disruption of Pseudomonas aeruginosa PAO1 biofilms in microfluidic channels. We show that while sophorolipids inflict little damage to the bacteria, they weaken the EPS biofilm matrix, leading to surface-detachment and breakup of the biofilm. Furthermore, we find that sophorolipids act cooperatively with the widely used surfactant, sodium dodecyl sulfate. When combined, concentrations ∼100-fold lower than the minimum effective concentration, when used independently, recover potency. Biosurfactants are typically expensive to produce, thus our work demonstrates a means to improve efficacy while simultaneously reducing both cost and the amount of environmentally harmful substances used.

Extracellular contractile injection systems (eCISs) are structurally similar to headless phages and are versatile nanomachines conserved among diverse classes of bacteria. Herein, Streptomyces species, which comprise filamentous Gram-positive bacteria and are ubiquitous in soil, were shown to produce Streptomyces phage tail-like particles (SLPs) from eCIS-related genes that are widely conserved among Streptomyces species. In some Streptomyces species, these eCIS-related genes are regulated by a key regulatory gene, which is essential for Streptomyces life cycle and is involved in morphological differentiation and antibiotic production. Deletion mutants of S. lividans of the eCIS-related genes appeared phenotypically normal in terms of morphological differentiation and antibiotic production, suggesting that SLPs are involved in other aspects of Streptomyces life cycle. Using co-culture method, we found that colonies of SLP-deficient mutants of S. lividans were more severely invaded by fungi, including Saccharomyces cerevisiae and Schizosaccharomyces pombe. In addition, microscopic and transcriptional analyses demonstrated that SLP expression was elevated upon co-culture with the fungi. In contrast, co-culture with Bacillus subtilis markedly decreased SLP expression and increased antibiotic production. Our findings demonstrate that in Streptomyces, eCIS-related genes affect microbial competition, and the patterns of SLP expression can differ depending on the competitor species.