Extracellular Vesicles and Bacteriophages: New Directions in Environmental Biocolloid Research

Abstract

There is a long-standing appreciation among environmental engineers and scientists regarding the importance of biologically derived colloidal particles and their environmental fate. This interest has been recently renewed in considering bacteriophages and extracellular vesicles, which are each poised to offer engineers unique insights into fundamental aspects of environmental microbiology and novel approaches for engineering applications, including advances in wastewater treatment and sustainable agricultural practices. Challenges persist due to our limited understanding of interactions between these nanoscale particles with unique surface properties and their local environments. This review considers these biological particles through the lens of colloid science with attention given to their environmental impact and surface properties. We discuss methods developed for the study of inert (nonbiological) particle-particle interactions and the potential to use these to advance our understanding of the environmental fate and transport of extracellular vesicles and bacteriophages.

Keywords: Smoluchowski; aggregation; bacteriophages; biocolloids; deposition; environmental fate; extracellular vesicles; outer membrane vesicles.

Figure 1.

(Top) Images of nanoparticles discussed in this review; (Bottom left) Transmission electron micrographs of uranyl acetate negatively stained Pseudomonas aeruginosa OMVs purified by density gradient from log-phase broth cultures. Size bar: 200 nm (A); and (Bottom right) T4 bacteriophage purified from Escherichia coli. Size bar: 50 nm (A). Images taken by Andrew Manning. See reference (Manning and Kuehn, 2011) for detailed methods.

Figure 2.

EVs from microbes can have a variety of possible fate outcomes in the natural environment. For example, in soil systems, EVs can deposit on soil particles, aggregate with other EVs or colloidal particles, be taken up by plants, among other possible fates. Created with Biorender.

Figure 3.

Schematic revealing differences and similarities between cellular and EV surfaces. a) Gram-negative bacteria produce OMVs from the blebbing of their outer membrane, resulting in the presence of outer membrane components, including LPS, on the surface of the EVs; b) Gram-positive bacterial CMVs originate from the cytoplasmic membrane and must traverse the thick peptidoglycan cell wall. LTA, but not WTA, are known to be present in CMVs in addition to other cell membrane components; and c) Yeast EVs are produced both from the cell membrane fusion of intracellularly produced MVBs and from the outward blebbing of the cell membrane. Proteins and lipids present on the surface of yeast EVs would distinguish these biogenesis routes. Created with Biorender.com.

Figure 4.

A diagram showing the viral shunt. The arrows show the movement of dissolved organic matter (DOM) and particulate organic matter (POM) in the environment.