Periplasmic enzymes in Bdellovibrio bacteriovorus and Bdellovibrio stolpii

Quantitative changes in the elasticity and adhesive properties of Escherichia coli ZK1056 prey cells during predation by bdellovibrio bacteriovorus 109J

Atomic force microscopy (AFM) was used to explore the changes that occur in Escherichia coli ZK1056 prey cells while they are being consumed by the bacterial predator Bdellovibrio bacteriovorus 109J. Invaded prey cells, called bdelloplasts, undergo substantial chemical and physical changes that can be directly probed by AFM. In this work, we probe the elasticity and adhesive properties of uninvaded prey cells and bdelloplasts in a completely native state in dilute aqueous buffer without chemical fixation. Under these conditions, the rounded bdelloplasts were shown to be shorter than uninvaded prey cells. More interestingly, the extension portions of force curves taken on both kinds of cells clearly demonstrate that bdelloplasts are softer than uninvaded prey cells, reflecting a decrease in bdelloplast elasticity after invasion by Bdellovibrio predators. On average, the spring constant of uninvaded E. coli cells (0.23 +/- 0.02 N/m) was 3 times stiffer than that of the bdelloplast (0.064 +/- 0.001 N/m) when measured in a HEPES-metals buffer. The retraction portions of the force curves indicate that compared to uninvaded E. coli cells bdelloplasts adhere to the AFM tip with much larger pull-off forces but over comparable retraction distances. The strength of these adhesion forces decreases with increasing ionic strength, indicating that there is an electrostatic component to the adhesion events.

Investigations into the life cycle of the bacterial predator Bdellovibrio bacteriovorus 109J at an interface by atomic force microscopy

Atomic force microscopy was used to image Bdellovibrio bacteriovorus 109J, a gram-negative bacterial predator that consumes a variety of other gram-negative bacteria. In predator-prey communities grown on filters at hydrated air-solid interfaces, repeated cycles of hunting, invasion, growth, and lysis occurred readily even though the cells were limited to near two-dimensional movement. This system allowed us to image the bacteria directly without extensive preparation or modification, and many of the cells remained alive during imaging. Presented are images of the life cycle in two species of prey organisms, both Escherichia coli (a small prey bacterium that grows two-dimensionally on a surface) and Aquaspirillum serpens (a large prey bacterium that grows three-dimensionally on a surface), including high-resolution images of invaded prey cells called bdelloplasts. We obtained evidence for multiple invasions per prey cell, as well as significant heterogeneity in morphology of bdellovibrios. Mutant host-independent bdellovibrios were observed to have flagella and to excrete a coating that causes the predators to clump together on a surface. Most interestingly, changes in the texture of the cell surface membranes were measured during the course of the invasion cycle. Thus, coupled with our preparation method, atomic force microscopy allowed new observations to be made about Bdellovibrio at an interface. These studies raise important questions about the ways in which bacterial predation at interfaces (air-solid or liquid-solid) may be similar to or different from predation in solution.

Formation of Stable Bdelloplasts as a Starvation-Survival Strategy of Marine Bdellovibrios

Several wild-type isolates of marine bdellovibrios formed stable bdelloplasts when they infected gram-negative bacterial prey under certain culture conditions. Synchronous predator-prey cultures and low nutrient concentrations increased the yield of stable bdelloplasts. The bdellovibrio cells retained in the stable bdelloplasts showed a high survival capacity in nutrient-depleted saline solution (10% viable Bdellovibrio cells after 3 months at 25°C), whereas Bdellovibrio attack-phase cells kept under the same starvation conditions lost viability more quickly (1% viable cells after 48 h). The addition of yeast extract to a stable bdelloplast suspension induced lysis of the bdelloplasts and release of motile infecting attack-phase Bdellovibrio cells. Other substances, such as free amino acids, protein hydrolysates, NH 4 + , carbohydrates, and organic amines, did not induce such a release. Stable bdelloplasts were highly hydrophobic and had a lower endogenous respiration rate than attack-phase cells. In general, stable bdelloplasts were almost as sensitive to temperature changes, desiccation, sonication, tannic acid, and Triton X-100 treatment as attack-phase cells. Electron microscopy of stable bdelloplasts did not reveal any extra cell wall layer, either in the bdelloplast envelope or in the retained Bdellovibrio cells, unlike the bdellocysts of the soil bacterium Bdellovibrio sp. strain W. We propose that formation of stable bdelloplasts is a survival strategy of marine bdellovibrios which occurs in response to nutrient- and prey-poor seawater habitats.

Metabolism of periplasmic membrane-derived oligosaccharides by the predatory bacterium Bdellovibrio bacteriovorus 109J

Membrane-derived oligosaccharides (MDO), a class of osmotically active carbohydrates, are the major organic solutes present in the periplasm of Escherichia coli and many other gram-negative bacteria when cells are grown in a medium of low osmolarity. Analyses of growing cells of Bdellovibrio bacteriovorus, a gram-negative predator of other bacteria, have confirmed that they also synthesize a characteristic MDO-like class of oligosaccharides. The natural growth environment of bdellovibrios is the periplasm of other gram-negative bacteria. Because of this location, prey cell MDO constitute a potential source of organic nutrients for growing bdellovibrios. Using cells of E. coli whose MDO were 3H labeled, we examined the extent to which B. bacteriovorus 109J metabolizes these prey cell components. Interestingly, there was neither significant degradation nor incorporation of prey cell MDO by bdellovibrios during the course of their intracellular growth. In fact, bdellovibrios had little capability either to degrade extracellular MDO that was made available to them or to transport glucose, the major monomeric constituent of prey cell MDO. Instead, periplasmic MDO were irreversibly lost to the extracellular environment during the period of bdellovibrio attack and penetration. Thus, although prey cell periplasmic proteins are retained, other important periplasmic components are released early in the bdellovibrio growth cycle. The loss of these MDO may aid in the destabilization of the prey cell plasma membrane, increasing the availability of cytoplasmic constituents to the periplasmic bdellovibrio.

An ATP transport system in the intracellular bacterium, Bdellovibrio bacteriovorus 109J

The intracellularly growing bacterium Bdellovibrio bacteriovorus 109J transports intact ATP by a specific, energy-requiring process. ATP transport does not involve either an ADP-ATP or an AMP-ATP exchange mechanism but, instead, has characteristics of an active transport permease. Kinetically distinct systems for ATP transport are expressed by the two developmental stages of the bdellovibrio life cycle.