Bdellovibrio bacteriovorus and Micavibrio aeruginosavorus are Gram-negative bacteria characterized by predatory behavior. The aim of this study was to evaluate the ability of the predators to prey in different oxygen environments. When placed on an orbital shaker, a positive association between the rate of aeration and predation was observed. To further examine the effects of elevated ambient oxygen levels on predation, a simple gasbag system was developed. Using the system, we were able to conduct experiments at ambient oxygen levels of 3% to 86%. When placed in gasbags and inflated with air, 50% O 2 , and 100% O 2 , positive predation was seen on both planktonic and biofilm-grown prey cells. However, in low-oxygen environments, predatory bacteria were able to attack only prey cells grown as biofilms. To further evaluate the gasbag system, biofilm development of Grampositive and Gram-negative microorganisms was also measured. Although the gasbag system was found to be suitable for culturing bacteria that require a low-oxygen environment, it was not capable of supporting, with its current configuration, the growth of obligate anaerobes in liquid or agar medium.A cute and chronic wounds are a major burden to public health and the economy (1). It is estimated that, in the United States alone, chronic wounds affect 6.5 million patients (2). One medical procedure used to promote wound healing is the use of oxygen therapy (3). For example, the use of oxygen under pressure or "hyperbaric oxygen therapy" (HBO 2 ) was shown to have a positive effect on ischemia and local wound hypoxia (4-6). In the last few years, additional medical procedures that allow topical administration of oxygen therapy directly to the wound site in order to support wound healing have been developed (7-9). One of the major complications affecting wound healing are infection, many of which are caused by multidrug-resistant pathogens and surface-associated (biofilm) bacteria (1, 10-12). It was previously suggested that predatory bacteria from the genus Bdellovibrio and Micavibrio could be used as live antibiotics to control wound infections (13,14).The purpose of this study was to evaluate the ability of predatory bacteria to prey in elevated ambient O 2 levels with the longterm goal of using predatory bacteria in combination with traditional oxygen therapy in order to enhance wound healing. To this end, a new gasbag system that allowed experiments to be conducted in diverse gas environments was developed. The system was also used to evaluate biofilm formation of medically relevant Gram-positive and Gram-negative bacteria in O 2 environments that were not examined previously. MATERIALS AND METHODSPredatory bacteria. The predatory bacteria used in this study were Micavibrio aeruginosavorus ARL-13 (15, 16), Bdellovibrio bacteriovorus 109J (ATCC 43826), B. bacteriovorus HD100 (17, 18), and a previously isolated host-independent (HI) variant of B. bacteriovorus 109J (19). The HI variant was cultured at 30°C in peptone-yeast extract (PYE) (10 g/liter p...