Measurement of Predation and Biofilm Formation under Different Ambient Oxygen Conditions Using a Simple Gasbag-Based System

Abstract

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...

Insights into Cystic Fibrosis Polymicrobial Consortia: The Role of Species Interactions in Biofilm Development, Phenotype, and Response to In-Use Antibiotics

“…Data obtained from single and dual cultures showed that the biofilm-producing ability was markedly higher under aerobic atmospheres. Kadouri and Tran (2013) measured biofilm formation by a variety of opportunistic pathogens, at different oxygen concentrations, and also established a positive correlation between oxygen levels and biofilm formation ability. Data also suggested that the changes in the overall biofilm mass and culturable cells of dual biofilms can be due to reciprocal interference between species in the consortia or even only triggered by P. aeruginosa .…”

Biotechnological Potential of Bdellovibrio and Like Organisms and Their Secreted Enzymes

“…It has even been suggested that B. bacteriovorus may contribute to health as part of the human gut microbiota (Iebba et al, 2013). Although considered as obligately aerobic bacteria, research has shown that BALOs can survive under anoxic conditions and that certain strains, including B. bacteriovorus, are able to grow and attack under microaerobic conditions (Kadouri and Tran, 2013;Patini et al, 2019). These findings further support the potential of using these predators as therapeutics in environments such as the gastrointestinal tracts (Sockett and Lambert, 2004;Dwidar et al, 2012b).…”

“…The level of oxygen is proven to be critical for B. bacteriovorus ability to prey upon cells. While maintaining the ability to reduce biofilms, lack of oxygen inhibits any predation upon planktonic cells (Kadouri and Tran, 2013;Patini et al, 2019).…”

Stenotrophomonas maltophilia biofilm reduction by Bdellovibrio exovorus

“…They typically have a broad prey range but are unable to attack Gram‐positive or eukaryotic cells in co‐cultures, making them and/or their lytic enzymes candidates for use as biological antimicrobials against Gram‐negative bacterial pathogens (Sockett and Lambert, ; Markelova, ; Dashiff and Kadouri, ; Kadouri et al ., ). The ability of Bdellovibrio bacteriovorus to disrupt biofilms formed by Gram‐negative bacteria (Kadouri and O'Toole, ; Van Essche et al ., ; Dwidar et al ., ; Kadouri and Tran, ; Chanyi and Koval, ) adds to the potential therapeutic use of BALOs. Interestingly, a recent study by Monnappa et al .…”

“…They typically have a broad prey range but are unable to attack Gram-positive or eukaryotic cells in co-cultures, making them and/or their lytic enzymes candidates for use as biological antimicrobials against Gram-negative bacterial pathogens (Sockett and Lambert, 2004;Markelova, 2010;. The ability of Bdellovibrio bacteriovorus to disrupt biofilms formed by Gramnegative bacteria (Kadouri and O'Toole, 2005;Van Essche et al, 2009;Dwidar et al, 2012;Kadouri and Tran, 2013;Chanyi and Koval, 2014) adds to the potential therapeutic use of BALOs. Interestingly, a recent study by Monnappa et al (2014) showed that extracellular proteases from a host(prey)-independent strain of B. bacteriovorus HD100 inhibited the formation of a biofilm by the Gram-positive pathogen Staphylococcus aureus and, thus, its virulence.…”