Bdellovibrio bacteriovorus and Micavibrio aeruginosavorus are highly motile Gram-negative predatory bacteria with the potential of being used as biocontrol agents or living antibiotics. It was suggested previously that sugar-binding proteins play a role in M. aeruginosavorus and B. bacteriovorus host specificity and predator-prey interactions. The effect of carbohydrates on predation was reexamined in this study. It was demonstrated that the presence of carbohydrates could indeed block predation. However, further investigation demonstrated that inhibition of predation was due to medium acidification by the metabolic activity of the host and not to a blocking of a putative sugar-binding protein. The data presented here might be of value when storing, growing, and cultivating predatory bacteria, as well as when considering environmental conditions that might influence predation in the field.Bdellovibrio and Micavibrio species are Gram-negative, motile, and uniflagellate bacteria characterized by predatory behavior or an obligatory parasitic life cycle. Recently, these bacteria have drawn new interest for their potential use as "live antibiotics" (9, 30). The Bdellovibrio life cycle, with Bdellovibrio bacteriovorus being the most studied representative of the genus, consists of an attack-phase cell that attaches to other Gram-negative bacteria, penetrates their periplasm, multiplies in the periplasmic space, and finally bursts the cell envelope to start the cycle anew (24,29,31). Unlike that of Bdellovibrio spp., our knowledge of Micavibrio biology is somewhat modest. Micavibrio belongs to the alpha subgroup of proteobacteria (11); they are small (0.5 to 1.5 m long), rod shaped, and curved and have a single polar flagellum. The Micavibrio life cycle includes the attachment, or leeching, of a motile attack-phase cell to its prey, followed by growth on the surface of the host and, finally, the death of the infected cells (2,18,19). Unlike B. bacteriovorus, which is considered to have a broad host range (9, 31), Micavibrio spp. such as M. aeruginosavorus are host specific (1,9,16,19). To date, one of the key questions puzzling researchers is what governs host specificity and host-predator recognition.One factor that might be involved in predator-prey interactions and host specificity is protein-carbohydrate interactions. Lectins are sugar-binding proteins that play a role in many biological recognition phenomena, one of which is recognition of host cells by microorganisms. For example, the adherence of bacteria to host cells is in many cases mediated by lectin-like adhesins on the bacterial surface that bind to carbohydrate receptors present on the host cell surface as part of the membrane glycoproteins and glycolipids (5,15,23). Lectins are also involved in recognition and attachment of fungi, protozoa, and viruses to their host cells during infection (3,13,20,25,32,34).In 1984, Chemeris and colleagues demonstrated that the predation of B. bacteriovorus could be inhibited by the addition of sugars to coculture media ...