Some energy-producing systems in Bdellovibrio bacteriovorus, strain 6-5-S

Abstract

Bdellovibrio bacteriovorus 6-5-S, an obligate bacterial parasite, was grown on cells of Spirillum serpens in 20 l of medium. Maximum numbers of the parasite were attained at 42–55 h, about 2–12 h after there were no viable host cells remaining. Growth of B. bacteriovorus occurred only under aerobic conditions. The organism is rich in catalase. Endogenous respiration of cells and oxidation of NADH by cell extracts is inhibited by cyanide and azide but not by carbon monoxide. Difference spectra indicate the parasite has a cytochrome system and likely couples oxidation to phosphorylation, although efforts to demonstrate fixation of inorganic 32P into organic phosphate failed. Glutamine, glutamate, and asparagine stimulate respiration, and cell extracts contain glutamate and alanine dehydrogenases. B. bacteriovorus 6-5-S also has a tricarboxylic acid cycle, as isocitric dehydrogenase, the α-ketoglutarate dehydrogenase system, succinyl-CoA synthetase, fumarase, and malate dehydrogenase were found in the soluble fraction of the cell extract, and a bound succinic dehydrogenase in the particulate fraction. The glyoxylate cycle may not be present since isocitric lyase could not be detected despite the presence of acetate in the growth medium. Tests on cell extracts for glucose kinase, glucose 6-phosphate dehydrogenase, and 6-phosphogluconate dehydrogenase were also negative. However, aldolase, glyceraldehyde 3-phosphate dehydrogenase, pyruvate kinase, and lactic acid dehydrogenase were present although at rather low levels, indicating that the parasite can obtain energy from the substrate-linked phosphorylations of the glycolytic system.

Molecular heterogeneity of the bdellovibrios: Metallo and serine proteases unique to each species

“…These enzymes can digest host cell protein during host-dependent growth or hydrolyze "conventional" proteins and peptides in commercial media during host-independent growth. Other studies on Bdellovibrio intracellular enzymes indicate a functional TCA cycle as well as an alanine and glutamic dchydrogenase (Seidler et al, 1972;Simpson and Robinson, 1968). These enzymes make it possible for amino acids to supply the carbon and energy sources needed for Bdellovibrio growth.…”

Host-independent Growth of Bdellovibrio bacteriovorus in Microbial Extracts

“…Evidence had accumulated, from the enzymic content of Bdellovibrio (Simpson & Robinson, 1968) and its ability to grow equally well on live, heat-killed and u.v.-killed hosts (Varon & Shilo, 1969b), that the role of the host bacteria in Bdellovibrio infection was limited to satisfying nutritional and/or physical requirements. The growth of bdellovibrios in bacterial extracts reported here further confirms this view.…”

“…Extracellular bdellovibrios demonstrate considerable metabolic activity (Simpson & Robinson, 1968;Varon & Shilo, 1969b). Differences were expected, however, between activities involving motility and maintenance, and those which involve growth.…”

The dual probiotic and antibiotic nature of Bdellovibrio bacteriovorus

“…In a subsequent study by the same group (25), they showed that different bacterial species involved in periodontitis can be attacked by one or more of Bdellovibrio strains, even if the prey was strict anaerobe. This is remarkable since, on the hand, BALOs are strict aerobes and require oxygen to complete the predation cycle (7,32) while, on the other hand, their prey will die if exposed to oxygen for too long.…”

“…However, since their effects on the natural flora of different body cavities has not been studied thoroughly and should be taken into consideration, the use of BALOs in this case would need to be monitored. According to early studies of BALOs (7,32), these bacteria were found to be strict aerobes, and this of course can be a drawback that limits their potential use in oxygen-limited environments within the human body, such as gut or urinary tract. However, it should be noted that according to a study done by Schoffield et al (54), BALO strains could survive for up to nine days under anoxic environments and some BALO strains could grow and attack under microaerobic conditions, albeit at a reduced rate compared to fully aerobic tests.…”