Two different propionicins produced by Propionibacterium thoenii P-127

The bacteriocin GBZ-1 was purified from the growth media of Propionibacterium thoenii P-127 and was found to have a molecular weight of 6000Da. P. thoenii P-127 also known as the producer of the bacteriocin PLG-1 (MW 10kDa). Under specific growth conditions, on semi-solid media, P. thoenii P-127 produced both PLG-1 and GBZ-1. The N-terminal of GBZ-1 was microsequenced, the gene was cloned and the DNA sequence was determined and identified. GBZ-1 is highly homologous to a protease-activated antimicrobial peptide (PAMP). In contrast to PAMP, it was purified in its active form and no protease digestion was required for its activation. The survival curve of indicator bacteria Lactobacillus delbrueckii subsp. lactic ATCC 4797 showed two phases. The fast phase of 20min was followed by a slow phase. While bacterial survival was reduced by 2logs during the fast phase, bacterial survival was reduced by additional 3logs up to 200min during the slow phase. GBZ-1 activity was affected by magnesium and its activity was completely abolished at 50mM magnesium chloride. Other divalent cations had no effect on GBZ-1 activity of GBZ-1. To the best of our knowledge this is the first report of a bacterium producing two different bacteriocins under different growth conditions.     

Host association of Borrelia burgdorferi sensu lato--the key role of host complement

Borrelia burgdorferi sensu lato (s.l.), the tick-borne agent of Lyme borreliosis, is a bacterial species complex comprising 11 genospecies. Here, we discuss whether the delineation of genospecies is ecologically relevant. We provide evidence that B. burgdorferi s.l. is structured ecologically into distinct clusters that are host specific. An immunological model for niche adaptation is proposed that suggests the operation of complement-mediated selection in the midgut of the feeding tick. We conclude that vertebrate hosts rather than tick species are the key to Lyme borreliosis spirochaete diversity.