Natural transformation of Clp mutants.

<p>Natural transformation efficiency of <i>C. jejuni</i> Clp deletion mutants and the complemented ClpP mutant (ΔClpP+ClpP) transformed with excess amounts of isogenic chromosomal Strep^R DNA. The results represent a mean of three replicates with standard deviations.</p

Natural Transformation of <em>Campylobacter jejuni</em> Occurs Beyond Limits of Growth

<div><p><em>Campylobacter jejuni</em> is a human bacterial pathogen. While poultry is considered to be a major source of food borne campylobacteriosis, <em>C. jejuni</em> is frequently found in the external environment, and water is another well-known source of human infections. Natural transformation is considered to be one of the main mechanisms for mediating transfer of genetic material and evolution of the organism. Given the diverse habitats of <em>C. jejuni</em> we set out to examine how environmental conditions and physiological processes affect natural transformation of <em>C. jejuni</em>. We show that the efficiency of transformation is correlated to the growth conditions, but more importantly that transformation occurs at growth-restrictive conditions as well as in the late stationary phase; hence revealing that growth <em>per se</em> is not required for <em>C. jejuni</em> to be competent. Yet, natural transformation of <em>C. jejuni</em> is an energy dependent process, that occurs in the absence of transcription but requires an active translational machinery. Moreover, we show the ATP dependent ClpP protease to be important for transformation, which possibly could be associated with reduced protein glycosylation in the ClpP mutant. In contrast, competence of <em>C. jejuni</em> was neither found to be involved in DNA repair following DNA damage nor to provide a growth benefit. Kinetic studies revealed that several transformation events occur per cell cycle indicating that natural transformation of <em>C. jejuni</em> is a highly efficient process. Thus, our findings suggest that horizontal gene transfer by natural transformation takes place in various habitats occupied by <em>C. jejuni</em>.</p> </div

Natural transformation is dependent on active electron transport.

a<p>Exponentially growing cells were incubated with the respiratory inhibitor for 2 h prior to a wash out of compound and addition of DNA.</p>b<p>The respiratory inhibitor were added to the exponentially growing cells together with the DNA.</p>c<p>Normalized to the negative control.</p>d<p>100 µg/ml.</p>e<p>500 µM.</p

Natural transformation of <i>C. jejuni</i> at varying temperature and atmospheric conditions^a,b.

a<p>Exponentially growing cells were supplied with isogenic chromosomal DNA at 1∶2.5 ratio (CFU:DNA) and transformation was allowed to proceed for 4 h before plating on selective agar. Results are the average of three independent experiments with two replicates.</p>b<p>Results are normalized to the number of transformants per ml at 37°C under microaerophilic conditions.</p>c<p>Not determined.</p

Natural transformation efficiency of <i>C. jejuni</i> NCTC11168.

a<p>Results are mean of three replicates with standard deviation.</p>b<p>Chromosomal DNA from <i>C. jejuni</i> NCTC11168 Δ<i>tlp1::Cam^R.</i></p>c<p>Limits of range tested: 10⁻⁴–10⁰ transformants/CFU.</p>d<p>Limits of range tested: 10⁻⁵–10⁻¹ transformants/DNA molecule.</p>e<p>Excess amounts of DNA.</p>f<p>Limited amounts of DNA.</p

Natural transformation in exponential and stationary growth phases.

a<p>Aggregates of bacterial cells resuspended before transformation.</p>b<p>Mean of four replicates with standard deviations.</p

Plaque assay of phage F380 on strain A. NCTC12662 and B. NCTC12662<i>∆kpsM</i>.

<p>Clearer lysis and plaque formation can be seen on the acapsular version of the <i>C. jejuni</i> strain. </p

Electron micrographs of <i>C. jejuni</i> bacteriophages F362 (a and b) and F386 (c and d).

<p>a. Normal phage particle with extended tail and folded-up fibers. b. Phage particle with contracted tail sticking in small globular vesicles. Note the tail fibers are no longer visible. c. Normal phage particle with extended tail and flexible fibers with attached small terminal globular structures. d. Phage particle with contracted tail. Note tail fibers are still visible. Phages were stained with 2% uranyl acetate and examined on a Tecnai 10 transmission electron microscope. </p