Friday, 22nd September 2017

Virology and Microbiology

        Effects of extrachromosomal elements on behaviour of its host and mechanisms of                 horizontal gene transfer in Bacillus.







Wilfried J.J Meijer







Research summary:

Inhibitory effect of pLS20-encoded protein Rok-LS20 on competence of B. subtilis. Competent cells are green due to expression of the green fluorescent protein engineered to be under the control of specific competence promoter. Membranes are stained red. The strain contains a copy of the pLS20-located gene rokLS20 under the control of an IPTG-inducible promoter. A and B. Cells without and with induction of Rok-LS20.


Genetic map of B. subtilis conjugative plasmid pLS20..

Mobile genetic elements (MGE), e.g. phages, plasmids, transposons and ICEs, can be transferred horizontally between cells affecting the genetic make-up and hence the behaviour of bacteria. Accordingly, horizontal gene transfer (HGT) has a crucial role in microbial evolution and has important implications in a myriad of environmental and public-health problems. For instance, HGT is mainly responsible for the emergence and dispersion of antibiotic resistance.
Little is known, especially in Gram-positive bacteria, about the transcriptional regulation of mobility genes or how MGE affects its host. A better understanding of these issues is warranted to face important threats, like antibiotic resistance. We study these issues using as host Bacillus subtilis and we limit the MGE to plasmids and phages.
We use B. subtilis because (i) it is probably the best studied Gram-positive bacterium; (ii) it is non-pathogenic; (iii) it is easy amenable to genetic manipulation; and (iv) B. subtilis is related to pathogenic/fastidious bacteria like Bacillus anthracis, B. cereus and, although more distantly, to Listeria monocytogenes. So far, no sequence of conjugative B. subtilis plasmids was known. We have now sequenced and annotated the two large B. subtilis plasmids and are functionally analyzing them with the major aims to get insight in regulation of the mobility genes and effect on their host.
Many Gram positive bacteria with industrial or scientific importance are reluctant to genetic manipulation. Our goal is to construct versatile vectors allowing easy genetic manipulation of such bacteria based on the conjugation systems we study. For this we study several additional aspects of the conjugative plasmids.
Upon infection, phages often drastically alter the behaviour of B. subtilis. However, neither sequence nor mechanistic information of how these phages exert their effects is known. We are attempting to understand the mechanism underlying these alterations using two temperate phages as model systems.


Relevant publications:

  • Singh, P. K., Ramachandran, G., Durán-Alcalde, L., Alonso, C. Wu, L.J., and Meijer, W.J.J. (2012) Inhibition of Bacillus subtilis natural competence by a native, conjugative plasmid-encoded comK repressor protein. Environ. Microbiol. 14, 2812-25