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Our next Journal club will be on the 28th of October 2014 at 8 pm on this paper here:

Regulation of the AbrA1/A2 Two-Component System in Streptomyces coelicolor and the Potential of Its Deletion Strain as a Heterologous Host for Antibiotic Production by Sergio Rico, Ana Yepes, Héctor Rodríguez, Jorge Santamaría, Sergio Antoraz, Eva M. Krause, Margarita Díaz, Ramón I. Santamaría, published on October 10, 2014 DOI:10.1371/journal.pone.0109844

Link: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0109844

Background
Streptomyces is a genus of actinobacteria, a group of Gram-positive soil bacteria with an unusual life cycle, involving substrate mycelium, formation of aerial hyphae and spore formation. They are prolific producers of bioactive metabolites, such as clavulinic acid or FK-506 and thus are of great interest for industry. The onset for the production of these metabolites usually happens when nutrients are limited and come along with the developmental stages. The regulation of antibiotic production has been extensively studied mainly in S.coelicolor which is one of the model organisms and many genetic tools are available. For more details see this review here: http://mmbr.asm.org/content/77/1/112.short
Regulation of the AbrA1/A2 Two-Component System in Streptomyces coelicolor and the Potential of Its Deletion Strain as a Heterologous Host for Antibiotic Production
By Sergio Rico, Ana Yepes, Héctor Rodríguez, Jorge Santamaría, Sergio Antoraz, Eva M. Krause, Margarita Díaz, Ramón I. Santamaría
Published on October 10, 2014DOI: 10.1371/journal.pone.0109844
Abstract
The Two-Component System (TCS) AbrA1/A2 from Streptomyces coelicolor M145 is a negative regulator of antibiotic production and morphological differentiation. In this work we show that it is able to auto-regulate its expression, exerting a positive induction of its own operon promoter, and that its activation is dependent on the presence of iron. The overexpression of the abrA2 response regulator (RR) gene in the mutant ΔabrA1/A2 results in a toxic phenotype. The reason is an excess of phosphorylated AbrA2, as shown by phosphoablative and phosphomimetic AbrA2 mutants. Therefore, non-cognate histidine kinases (HKs) or small phospho-donors may be responsible for AbrA2 phosphorylation in vivo. The results suggest that in the parent strain S. coelicolor M145 the correct amount of phosphorylated AbrA2 is adjusted through the phosphorylation-dephosphorylation activity rate of the HK AbrA1. Furthermore, the ABC transporter system, which is part of the four-gene operon comprising AbrA1/A2, is necessary to de-repress antibiotic production in the TCS null mutant. Finally, in order to test the possible biotechnological applications of the ΔabrA1/A2strain, we demonstrate that the production of the antitumoral antibiotic oviedomycin is duplicated in this strain as compared with the production obtained in the wild type, showing that this strain is a good host for heterologous antibiotic production. Thus, this genetically modified strain could be interesting for the biotechnology industry.

Discussion points:
1. Is the paper well written?
2. Were the methods appropriate?
3. Do the results reflect the conclusion?
4. What else could be done?

Hi everyone!

Welcome to #MicroTwJC 55, hosted on 14/10/2014 by @_LisaKWilliams_ and @Stewart_Barker.

This week we will be discussing the fascinating world of virophages – that is viruses which attack other viruses. The paper can be found here: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0094923

Following a previous #MicroTwJC discussion on the largest discovered viruses, this fairly recent paper describes a satellite virus (or virophage) named Zamilon that is associated with the giant virus family Mimiviridae. Zamilon is similar to other described virophages which have negative effects on their host – Sputnik virophages, yet does not appear to inhibit it’s host in any way…

 

“The host-specificity of the Zamilon virophage supports the distinction between satellite viruses (opportunistic entities associated with a virus) and virophages, which target specific hosts.”

 

Aside from what we think is an interesting paper and concept, the above quote is a crucial point of the paper. We leave you with the abstract and questions to consider below, and look forward to a lively debate!

Abstract

Virophages, which are potentially important ecological regulators, have been discovered in association with members of the order Megavirales. Sputnik virophages target the Mimiviridae, Mavirus was identified with the Cafeteria roenbergensis virus, and virophage genomes reconstructed by metagenomic analyses may be associated with the Phycodnaviridae. Despite the fact that the Sputnik virophages were isolated with viruses belonging to group A of theMimiviridae, they can grow in amoebae infected by Mimiviridae from groups A, B or C. In this study we describe Zamilon, the first virophage isolated with a member of group C of theMimiviridae family. By co-culturing amoebae with purified Zamilon, we found that the virophage is able to multiply with members of groups B and C of the Mimiviridae family but not with viruses from group A. Zamilon has a 17,276 bp DNA genome that potentially encodes 20 genes. Most of these genes are closely related to genes from the Sputnik virophage, yet two are more related to Megavirus chiliensis genes, a group B Mimiviridae, and one to Moumouvirus monve transpoviron.

 

Points to consider

  1. Is the paper well written?
  2. Do the methods fully investigate whether the Zamilon virophage has a disruptive effect on its host?
  3. Are the results and discussion appropriate?
  4. Is Zamilon a virophage, or a satellite virus? Is there actually a difference between the two terms?