“Bacterial Fortresses” and “gene-trafficking phages”, in my picks of the week from RB

Another week has gone by and some very interesting molbio blog posts have been aggregated to Researchblogging.org. Every week [see my opening post on the matter], I'll select some blog posts I consider particularly interesting in the field of molecular biology [see here to get a sense of the criteria that will be used], briefly describe them and list them here for you to check out.

Note that I'm only taking into consideration the molbio-related blog posts aggregated under "Biology".

Congratulations to everyone who got their post selected.

1) As I’ve commented before, in a previous issue of my Picks of the Week, under certain conditions bacteria can cooperate as a population to create biofilms, which consist of “sessile aggregates of bacteria embedded in a self-made extracellular polymeric matrix”.
Interestingly, this matrix can act as “tough physical barriers that are immune to attacks by many antibiotics and other bacteriocidal agents”, including the action of the host defence system.

Pseudomonas aeruginosa, an opportunistic pathogen, is capable of forming such biofilms, and Lab Rat discusses an interesting new article reporting that biofilm P. aeruginosa cells can react to the presence of polymorphonuclear neutrophilic leukocytes (phagocytic cells which are important players in the innate immune response since they produce a range of antimicrobial molecules able to kill pathogens) by producing a “shield” made of a particular glycolipid biosurfactant called rhamnolipid, which can cause lysis of these immune cells. Interestingly, the synthesis of these lipids is under control of the quorum-sensing system.

2) Hundreds of bacterial genomes have been sequenced and are now available for comparative genomics. Perhaps one of the most fascinating discoveries has been that the genomic diversity, even among the genomes of closely related species, can be enormous.
Bacteriophages have played an important role in shaping bacterial genomes, particularly by contributing to lateral gene transfer through transduction.

From the article:

“Bacteriophages have the ability to manipulate the life histories and evolution of their hosts and evolved many adaptation and defence mechanisms for efficient survival and multiplication. Most of these involve manipulation of the host DNA, as well as the incorporation, into the phage genomes, of bacterial genes that encode proteins with a potential to facilitate bacteriophage reproduction” (my emphasis)

Apparently, the latter is the case with cyanophages and cyanobacteria, as discussed by Iddo Friedberg at Byte Size Bio. He comments on a recent (and purely bioinformatic) Nature article reporting “the presence of photosystem I (PSI) genes in the genomes of viruses that infect marine cyanobacteria, [by] using pre-existing metagenomic data from a global ocean sampling expedition as well as from viral biomes”. Further, they show (by modeling) that apparently, the use of one of these proteins encoded in the phage genome can make the bacterial PSI function more efficiently.


That's it for this week. Stay tuned for more MolBio Research Highlights!

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Some of the articles discussed in this week's selected posts:

Alhede M, Bjarnsholt T, Jensen PØ, Phipps RK, Moser C, Christophersen L, Christensen LD, van Gennip M, Parsek M, Høiby N, Rasmussen TB, & Givskov M (2009). Pseudomonas aeruginosa recognizes and responds aggressively to the presence of polymorphonuclear leukocytes. Microbiology (Reading, England), 155 (Pt 11), 3500-8 PMID: 19643762


Sharon, I., Alperovitch, A., Rohwer, F., Haynes, M., Glaser, F., Atamna-Ismaeel, N., Pinter, R., Partensky, F., Koonin, E., Wolf, Y., Nelson, N., & Béjà, O. (2009). Photosystem I gene cassettes are present in marine virus genomes Nature, 461 (7261), 258-262 DOI: 10.1038/nature08284