Phenotypic Variation and Bistable Switching in Bacteria

Microbial research generally focuses on clonal populations. However, bacterial cells with identical genotypes frequently display different phenotypes under identical conditions. This microbial cell individuality is receiving increasing attention in the literature because of its impact on cellular differentiation, survival under selective conditions, and the interaction of pathogens with their hosts. It is becoming clear that stochasticity in gene expression in conjunction with the architecture of the gene network that underlies the cellular processes can generate phenotypic variation. An important regulatory mechanism is the so-called positive feedback, in which a system reinforces its own response, for instance by stimulating the production of an activator. Bistability is an interesting and relevant phenomenon, in which two distinct subpopulations of cells showing discrete levels of gene expression coexist in a single culture. In this chapter, we address techniques and approaches used to establish phenotypic variation, and relate three well-characterized examples of bistability to the molecular mechanisms that govern these processes, with a focus on positive feedback.

Comparing recovering efficiency of immunomagnetic separation and centrifugation of mycobacteria in metalworking fluids

The accurate detection and enumeration of Mycobacterium immunogenum in metalworking fluids (MWFs) is imperative from an occupational health and industrial fluids management perspective. We report here a comparison of immunomagnetic separation (IMS) coupled to flow-cytometric enumeration, with traditional centrifugation techniques for mycobacteria in a semisynthetic MWF. This immunolabeling involves the coating of laboratory-synthesized nanometer-scale magnetic particles with protein A, to conjugate a primary antibody (Ab), specific to Mycobacterium spp. By using magnetic separation and flow-cytometric quantification, this approach enabled much higher recovery efficiency and fluorescent light intensities in comparison to the widely applied centrifugation technique. This IMS technique increased the cell recovery efficiency by one order of magnitude, and improved the fluorescence intensity of the secondary Ab conjugate by 2-fold, as compared with traditional techniques. By employing nanometer-scale magnetic particles, IMS was found to be compatible with flow cytometry (FCM), thereby increasing cell detection and enumeration speed by up to two orders of magnitude over microscopic techniques. Moreover, the use of primary Ab conjugated magnetic nanoparticles showed better correlation between epifluorescent microscopy counts and FCM analysis than that achieved using traditional centrifugation techniques. The results strongly support the applicability of the flow-cytometric IMS for microbial detection in complex matrices.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47949/1/10295_2005_Article_238.pd

Thymidine incorporations and exoproteolytic activity of bacterial population from inshore waters in Barcelona

14 pages, 1 figure, 5 tables[EN] To investigate the bacterial population in coastal waters from Barcelona (Spain), 3H-thymidine incorporation, exoproteolytic activity and direct counts of bacteria by epifluorescence were determined in samples from nine sampling locations at two rivers, wich are the main pollution focus of this coast. [...][ES] En el estudio de la población bacteriana de las aguas costeras de Barcelona (España), se determinó la incorporación de timidina tritiada, la actividad exoproteolítica y número de bacterias por epifluorescencia, en nueve estaciones de playa y seis estaciones en los dos rios, que son ei principał foco de polución de esta costa. Los tres parárnetros muestran nivełes altos y muy variables a ło largo del período estudiado Los resultados se discuten a partir de las correlaciones entre población bacteriana y su actividad, asi como por la interacción entre las aguas de los ríos y el mar en las zonas de confluencia. [...]Peer Reviewe

Effect of the Besós River discharge (Barcelona, Spain) on the bacterial population of the receiving water from Mediterranean Sea

10 pages, 1 figure, 1 table[EN] The Besós River is the main wastewater discharge in the coastal area between Barcelona and Montgat (Spain). The impact of this waste dumping on the sea bacterial populations was studied by means of thymidine incorporation and epifluorescence bacterial counts. The decrease of CDO and the variations in bacterial production, indicate the existece of two types of organic matter, which support different kinetic of bacterial growth. [...][ES] El rio Besós es el principal foco de contarminación de la zona costera comprendida entre Barcelona y Montgat (España) Se ha estudiado ei impacto de estos vertidos en la población bacteriana marina, por incorporación de timidina y enuncración bacteriana por epifluorescencia. A partir de la disminución de la DQO y de las variaciones de la producción bacteriana, se propone la existencia de dos tipos de materia orgánica, en función deł crecimiento obtenido. [...]Peer Reviewe

Determining [(3)H]Thymidine Incorporation into Bacterioplankton DNA: Improvement of the Method by DNase Treatment

Determination of [(3)H] thymidine incorporation into bacterial DNA versus other macromolecules is usually achieved by NaOH and hot trichloroacetic acid hydrolysis. This procedure was found not to be specific enough. An alternative method founded on DNase treatment is proposed. Under the new method, the fraction of thymidine incorporated into DNA ranged from 10 to 83%

Surfactant Biodegradation in Sea Water : Primary Biodegradation and Bacterial Population Response in Sea Water

3 pages, 3 figuresPeer Reviewe