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Quorum Sensing-Controlled Biofilm Development in Serratia liquefaciens MG1. Maurizio Labbate, 2004.Serratia liquefaciens MG1 contains an N-acylhomoserine lactone-mediated quorum-sensing system that is known to regulate swarming motility colonization . In this study, we describe for S . liquefaciens MG1 the development of a novel biofilm consisting of cell aggregates and differentiated cell types, such as cell chains and long filamentous cells . Furthermore, quorum sensing is shown to be crucial for normal biofilm development and for elaborate differentiation . A mutant of S . liquefaciens MG1 that was incapable of synthesizing extracellular signal formed a thin and nonmature biofilm lacking cell aggregates and differentiated cell chains . Signal-based complementation of this mutant resulted in a biofilm with the wild-type architecture . Two quorum-sensing-regulated genes (bsmA and bsmB) involved in biofilm development were identified, and we propose that these genes are engaged in fine-tuning the formation of cell aggregates at a specific point in biofilm development . Direct Correlation between Rates of Anaerobic Respiration and Levels of mRNA for Key Respiratory Genes in Geobacter sulfurreducens. Kuk-Jeong Chin, 2004.The predominance of Geobacter species in environments in which Fe(III) reduction is important has suggested that Fe(III) reduction rates might be estimated in Geobacter-dominated environments by assessing in situ activity with molecular techniques . To determine whether mRNA levels of key respiratory genes might be correlated with respiration rates in Geobacter sulfurreducens, studies were conducted with fumarate as the electron acceptor and acetate as the limiting electron donor in anaerobic continuous cultures . Levels of mRNA for a fumarate reductase gene, frdA, quantified by real-time reverse transcription-PCR were directly correlated with fumarate reduction rates . In similar studies with Fe(III) as the electron acceptor, mRNA levels for omcB, a gene for an outer membrane c-type cytochrome involved in Fe(III) reduction, were positively correlated with Fe(III) reduction rates . Levels of mRNA for frdA and omcB were also positively correlated with fumarate and Fe(III) reduction rates, respectively, when growth was limited by the availability of fumarate or Fe(III), but mRNA levels were higher than in acetate-limited cultures . Levels of mRNA for omcC, which encodes a c-type cytochrome highly similar to OmcB but not necessary for Fe(III) reduction, followed patterns different than those of omcB . This agrees with the previous finding that OmcC is not involved in Fe(III) reduction and suggests that changes in mRNA levels of omcB are related to its role in Fe(III) reduction . These results demonstrate that mRNA levels for respiratory genes might be used to estimate in situ Fe(III) reduction rates in Geobacter-dominated environments but suggest that information on environmental conditions and/or the metabolic state of Geobacter species is also required for accurate rate estimates . Cloning and Expression Analysis of the pcbAB-pcbC ß-Lactam Genes in the Marine Fungus Kallichroma tethys. Chi-fai Kim, 2003.Here we report the identification of the ß-lactam biosynthesis genes pcbAB and pcbC from a cosmid genomic DNA library of the marine fungus Kallichroma tethys. A BLAST homology search showed that they share high sequence identity with the  -(L- -aminoadipyl)-L-cysteinyl-D-valine (ACV) synthetases and isopenicillin N synthases, respectively, of various fungal and bacterial ß-lactam producers, while phylogenetic analysis indicated a close relationship with homologous genes of the cephalosporin-producing pyrenomycete Acremonium chrysogenum . Expression analysis by reverse transciption-PCR suggested that both genes are highly regulated and are expressed in the late growth phase of K . tethys cultures . Complementation of an Aspergillus nidulans strain deficient in ACV synthetase suggested that at least pcbAB is functional, although attempts to isolate active antibiotic from K . tethys were unsuccessful .
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