Long-term capacity for organic-substrate removal by bacterial films

When wastewater is discharged to small streams, the effluent quality normally obtained from a sewage treatment plant is often not good enough to prevent serious water-quality deterioration. Hence, enhanced removal of organic pollutants is required. Efficient and economic removal of organics to very low concentrations is best achieved by biofilm processes, in which bacteria are attached to a fixed media and remove the organic compounds from the wastewater flowing past. Laboratory-scale reactors were utilized to evaluate the ability of biofilms to remove low levels of organic contaminants in water during extended operation. Nonsteady-state operation, in which trace concentrations of organic substrate were treated with a biofilm previously grown on a relatively high concentration feed, demonstrated that a slowly decaying biofilm was able to bring about high efficiency removal of the trace compound for extended periods, up to 7 months in this study. A kinetic model to describe the transient growth and decay of the biofilm was developed, and it predicted the growth and steady-state phases of the biofilm when input parameters were determined independently. The observed slow decay rate of the biofilm prolonged the usefulness of the nonsteady­state biofilm and was explained by adaptation to oligotrophic (low concentration) conditions and the growth of nitrifying bacteria which produced supplemental organic substrate to sustain the organic-utilizing bacteria. The results of this study demonstrated that nonsteady-state­biofilm processes can sustainably achieve organic concentrations much lower than conventional wastewater treatment.U.S. Department of the InteriorU.S. Geological SurveyOpe

Robust Identities or Non-Entities? Typecasting in the Feature Film Labor Market

We provide a framework for reconciling two seemingly incompatible claims regarding identity in social and economic arenas: (a) that complex, multivalent identities are advantageous because they afford greater flexibility; and (b) that simple, generic identities are advantageous because they facilitate interpretation by key audiences. Following Faulkner (1983), we argue that these claims do not conflict with one another but that they apply to different contexts. A generic identity is helpful in gaining the recognition necessary for sustained participation in a social arena. However, as one becomes better established, the limitations entailed by a simple, “typecast” identity increasingly rival the benefits. We test these hypotheses in an analysis of the labor market for actors in the feature film industry. Interviews with key informants and analysis of comprehensive data from the Internet Movie Database support the proposed theoretical framework. In addition, the evidence supports the salience of the hypothesized typecasting processes even in the presence of related processes based on underlying skill differences and social networks. Our results have important implications for research on identity formation in various social arenas, categorical boundaries in external labor markets, and more generally, the interplay between actor and position inherent in market dynamic

Identification of an α(1→6) mannopyranosyltransferase (MptA), involved in Corynebacterium glutamicum lipomanann biosynthesis, and identification of its orthologue in Mycobacterium tuberculosis

Corynebacterium glutamicum and Mycobacterium tuberculosis share a similar cell wall architecture, and the availability of their genome sequences has enabled the utilization of C. glutamicum as a model for the identification and study of, otherwise essential, mycobacterial genes involved in lipomannan (LM) and lipoarabinomannan (LAM) biosynthesis. We selected the putative glycosyltransferase-Rv2174 from M. tuberculosis and deleted its orthologue NCgl2093 from C. glutamicum. This resulted in the formation of a novel truncated lipomannan (Cg-t-LM) and a complete ablation of LM/LAM biosynthesis. Purification and characterization of Cg-t-LM revealed an overall decrease in molecular mass, a reduction of α(1→6) and α(1→2) glycosidic linkages illustrating a reduced degree of branching compared with wild-type LM. The deletion mutant's biochemical phenotype was fully complemented by either NCgl2093 or Rv2174. Furthermore, the use of a synthetic neoglycolipid acceptor in an in vitro cell-free assay utilizing the sugar donor β-d-mannopyranosyl-1-monophosphoryl-decaprenol together with the neoglycolipid acceptor α-d-Manp-(1→6)-α-d-Manp-O-C8 as a substrate, confirmed NCgl2093 and Rv2174 as an α(1→6) mannopyranosyltransferase (MptA), involved in the latter stages of the biosynthesis of the α(1→6) mannan core of LM. Altogether, these studies have identified a new mannosyltransferase, MptA, and they shed further light on the biosynthesis of LM/LAM in Corynebacterianeae

Modeling lipid accumulation in oleaginous fungi in chemostat cultures. II: Validation of the chemostat model using yeast culture data from literature

A model that predicts cell growth, lipid accumulation and substrate consumption of oleaginous fungi in chemostat cultures (Meeuwse et al. in Bioproc Biosyst Eng. doi:10.1007/s00449-011-0545-8, 2011) was validated using 12 published data sets for chemostat cultures of oleaginous yeasts and one published data set for a poly-hydroxyalkanoate accumulating bacterial species. The model could describe all data sets well with only minor modifications that do not affect the key assumptions, i.e. (1) oleaginous yeasts and fungi give the highest priority to C-source utilization for maintenance, second priority to growth and third priority to lipid accumulation, and (2) oleaginous yeasts and fungi have a growth rate independent maximum specific lipid production rate. The analysis of all data showed that the maximum specific lipid production rate is in most cases very close to the specific production rate of membrane and other functional lipids for cells growing at their maximum specific growth rate. The limiting factor suggested by Ykema et al. (in Biotechnol Bioeng 34:1268–1276, 1989), i.e. the maximum glucose uptake rate, did not give good predictions of the maximum lipid production rate

An Environment-Sensitive Synthetic Microbial Ecosystem

Microbial ecosystems have been widely used in industrial production, but the inter-relationships of organisms within them haven't been completely clarified due to complex composition and structure of natural microbial ecosystems. So it is challenging for ecologists to get deep insights on how ecosystems function and interplay with surrounding environments. But the recent progresses in synthetic biology show that construction of artificial ecosystems where relationships of species are comparatively clear could help us further uncover the meadow of those tiny societies. By using two quorum-sensing signal transduction circuits, this research designed, simulated and constructed a synthetic ecosystem where various population dynamics formed by changing environmental factors. Coherent experimental data and mathematical simulation in our study show that different antibiotics levels and initial cell densities can result in correlated population dynamics such as extinction, obligatory mutualism, facultative mutualism and commensalism. This synthetic ecosystem provides valuable information for addressing questions in ecology and may act as a chassis for construction of more complex microbial ecosystems