Phenotype Fingerprinting Suggests the Involvement of Single-Genotype Consortia in Degradation of Aromatic Compounds by Rhodopseudomonas palustris

Anaerobic degradation of complex organic compounds by microorganisms is crucial for development of innovative biotechnologies for bioethanol production and for efficient degradation of environmental pollutants. In natural environments, the degradation is usually accomplished by syntrophic consortia comprised of different bacterial species. This strategy allows consortium organisms to reduce efforts required for maintenance of the redox homeostasis at each syntrophic level. Cellular mechanisms that maintain the redox homeostasis during the degradation of aromatic compounds by one organism are not fully understood. Here we present a hypothesis that the metabolically versatile phototrophic bacterium Rhodopseudomonas palustris forms its own syntrophic consortia, when it grows anaerobically on p-coumarate or benzoate as a sole carbon source. We have revealed the consortia from large-scale measurements of mRNA and protein expressions under p-coumarate, benzoate and succinate degrading conditions using a novel computational approach referred as phenotype fingerprinting. In this approach, marker genes for known R. palustris phenotypes are employed to determine the relative expression levels of genes and proteins in aromatics versus non-aromatics degrading condition. Subpopulations of the consortia are inferred from the expression of phenotypes and known metabolic modes of the R. palustris growth. We find that p-coumarate degrading conditions may lead to at least three R. palustris subpopulations utilizing p-coumarate, benzoate, and CO2 and H2. Benzoate degrading conditions may also produce at least three subpopulations utilizing benzoate, CO2 and H2, and N2 and formate. Communication among syntrophs and inter-syntrophic dynamics in each consortium are indicated by up-regulation of transporters and genes involved in the curli formation and chemotaxis. The N2-fixing subpopulation in the benzoate degrading consortium has preferential activation of the vanadium nitrogenase over the molybdenum nitrogenase. This subpopulation in the consortium was confirmed in an independent experiment by consumption of dissolved nitrogen gas under the benzoate degrading conditions

Flexible Sojourning in the Era of Globalization: Cross-border Population Mobility in the Hong Kong-Guangdong Border Region

This study of cross-border population mobility in the Hong Kong-Guangdong region adopts a humanistic and disaggregate approach to analyzing how ordinary and sometimes underrepresented people, such as housewives, workers, low-income households and elderly retirees, have engaged in border-crossing as a personal strategy to actively negotiate with the reproduction of regional asymmetry in the era of uneven globalization. Flexible sojourning across the border has long been pursued by the local population in this region as a means of survival during natural catastrophes, economic downturns, wars and political turmoil. Cross-border population mobility has acquired a new momentum in recent years subsequent to the uneven economic and social changes on the two sides of the border. The border-crossers are, seemingly, a uniform group of people whose travel behavior does not deviate from the expectation of conventional wisdom. However, a closer analysis reveals significant differences among the border-crossers. Four main types of border-crossers are identified: shoppers, workers, homebuyers and elderly retirees. Each type demonstrates distinct patterns of border-crossing and makes the trip out of different considerations. Border-crossing has different meanings to people of different social identities. Cross-border mobility can be and has been used by different kinds of people in different ways as a personal strategy to take on the challenges of structural changes at home and across the border. The article calls for an extension of border studies beyond the existing emphasis on border functioning, nation-states and regional development toward examining more seriously and carefully the ordinary people who are involved in border-crossing as a practice of their everyday life. © Joint Editors and Blackwell Publishing Ltd 2005.link_to_subscribed_fulltex