Multiplicity of aspartate transport in thin wastewater biofilms

Indo-Pacific Walker circulation drove Pleistocene African aridification

Today, the eastern African hydroclimate is tightly linked to fluctuations in the zonal atmospheric Walker circulation^1,2. A growing body of evidence indicates that this circulation shaped hydroclimatic conditions in the Indian Ocean region also on much longer, glacial-interglacial timescales^3-5, following the development of Pacific Walker circulation around 2.2-2.0 million years ago (Ma)^6,7. However, continuous long-term records to determine the timing and mechanisms of Pacific-influenced climate transitions in the Indian Ocean have been unavailable. Here we present a seven-million-year-long record of wind-driven circulation of the tropical Indian Ocean, as recorded in Mozambique Channel Throughflow (MCT) flow-speed variations. We show that the MCT flow speed was relatively weak and steady until 2.1 ± 0.1 Ma, when it began to increase, coincident with the intensification of the Pacific Walker circulation^6,7. Strong increases during glacial periods, which reached maxima after the Mid-Pleistocene Transition (0.9-0.64 Ma; ref. ⁸), were punctuated by weak flow speeds during interglacial periods. We provide a mechanism explaining that increasing MCT flow speeds reflect synchronous development of the Indo-Pacific Walker cells that promote aridification in Africa. Our results suggest that after about 2.1 Ma, the increasing aridification is punctuated by pronounced humid interglacial periods. This record will facilitate testing of hypotheses of climate-environmental drivers for hominin evolution and dispersal.

Kinetics of mixed microbial assemblages enhance removal of highly dilute organic substrates

Our experiments with selected organic substrates reveal that the rate-limiting process governing microbial degradation rates changes with substrate concentration, S, in such a manner that substrate removal is enhanced at lower values of S. This enhancement is the result of the dominance of very efficient systems for substrate removal at low substrate concentrations. The variability of dominant kinetic parameters over a range of S causes the kinetics of complex assemblages to be profoundly dissimilar to those of systems possessing a single set of kinetic parameters; these findings necessitate taking a new approach to predicting substrate removal rates over wide ranges of S.

Thymidine Incorporation by the Microbial Community of Standing Dead Spartina alterniflora

Thymidine incorporation by the microbial community on standing dead leaves of Spartina alterniflora did not obey many of the assumptions inherent in the use of the technique in planktonic systems. Incorporation rates of [ methly - 3 H]thymidine were nonsaturable over a wide concentration range (10 1 to 10 5 nM). Owing to metabolism by both fungi and bacteria, a major fraction of the radiolabel (mean, 48%) appeared in protein. Extraction of the radiolabeled macromolecules was inefficient, averaging 8.8%. Based on an empirically derived conversion factor, 4 × 10 18 cells · mol of thymidine −1 , doubling times ranged from 4 to 69 h for the epiphytic bacterial assemblage.

Multiphasic Kinetics for Transformation of Methyl Parathion by Flavobacterium Species

Transformation rates of an insecticide, methyl parathion, in pure cultures of Flavobacterium sp. followed multiphasic kinetics involving at least two systems (I and II). System I was a high-affinity, low-capacity system, and system II was a low-affinity, high-capacity system. Data from rate experiments suggested that metabolites formed via system II inhibited system I such that only one system operated at a time. System I operated at approximately 20 μg liter −1 and less; system II operated at approximately 4 mg liter −1 and less. These results show that xenobiotic chemicals, like naturally occurring substrates, can be transformed via multiple uptake and transformation systems even by a pure culture. Furthermore, computer simulation models of pollutant transformation rates based on kinetic constants determined in this study show that large errors can occur in predicted rates when the multiphasicity of kinetics is neglected.

Effect of Reactor Turbulence on the Binding-Protein-Mediated Aspartate Transport System in Thin Wastewater Biofilms

This research documents an effect of reactor turbulence on the ability of gram-negative wastewater biofilm bacteria to actively transport l -aspartate via a binding-protein-mediated transport system. Biofilms which were not preadapted to turbulence and which possessed two separate and distinct aspartate transport systems (systems 1 and 2) were subjected to a turbulent flow condition in a hydrodynamically defined closed-loop reactor system. A shear stress treatment of 3.1 N · m −2 for 10 min at a turbulent Reynolds number (Re = 11,297) inactivated the low-affinity, high-capacity binding-protein-mediated transport system (system 2) and resolved the high-affinity, low-capacity membrane-bound proton symport system (system 1). The K t and V max values for the resolved system were statistically similar to K t and V max values for system 1 when system 2 was inactivated either by osmotic shock or arsenate, two treatments which are known to inactivate binding-protein-mediated transport systems. We hypothesize that shear stress disrupts system 2 by deforming the outer membranes of the firmly adhered gram-negative bacteria.