PubMed · 11966818
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David C White. 2002. Microbial community analysis.. https://doi.org/10.1046/j.1462-2920.2002.t01-2-00257.x
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Based on work in marine sediments it can be hypothesized that (i) overall OM mineralization depends on the enzymatic capacity and is largely independent from the energy yield, (ii) similar oxic and anoxic rates are expected for fresh OM, while oxic rates should be faster for old OM that is partially degraded or adsorbed to particles, and (iii) that the thermodynamic energy yield does not regulate mineralization, but primarily determines the energy fraction allocated to bacterial production (BP). We addressed these hypotheses by simultaneous measurements of mineralization rates (MR) and BP in sediments from a eutrophic lake, along with MR measurements in sediments of a dystrophic lake. Anoxic MR were 44 and 78% of oxic MR in the eutrophic and dystrophic lake, respectively, which was always higher than expected given the theoretical energy yields. The BP:MR ratio was 0.94 and 0.24 in the oxic and anoxic treatments, respectively, in accordance with the expected energy yields. Thus, the results support all three hypotheses above. We also critically discuss BP measurements in sediments and suggest that bacterial growth efficiency values from simultaneous MR and BP measurements can be used to evaluate the reliability of BP estimates.
In bacteria, the chemotactic signal is greatly amplified between the chemotaxis receptors and the flagellar motor. In Escherichia coli, part of this amplification occurs at the flagellar switch. However, it is not known whether the amplification results from cooperativity of CheY binding to the switch or from a post-binding step. To address this question, we purified the intact switch complex (constituting the switch proteins FliG, FliM, and FliN and the scaffolding protein FliF) in quantities sufficient for biochemical work and used it to investigate whether the binding of CheY to the switch complex is cooperative. As a negative control, we used complexes of switchless basal bodies, formed from the proteins FliF and FliG and similarly isolated. Using double-labeling centrifugation assays for binding, we found that CheY binds to the isolated, intact switch complex in a phosphorylation-dependent manner. We observed no significant phosphorylation-dependent binding to the negative control of the switchless basal body. The dissociation constant for the binding between the switch complex and phosphorylated CheY (CheY approximately P) was 4.0 +/- 1.1 microm, well in line with the published range of CheY approximately P concentrations to which the flagellar motor is responsive. Furthermore, the binding was not cooperative (Hill coefficient approximately 1). This lack of CheY approximately P-switch complex binding cooperativity, taken together with earlier in vivo studies suggesting that the dependence of the rotational state of the motor on the fraction of occupied sites at the switch is sigmoidal and very steep (Bren, A., and Eisenbach, M. (2001) J. Mol. Biol. 312, 699-709), indicates that the chemotactic signal is amplified within the switch, subsequent to the CheY approximately P binding.
Bacteria associated with plants have been observed frequently to form assemblages referred to as aggregates, microcolonies, symplasmata, or biofilms on leaves and on root surfaces and within intercellular spaces of plant tissues. In a wide range of habitats, biofilms are purported to be microniches of conditions markedly different from those of the ambient environment and drive microbial cells to effect functions not possible alone or outside of biofilms. This review constructs a portrait of how biofilms associated with leaves, roots and within intercellular spaces influence the ecology of the bacteria they harbor and the relationship of bacteria with plants. We also consider how biofilms may enhance airborne dissemination, ubiquity and diversification of plant-associated bacteria and may influence strategies for biological control of plant disease and for assuring food safety. Trapped by a nexus, coordinates uncertain Ever expanding or contracting Cannibalistic and scavenging sorties Excavations through signs of past alliances Consensus signals sound revelry Then time warped by viscosity Genomes showing codependence A virtual microbial beach party With no curfew and no time-out A few estranged cells seeking exit options, Looking for another menagerie. David Sands, Montana State University, Bozeman, February 2003