Microorganisms and nitrogen sources.
01 Jan 1980-
About: The article was published on 1980-01-01 and is currently open access. It has received 179 citations till now.
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TL;DR: Aminophosphonates are analogues of amino acids in which a carboxylic moiety is replaced by phosphonic acid or related groups that inhibit enzymes involved in amino acid metabolism and thus affect the physiological activity of the cell.
Abstract: Aminophosphonates are analogues of amino acids in which a carboxylic moiety is replaced by phosphonic acid or related groups. Acting as antagonists of amino acids, they inhibit enzymes involved in amino acid metabolism and thus affect the physiological activity of the cell. These effects may be exerted as antibacterial, plant growth regulatory or neuromodulatory. Chosen representative examples of biologically active aminophosphonates are presented in some detail.
899 citations
01 Jan 1991
TL;DR: The majority (>95%) of organic matter in aquatic environments is composed of polymeric, high-molecular-weight compounds, and only a small portion of the total dissolved organic matter (DOM) is readily utilizable in natural waters.
Abstract: The majority (>95%) of organic matter in aquatic environments is composed of polymeric, high-molecular-weight compounds (Allen, 1976; Romankevich, 1984; Cole et al., 1984; Thurman. 1985; Munster and Chrost, 1990). Because the passage of organic molecules across the microbial cytoplasmic membrane is an active process requiring specific transport enzymes (permeases), only small (low-molecular-weight) and simple molecules can be directly transferred from the environment into the cell (Rogers, 1961; Payne, 1980a; Geller, 1985). This means that only a small portion of the total dissolved organic matter (DOM) is readily utilizable in natural waters (Munster, 1985; Azam and Cho, 1987; Jorgensen, 1987), and that the majority of DOM cannot be directly transported to microbial cells because of the large size of its molecules.
613 citations
TL;DR: Natural assemblages of marine bacteria were cultured on combinations of C and N sources (amino acids, glucose, and NH,‘) to span a range of substrate C: N ratios to speculate that C : Ns of available substrates in marine waters is > 10 : 1.
Abstract: Natural assemblages of marine bacteria were cultured on combinations of C and N sources (amino acids, glucose, and NH,‘) to span a range of substrate C: N ratios from 1.5 : 1 to 10 : 1. Catabolic metabolism of the N component of amino acid substrates led to NH,+ regeneration during exponential growth. The efficiency of this regeneration (RN) and also of the carbon gross growth efficiency (GGE) generally was independent of the sources of C and N, but increased as the C : N ratio of the substrate (C : NJ decrcascd relative to the C : N ratio of the bacterial biomass (C : NJ. The clemental chemical composition (C : N: P ratio) of the bacterial biomass was relatively invariant at about 45 : 9 : 1 and the gross growth efficiency varied from a threshold value of about 40-50% at C : Ns > 6 : 1 up to 94% when C : N, was 1.5 : 1. Hence, R, varied from 00/o when C : N, was 10: 1 up to 86% when C: N, was 1.5 : 1. Inorganic sources of both N and P were taken up only in stoichiometric quantities during this phase of growth. Regeneration of NH,+ during the stationary phase as well as of POd3- occurred, most likely due to endogenous metabolism or cell death, but the magnitude of this regeneration seemed to increase greatly only when C: N, was ~6 : 1. Considering that amino acids frequently do not provide all of the N required and that carbohydrates often are the major C source for growth of marine bacteria, we speculate that C : Ns of available substrates in marine waters is > 10 : 1. Hence, actively growing bacteria may be inefficient remineralizers of N.
557 citations
TL;DR: In this paper, the authors hypothesize that DON uptake from the soil may not contribute largely to N acquisition by plants but may instead be primarily involved in the recapture of DON previously lost during root exudation.
Abstract: The direct uptake of dissolved organic nitrogen (DON) by plants has the potential to be a primary Factor in ecosystem functioning and vegetation succession particularly in N-limiting environments. Clear experimental evidence to support this view, however, is still lacking. Further, many of the experimental approaches used to assess whether DON is important may be compromised due to the use of inappropriate methods for comparing and quantifying plant available inorganic and organic soil N pools. In addition, experiments aimed at quantifying plant DON capture using dual-labelled (15N, 13C) organic N tracers often do not consider important aspects such as isotope pool dilution, differences in organic and inorganic N pool turnover times, bi-directional DON flows at the soil–root interface, and the differential fate of the 15N and 13C in the tracer compounds. Based upon experimental evidence, we hypothesize that DON uptake from the soil may not contribute largely to N acquisition by plants but may instead be primarily involved in the recapture of DON previously lost during root exudation. We conclude that while root uptake of amino acids in intact form has been shown, evidence demonstrating this as a major plant N acquisition pathway is still lacking.
553 citations
TL;DR: In this paper, the authors review the current knowledge about the regulation of the enzyme systems involved in the acquisition of N and propose a conceptual model on the factors affecting the relative importance of organic and mineral N uptake.
Abstract: Microorganisms are able to utilize nitrogen (N) from a wide range of organic and mineral compounds. In this paper, we review the current knowledge about the regulation of the enzyme systems involved in the acquisition of N and propose a conceptual model on the factors affecting the relative importance of organic and mineral N uptake. Most of the N input into soil is in the form of polymers, which first have to be broken down into smaller units by extracellular enzymes. The small organic molecules released by the enzymes can then be taken up directly or degraded further and the N taken up as ammonium (NH4+). When NH4+ is available at high concentrations, the utilization of alternative N sources, such as nitrate (NO3−) and organic molecules, is generally repressed. In contrast, when the NH4+ availability is low, enzyme systems for the acquisition of alternative N sources are de-repressed and the presence of a substrate can induce their synthesis. These mechanisms are known as N regulation. It is often assumed that most organic N is mineralized to NH4+ before uptake in soil. This pathway is generally known as the mineralization-immobilization-turnover (MIT) route. An advantage of the MIT route is that only one transporter system for N uptake is required. However, organic N uptake has the advantage that, in addition to N, it supplies energy and carbon (C) to sustain growth. Recent studies have shown that the direct uptake of organic molecules can significantly contribute to the N nutrition of soil microorganisms. We hypothesize that the relative importance of the direct and MIT route during the decomposition of residues is determined by three factors, namely the form of N available, the source of C, and the availability of N relative to C. The regulation system of soil microorganisms controls key steps in the soil N cycle and is central to determining the outcome of the competition for N between soil microorganisms and plants. More research is needed to determine the relative importance of the direct and MIT route in soil as well as the factors affecting the enzyme systems required for these two pathways.
521 citations
Additional excerpts
...The uptake of peptides as opposed to corresponding mixtures of amino acids generally requires less energy and has been shown to be nutritionally superior (Matthews and Payne, 1980)....
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