Environment oligotrophic

There is an indeterminacy in the term oligotroph, and the dilemma is exacerbated by the fact that it may be impossible to isolate obligate oligotrophs by established procedures. The application of DNA probes should, however, contribute to an understanding of the role of these noncultivable organisms. Oligotrophic bacteria in the marine environment are able to utilize low substrate concentrations, and they may be important in pristine environments. 

Kamagata Y, RR Fulthorpe, K Tamura, H Takami, LJ Forney, JM Tiedje (1997) Pristine environments harbor a new group of oligotrophic 2,4-dichlorophenoxyacetic acid-degrading bacteria. Appl Environ Microbiol 63 2266-2272. 

Martin P, RA MacLeod (1984) Observations on the distinction between oligotrophic and eutrophic marine bacteria. Appl Environ Microbiol 47 1017-1022. 

Hendricks B, and 11 coauthors (2005) Dynamics of an oligotrophic bacterial aquifer community during contact with a groundwater plume contaminated with benzene, toluene, ethylbenzene, and xylenes an in situ mesocosm study. Appl Environ Microbiol 71 3815-3823. 

Kitagawa W, S Takami, K Miyauchi, E Masai, Y Kamagata, JM Tiedje, M Fukuda (2002) Novel 2,4-dichlo-rophenoxyacetic acid degradation genes from oligotrophic Bradyrhizobium sp. strain HW 13 isolated from a pristine environment. J Bacterial 184 509-518. 

Orlandini KA, Penrose WR, Harvey BR, et al. 1990. Colloidal behavior of actinides in an oligotrophic lake. Environ Sci Technol 24(5) 706-712. 

The data in Table V indicate that runoff of CGA-72662 from 12 applications would result in extremely low concentrations of CGA-72662 in ponds and lakes. The water column in all cases would contain all of the chemical, the sediment little or no CGA-72662. It follows from these data that exposure of CGA-72662 to aquatic organisms would be low. The data in Table V also shows that CGA-72662 would be persistent only in eutrophic lake environments. After the load is removed, the half-life of CGA-72662 in ponds, eutrophic lakes and oligotrophic lakes was 13, 62, and 5 days respectively. Self purification times were 9, 12, and 3 months respectively. 

The characterisation of LAS degradation in the marine environment requires laboratory experiments, although due to the special characteristics of this compartment (e.g. its high salinity and its normally oligotrophic status) and the numerous variables that affect it, divergent results may be obtained. Marine-specific bacterial communities cannot be cultivated as a whole in standard media due to the difficulty of reproducing original ecosystem conditions where they have been... 

Again, the absence of monitoring data does not necessarily indicate a lack of cresols in the environment. Cresols are widely occurring natural and anthropogenic products. However, biodegradation is probably the dominant mechanism responsible for the rapid removal of cresols from surface waters (see Section 5.3.2.2). Nevertheless, cresols may persist in extremely oligotrophic waters, in waters with limited microbial communities, and/or under anaerobic conditions such as in some sediments and groundwater aquifers. 

Below about 200 m, PON concentrations tend to asymptote to similar levels of about 0.1 to 0.3 pmol kg", irrespective of the large differences in PON in the euphotic zone. Overall, PON dynamics in the aphotic zone tends to follow that of particulate organic carbon (POC), with a stoichiometric C N ratio of about 7.1 0.1 (equivalent to 16 114 2) for the particles sinking out of the euphotic zone (Schneider et al, 2003) (see also Hebei and Karl (2001) for long-term observations of the POC and PON dynamics in an oligotrophic environment). In their analysis of sediment trap samples and particles collected by in situ pumps, Schneider et al (2003) also noticed a slight increase of this ratio with depth of about 0.2 per 1000 m, so that particles sinking across 1000 m have a C N ratio very close to the 117 16 ratio proposed by Anderson and Sarmiento (1994). 

Zehr, J. P., Mellon, M. T., and Zani, S. (1998). New nitrogen-fixing microorganisms detected in oligotrophic oceans by the amplification of nitrogenase (nifH) genes. Appl. Environ. Microbiol. 64, 3444-3450. 

Generally, there are several transporters and uptake systems for common N compounds. For example, permeases or other transporters seem to be necessary for uptake of NH4 at low concentrations (<1 iM most oligotrophic environments) (Herrero et al, 2001). Genes encoding permeases have been found and one amtl) seems responsible for most transport when there are micromolar concentrations (Herrero et al, 2001 Montesinos et al, 1998). More recent evidence in the marine diatom Cylindrothecafusiformis suggest that there are two subgroups of NH4+ transporters, amtl and amt2, with multiple copies of each (Hildebrand, 2005). 

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