Microbial adaptation evidence

There is much evidence from observational and molecular research that indicates microbial adaptation for the mineralization of v-triaziiie herbicides has occurred since their first introduction into agriculture in the mid-1950s ... 

It has also become evident that microorganisms are continuously adapting to survive in the presence of previously effective control methods (Rico et ah, 2008). In response to safety concerns from these dilemmas, research intensified to address new techniques demanded in all steps of the production and distribution chain for maintaining required food quality that will at the same time inhibit undesired microbial growth (Rico et ah, 2008 Samelis et ah, 2002). Research has also shifted the focus to the potential implications of new decontamination techniques on pathogen behavior as well as on the microbial ecology of food products (Samelis et ah, 2002). 

Field studies on the microbial communities of boreal coniferous forest humus exposed to environmental stress showed that the structure of the microbial community was influenced by changes in humus pH and metal concentrations at levels where few or no effects were evident on microbial biomass or metabolic activity. Changes in the relative proportions of gram-negative and gram-positive bacteria, including actinomycetes, occurred as well as adaptation to the environmental disturbance in question. Increased metal tolerance of the humus bacterial community resulted partly from a change in microbial species composition (Pennanen, 2001). 

In addition to the amount of pesticide present, the degradation rate could be affected by the availability of the chemical for degradation. Ogram et al. (30) have recently presented evidence suggesting that only the 2,4-D (2,4-dichloro phenoxyacetic acid) in soil solution, but not that adsorbed on soil colloids, could be degraded by soil microbes both in soil solution and sorbed on soil colloids. Other considerations should also be given to the nature and quantity of soil microbial biomass present in relation to nutrient availability (26,28,31) and the adaptability of microbes, either by natural selection or by genetic manipulation, to attack and utilize the pesticide chemical (32). 

Adaptability of Shewanella oneidensis MRl and Escherichia coli in these experiments indicates that microorganisms can continue to metabolize substrate at pressures far beyond those previously reported [34, 35,41], Although an evolutionary component to the adaptation of microbial communities to temperature and salinity is well known [71], whether there might be any evolutionary component for pressure adaptation is still in question. Shewanella MRl belongs to a genus that contains a number of piezophiles however, E. coli clearly does not. Despite this, there is evidence that exposure of E. coli to pressures up to 800 MPa selects a population of cells less sensitive to pressure inactivation [71]. Furthermore, it is well known that the increase in pressure tolerance is also associated with heat tolerance [71]. 

Diazinon. 2-Isopropyl-6-methyl-4-hydroxypyrimidine, the hydrolysis product of diazinon, did not condition the soils for enhanced degradation of diazinon (Table II). Despite the low microbial toxicity and high availability (discussed elsewhere in this chapter), the hydroxypyrimidine metabolite did not predispose soils for rapid degradation of diazinon. Enhanced biodegradation of diazinon in rice soils has been previously reported (1). Evidently, the soil we studied did not contain microbes capable of adapting for diazinon enhanced degradation. 

What evidence exists that the niche affects microbial distributions We surveyed the literature for studies examining either niche or distribution for organisms with propagules < 1-2 mm. While many studies report ecological differences between species, we focused our search on those studies of quantitative niche characteristics that cause spatial segregation between species or result in apparent distributional boundaries at some scale. All studies we found consistently reported niche differences or local adaptation at intra- or interspecific levels, consistent with the fundamental niche in all cases and potentially related to the realised niche in a few cases (Table 15.1). Given that niche constraints on local persistence/occurrence have been observed for microbes, it is reasonable to expect that niche affects distribution of multiple microbial species, consistent with the environment selects portion of the EiE claim (and with much of evolutionary ecology). Tests for source-sink dynamics or dispersal limitation as alternative explanations of microbial niche-distribution relationships will require that the fundamental niche for a species is already... 

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