Evidence for differential effects of 2,4,6‐trinitrotoluene and other munitions compounds on specific subpopulations of soil microbial communities

Abstract

Abstract-The effects of 2,4,6-trinitrotoluene (TNT) and other munitions compounds on indigenous microbial communities in several soils were examined. Culturable heterotrophs, concentrations of phospholipid fatty acid (PLFA), and basal respiration rates exhibited slight negative correlations with high TNT and 1,3,5-trinitrobenzene (TNB) levels. Heat-shock-resistant culturable heterotrophs, percentage of gram-positive soil isolates, mole percent of branched PLFA, and 10Me18:0 (tuberculostearic acid) were observed to be significantly lower in highly contaminated soils. Total soil nitrogen levels were positively correlated with high TNT and TNB concentrations, whereas total soil carbon exhibited no significant correlation with either compound. Multivariate analysis of PLFA data resulted in distinct separation of soils with respect to their degree of contamination, with specific signature PLFAs for gram-positive bacteria, fungi, and protozoa being negatively associated with high contaminant levels. Apparent concentrations of TNT resulting in 50% reductions in indicators of gram-positive populations were much higher than values from pure culture experiments, possibly as a result of low bioavailability due to sorption onto clay and soil organic matter. Few effects of other munitions compounds were observed. Closer examination of a highly contaminated soil revealed that the number of culturable heterotrophs growing on 0.3% molasses plates decreased by 50% when 67 g TNT/ml was added to the medium; a 99% decrease was observed for soil contaminated with less than 20 g TNT/g. Highly contaminated soil harbored a greater number of organisms that were able to grow on plates amended with greater than 10 g TNT/ml. Gram-positive isolates from both soils demonstrated marked growth inhibition when greater than 8-16 g TNT/ml was present in the culture medium. These results indicate that chronic exposure to munitions compounds can dramatically alter soil microbial communities.

Mineralization of 2,4,6-Trinitrotoleune (TNT) in Coastal Waters and Sediments

“…Virtually all of the published information on bacterial NEC metabolism is derived from work in terrestrial soil (e.g., Drzyzga et al 1999, Steffan andDrew 1995), groundwater (e.g., Krumholz et al 1997) and freshwater systems (e.g., Spain et al 2000). These studies provide a substantial amount of information on enzymatic pathways (see review by Peres and Aganthos 2000), production of intermediates or dead end products (Drzyzga et al 1998), strain identification (Lessner et al 2002, Smets andMueller 2001) and some genetic information on the natural assemblage (Fuller and Manning 1998). Typically, some combination of aerobic and anaerobic metabolism is required for near complete transformation of TNT carbon and this often starts with denitration prior to ring cleavage (Fiorella and Spain 1997).…”

“…Leungsakul et al (2005) were able to use enzyme engineering strategies to enhance degradation of NECs including 2,5-DNT by Burkholderia sp. Relative to the amount of information on TNT biodegradation by cultured isolates, there are only scattered reports using mixed or natural assemblages and these include work on sludge (Kroger et al 2004), groundwater and aquifer sediment (Krumholz et al 1997), lake surface water (Spanggord et al 1983, Talmage et al 1999, Zeng et al 2004, lake sediment (Boopathy and Kulpa 1994), and soils (Fuller and Manning 1998, Miyares and Jenkins 2000, Siciliano et al 1999). It seems difficult to imagine that natural assemblages of bacteria and protozoa grazers would be unable to mineralize NEC carbon and nitrogen given the importance of nitrogen as a growth-limiting nutrient in marine systems and the ubiquity of enzyme systems for metabolizing aromatic carbon compounds in nature: (Diaz 2004) Reports of TNT half lives in natural environmental samples range from 1.1 days (Miyares and Jenkins 2000) to weeks (Boopathy et al 1997) to months (Talmage et al 1999).…”

Union Support Recovery in High-Dimensional Multivariate Regression

“…Spain et al 2000). These studies provide a substantial amount of information on enzymatic pathways (see review by Peres and Aganthos 2000), production of intermediates or dead end products (Drzyzga et al 1998), strain identification (Lessner et al 2002, Smets andMueller 2001) and some genetic information on the natural assemblage (Fuller and Manning 1998). Typically, some combination of aerobic and anaerobic metabolism is required for near complete transformation of TNT carbon and this often starts with denitration prior to ring cleavage (Fiorella and Spain 1997).…”

“…Leungsakul et al (2005) were able to use enzyme engineering strategies to enhance degradation of NECs including 2,5-DNT by Burkholderia sp. Relative to the amount of information on TNT biodegradation by cultured isolates, there are only scattered reports using mixed or natural assemblages and these include work on sludge (Kroger et al 2004), groundwater and aquifer sediment (Krumholz et al 1997), lake surface water (Spanggord et al 1980, Talmage et al 1999, Zeng et al 2004, lake sediment (Boopathy and Kulpa 1994), and soils (Fuller et al 1998, Miyares and Jenkins 2000, Siciliano et al 1999). It seems difficult to imagine that natural assemblages of bacteria and protozoan grazers would be unable to mineralize NEC carbon and nitrogen given the importance of nitrogen as a growthlimiting nutrient in marine systems and the ubiquity of enzyme systems for metabolizing aromatic carbon compounds in nature: (Diaz 2004) Reports of TNT half lives in natural environmental samples range from 1.1 days (Miyares and Jenkins 2000) to weeks (Boopathy et al 1997) to months (Talmage et al 1999).…”

“…Exposuring soil assemblages to TNT can lead to a shift in the bacterial community structure (Fuller et al 1998, Siciliano et al 1999) and metabolic rate lowering (Zeng et al 2004). There was a positive correlation between NEC concentrations and the presence of the genes responsible for denitrification (nirK, nirS or nosZ) in DNA extracted from the whole community, as well as in culturable strains isolated from the community, though denitrification rates decreased with increasing TNT concentrations (Siciliano et al 2000).…”