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Metal Toxicity Affects Fungal and Bacterial Activities in Soil Differently. R. M. C. P. Rajapaksha, 2004.Although the toxic effect of heavy metals on soil microorganism activity is well known, little is known about the effects on different organism groups . The influence of heavy metal addition on total, bacterial, and fungal activities was therefore studied for up to 60 days in a laboratory experiment using forest soil contaminated with different concentrations of Zn or Cu . The effects of the metals differed between the different activity measurements . During the first week after metal addition, the total activity (respiration rate) decreased by 30% at the highest level of contamination and then remained stable during the 60 days of incubation . The bacterial activity (thymidine incorporation rate) decreased during the first days with the level of metal contamination, resulting in a 90% decrease at the highest level of contamination . Bacterial activity then slowly recovered to values similar to those of the control soil . The recovery was faster when soil pH, which had decreased due to metal addition, was restored to control values by liming . Fungal activity (acetate-in-ergosterol incorporation rate) initially increased with the level of metal contamination, being up to 3 and 7 times higher than that in the control samples during the first week at the highest levels of Zn and Cu addition, respectively . The positive effect of metal addition on fungal activity then decreased, but fungal activity was still higher in contaminated than in control soil after 35 days . This is the first direct evidence that fungal and bacterial activities in soil are differently affected by heavy metals . The different responses of bacteria and fungi to heavy metals were reflected in an increase in the relative fungal/bacterial ratio (estimated using phospholipid fatty acid analysis) with increased metal load . Effects of Cultivation Conditions on Folate Production by Lactic Acid Bacteria. Wilbert Sybesma, 2003.A variety of lactic acid bacteria were screened for their ability to produce folate intracellularly and/or extracellularly . Lactococcus lactis, Streptococcus thermophilus, and Leuconostoc spp . all produced folate, while most Lactobacillus spp., with the exception of Lactobacillus plantarum, were not able to produce folate . Folate production was further investigated in L . lactis as a model organism for metabolic engineering and in S . thermophilus for direct translation to (dairy) applications . For both these two lactic acid bacteria, an inverse relationship was observed between growth rate and folate production . When cultures were grown at inhibitory concentrations of antibiotics or salt or when the bacteria were subjected to low growth rates in chemostat cultures, folate levels in the cultures were increased relative to cell mass and (lactic) acid production . S . thermophilus excreted more folate than L . lactis, presumably as a result of differences in the number of glutamyl residues of the folate produced . In S . thermophilus 5,10-methenyl and 5-formyl tetrahydrofolate were detected as the major folate derivatives, both containing three glutamyl residues, while in L . lactis 5,10-methenyl and 10-formyl tetrahydrofolate were found, both with either four, five, or six glutamyl residues . Excretion of folate was stimulated at lower pH in S . thermophilus, but pH had no effect on folate excretion by L . lactis . Finally, several environmental parameters that influence folate production in these lactic acid bacteria were observed; high external pH increased folate production and the addition of p-aminobenzoic acid stimulated folate production, while high tyrosine concentrations led to decreased folate biosynthesis .
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