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Controlled Initiation of Chromosomal Replication in Escherichia coli Requires Functional Hda Protein. Johanna Eltz Camara, 2003.Regulatory inactivation of DnaA helps ensure that the Escherichia coli chromosome is replicated only once per cell cycle, through accelerated hydrolysis of active replication initiator ATP-DnaA to inactive ADP-DnaA . Analysis of  hda
strains revealed that the regulatory inactivation of DnaA component
Hda is necessary for maintaining controlled initiation but not for
cell growth or viability .
Nonlegumes, Legumes, and Root Nodules Harbor Different Arbuscular Mycorrhizal Fungal Communities. Tanja R. Scheublin, 2004.Legumes are an important plant functional group since they can form a tripartite symbiosis with nitrogen-fixing Rhizobium bacteria and phosphorus-acquiring arbuscular mycorrhizal fungi (AMF) . However, not much is known about AMF community composition in legumes and their root nodules . In this study, we analyzed the AMF community composition in the roots of three nonlegumes and in the roots and root nodules of three legumes growing in a natural dune grassland . We amplified a portion of the small-subunit ribosomal DNA and analyzed it by using restriction fragment length polymorphism and direct sequencing . We found differences in AMF communities between legumes and nonlegumes and between legume roots and root nodules . Different plant species also contained different AMF communities, with different AMF diversity . One AMF sequence type was much more abundant in legumes than in nonlegumes (39 and 13%, respectively) . Root nodules contained characteristic AMF communities that were different from those in legume roots, even though the communities were similar in nodules from different legume species . One AMF sequence type was found almost exclusively in root nodules . Legumes and root nodules have relatively high nitrogen concentrations and high phosphorus demands . Accordingly, the presence of legume- and nodule-related AMF can be explained by the specific nutritional requirements of legumes or by host-specific interactions among legumes, root nodules, and AMF . In summary, we found that AMF communities vary between plant functional groups (legumes and nonlegumes), between plant species, and between parts of a root system (roots and root nodules) . Acidified Litter Benefits the Intestinal Flora Balance of Broiler Chickens. Margarita Novoa Garrido, 2004.The alterations in the balance of the normal intestinal bacterial flora of chickens exposed to acidified wood-derived litter were analyzed and compared to those of a control group exposed to nonacidified litter . A total of 1,728 broilers were divided into two groups, with six replicates in each . One group was exposed to dry wood-derived litter, and the other was exposed to dry wood-derived litter sprayed with a mixture of sodium lignosulfonate, formic acid, and propionic acid . At five different times, five chickens from each pen were killed and the intestinal contents from ileum and caeca were collected . The samples were diluted and plated onto selective media to identify coliforms, Lactobacillus spp., Clostridium perfringens, and Enterococcus spp . Covariance analysis of bacterial counts showed significantly lower counts for C . perfringens in the caeca and the ileum and for Enterococcus spp . and Lactobacillus spp . in the ileum in chickens exposed to the acidified litter . Lactobacillus spp . showed significantly higher counts in the caeca in chickens exposed to acidified litter . There was no difference between the two litters with regard to coliforms in the ileum and the caeca or to Enterococcus spp . in the caeca . The study shows that exposing the chickens to acidified litter lowers the intestinal bacterial number, especially in the ileum, without negative consequences for the chicken's health or performance . Of special interest are the lower counts of C . perfringens and Enterococcus spp . that might reduce the risk of developing clinical or subclinical necrotic enteritis and growth depression . A Bacterial Signal Transduction System Controls Genetic Exchange and Motility. Andrew S. Lang, 2002.The bacterium Rhodobacter capsulatus is capable of an unusual form of genetic exchange, mediated by a transducing bacteriophage-like particle called the gene transfer agent (GTA) . GTA production by R . capsulatus is controlled at the level of transcription by a cellular two-component signal transduction system that includes a putative histidine kinase (CckA) and response regulator (CtrA) . We found that, in addition to regulating genetic exchange by R . capsulatus, this signal transduction system controls motility . As with the regulation of GTA production, the control of motility by CckA and CtrA occurs through modulation of gene transcription . Disruptions of the cckA and ctrA genes resulted in a loss of class II, class III, and class IV flagellar gene transcripts, suggesting that cckA and ctrA function in motility as class I flagellar genes . We also found that, analogous to the GTA genes, transcription of R . capsulatus flagellar genes appears to be growth phase dependent: class II flagellar gene transcripts are maximal in the mid-log phase of the culture growth cycle, whereas class III gene transcripts are maximal in the late-log phase of growth . We speculate that coordinate regulation of motility and GTA-mediated genetic exchange in R . capsulatus exists because these two processes are complementary mechanisms for cells to cope with unfavorable conditions in natural environments . Regulation of Expression of Scaffoldin-Related Genes in Clostridium thermocellum. Tali W. Dror, 2003.Clostridium thermocellum produces an extracellular multienzyme complex, termed the cellulosome, that allows efficient solubilization of crystalline cellulose . The complex is organized around a large noncatalytic protein subunit, termed CipA or scaffoldin, and is found either free in the supernatant or cell bound . The binding of the complex to the cell is mediated by three cell surface anchoring proteins, OlpB, Orf2p, and SdbA, that interact with the CipA scaffoldin . The transcriptional level of the olpB, orf2, sdbA, and cipA genes was determined quantitatively by RNase protection assays in batch and continuous cultures, under carbon and nitrogen limitation . The mRNA level of olpB, orf2, and cipA varied with growth rate, reaching 40 to 60 transcripts per cell under carbon limitation at a low growth rate of 0.04 h-1 and 2 to 10 transcripts per cell at a growth rate of 0.35 h-1 in batch culture . The mRNA level of sdbA was about three transcripts per cell and was not influenced by growth rate . Primer extension analysis revealed two major transcriptional start sites, at -81 and -50 bp, upstream of the translational start site of the cipA gene . The potential promoters exhibited homology to the known sigma factors  A and
L (54) of Bacillus subtilis . Transcription from the
L-like promoter was found under all growth conditions, whereas transcription from the
A-like promoter was significant only under carbon limitation . The overall expression level obtained in the primer extension analysis was in good agreement with the results of the RNase-protection assays .
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