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atxA Controls Bacillus anthracis Capsule Synthesis via acpA and a Newly Discovered Regulator, acpB. Melissa Drysdale, 2004.Two regulatory genes, acpA and atxA, have been reported to control expression of the Bacillus anthracis capsule biosynthesis operon capBCAD . The atxA gene is located on the virulence plasmid pXO1, while pXO2 carries acpA and the cap genes . acpA has been viewed as the major regulator of the cap operon because it is essential for capsule gene expression in a pXO1- pXO2+ strain . atxA is essential for toxin gene transcription but has also been implicated in control of the cap genes . The molecular functions of the regulatory proteins are unknown . We examined cap gene expression in a genetically complete pXO1+ pXO2+ strain . Our results indicate that another pXO2 gene, acpB (previously called pXO2-53; accession no. NC002146.1:49418-50866), has a role in cap expression . The predicted amino acid sequence of AcpB is 62% similar to that of AcpA and 50% similar to that of AtxA . Assessment of cap gene transcription revealed that cap expression was not affected in a pXO1+ pXO2+ acpB-null mutant and was slightly reduced in an isogenic acpA mutant . However, cap gene expression was abolished in an acpA acpB double mutant . Microscopic examination of capsule synthesis by the mutants corroborated these findings . acpA and acpB expression is controlled by atxA; capsule synthesis and transcription of acpA and acpB were markedly reduced in an atxA mutant . The data suggest that, in a strain containing both virulence plasmids, atxA is the major regulator of capsule synthesis and controls capBCAD expression indirectly, via positive regulation of acpA and acpB . Electrophoretic Mobility of Mycobacterium avium Complex Organisms. Darren Lytle, 2004. Relationship between Spatial and Genetic Distance in Agrobacterium spp . in 1 Cubic Centimeter of Soil. J. Vogel, 2003.The spatial and genetic unit of bacterial population structure is the clone . Surprisingly, very little is known about the spread of a clone (spatial distance between clonally related bacteria) and the relationship between spatial distance and genetic distance, especially at very short scale (microhabitat scale), where cell division takes place . Agrobacterium spp . Biovar 1 was chosen because it is a soil bacterial taxon easy to isolate . A total of 865 microsamples 500 µm in diameter were sampled with spatial coordinates in 1 cm3 of undisturbed soil . The 55 isolates obtained yielded 42 ribotypes, covering three genomic species based on amplified ribosomal DNA restriction analysis (ARDRA) of the intergenic spacer 16S-23S, seven of which contained two to six isolates . These clonemates (identical ARDRA patterns) could be found in the same microsample or 1 cm apart . The genetic diversity did not change with distance, indicating the same habitat variability across the cube . The mixing of ribotypes, as assessed by the spatial position of clonemates, corresponded to an overlapping of clones . Although the population probably was in a recession stage in the cube (103 agrobacteria g-1), a high genetic diversity was maintained . In two independent microsamples (500 µm in diameter) at the invasion stage, the average genetic diversity was at the same level as in the cube . Quantification of the microdiversity landscape will help to estimate the probability of encounter between bacteria under realistic natural conditions and to set appropriate sampling strategies for population genetic analysis . Inhibitory Effect of Maillard Reaction Products on Growth of the Aerobic Marine Hyperthermophilic Archaeon Aeropyrum pernix. Kee Woung Kim, 2003.It was found that the growth of Aeropyrum pernix was severely inhibited in a medium containing reducing sugars and tryptone due to the formation of Maillard reaction products . The rate of the Maillard browning reaction was markedly enhanced under aerobic conditions, and the addition of Maillard reaction products to the culture medium caused fatal growth inhibition .
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