Genetics of the Enterobacteriaceae. A. Genetic homology in the Enterobacteriaceae

Exploring the links between groundwater quality and bacterial communities near oil and gas extraction activities

Bacterial communities in groundwater are very important as they maintain a balanced biogeochemical environment. When subjected to stressful environments, for example, due to anthropogenic contamination, bacterial communities and their dynamics change. Studying the responses of the groundwater microbiome in the face of environmental changes can add to our growing knowledge of microbial ecology, which can be utilized for the development of novel bioremediation strategies. High-throughput and simpler techniques that allow the real-time study of different microbiomes and their dynamics are necessary, especially when examining larger data sets. Matrix-assisted laser desorption-ionization (MALDI) time-of-flight mass spectrometry (TOF-MS) is a workhorse for the high-throughput identification of bacteria. In this work, groundwater samples were collected from a rural area in southern Texas, where agricultural activities and unconventional oil and gas development are the most prevalent anthropogenic activities. Bacterial communities were assessed using MALDI-TOF MS, with bacterial diversity and abundance being analyzed with the contexts of numerous organic and inorganic groundwater constituents. Mainly denitrifying and heterotrophic bacteria from the Phylum Proteobacteria were isolated. These microorganisms are able to either transform nitrate into gaseous forms of nitrogen or degrade organic compounds such as hydrocarbons. Overall, the bacterial communities varied significantly with respect to the compositional differences that were observed from the collected groundwater samples. Collectively, these data provide a baseline measurement of bacterial diversity in groundwater located near anthropogenic surface and subsurface activities.

Genome size variation among recent human isolates of Salmonella typhi

We performed genome size estimation of 17 recent human isolates of Salmonella typhi from geographically diverse regions using pulsed-field gel electrophoresis (PFGE) after digestion of chromosomal DNA with restriction endonucleases XbaI (5'-TCTAGA-3'), AvrII (5'-CCTAGG-3') and SpeI (5'-ACTAGT-3'), and summation of the sizes of restriction fragments obtained. All 17 isolates had circular chromosomes, and genome sizes differed by as much as 959 kb, ranging from 3,964 to 4,923 kb (mean genome size = 4,528 kb). The data obtained confirm the usefulness of PFGE in studies of bacterial genome size and are in agreement with recent results indicating considerable genetic diversity and genomic plasticity of S. typhi. The variation in genome sizes noted may be relevant to the observed biological properties of this important human pathogen, including its virulence.

Heterogeneity of genome sizes among natural isolates of Escherichia coli

Comparisons of the genetic maps of Escherichia coli K-12 and Salmonella typhimurium LT2 suggest that the size and organization of bacterial chromosomes are highly conserved. Employing pulsed-field gel electrophoresis, we have estimated the extent of variation in genome size among 14 natural isolates of E. coli. The BlnI and NotI restriction fragment patterns were highly variable among isolates, and genome sizes ranged from 4,660 to 5,300 kb, which is several hundred kilobases larger than the variation detected between enteric species. Genome size differences increase with the evolutionary genetic distance between lineages of E. coli, and there are differences in genome size among the major subgroups of E. coli. In general, the genomes of natural isolates are larger than those of laboratory strains, largely because of the fact that laboratory strains were derived from the subgroup of E. coli with the smallest genomes.

Genetic mapping of the antigenic determinants of two polysaccharide K antigens, K10 and K54, in Escherichia coli

The genes controlling synthesis of the Escherichia coli acidic polysaccharide capsular antigens K10 and K54 were transferred by conjugation to E. coli strains of other serotypes. The genes concerned with these K antigen determinants showed genetic linkage with the serA locus. We propose to name the K antigen-controlling gene kpsA. The genetic determinants of the two K antigens could also be transferred to enteropathogenic serotypes, even though such strains have never been found in nature with special acidic polysaccharide K antigens. A noncapsulated derivative, K(-), of the K10 strain can transfer the genetic determinant of the K antigen, demonstrating the probable existence of another chromosomal locus involved in the production of such acidic polysaccharide K antigens.

Gene order and co-transduction in the leu-ara-fol-pyrA region of the Salmonella typhimurium linkage map

The gene order and orientation in the leu-pyrA region of the Salmonella typhimurium linkage map was established by phage P22-mediated transductions. The gene order, in counterclockwise orientation, is leuO-leuA-leuB-leuC-leuD-ara-fol-pyrA. The fol locus is co-transducible with either the ara and leu loci or the pyrA locus, whereas no co-transduction for the ara and pyrA loci can be found.

Genetic fine structure of the leucine operon of Escherichia coli K-12

The order of mutational sites in 10 independently isolated leucine auxotrophys of Escherichia coli K-12 was determined by three-point reciprocal transductions. The sites of mutation mapped in linear sequence in a cluster; all leucine auxotrophic mutations were cotransducible with mutations in the arabinose operon. The mutations were assigned to four complementation groups by abortive transduction tests, designated D, C, B, and A, reading in a clockwise direction from the arabinose operon. Enzyme analyses showed that strains with a mutation in gene A lacked alpha-isopropylmalate synthetase activity (EC 4.1.3), and those with a mutation in gene B lacked beta-isopropylmalate dehydrogenase activity (EC 1.1.1). It is concluded that the gross structure of the leucine operon in E. coli is closely similar to, if not identical with, the gross structure of the leucine operon in Salmonella typhimurium.