Survival Of Bacterial Cells Research Articles

A new regulatory DNA motif of the gamma subclass Proteobacteria: identification of the LexA protein binding site of the plant pathogen Xylella fastidiosa.

Escherichia coli LexA protein is the repressor of a gene network whose members are directly involved in the repair of damaged DNA and in the survival of bacterial cells until DNA lesions have been eliminated. The lexA gene is widely present in bacteria, although the sequences of only three LexA-binding sites are known: Gram-positive, alpha Proteobacteria and some members of gamma Proteobacteria represented by E. coli. Taking advantage of the fact that the genome sequence of the plant-pathogenic bacterium Xylella fastidiosa has been determined, its lexA gene has been cloned and overexpressed in E. coli to purify its product. After demonstration that X. fastidiosa lexA and recA genes are co-transcribed, gel mobility shift assays and directed mutagenesis experiments using the promoter of the lexA-recA transcriptional unit demonstrated that the X. fastidiosa LexA protein specifically binds the imperfect palindrome TTAGN(6)TACTA. This is the first LexA binding sequence identified in the gamma Proteobacteria differing from the E. coli-like LexA box. Although a computational search has revealed the presence of TTAGN(6)TACTA-like motifs upstream of X. fastidiosa genes other than lexA, X. fastidiosa LexA only binds the promoter of one of them, XF2313, encoding a putative DNA-modification methylase. Moreover, X. fastidiosa LexA protein does not bind any of the other genes whose homologues are regulated by the LexA repressor in E. coli (uvrA, uvrB, ssb, ruvAB, ftsK, dinG, recN and ybfE). RT-PCR quantitative analysis has also demonstrated that lexA-recA and XF2313 genes, as well as the X. fastidiosa genes which are homologues to those of E. coli belonging to the LexA regulon, with the exception of ssb, are DNA damage-inducible in X. fastidiosa.

Heavy metal particle resistance in Thiobacillus intermedius 13-1 isolated from corroded concrete

The effect of exposure to heavy metal particles on the growth and survival of bacterial cells was investigated. Thiobacillus intermedius 13-1, Escherichia coli JM109, and Agrobacterium radiobacter IFO12665b1 were cultured on LB solid medium or in 5 ml of liquid medium containing 0.03 or 0.1 g respectively of the heavy metals, aluminum, cadmium, iron, lead, molybdenum, nickel, and zinc. Cadmium, nickel and zinc strongly inhibited cell growth in the three strains. In contrast, the bacterial cells were not inhibited by aluminum, iron, or lead in the solid or liquid medium. When these bacteria were exposed to heavy metals by vigorous shaking for 10 min, lead and molybdenum, but not nickel and zinc, were markedly toxic to the bacterial cells. Different reaction were thus observed under low-level, long-term and high-level, short-term exposure conditions. T. intermedius showed more resistance to zinc and nickel, and was more sensitive to molybdenum exposure, than E. coli and A. radiobacter.

Water flow induced transport of Pseudomonas fluorescens cells through soil columns as affected by inoculant treatment

Water flow induced transport of Pseudomonas fluorescens cells through soil columns was measured as affected by the inoculant treatment. Bacterial cells were introduced into the topsoil of columns, either encapsulated in alginate beads of different types or mixed with bentonite clay in concentrations ranging from 0.5 to 5.0% (w/v). Survival of bacterial cells was improved with the use of alginate or bentonite. Transport, as determined by destructive sampling of the columns, was reduced with the use of alginate encapsulation. Drying of the beads had no influence on transport. The presence of bentonite in the topsoil, either pre-mixed through the soil, or applied as a slurry together with the bacteria, also reduced transport, except when 0.5% was pre-mixed through the soil. P. fluorescens cells encapsulated in alginate beads prepared with water and supplemented with skim milk powder and bentonite showed the best survival during the time of the experiment and the most reduced transport compared to the control. Therefore, cells encapsulated in this way are suitable, due to their optimal survival and reduced spread, for use in a field experiment with genetically manipulated bacteria.

Oxygen tolerance of oral and non-oral black-pigmentedBacteroidesspecies

The oxygen tolerance of 24 black-pigmented Bacteroides (BPB) strains, including 9 species, was investigated. For this study the survival of single bacterial cells on blood agar medium was determined. It was found that BPB species are not equally tolerant to atmospheric oxygen at room temperature. Among the asaccharolytic species, B. endodontalis showed the highest oxygen sensitivity, while B. gingivalis and B. asaccharolyticus survived for more than 24 h under atmospheric conditions. All saccharolytic species survived at least 4 h of exposure to air.

Effect of Cooking on Bacteriological Populations of “Soul Foods”

Effect of typical cooking procedures on viable bacteria present in “soul foods” was determined. Time and temperature used were those determined to give a satisfactory product. Except for an aerobic plate count of 60 CFU/g in puddings (liver) and 10 CFU/g in jaws and neckbones, survival of vegetative bacterial cells in the cooked foods was nil.

Effect of leukocyte hydrolases on bacteria XVI. Activation by leukocyte factors and cationic substances of autolytic enzymes in Staphylococcus aureus: modulation by anionic polyelectrolytes in relation to survival of bacteria in inflammatory exudates.

The mechanisms involved in the activation of autolytic enzymes in Staphylococcus aureus, by leukocyte extracts, cationic proteins, phospholipase A2, amines, and membrane-damaging agents was studied in a resting cell system as well as by growing staphylococci. The bacteria were labeled with [14C]N-acetylglucosamine and were subjected to a variety of agents either in 0.1 M acetate buffer, pH 5.0, or in phosphate buffer, pH 7.4. While intact log-phase cultures were found to undergo partial autolysis at pH 5.0 and almost complete lysis at pH 7.4, both heat-killed bacteria and bacterial cell walls were completely resistant to autolysis in buffers. Autolysis at pH 5.0 can be further activated by leukocyte extracts, nuclear histone, crystalline ribonuclease, egg-white and human lysozyme, phospholipase A2, as well as by spermine, spermidine, and polymyxins B and E. The addition of viable log-phase bacteria to radiolabeled heat-killed staphylococci or to radiolabeled cell walls which had been cleaned off autolytic enzymes resulted in degradation of the radiolabeled targets. The data suggest that the various inducers of autolysin activation caused leakage of autolytic enzymes from the intact bacteria which attacked the depolymerized the bacterial cell walls. Anionic polyelectrolytes like heparin, dextran sulfate, suramine, polyglutamic acid, and liquid (polyanethole sulfonic acid) markedly inhibited both spontaneous and induced lysis. Staphylococci which had grown in the presence of anionic polyelectrolytes became highly resistant to lysis triggered by any of the inducers of autolysis. Since inflammatory exudates are known to be rich in anionic polyelectrolytes, it is suggested that the prolonged survival of intact bacterial cells in such a milieu may be due to the inactivation of autolytic enzymes. It is also postulated that the degradation of certain bacterial species following phagocytosis or extracellular degradation may not be the result of the action of hydrolytic enzymes but rather the result of activation by leukocyte factors of autolytic enzymes which lead to bacteriolysis.

Increased bactericidal activity of dilute preparations of povidone-iodine solutions.

Recent confirmation of intrinsic bacterial contamination of 10% povidone-iodine solution has raised questions regarding the bactericidal mechanism of iodophors and the possibility for survival of vegetative bacterial cells in iodophor solutions. In this laboratory investigation, five different species were exposed to various dilutions of three commercial preparations of 10% povidone-iodine solution; survival was assessed after exposure for time periods varying between 0 and 8 min. All brands of povidone-iodine solution tested demonstrated more rapid killing of Staphylococcus aureus and Mycobacterium chelonei at dilutions of 1:2, 1:4, 1:10, 1:50, and 1:100 than did the stock solutions, S. aureus survived a 2-min exposure to full-strength povidone-iodine solution but did not survive a 15-s exposure to a 1:100 dilution of the iodophor. Both stock and dilute preparations of 10% povidone-iodine solution demonstrated rapid bactericidal action against Klebsiella pneumoniae, Pseudomonas cepacia, and Streptococcus mitis.

Pyrimidine dimer excision in surviving and nonsurviving cells of ultraviolet-irradiated cultures of Escherichia coli.

We compared dimer excision in viable and nonviable cells fractions separated from Escherichia coli B/r cultures exposed to ultraviolet (UV) irradiation. For cells grown on minimal medium with glycerol as a carbon source, both fractions from the irradiated (20 J/m2, 5% survival) culture excised 60 to 70% of the thymine dimers from prelabeled DNA within 120 min. This percentage was, within experimental error, the same as that obtained from unseparated cultures. When isolated viable and nonviable populations were given a second UV exposure (20 J/m2) both types of cells were again able to excise dimers. The UV survival curve for the isolated viable population indicates that these cells are no more sensitive to radiation than exponentially growing cells not previously exposed to UV. The extent of dimer excision after UV irradiation was also the same in viable and nonviable cells separated from cultures grown on a glucose minimal medium in which both populations excised about 85% of the dimers within 120 min. These results show that the extent of removal of pyrimidine dimer from deoxyribonucleic acid is not precisely correlated with survival of repair-competent bacterial cells after exposure to UV light.

Function of Peroxidase in Resistance of Soybean to Bacterial Pustule1

Peroxidase activity of soybean [Glycine max (L.) Merr.] plants was determined to investigate its possible role in disease resistance. Activity of the enzyme was determined in mitochondrial and supernatant fractions obtained from roots of the near‐isogenic soybean cultivars ‘Clark’ and ‘Clark 63,’ susceptible and resistant, respectively, to bacterial pustule disease caused by Xanthomonas phaseoli var. sojensis. Peroxidase activity in both mitochondrial and supernatant fractions from roots of Clark 63 was greater than in those from Clark. Peroxidase activity was higher in the mitochondrial fraction than in the supernatant fraction from Clark 63.Peroxidase activity of the mitochondrial fraction from Clark 63 was threefold greater than that of Clark. Peroxidase was partially purified from mitochondria from roots of both cultivars. The peroxidase preparation from Clark 63 had greater bactericidal activity in the presence of hydrogen peroxide than that of Clark. There was a highly significant correlation between peroxidase activity per mg protein in the root preparations and percent survival of bacterial cells. A correlation coefficient of ∓0.7112 was obtained when ascorbic acid was present in the bactericidal assay system, and a coefficient of ∓0.6141 was obtained when ascorbic acid was omitted from the system.

Postirradiation Growth, Division, and Recovery in Bacteria

The survival of bacterial cells after exposure to ionizing radiation is often estimated by the observation of macrocolonies produced on solid media. A variety of postirradiation treatments affects the ability of cells to form macrocolonies. For example, Escherichia coli B cells recover from radiation damage if plated on poor growth media (1-3) or exposed to temperatures above the growth optimum (4, 5), whereas E. coli B/r, a closely related strain, recovers on rich media and at temperatures below its growth optimum (6). Such apparently contradictory observations are disturbing to investigators interested in this subject. Our recent experiments with a mutant in which the division mechanism is particularly radiation-sensitive have led us to postulate that recovery conditions can be grouped into two types: (1) those that promote colony formation by stimulating cell division, and (2) those that promote colony formation by stimulating cell growth. We have developed a technique that allows us to predict which of the two types of recovery conditions will be effective in promoting survival for a given bacterial strain.