Starvation and nutrient resuscitation of Klebsiella pneumoniae isolated from oil well waters

Microbial communities in crude oil phase and filter-graded aqueous phase from a Daqing oilfield after polymer flooding

AIMS

The aim was to characterize indigenous microorganisms in oil reservoirs after polymer flooding (RAPF).

METHODS

The microbial communities in the crude oil phase (Oil) and in the filter-graded aqueous phases Aqu0.22 (>0.22 μm) and Aqu0.1 (0.1~0.22 μm) were investigated by 16S rRNA gene high-throughput sequencing.

RESULTS

Indigenous microorganisms related to hydrocarbon degradation prevailed in the three phases of each well. However, obvious differences of bacterial compositions were observed among the three phases of the same well and among the same phase of different wells. The crude oil and Aqu0.22 shared many dominant bacteria. Aqu0.1 contained a unique bacterial community in each well. Most bacteria in Aqu0.1 were affiliated to culturable genera, suggesting that they may adapt to the oil reservoir environment by reduction of cell size. Contrary to the bacterial genera, archaeal genera were similar in the three phases but varied in relative abundances. The observed microbial differences may be driven by specific environmental factors in each oil well.

CONCLUSIONS

The results suggest an application potential of microbial enhanced oil recovery (MEOR) technology in RAPF. The crude oil and Aqu0.1 contain many different functional microorganisms related to hydrocarbon degradation. Both should not be overlooked when investing and exploring the indigenous microorganisms for MEOR.

SIGNIFICANCE AND IMPACT OF THE STUDY

This work facilitates the understanding of microbial community structures in RAPF and provides information for microbial control in oil fields.

Measurement of the interconnected turgor pressure and envelope elasticity of live bacterial cells

Turgor pressure and envelope elasticity of bacterial cells are two mechanical parameters that play a dominant role in cellular deformation, division, and motility. However, a clear understanding of these two properties is lacking because of their strongly interconnected mechanisms. This study established a nanoindentation method to precisely measure the turgor pressure and envelope elasticity of live bacteria. The indentation force-depth curves of Klebsiella pneumoniae bacteria were recorded with atomic force microscopy. Through combination of dimensional analysis and numerical simulations, an explicit expression was derived to decouple the two properties of individual bacteria from the nanoindentation curves. We show that the Young's modulus of bacterial envelope is sensitive to the external osmotic environment, and the turgor pressure is significantly dependent on the external osmotic stress. This method can not only quantify the turgor pressure and envelope elasticity of bacteria, but also help resolve the mechanical behaviors of bacteria in different environments.

Molecular subtyping of mastitis-associated Klebsiella pneumoniae isolates shows high levels of diversity within and between dairy herds

Despite advances in controlling mastitis (inflammation of the mammary gland), udder infections caused by Klebsiella pneumoniae continue to affect dairy cattle. Mastitis caused by K. pneumoniae responds poorly to antibiotic treatment, and as a consequence, infections tend to be severe and long lasting. We sought to determine whether a nonrandom distribution of specific genotypes of K. pneumoniae was associated with mastitis from 6 dairy herds located in 4 different states. A total of 635 isolates were obtained and fingerprinted by repetitive DNA sequence PCR. Significant genetic diversity was observed in 4 of the 6 dairy herds analyzed, and a total of 49 genotypic variants were identified. Within a herd, Simpson's diversity indices were 91.0, 94.1, 91.7, 88.6, 53.3, and 64.3% for dairies A, B, C, D, E, and F, respectively. The association between matrices of genetic similarity and matrices of temporal distance was negative in all the dairies analyzed. Four dairies had a high incidence of K. pneumoniae mastitis during the winter. The majority of genotypes were unique to herds of origin, and only 5 genotypes were detected in more than 2 dairies. Genotype 1 (arbitrary designation) occurred most frequently across dairies and was found in 25.2% of all mastitis cases and among 22.8% of reinfected and culled cows in dairy A. Specific genotypes also tended to be associated with a specific bedding type and dairy location. Analysis of molecular variance showed that 18% of the genetic diversity was due to variation among herds within states, and 82% of the genetic diversity was accounted for by variation of genotypes within herds. The data support the idea that mastitis is caused by a diverse group of K. pneumoniae genotypes and thus has major implications for the diagnosis, prevention, and treatment of udder infections in dairy cows.

Impact of Pseudomonas aeruginosa quorum sensing on biofilm persistence in an in vivo intraperitoneal foreign-body infection model

Pseudomonas aeruginosa is an opportunistic human pathogen that causes chronic biofilm-based infections in host organisms. P. aeruginosa employs quorum sensing (QS) to control expression of its virulence, and to establish and maintain chronic infections. Under such conditions, the biofilm mode of growth contributes significantly to P. aeruginosa tolerance to the action of the innate and adaptive defence system and numerous antibiotics. In the present study, an in vivo foreign-body infection model was established in the peritoneal cavity of mice. Experimental data showed that QS-deficient P. aeruginosa are cleared more rapidly from silicone implants as compared to their wild-type counterparts. Concurrently, treatment with the QS inhibitor furanone C-30 of mice harbouring implants colonized with the wild-type P. aeruginosa resulted in a significantly faster clearing of the implants as compared to the placebo-treated group. These results were obtained with both an inbred (BALB/c) and an outbred (NMRI) mouse strain. The present results support a model by which functional QS systems play a pivotal role in the ability of bacteria to resist clearing by the innate immune system and strongly suggest that the efficiency of the mouse innate defence against biofilm-forming P. aeruginosa is improved when the bacteria are treated with QS drugs that induce QS deficiency.

Detection and characterization of filterable heterotrophic bacteria from rural groundwater supplies

AIMS

The chemical/physical environment of groundwater may contribute to the existence of a subpopulation of small-sized bacteria (filterable bacteria) that fails to be trapped on conventional 0.45 microm-pore-size membrane filters during routine bacteriological water quality analyses. Efforts were directed to determining an efficient recovery method for detection of such cells.

METHODS AND RESULTS

Individual groundwater supplies in a rural setting were examined by a double membrane filtration procedure to determine the presence of heterotrophic plate count (HPC) bacteria capable of escaping detection on conventional pore size (0.45 microm) membrane filters but retained on 0.22 microm-pore-size filters. Since optimum cultural conditions for recovery of filterable bacteria are not well defined, initial efforts focused on evaluation of various media (R2A, m-HPC and NWRI) and incubation temperatures (15, 20, 28 and 35 degrees C) for specific recovery of filterable bacteria. Maximum recovery of small-sized HPC bacteria occurred on low-nutrient concentration R2A agar incubated for 7 d at 28 degrees C. Similarly, identical cultural conditions gave enhanced detection of the general HPC population on 0.45 microm-pore-size filters. A 17-month survey of 10 well water supplies conducted with the cultural conditions described above resulted in detection of filterable bacteria (ranging in density from 9 to 175 cfu ml-1) in six of the groundwater sources. The proportion of filterable bacteria in any single sample never exceeded 10% of the total HPC population. A majority of the colonies appearing on the 0.22 microm membrane filters was pigmented (50-90%), whereas the proportion of colonies demonstrating pigmentation on the larger porosity filters failed to exceed 50% for any of the samples (19-49%).

CONCLUSION

A reliable recovery method was developed for the detection of filterable bacteria from groundwater. During a subsequent survey study using this procedure, filterable bacteria were detected in a majority of the groundwater supplies examined; however, the density of filterable bacteria in any single sample never exceeded 10% of the total HPC population. Identification of randomly selected isolates obtained on the 0.22 microm filters indicated that some of these filterable bacteria have been implicated as opportunistic pathogens.

SIGNIFICANCE AND IMPACT OF THE STUDY

We have determined the presence of small-sized HPC bacteria in ground water that may go undetected when using standard porosity membrane filters for water quality analyses. Further study is needed to assess the significance and possible health risk associated with presence of filterable bacteria in drinking water supplies from groundwater sources.

Adaptation to nutrient starvation in Rhizobium leguminosarum bv. phaseoli: analysis of survival, stress resistance, and changes in macromolecular synthesis during entry to and exit from stationary phase

The nitrogen-fixing bacterium Rhizobium leguminosarum bv. phaseoli often has to survive long periods of starvation in the soil, when not in a useful symbiotic relationship with leguminous plants. We report that it can survive carbon, nitrogen, and phosphorus starvation for at least 2 months with little loss of viability. Upon carbon starvation, R. leguminosarum cells were found to undergo reductive cell division. During this period, they acquired the potential for long-term starvation-survival, levels of protein, DNA, and RNA synthesis were decreased to base levels, and pool mRNA was stabilized. The starved cells are ready to rapidly restart growth when nutrients become available. Upon addition of fresh nutrients, there is an immediate increase in the levels of macromolecular synthesis, pool mRNA destabilizes, and the cultures enter exponential growth within 5 to 8 h. The starved cells were cross-protected against pH, heat, osmotic, and oxidative shock. These results provide evidence for a general starvation response in R. leguminosarum similar to that previously found in other bacteria such as Escherichia coli and Vibrio sp.

Synergism in biofilm formation between Salmonella enteritidis and a nitrogen-fixing strain of Klebsiella pneumoniae

A laboratory reactor, which simulates biofilm formation in water pipes, was used to study interactions in biofilm formation between a nitrogen-fixing strain of Klebsiella pneumoniae and Salmonella enteritidis. The level of attachment of Salm. enteritidis was higher in the binar biofilm than in the single species biofilm. In the initial colonization phase the binary biofilm contained a much higher proportion of metabolically active cells than in single species biofilms formed by either Salm. enteritidis or Kl. pneumoniae. When a pulse of Salm. enteritidis was passed over an already established biofilm of Kl. pneumoniae it rapidly became integrated into the biofilm, from where it was subsequently released into the water column, along with Kl. pneumoniae. Klebsiella pneumoniae fixed nitrogen in the presence of Salm. enteritidis in both types of biofilm.

Morphological and metabolic responses to starvation by the dissimilatory metal-reducing bacterium Shewanella alga BrY

The response of the dissimilatory metal-reducing bacterium Shewanella alga BrY to carbon and nitrogen starvation was examined. Starvation resulted in a gradual decrease in the mean cell volume from 0.48 to 0.2 micron 3 and a dramatic decrease in Fe(III) reductase activity. Growth of starved cultures was initiated with O2, ferric oxyhydroxide, Co(III)-EDTA, or Fe(III)-bearing subsurface materials as the sole electron acceptor. Microbially reduced subsurface materials reduced CrO(4)2-. Starvation of dissimilatory metal-reducing bacteria may provide a means of delivering this metabolism to contaminated subsurface environments for in situ bioremediation.

Starvation-survival of a p-nitrophenol-degrading bacterium

An environmental actinomycetes, capable of utilizing p-nitrophenol as its sole carbon and nitrogen source, was starved for an 8-week period and showed no reduction in its ability to biodegrade p-nitrophenol. Microscopic examination revealed that starvation of the bacterium resulted in the fragmentation of filaments into individual cells.

Physiological studies of chloramine resistance developed by Klebsiella pneumoniae under low-nutrient growth conditions

This study investigated the physiological mechanisms of resistance to chloramines developed by Klebsiella pneumoniae grown in a nutrient-limited environment. Growth under these conditions resulted in cells that were smaller than cells grown under high-nutrient conditions and extensively aggregated. Cellular aggregates ranged from 10 to more than 10,000 cells per aggregate, with a mean population aggregate size of 90 cells. This aggregation may have been facilitated by the presence of extracellular polymer material. By using glucose as a reference of capsule content, it was determined that growth under low-nutrient conditions produced cells with 8 x 10(-14) to 41 x 10(-14) g of carbohydrate per cell, with a mean +/- standard deviation of 27 x 10(-14) +/- 16 x 10(-14) g of carbohydrate per cell. In comparison, growth under high-nutrient conditions resulted in 2.7 x 10(-14) to 5.9 x 10(-14) g of carbohydrate per cell, with a mean and standard deviation of 4.3 x 10(-14) +/- 1.2 x 10(-14) g of carbohydrate per cell. Cell wall and cell membrane lipids also varied with growth conditions. The ratio of saturated to unsaturated fatty acids in cells grown under low-nutrient conditions was approximately five times greater than that in cells grown under high-nutrient conditions, suggesting possible differences in membrane permeability. An analysis of sulfhydryl (-SH) groups revealed no quantitative difference with respect to growth conditions. However, upon exposure to chloramines, only 33% of the -SH groups of cells grown under low-nutrient conditions were oxidized, compared with 80% oxidization of -SH groups in cells grown under high-nutrient conditions. The reduced effectiveness of chloramine oxidization of -SH groups in cells grown under low-nutrient conditions may be due to restricted penetration of chloramines into the cells, conformational changes of enzymes, or a combination of both factors. The results of this study suggest that chloramine resistance developed under low-nutrient growth conditions may be a function of multiple physiological factors, including cellular aggregation and protection of sulfhydryl groups within the cell.

Detection and identification of groundwater bacteria capable of escaping entrapment on 0.45-micron-pore-size membrane filters

Rural drinking water systems supplied by untreated groundwater were examined to determine whether coliform or heterotrophic plate count bacteria are capable of escaping entrapment on standard porosity (0.45-micron-pore-size) membrane filters. Filterable bacteria were present in 42% of the 24 groundwater sources examined by using nonselective media (R2A, full strength m-HPC, and 0.1x m-HPC agars). Pseudomonads were the most frequently identified group of filterable bacteria detected. Flavobacterium, Alcaligenes, Acinetobacter, and Achromobacter isolates were also identified. Total coliforms were not recovered from any of the 24 groundwater samples following filtration through 0.45-micron-pore-size membrane filters by using selective M-Endo LES agar or mT7 agar. In addition, none of the isolates identified from nonselective media were coliforms. Similarly, neither total coliforms nor specifically Escherichia coli were detected in these filtrates when Colilert P/A medium was used.