Differences in lipid composition between free-living and initially adhered cells of a Gram-negative bacterium

Modification of Fatty Acid Composition of Escherichia coli by Co-Expression of Fatty Acid Desaturase and Thioesterase from Arabidopsis thaliana

Fatty acid composition has an important influence on the fluidity of biological membranes, which is a key factor for the survival of Escherichia coli. With the aim to modify fatty acid composition in this experimentally friendly microorganism, the AtFab2 gene, encoding the Arabidopsis thaliana fatty acid desaturase, was expressed separately and jointly with AtFatA, a fatty acid thioesterase of the same plant origin. The expression of ATFab2 desaturase resulted in an enhancement of cis-vaccenic acid (18:1Δ11) contents, while amounts of palmitioleic acid (16:1Δ9) accumulated by E. coli were increased by 130% for the expression of the AtFatA thioesterase. In the final engineered strain co-expressing AtFab2 and AtFatA, the percentage of palmitic acid (16:0), the most abundant saturated fatty acid found in E. coli, was reduced to 29.9% and the ratio of unsaturated fatty acid to saturated fatty acid reached 2:1. Free fatty acids accounted for about 40% of total fatty acid profiles in the recombinant strain expressing both two genes, and the unsaturated fatty acid contents reached nearly 75% in the free fatty acid profiles. The increase of unsaturated fatty acid level might provide some implication for the construction of cold tolerant strains.

Biofouling and biocorrosion in industrial water systems

Corrosion associated with microorganisms has been recognized for over 50 years and yet the study of microbiologically influenced corrosion (MIC) is relatively new. MIC can occur in diverse environments and is not limited to aqueous corrosion under submerged conditions, but also takes place in humid atmospheres. Biofouling of industrial water systems is the phenomenon whereby surfaces in contact with water are colonized by microorganisms, which are ubiquitous in our environment. However, the economic implications of biofouling in industrial water systems are much greater than many people realize. In a survey conducted by the National Association of Corrosion Engineers of the United States ten years ago, it was found that many corrosion engineer did not accept the role of bacteria in corrosion, and many of then that did, could not recognize and mitigate the problem. Biofouling can be described in terms of its effects on processes and products such as material degradation (bio-corossion), product contamination, mechanical blockages, and impedance of heat transfer. Microorganisms distinguish themselves from other industrial water contaminants by their ability to utilize available nutrient sources, reproduce, and generate intra- and extracellular organic and inorganic substances in water. A sound understanding of the molecular and physiological activities of the microorganisms involved is necessary before strategies for the long term control of biofouling can be format. Traditional water treatment strategies however, have largely failed to address those factors that promote biofouling activities and lead to biocorrosion. Some of the major developments in recent years have been a redefinition of biofilm architecture and the realization that MIC of metals can be best understood as biomineralization.

Effect of oxygen and growth medium onin vitrobiofilm formation byEscherichia coli

The effects of oxygen availability onin vitrobiofilm formation by anEscherichia coliK-12 strain and 13 clinicalE. colistrains were compared. AllE. colistrains were capable of forming monospecies biofilm on polystyrene in aerobic media. The K-12 strain produced biofilm in both aerobic glucose minimal medium (ABTG), and aerobic trypticase soy broth (TSB) whereas the majority of the clinical strains produced significant biofilm only in aerobic TSB (9 of 13). In anaerobic media,E. coliK-12 and 9 of the 13 clinical strains were capable of forming biofilmin vitro. Only three clinical strains formed biofilm in anaerobic TSB whereas six clinical strains produced detectable biofilm in anaerobic ABTG. None of the strains tested were capable of forming biofilm in both anaerobic ABTG and anaerobic TSB. Strains that were good biofilm formers in aerobic ABTG also produced the highest amount of biofilm in anaerobic ABTG (R2= 0.90). Image analysis revealed notable differences in architecture for biofilms grown in the presence and in the absence of oxygen. In aerobic ABTG, the biofilm was dominated by tall, mushroom-shaped microcolonies with pores and channels whereas biofilm in anaerobic ABTG was thinner and less heterogeneous, resulting in reduced maximum thickness and biovolume. Analysis of phospholipid fatty acid (PLFA) profiles fromE. coliK-12 and three clinical strains did not reveal a specific pattern associated with the biofilm phenotypes. Interestingly, the clinicalE. colistrains adjusted their PLFA composition much more than didE. coliK-12 in response to changes in growth regimens. Collectively, the results indicate that oxygen availability may affectE. colibiofilm formation in minimal and complex media. The results confirm thatE. coliK-12 and some clinicalE. colistrains are capable of formingin vitrobiofilm under anaerobic conditions. However, the data also suggest that this attribute is highly strain dependent and may vary significantly among clinical isolates.

Fatty acids of lipid fractions in extracellular polymeric substances of activated sludge flocs

Phospholipid (PL), glycolipid (GL), and neutral lipid (NL) FA, and the lipopolysaccharide 2- and 3-hydroxy (LPS 2-OH and 3-OH) FA of activated sludges and extracted extracellular polymeric substances (EPS) were determined on samples collected from two wastewater treatment plants. EPS extracted from sludges by means of sonication and cation exchange contained proteins (43.4%), humic-like substances (11.5%), nucleic acids (10.9%), carbohydrates (9.9%), and lipid-bound FA (1.8%). The lipids associated with EPS were composed of GL, PL, NL, and LPS acids in proportions of 61, 21, 16, and 2%, respectively. The profiles of lipid-bound FA in activated sludges and EPS were similar (around 85 separate FA were identified). The FA signatures observed can be attributed to the likely presence of yeasts, fungi, sulfate-reducing bacteria, gram-positive and gram-negative bacteria, and, in lesser quantities, mycobacteria. Comparison of data from the dates of sampling (January and September) showed that there were more unsaturated PLFA in the EPS extracted from the activated sludges sampled in January. This observation could be partly related to microorganism adaptation to temperature variations. The comparison between two wastewater treatment plants showed that the FA profiles were similar, although differences in microbial community structure were also seen. Most of the FA in sludges had an even number of carbons.

The microbial community structure of drinking water biofilms can be affected by phosphorus availability

Microbial communities in biofilms grown for 4 and 11 weeks under the flow of drinking water supplemented with 0, 1, 2, and 5 microg of phosphorus liter(-1) and in drinking and warm waters were compared by using phospholipid fatty acids (PLFAs) and lipopolysaccharide 3-hydroxy fatty acids (LPS 3-OH-FAs). Phosphate increased the proportion of PLFAs 16:1 omega 7c and 18:1 omega 7c and affected LPS 3-OH-FAs after 11 weeks of growth, indicating an increase in gram-negative bacteria and changes in their community structure. Differences in community structures between biofilms and drinking and warm waters can be assumed from PLFAs and LPS 3-OH-FAs, concomitantly with adaptive changes in fatty acid chain length, cyclization, and unsaturation.

Effect of cadmium and zinc on attachment and detachment interactions of Pseudomonas fluorescens H2 with glass

The physiological and physicochemical bases for the effect of 5, 10, 50, or 100 micrograms of Cd and Zn ml-1 on the attachment and detachment interactions of Pseudomonas fluorescens H2 with glass substrata were determined. Attachment and detachment varied with the type and concentration of metal and the time at which cells were exposed to the metal. The largely inhibitory effect of the metals on bacterial motility and physiological activity did not directly influence attachment. The amount of Cd or Zn accumulated by the cells increased with metal concentration and was greater for free than for attached cells. The hydrophobicity and negative and positive charges of the bacterial surfaces (measured by hydrophobic and electrostatic interaction chromatography) were increased by cell exposure to the metals, particularly after Cd treatment. Cells exposed to Cd prior to attachment showed increased adhesion. Zinc-treated cells did not. There was a positive correlation between adhesion and Cd concentration in the attachment solution. No such relationship existed for Zn. P. fluorescens H2 exposed to Cd prior to attachment desorbed similarly to untreated controls. Zinc pretreatment resulted in decreased desorption. Cells attached in 5 or 10 micrograms of Cd or Zn ml-1 detached less than those attached in 50 or 100 micrograms of Cd or Zn ml-1. The presence of Cd or Zn during detachment had little effect on desorption. The dominant influence of Cd and Zn on attachment and detachment appears to be through modification of the bacterial surface. In natural ecosystems, heavy metals may influence the distribution of bacteria between the solid and liquid phases.

Soil and groundwater transport of microorganisms

Releases of GEMs into the environment are expected to increase in the next few years, with the most dramatic increases resulting from the application of pest-control agents in agriculture and forestry. Of major significance in assessing the environmental risk impact of GEMs is an understanding of their survival and transport in soil and subsurface environments. While information on the transport and survival of microorganisms through soil is available, it is neither abundant nor extensive in terms of microbial types tested or soils examined. Though the transport of microorganisms from an application site depends primarily upon passive mechanisms, broad generalizations pertaining to the transportability of a specific microorganism within a particular soil environment may not be possible. Indeed, to extrapolate from information about one microbe to another, or from one geographical location to another, may not be appropriate. What is clear, however, is that the broader the data base, the more powerful the argument for making reasoned judgement, and consequently the more satisfactory the results of the predictive process. Several inherent difficulties exist in studying the transport behavior of GEMs in soil and subsurface environments. Detection of low microbial numbers or of stressed microbial populations is exceedingly difficult with traditional technology. In an effort to improve detection sensitivity, many improved methods of monitoring GEMs in the soil and subsurface are currently under development (Chaudhry et al. 1989). Beyond the difficulties of making accurate measurements of microorganisms to determine their spatial and temporal situation in the soil and subsurface environment, lies the need to ascertain the dynamic relationships between indigenous populations of microorganisms and how they may interact with a released GEM. Also, research strategies have not adequately addressed methods to predict the potential interactions between GEMs and natural microorganisms. These issues must be addressed if environmental risk assessment is to be valuable. There is clearly a need for focused research on the survival and transport of GEMs in these environments.