Slime-forming Bacteria Research Articles

Metal Bionanohybrids against Microbiologically Influenced Corrosion (MIC) Consortia.

In search of new materials that would help to prevent microbiologically influenced corrosion (MIC), we have designed and synthetized six different copper and copper-silver nanoparticle-enzyme hybrids using a mild-conditions method carried out in water and r.t. Characterization analyses exhibited the presence of small crystalline nanoparticles with diameters from 2 to 20 nm. X-ray diffraction determined that the Cu hybrids were composed of different copper species, depending on the synthetic protocol used, while the Cu-Ag hybrids were mainly composed of copper and silver phosphate metallic species. Then, the bacterial viability of three MIC-relevant enrichments, sulfate-reducing bacteria (SRB), slime-forming bacteria (SFB), and acid-producing bacteria (APB), was studied in the presence of the bionanohybrids. The results demonstrated a notable effect of all bionanohybrids against SRB, one of the most prominent bacteria associated with MIC. In particular, Cu-2 and Cu-Ag-2 showed a reduction in bacterial cells of 94% and 98% after 48 h, respectively, at a concentration of 100 ppm. They also exhibited high efficiencies against SFB, with Cu-Ag-1 and Cu-Ag-2 hybrids being the best, with bacterial reduction percentages of 98% after 45 h of exposition at a concentration of 100 ppm. However, in the case of APB, the effect of the hybrids was lost due to the low pH level generated during the experiment. Finally, the capacity of Cu-2 and Cu-Ag-2 to inhibit the adhesion of SRB to the surface of carbon steel coupons was evaluated. Fluorescence imaging of the surface of the coupons at 24 h demonstrated that the presence of the hybrids inhibited the growth of SRB, obtaining a maximum reduction of 98% with Cu-2. Overall, the results of this study demonstrate that these novel nanomaterials have a wide-range antibacterial effect and may have a promising future in the prevention and treatment of MIC.

Gene Regulatory Network Construction Based on a Particle Swarm Optimization of a Long Short-term Memory Network

Background: The Gene Regulatory Network (GRN) is a model for studying the function and behavior of genes by treating the genome as a whole, which can reveal the gene expression mechanism. However, due to the dynamics, nonlinearity, and complexity of gene expression data, it is a challenging task to construct a GRN precisely. And in the circulating cooling water system, the Slime-Forming Bacteria (SFB) is one of the bacteria that helps to form dirt. In order to explore the microbial fouling mechanism of SFB, constructing a GRN for the fouling-forming genes of SFB is significant. Objective: Propose an effective GRN construction method and construct a GRN for the foulingforming genes of SFB. Methods: In this paper, a combination method of Long Short-Term Memory Network (LSTM) and Mean Impact Value (MIV) was applied for GRN reconstruction. Firstly, LSTM was employed to establish a gene expression prediction model. To improve the performance of LSTM, a Particle Swarm Optimization (PSO) was introduced to optimize the weight and learning rate. Then, the MIV was used to infer the regulation among genes. In view of the fouling-forming problem of SFB, we have designed electromagnetic field experiments and transcriptome sequencing experiments to locate the fouling-forming genes and obtain gene expression data. Results: In order to test the proposed approach, the proposed method was applied to three datasets: a simulated dataset and two real biology datasets. By comparing with other methods, the experimental results indicate that the proposed method has higher modeling accuracy and it can be used to effectively construct a GRN. And at last, a GRN for fouling-forming genes of SFB was constructed using the proposed approach. Conclusion: The experiments indicated that the proposed approach can reconstruct a GRN precisely, and compared with other approaches, the proposed approach performs better in extracting the regulations among genes.

Experimental Investigation of Microbial Fouling and Heat Mass Transfer Characteristics on Ni-P Modified Surface of Heat Exchanger

Fouling deposition problem on heat transfer surface is widely distributed in the field of energy and chemical industry, and microbial fouling is a common fouling type in heat exchanger. In this article, the surface modification was used for inhibiting or mitigating the microbial fouling deposition on heat exchange surface. Firstly, the experimental system for real-time monitoring the fouling deposition process was built, and then the Ni-P modified surface was prepared. Further, the slime forming bacteria (SFB) microbial fouling characteristics and corresponding influencing factors on Ni-P modified surface were investigated experimentally. The results indicated that Ni-P modified surface had an excellent fouling inhibition property. Comparing with carbon steel, Ni-P modified surface reduced the fouling heat resistance by 80%. Accordingly, the influencing factors of microbial fouling deposition including temperature, flow rate and microbial concentrations were discussed. With cooling water temperature increasing given in the experiment arrangement, the microbial fouling resistance was increased first and then decreased, while with bacteria concentration and flow rate increasing, the fouling resistance was increased and decreased separately. The work can provide experimental reference for the fouling inhibition surface development and fouling inhibition mechanism study.

Enhancement of A Cationic Surfactant by Capping Nanoparticles: Synthesis, Characterization and Multiple Applications.

There is scarce information on cationic surfactants’ biocidal and corrosion inhbibition effects on Slime-Forming Bacteria (SFB) isolated from oil field formation water. Therefore, this work focused on the the synthesis of a cationic surfactant (CS) to increase its features by capping different metal nanoparticles (zinc, ZnNPs-C-CS; manganese, MnNPs-C-CS and tin, SnNPs-C-CS) and used them as biocides and corrosion inhibitors. The cationic surfactant was synthesized and characterized by Fourier-Transform Infrared (FTIR) and Nuclear Magnetic Resonance (NMR) spectroscopy. Afterwards, different nanoparticles were synthesized, characterized, and exploited to cap by the CS. The CS and the different nanoparticles capped by the CS were tested for their antimicrobial susceptibility against standard bacterial and yeast strains. The synthesized compounds were further evaluated as anti-biofilms agents against positively-developed bacterial biofilms. Moreover, the CS and the ZnNPs-C-CS, MnNPs-C-CS, and SnNPs-C-CS were assessed as potential biocides against SFB, particularly Pseudomonas sp. (isolated from contaminated formation water), and as corrosion inhibitors against cultivated salinity. The results revealed the great effect of the different CS-capped NPs as broad-spectrum antimicrobial and anti-biofilm agents at lower Minimum Inhibitory Concentrations (MICs), Minimum Bactericidal Concentrations (MBCs), Minimum Fungicidal Concentrations (MFCs) and Minimum Biofilm Inhibitory Concentrations (MBICs), and the activities were reported in order of SnNPs-C-CS > MnNPs-C-CS > ZnNPs-C-CS > CS. Furthermore, the ZnNPs-C-CS, MnNPs-C-CS, and SnNPs-C-CS demonstrated biocidal and corrosion inhibition effects against Pseudomonas sp. at a salinity of 3.5% NaCl, with metal corrosion inhibition efficiencies of 88.6, 94.0 and 96.9%, in comparison to a CS efficiency of 85.7%. In conclusion, the present work provides a newly synthesized cationic surfactant and has enhanced its antimicrobial and its metal corrosion inhibition effects by capping different nanoparticles, and it has been successfully applied against slime-forming bacteria at a salinity of 3.5% NaCl.

Adaptive Elman Model of Gene Regulation Network Based on Time Series Data

Background:Time series expression data of genes contain relations among different genes, which are difficult to model precisely. Slime-forming bacteria is one of the three major harmful bacteria types in industrial circulating cooling water systems.Objective:This study aimed at constructing gene regulation network(GRN) for slime-forming bacteria to understand the microbial fouling mechanism.Methods:For this purpose, an Adaptive Elman Neural Network (AENN) to reveal the relationships among genes using gene expression time series is proposed. The parameters of Elman neural network were optimized adaptively by a Genetic Algorithm (GA). And a Pearson correlation analysis is applied to discover the relationships among genes. In addition, the gene expression data of slime-forming bacteria by transcriptome gene sequencing was presented.Results:To evaluate our proposed method, we compared several alternative data-driven approaches, including a Neural Fuzzy Recurrent Network (NFRN), a basic Elman Neural Network (ENN), and an ensemble network. The experimental results of simulated and real datasets demonstrate that the proposed approach has a promising performance for modeling Gene Regulation Networks (GRNs). We also applied the proposed method for the GRN construction of slime-forming bacteria and at last a GRN for 6 genes was constructed.Conclusion:The proposed GRN construction method can effectively extract the regulations among genes. This is also the first report to construct the GRN for slime-forming bacteria.

INVESTIGATION OF DISINFECTANT’S EFFECTIVENESS AS TO CONTAMINATING MICROFLORA IN SUGAR PRODUCTION

The article presents the results of the studies of the effectiveness of disinfection means, based on chlorinated guanidines, tetradic ammonium salts, dichlorisocyanuric acid, peracetic acid and hydrogen peroxide as to the contaminating microflora of sugar beets. There was investigated the influence of disinfectants on bacteria Bacillus subtilis, Leuconostoс mesenteroides, mycelia fungi Aspergillus niger, Penicillium chrysogenum and yeast Sacharomyses сerevisiae. It was experimentally established, that the studied means has the high effectiveness as to most microorganisms that cause saccharose losses in the process of its extracting from beet chip and result in worsening a technological quality of semi-products of beet-sugar. There was established the high effectiveness of modern disinfection means as to inhibiting slime-forming bacteria of Leuconostoc generis. There was proved a possibility of their use at different technological stages of beet-sugar production for preventing the development of mucous bacteriosis. It was determined that means consumption depends on a type and extent of microbiological contamination of raw materials, semi-products, technological waters at sugar production. There were established concentrations of the studied means as to inhibiting the development of main contaminants of the microflora of raw materials and semi-products in sugar production. There is offered to use the studied means in industrial beet-sugar production that would favor the decrease of microbial contamination of semi-products and the increase of a sugar output from a raw material unit.

Microbiological corrosion: mechanism, control and impact—a review

This article reports a review of microbiological corrosion. It addresses the general perspectives of the various bacteria involved in the biocorrosion, and these include sulphate-reducing bacteria, slime-forming bacteria, iron-oxidizing bacteria and sulphur bacteria. The review also reported on biofilms and effects, various sulphate-reducing bacteria mechanisms, the biodeterioration control methods, environment, fouling and the impact of microbiological corrosion. Microbial corrosion, as it affects stainless steel, mildsteel, aluminium alloy, the AL6XN (N083677) super austenitic stainless steel, and manufacturing and transportation, were reviewed

A Study on Mineralogical and Microbiological Clogging in Water Curtain System of Underground Hydrocarbon Storage Caverns - Calcite and Slime-Forming Bacteria

A Study on Mineralogical and Microbiological Clogging in Water Curtain System of Underground Hydrocarbon Storage Caverns - Calcite and Slime-Forming Bacteria

Experimental study on microbial fouling characteristics of the plate heat exchanger

Iron bacteria (IB) and slime-forming bacteria (SFB) are the most common in circulating cooling water. In order to study on the characteristics of microbial fouling in plate heat exchangers, an experimental study was carried out for the fouling characteristics of IB and SFB. The fouling characteristics in the plate heat exchanger under the different flow velocity, temperature and concentration were investigated for these two bacteria and the mixture of them. The results show that the asymptotic value of fouling resistance and the time of reaching the asymptotic value decreases with the increase of fluid velocity. The asymptotic value of fouling resistance increases with the increase of concentration. And the influence of temperature is different for the two kinds of bacteria. When these two bacteria are mixed, the IB and the SFB grow synergistically because the IB have strong ability in microbial fouling and the SFB have the high secretion rate of extracellular polymeric substances.

Microbially influenced corrosion of steels by Pseudomonas aeruginosa

AbstractMicrobially influenced corrosion (MIC) is a destructive type of corrosion that is initiated, facilitated, or accelerated by the presence and metabolic activity of bacteria. MIC of steels is a great issue in many industries such as marine, freshwater systems, and gas/oil pipelines.Pseudomonas aeruginosais one of the aerobic slime-forming bacteria that are ubiquitous in marine environment that corrode steel structures. This article aims to provide a review on MIC of steels caused by bacteria, mostly in the case ofP. aeruginosa. The mechanisms of MIC will be discussed based on bacteria-metal reactions and emphasize the role ofP. aeruginosaon corrosion of steels.

Effect of Different Biofouling Characteristics on Heat Transfer of the Heat Exchanger

This study, conducted with the dynamic simulation equipment under constant conditions of water temperature 30°C and flow rate 0.4 m.s-1, is intended to simulate dynamically the fouling process on stainless steel tube heat exchanger of three types of fouling microorganisms, iron bacteria (IB), sulfate-reducing bacteria (SRB) and slime forming bacteria (HB), which are isolated from the slime in the bottom of circulating cooling tower. This experiment was tested through the on-line monitoring of fouling resistant and analysis of the characteristics of heat transfer ,the results indicate that induction period for the formation of biofouling in the stainless steel tube by slime-forming bacteria is 56 h, Iron bacteria is 25h, and sulfate-reducing bacteria is 22h. Among these bacteria, the greatest impact on the heat transfer is taken by the iron bacteria, and the sulfate-reducing bacteria are next.

Microbiologically Influenced Corrosion in UNS S31653: Detection and Analysis Using Electrochemical Noise Technique

Abstract Austenitic stainless steels are susceptible to microbiologically influenced corrosion (MIC), and biofilms of slime-forming bacteria can affect the integrity of the passive film of the stainless steel components. An attempt was made to detect and analyze the MIC on UNS S31653 using electrochemical noise (EN) technique. The progress of MIC was monitored in natural reservoir water, concentrated with biofilm-forming microbes along with 0.5 M sodium chloride (NaCl) and nutrients, as well as in a similar media minus microbes (made sterile by autoclaving) using two nominally identical UNS S31653 cylindrical specimens for about 3 weeks, where current and potential noise signals were collected at 1 Hz sampling frequency. Analysis of the shot-noise parameters like frequency of corrosion events, average charge in each event, true coefficient of variation, and noise resistance showed that initiation and propagation of MIC was marked by significant changes in these parameters. The presence of crevice corrosio...

Biodeterioration of asbestos cement (AC) pipe in drinking water distribution systems

Various types of microorganisms have been found to inhabit the inner surfaces of asbestos cement (AC) pipe and their activities can cause significant structural damage. They cause a patina to form on the inside surface of AC pipes as a distinctively continuous coating, commonly 2–5 mm in thickness and generally pigmented as yellow, orange, brown or black depending on the metallic cations that have been incorporated into the surface of biofilm (bioaccumulation). Four sublayers can be identified in the patina, from the outer sublayer that directly interacts with the conveyed drinking water to the inner sublayer that is in proximity of the intact cement matrix. The microbes in the outer sublayer are composed mainly of inactive biomass that separates the aerobic environment of the flowing water from the anaerobic conditions inside the patina. The bacteriological community structure shifts from mixed heterotrophic bacteria (HAB), iron-related bacteria (IRB) and slime-forming bacteria (SLYM) in the outer layer, to a more diverse community with IRB, acid-producing bacteria (APB) and SLYM and HAB in the middle sublayer, and further to the SLYM dominated in the inner sublayer. By directly interacting with cementitious materials, including generating organic acids, IRB and APB play important roles in the leaching of free lime and the dissolution of calcium (Ca)-bearing hydrated components of AC pipes, creating porous structure and reducing the pipe strength. Scanning electron microscopy with an energy dispersive X-ray has revealed that bacterial activity on the internal AC pipe wall had resulted in a significant loss of hydrated cement matrix, which can cause pipe failure when stresses imposed on the pipe exceed the remaining pipe strength.

Experimental Study on Dynamic Simulation of Circulating Cooling Water Biofouling

To study the formation mechanism and the chemical component of biofouling, the biofouling formation was simulated by the dynamic simulation device of circulating cooling water under the constant condition of 30°C and 0.4 m/s. The slime-forming bacteria and Iron Bacteria were selected as the research subject. Adsorption theory of bacteria in the solid/liquid interface was analyzed by colloidal stability theory. The two kinds of bacteria on heat transfer and the relationship between the total number of bacteria and fouling resistance were studied. The main component of biofouling was characterized using XPS. The results show that Iron Bacteria on the negative effects of heat transfer is greater than the slime-forming bacteria. The total number of bacteria is the maximum in the end of the induction period. The main component of biofouling of the slime-forming bacteria of iron bacteria is C, O, N, Fe, Ca, Mg, etc. The major elements of the ratio in different strains exists diversity in the stainless steel heat exchanger, but the most important elements is carbon and oxygen.

Controlling Bacteria in Recycled Production Water for Completion and Workover Operations

Summary Reusing flowback water and produced water from active wells becomes more and more important in today's oil and gas operations to control surface water volumes in order to keep surface water-disposal costs (reinjection or trucking off the premises) to a minimum, especially in operations that do not require secondary-lift support. However, reusing untreated produced and flowback water in workover and completion operations can promote bacteria growth both above and below ground. Water produced from oil and gas wells is a perfect environment for sulfate-reducing bacteria (SRB) and certain types of acid-forming bacteria (AFB) because of its anaerobic nature [less than 2 ppm (O2) content] and high nutrients content (e.g., organics, free iron). Reuse of water introduces enough oxygen through regular pumping operations to allow aerobic bacteria to grow mostly slime-forming bacteria (SFB) and other species of AFB. The oxygen content is high enough for aerobic bacteria to grow but is too low to kill anaerobic bacteria. The oxygen content will cause the anaerobic bacteria to stay in a biostatic state that does not kill them, but prevents them from multiplying. As soon as the bacteria find an environment that is conducive to growth, they will become active again and start multiplying. The anaerobic environment in the formation is ideal for growth of bacteria such as SRB and certain types of AFB. The aerobic environment of the wellbore is conducive for SFB and certain types of AFB. The growth of SRB will not only lead to health and safety (H&S) concerns because of increased sour-gas or hydrogen sulfide (e.g., H2S) production, but also to a slow souring of the formation. This also increases operation expenses because of added corrosion (H2S pitting, stress cracking, microbiologically influenced corrosion) in surface and increases subsurface tubulars and related prevention expenses. Other challenges in production can be related to AFB (pitting) and SFBs (emulsion like materials may form). Different methods can be applied to prevent bacteria growth and reduce operational expenses related to corrosion prevention, remediation of corrosion effects, and remediation of emulsified produced fluids. This paper will take a closer look at the methods of aeration, chlorine-based applications (sodium hypochlorite, calcium hypochlorite, and chlorine dioxide), and biocide application. The different methods will be compared through laboratory tests, actual field application, and a rating system. The rating system incorporates environmental, health, and safety (EH&S) concerns, operational application/considerations, effectiveness of the method, and cost. Each method will be discussed and the pros and cons presented. The pros and cons will be supported by laboratory and field data. The conclusion portion of the paper will discuss why and how the current method of application was chosen and discuss future improvements and testing.

THE EFFECT OF PROTEOLYTIC ENZYME SERRATIOPEPTIDASE IN THE TREATMENT OF EXPERIMENTAL IMPLANT-RELATED INFECTION

Background: Infection around an implanted orthopaedic device is a devastating complication, and the treatment of infections involving slime-forming bacteria is especially difficult. The purpose of the present study was to evaluate the effectiveness of a proteolytic enzyme, serratiopeptidase, in the eradication of a periprosthetic infection in an in vivo animal model. Methods: In sixty Sprague-Dawley rats, the medullary canal of the right femur was drilled through the intercondylar notch and was inoculated with a Staphylococcus epidermidis strain (ATCC 35984) with a high slime-producing capacity. The cavity was filled with polymethylmethacrylate cement, and a Kirschner wire that had contact with the knee joint was inserted. None of the animals received any treatment for two weeks. Twenty rats were killed at two weeks after the inoculation in order to determine if the infection had become established. The remaining forty rats were randomized into two groups. One group received serratiopeptidase enzyme injections into the knee joint in addition to antibiotic therapy for four weeks, and the other group received intra-articular saline solution injections together with the same antibiotic therapy. The animals from both groups were killed two weeks after the end of therapy (on Day 56). The knee specimens were evaluated bacteriologically and histologically to determine the prevalence of persistent infection and the effects of the enzyme on local tissue. Results: At two weeks, inoculated bacteria grew on culture of specimens from twelve (63.2%) of nineteen animals in the no-treatment group. Microbiological testing suggested that infection persisted in only one (5.6%) of eighteen animals in the serratiopeptidase-and-antibiotic group, whereas it was present in six (37.5%) of sixteen animals in the antibiotic-only group (p = 0.001). Histological evaluation showed similar results (kappa = 0.92). Conclusions: Serratiopeptidase was effective for eradicating infection caused by biofilm-forming bacteria in this experimental animal model. The antibiofilm property of the enzyme may enhance antibiotic efficacy in the treatment of staphylococcal infections.

The Effect of Proteolytic Enzyme Serratiopeptidase in the Treatment of Experimental Implant-Related Infection

Infection around an implanted orthopaedic device is a devastating complication, and the treatment of infections involving slime-forming bacteria is especially difficult. The purpose of the present study was to evaluate the effectiveness of a proteolytic enzyme, serratiopeptidase, in the eradication of a periprosthetic infection in an in vivo animal model. In sixty Sprague-Dawley rats, the medullary canal of the right femur was drilled through the intercondylar notch and was inoculated with a Staphylococcus epidermidis strain (ATCC 35984) with a high slime-producing capacity. The cavity was filled with polymethylmethacrylate cement, and a Kirschner wire that had contact with the knee joint was inserted. None of the animals received any treatment for two weeks. Twenty rats were killed at two weeks after the inoculation in order to determine if the infection had become established. The remaining forty rats were randomized into two groups. One group received serratiopeptidase enzyme injections into the knee joint in addition to antibiotic therapy for four weeks, and the other group received intra-articular saline solution injections together with the same antibiotic therapy. The animals from both groups were killed two weeks after the end of therapy (on Day 56). The knee specimens were evaluated bacteriologically and histologically to determine the prevalence of persistent infection and the effects of the enzyme on local tissue. At two weeks, inoculated bacteria grew on culture of specimens from twelve (63.2%) of nineteen animals in the no-treatment group. Microbiological testing suggested that infection persisted in only one (5.6%) of eighteen animals in the serratiopeptidase-and-antibiotic group, whereas it was present in six (37.5%) of sixteen animals in the antibiotic-only group (p = 0.001). Histological evaluation showed similar results (kappa = 0.92). Serratiopeptidase was effective for eradicating infection caused by biofilm-forming bacteria in this experimental animal model. The antibiofilm property of the enzyme may enhance antibiotic efficacy in the treatment of staphylococcal infections.

Electrolytically generated silver and copper ions to treat cooling water: an environmentally friendly novel alternative

The effect of electrolytically generated silver and copper ions on the abatement of iron-related bacteria, sulfate-reducing bacteria, slime-forming and coliform bacteria in the cooling systems was investigated in this work. These bacteria, commonly found in cooling tower systems, are usually controlled with chlorine. The effect of chlorine and its combination with these ions was also studied on the microbiology of the water. Silver/copper/chlorine concentration relationships ( 1.2 mg l −1 silver/0.6 mg l −1 copper/0.0 mg l −1 chlorine and 0.2 mg l −1 silver/1.2 mg l −1 copper/0.3 mg l −1 chlorine) proved to be good alternatives to replace or decrease appreciably the chlorine consumption in the cooling systems using relatively low concentrations of silver and copper with a minimum environmental impact. These relationships established a very effective treatment with 99% of control for the iron-related bacteria, sulfate-reducing bacteria and slime-forming bacteria abating more than 99% of such bacteria. Chlorine concentrations of 1.0 and 3.0 mg l −1 decreased more than 90% of some of the iron-related bacteria population. These systems have shown to decrease the aggressiveness of bacteria population that promote microbiologically influenced corrosion and biofilm formation to levels that compete with the traditional water treatment of cooling water. Coliform bacteria were also reduced below the levels accepted by the Mexican Official Norm.

Iodine and microbial interactions in an organic soil

Iodine-129 in groundwater discharging from a geologic disposal vault could accumulate in wetlands by chemical sorption onto low pH, highly organic solid surfaces or by direct or indirect microbial processes. Previous work indicated that saturation of anion sorption sites, microbial toxicity, or swamping of the I reduction/oxidation reaction decreased the retention of a wetland sphagnum for iodine with increased iodine porewater concentrations. Bog water and peat of an iodine-rich bog were studied to elucidate the role of micro-organisms in the retention and accumulation of iodine in a temperate wetland. Agar plate culture of a wide spectrum of microbes, including yeasts and moulds, with bog groundwater showed anaerobes to be more sensitive to high iodine concentrations than aerobes. Toxicity to anaerobes may occur at 110 mg I litre −1 groundwater. Although iron-related and slime-forming bacteria were not affected at 2000 mg I litre −1, iodine was toxic to sulphate-related bacteria (SRB), as indicated by Biological Activity Reaction Tests. A 50% reduction in the SRB population occurred at groundwater concentrations of 75 mg I litre −1. Microbe enumeration in iodine-rich bog groundwater, using acridine orange staining, showed that the native wetland microbe population was sensitive to concentrations in excess of 200 mg I litre −1 groundwater. Three independent experiments confirm the toxicity threshold concentration for anaerobic and native microbes is ~100mg I litre −1 groundwater. Iodine sorption to fresh peat was slightly slower and more limited under anoxic conditions. Autoclaving the peat, reinoculation following autoclaving and a sucrose addition all inhibited iodine sorption. These results suggest that microbes may only play a minor and indirect role in iodine sorption through the decomposition of organic matter.

Injection of Electrolytically Generated Chlorine into Citrus Microirrigation Systems for the Control of Certain Waterborne Root Pathogens

Electrolytically generated chlorine was injected into citrus microirrigation systems. Propagules of Phytophthora nicotianae var. parasitica, P. citrophthora, Fusarium spp., algae, and slime-forming bacteria were killed. Nematodes were found to resist free-chlorine levels in water of up to 50 μg ml -1 . Microemitters delivering chlorinated water were less frequently blocked by bacterial and/or bacterial slime than those delivering unchlorinated water. Soil and root populations of Phytophthora and nematodes under citrus trees in the field were unaffected by chlorinated water. No chlorine-induced phytotoxicity was observed on field-grown plants(.)