Effect of oxidizing and non-oxidizing biocides on biofilm at different substrate levels in the model recirculating cooling water system

With the reducing of water resources, using advanced treated refinery wastewater as recirculating cooling water is an effective method to save water and to reduce the pollution of petroleum and petrochemical industry. However, the control of biofilm is a bottleneck in the application of this technology. To resolve the problem of biofilm formation and development, antimicrobial characteristics of chlorine dioxide and benzyldimethyldodecyl-ammonium chloride on biofilm at different substrate levels were investigated. Biofilm detachment ratio and TTC-dehydrogenase activity (DHA) were two indexes to discuss the antimicrobial effects. The results showed that at the high substrate level, the biofilms characteristics (biomass, the content of protein, polysaccharide and EPS) were the higher than those at the medium and low substrate levels, however biofilm’s DHA at the medium substrate level (12.97 μgTF/(g h)) was higher than those at the medium substrate level (7.64 μgTF/(g h)) and low substrate level (1.94 μgTF/(g h). The difference of substrate level in the media resulted in different biofilm structure. By contrast with the control experiment, biofilm detachment ratios were all increased in three media with ClO₂ and BDMDAC addition. After ClO₂ addition, MITs were 30, 120 and 240 min and MIC was 1, 4 and 6 mg/L, respectively, at the low, medium and high substrate level. After BDMDAC addition, MITs in three media were all longer than those after ClO₂ addition, MIC was 200, 300 and 400 mg/L, respectively, at the low, medium and high substrate level.     

Formation of extracellular polymeric substances from acidogenic sludge in H<Subscript>2</Subscript>-producing process

In this study, the formation of extracellular polymeric substances (EPS) and surface characteristics of an acidogenic sludge in anaerobic H₂-producing process was investigated. Results show that carbohydrates, proteins, and humic substances were the dominant components in bound EPS (BEPS), while in soluble EPS (SEPS), carbohydrates were the main component. The total content of BEPS initially increased but then kept almost unchanged during fermentation from 25 to 35 h; after that, it slightly decreased. The total content of SEPS increased to 172.5 ± 0.05 mg C g⁻¹ volatile suspended solid with the time that increased to 23.5 h, and then rapidly decreased until 43 h; thereafter, it kept almost unchanged. The SEPS had good correlations with the specific H₂ production rate, substrate degradation rate, and specific aqueous products formation rate, but the BEPS seemed to have no such correlations with these specific rates. Results also confirm that part of EPS could be utilized by the H₂-producing sludge. As the substrate was in short supply, the EPS would be hydrolyzed to sever as carbon and energy source.     

Calcium carbonate precipitation by heterotrophic bacteria isolated from biofilms formed on deteriorated ignimbrite stones: influence of calcium on EPS production and biofilm formation by these isolates

Heterotrophic CaCO₃-precipitating bacteria were isolated from biofilms on deteriorated ignimbrites, siliceous acidic rocks, from Morelia Cathedral (Mexico) and identified as Enterobacter cancerogenus (22e), Bacillus sp. (32a) and Bacillus subtilis (52g). In solid medium, 22e and 32a precipitated calcite and vaterite while 52g produced calcite. Urease activity was detected in these isolates and CaCO₃ precipitation increased in the presence of urea in the liquid medium. In the presence of calcium, EPS production decreased in 22e and 32a and increased in 52g. Under laboratory conditions, ignimbrite colonization by these isolates only occurred in the presence of calcium and no CaCO₃ was precipitated. Calcium may therefore be important for biofilm formation on stones. The importance of the type of stone, here a siliceous stone, on biological colonization is emphasized. This calcium effect has not been reported on calcareous materials. The importance of the effect of calcium on EPS production and biofilm formation is discussed in relation to other applications of CaCO₃ precipitation by bacteria.     

Biofilm growth kinetics and nutrient (N/P) adsorption in an urban lake using reclaimed water: A quantitative baseline for ecological health assessment

Reclaimed wastewater reuse represents an effective method for partial resolution of increasing urban water shortages; however, reclaimed water may be characterized by significant contaminant loading, potentially affecting receiving ecosystem (and potentially human) health. The current study examined biofilm growth and nutrient adsorption in Olympic Lake (Beijing), the largest artificial urban lake in the world supplied exclusively by reclaimed wastewater. Findings indicate that solid particulate, extracellular polymeric substance (EPS) and metal oxide (Al, Fe, Mn) constituent masses adhere to a bacterial growth curve during biofilm formation and growth. Peak values were observed after ≈30 days, arrived at dynamic stability after ≈50 days and were affected by growth matrix surface roughness. These findings may be used to inform biofilm cultivation times for future biomonitoring. Increased growth matrix surface roughness (10.0 μm) was associated with more rapid biofilm growth and therefore an increased sensitivity to ecological variation in reclaimed water. Reclaimed water was found to significantly inhibit biofilm nutrient adsorption when compared with a “natural water” background, with elevated levels of metal oxides (Al, Fe, and Mn) and EPS representing the key substances actively influencing biofilm nutrient adsorption in reclaimed water. Results from the current study may be used to provide a quantitative baseline for future studies seeking to assess ecosystem health via monitoring of biofilms in the presence of reclaimed water through an improved quantitative understanding of biofilm kinetics in these conditions.     

The effect of catchment urbanization on nutrient uptake and biofilm enzyme activity in Lake Superior (USA) tributary streams

We compared landscape, habitat, and chemistry variables with nutrient spiraling and biofilm extracellular enzyme activity (EEA), to assess the response of nine Lake Superior tributaries to the level of urbanization in their catchments. We found no significant correlation between uptake metrics for NH₄ ⁺ and PO₄ ^3? and the level of catchment urbanization. NH₄ ⁺ and PO₄ ^3– uptake velocities (V _f) were, however, positively correlated with biofilm EEA and with biofilm respiration (DHA). In general, biofilm EEA was negatively correlated with indicators of increased urbanization (e.g., % impervious surface cover and Cl^? concentration) and positively correlated with % forest cover. Biofilm respiration measured as dehydrogenase activity (DHA) decreased with indicators of increased urbanization (e.g., % ISC, storm sewer length, % of the stream channel shaded by the riparian canopy, and Cl^?) and increased with non-urban indicators (e.g., % forest, % wetland, and stream width and depth). Regression of V _f and uptake rate (U) versus ambient nutrient concentrations indicated phosphorus limitation in the study streams, a result supported by regression biofilm peptidase versus phosphatase activity. There was no evidence of NH₄ ⁺ saturation or limitation. This is the first study to demonstrate correlations between nutrient uptake and biofilm EEA in streams, with linkages to catchment-scale disturbances.     

Photosynthetic CO<Subscript>2</Subscript>/H<Subscript>2</Subscript>O gas exchange and dynamics of carbohydrates content in maize leaves under drought

We studied the temporal sequence of changes in the photosynthetic CO₂/H₂O gas exchange intensity, as well as leaf water status, contents of soluble carbohydrates, starch, proline, pigments, and MDA, in maize seedlings (Zea mays L., cv. Luchistaya) under adaptation to increasing water deficit. The duration of drought was 2, 3, 5, and 6 days. Withholding water from maize plants caused gradual increase in the intensity of water deficit: from mild (2 or 3 days) to moderate (5 days) and nearly severe (6 days) water stress. After 6 days, relative leaf water content decreased by 19.8% as compared to the control. On the second day after the onset of drought, slight reduction in the photosynthetic CO₂/H₂O gas exchange intensity of the treated plants was observed. After 6 days, photosynthesis and transpiration of leaves synchronously reduced almost threefold due to stomatal closure. The progressive soil drought had substantial impact on the carbohydrate metabolism. After 2 days of water deficit, the content of reducing sugars and sucrose increased slightly, whereas after 6 days, it increased ten and four times, respectively. After 2, 3, and 5 days of drought, the starch content declined slightly; however, under severe drought (6 days), it increased by 30% as compared to the control. Simultaneously with the increase in the content of soluble sugars, proline content increased significantly and it was the highest on the sixth day of drought. At all stages of water deficit, the proline content increased more significantly than the content of reducing carbohydrates and sucrose. Under increasing water deficit (5 and 6 days), the content of MDA was found to rise. At the initial drought stage (2 or 3 days) and under severe water deficit (6 days), no significant changes in the pigment content were observed. Thus, at the initial stages of progressive drought, in the leaves of this maize cultivar, a decline in photosynthetic activity proceeded simultaneously with accumulation of reducing sugars, sucrose, and proline. The results obtained showed that, at the first stages of adaptation of maize seedlings to drought, the changes in carbohydrate and proline metabolism have been observed, which have increased upon further plant dehydration.     

Extracellular polysaccharides produced by cooling water tower biofilm bacteria and their possible degradation

The extracellular polymers (EPS) of biofilm bacteria that can cause heat and mass transfer problems in cooling water towers in the petrochemical industry were investigated. In addition, these microorganisms were screened for their ability to grow and degrade their own EPS and the EPS of other species. Twelve bacteria producing the most EPS were isolated from cooling water towers and characterized biochemically by classic and commercial systems. These were species of Pseudomonas, Burkholderia, Aeromonas, Pasteurella, Pantoea, Alcaligenes and Sphingomonas. EPS of these species were obtained by propan-2-ol precipitation and centrifugation from bacterial cultures in media enriched with glucose, sucrose or galactose. EPS yields were of 1.68-4.95 g l(-1). These EPS materials were characterized for total sugar and protein contents. Their total sugar content ranged from 24 to 56% (g sugar g(-1) EPS), and their total protein content ranged from 10 to 28% (g protein g(-1) EPS). The monosaccharide compositions of EPS were determined by HPLC. Generally, these compositions were enriched in galactose and glucose, with lesser amounts of mannose, rhamnose, fructose and arabinose. All bacteria were investigated in terms of EPS degradation. Eight of the bacteria were able to utilize EPS from Burkholderia cepacia, seven of the bacteria were able to utilize EPS from Pseudomonas sp. and Sphingomonas paucimobilis. The greatest viscosity reduction of B. cepacia was obtained with Pseudomonas sp. The results show that the bacteria in this study are able to degrade EPS from biofilms in cooling towers.     

A multi-phase mathematical model of quorum sensing in a maturing Pseudomonas aeruginosa biofilm

It is well known that sessile bacteria have a strong tendency to exist in a biofilm phenotype, whereby bacterial cells aggregate and produce a gel-like extracellular matrix, which, in an infection scenario, offers a significant barrier to attack by conventional antibiotics and the immune system. In this paper we develop a multi-phase model of a maturing Pseudomonas aeruginosa biofilm, allowing for the production and secretion of exopolysaccharide (EPS). The primary quorum-sensing system of P. aeruginosa (namely the lasR system) is believed to be required for full biofilm development, and we thus take the synthesis of EPS to be regulated by the cognate signal molecule, 3-oxo-C12-HSL. We also take EPS and signal production, along with bacterial growth, to be limited by oxygen availability, thus factoring in the nutrient poor conditions deep inside the biofilm. We use simulations to examine the role played by quorum sensing in the biofilm maturation process, and to investigate the effect of anti-quorum sensing and antibiotic treatments on EPS concentration, signal level, bacterial numbers and biofilm growth rate. In addition, we undertake analysis of the associated travelling-wave behaviour.     

Characterization of the <Emphasis Type="Italic">codY</Emphasis> gene and its influence on biofilm formation in <Emphasis Type="Italic">Bacillus </Emphasis><Emphasis Type="Italic">cereus</Emphasis>

The foodborne pathogen Bacillus cereus can form biofilms on various food contact surfaces, leading to contamination of food products. To study the mechanisms of biofilm formation by B. cereus, a Tn5401 library was generated from strain UW101C. Eight thousand mutants were screened in EPS, a low nutrient medium. One mutant (M124), with a disruption in codY, developed fourfold less biofilm than the wild-type, and its defective biofilm phenotype was rescued by complementation. Addition of 0.1% casamino acids to EPS prolonged the duration of biofilms in the wild-type but not codY mutant. When decoyinine, a GTP synthesis inhibitor, was added to EPS, biofilm formation was decreased in the wild-type but not the mutant. The codY mutant produced three times higher protease activity than the wild-type. Zymogram and SDS-PAGE data showed that production of the protease (∼130 kDa) was repressed by CodY. Addition of proteinase K to EPS decreased biofilm formation by the wild-type. Using a dpp-lacZ fusion reporter system, it was shown that that the B. cereus CodY can sense amino acids and GTP levels. These data suggest that by responding to amino acids and intracellular GTP levels CodY represses production of an unknown protease and is involved in biofilm formation.     

Synthesis of DHA/EPA-rich phosphatidylcholine by immobilized phospholipase A<Subscript>1:</Subscript> effect of water addition and vacuum condition

DHA/EPA-rich phosphatidylcholine (PC) was successfully synthesized by immobilized phospholipase A₁ (PLA₁)-catalyzed transesterification of PC and DHA/EPA-rich ethyl esters in a solvent-free system. Effects of reaction temperature, water addition and substrate mass ratio on the incorporation of DHA/EPA were evaluated using response surface methods (RSM). Water addition had most significant effect on the incorporation. Reaction temperature and substrate mass ratio, however, had no significant effect on the incorporation. The maximal incorporation was 19.09 % (24 h) under the following conditions: temperature 55.7 °C, water addition 1.1 wt % and substrate mass ratio (ethyl esters/PC) 6.8:1. Furthermore, effects of water addition (from 0 to 1.25 wt %) on DHA/EPA incorporation and the composition of products were further investigated. The immobilized PLA₁ was more active when water addition was above 0.5 wt %. By monitoring the reaction processes with different water addition, a possible reaction scheme was proposed for transesterification of PC with DHA/EPA-rich ethyl esters. In summary, PC and sn2-lysophosphatidylocholine (LPC) were predominant in the mixtures at early stages of reaction, whereas sn1-LPC and glycerophosphocholine (GPC) predominant at later stages. The vacuum employed after 24 h significantly increased the incorporation of DHA/EPA and the composition of PC, and the highest incorporation (30.31 %) of DHA/EPA was obtained at 72 h and the yield of PC was 47.2 %.     

Potent in vitro synergism of fusidic acid (FA) and berberine chloride (BBR) against clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA)

It was found in the present study that combined use of fusidic acid (FA) and berberine chloride (BBR) offered an in vitro synergistic action against 7 of the 30 clinical methicillin-resistant Staphylococcus aureus (MRSA) strains, with a fractional inhibitory concentration (FIC) index ranging from 0.5 to 0.19. This synergistic effect was most pronounced on MRSA 4806, an FA-resistant isolate, with a minimum inhibitory concentration (MIC) value of 1,024 μg/ml. The time-kill curve experiment showed that FA plus BBR yielded a 4.2 log₁₀ c.f.u./ml reduction in the number of MRSA 4806 bacteria after 24-h incubation as compared with BBR alone. Viable count analysis showed that FA plus BBR produced a 3.0 log₁₀ c.f.u./ml decrease in biofilm formation and a 1.5 log₁₀ c.f.u./ml decrease in mature biofilm in viable cell density as compared with BBR alone. In addition, phase contrast micrographs confirmed that biofilm formation was significantly inhibited and mature biofilm was obviously destructed when FA was used in combination with BBR. These results provide evidence that combined use of FA and BBR may prove to be a promising clinical therapeutic strategy against MRSA.     

Partitioning of photosynthetic electron flow between CO<Subscript>2</Subscript> assimilation and O<Subscript>2</Subscript> reduction in sunflower plants under water deficit

In sunflower (Helianthus annuus L.) grown under controlled conditions and subjected to drought by withholding watering, net photosynthetic rate (P _N) and stomatal conductance (g _s) of attached leaves decreased as leaf water potential (Ψ_w) declined from −0.3 to −2.9 MPa. Although g _s decreased over the whole range of Ψ_w, nearly constant values in the intercellular CO₂ concentrations (C _i) were observed as Ψ_w decreased to −1.8 MPa, but C _i increased as Ψ_w decreased further. Relative quantum yield, photochemical quenching, and the apparent quantum yield of photosynthesis decreased with water deficit, whereas non-photochemical quenching (q_NP) increased progressively. A highly significant negative relationship between q_NP and ATP content was observed. Water deficit did not alter the pyridine nucleotide concentration but decreased ATP content suggesting metabolic impairment. At a photon flux density of 550 μmol m⁻² s⁻¹, the allocation of electrons from photosystem (PS) 2 to O₂ reduction was increased by 51 %, while the allocation to CO₂ assimilation was diminished by 32 %, as Ψ_w declined from −0.3 to −2.9 MPa. A significant linear relationship between mean P _N and the rate of total linear electron transport was observed in well watered plants, the correlation becoming curvilinear when water deficit increased. The maximum quantum yield of PS2 was not affected by water deficit, whereas q_P declined only at very severe stress and the excess photon energy was dissipated by increasing q_NP indicating that a greater proportion of the energy was thermally dissipated. This accounted for the apparent down-regulation of PS2 and supported the protective role of q_NP against photoinhibition in sunflower.     

Dynamics of <Superscript>18</Superscript>O Incorporation from H <Subscript>2</Subscript><Superscript>18</Superscript>O into Soil Microbial DNA

Heavy water (H₂¹⁸O) has been used to label DNA of soil microorganisms in stable isotope probing experiments, yet no measurements have been reported for the ¹⁸O content of DNA from soil incubated with heavy water. Here we present the first measurements of atom% ¹⁸O for DNA extracted from soil incubated with the addition of H₂¹⁸O. Four experiments were conducted to test how the atom% ¹⁸O of DNA, extracted from Ponderosa Pine forest soil incubated with heavy water, was affected by the following variables: (1) time, (2) nutrients, (3) soil moisture, and (4) atom% ¹⁸O of added H₂O. In the time series experiment, the atom% ¹⁸O of DNA increased linearly (R ² = 0.994, p < 0.01) over the first 72 h of incubation. In the nutrient addition experiment, there was a positive correlation (R ² = 0.991, p = 0.006) between the log₁₀ of the amount of tryptic soy broth, a complex nutrient broth, added to soil and the log₁₀ of the atom% ¹⁸O of DNA. For the experiment where soil moisture was manipulated, the atom% ¹⁸O of DNA increased with higher soil moisture until soil moisture reached 30%, above which ¹⁸O enrichment of DNA declined as soils became more saturated. When the atom% ¹⁸O for H₂O added was varied, there was a positive linear relationship between the atom% ¹⁸O of the added water and the atom% ¹⁸O of the DNA. Results indicate that quantification of ¹⁸O incorporated into DNA from H₂¹⁸O has potential to be used as a proxy for microbial growth in soil.     

Exopolysaccharide production in <Emphasis Type="Italic">Anabaena</Emphasis> sp. PCC 7120 under different CaCl<Subscript>2</Subscript> regimes

Influence of various levels of CaCl₂ (0, 1, 10 and 100 mM) on exopolysaccharide production has been investigated in the cyanobacterium Anabaena 7120. At the concentration of 1 mM CaCl₂, growth was found to be stimulatory while 100 mM was sub lethal for the cyanobacterial cells. Estimation of EPS content revealed that EPS production depends on the concentration of calcium ions in the immediate environment with maximum being at10 mM CaCl₂. A possible involvement of alr2882 gene in the process of EPS production was also revealed through qRT-PCR. Further, FTIR-spectra marked the presence of aliphatic alkyl-group, primary amine-group, and polysaccharides along with shift in major absorption peaks suggesting that calcium levels in the external environment regulate the composition of EPS produced by Anabaena 7120. Thus, both quantity and composition of EPS is affected under different calcium chloride concentrations presenting possibilities of EPS with novel unexplored features that may offer biotechnological applications.     

Response of performance and bacterial community to oligotrophic stress in biofilm systems for raw water pretreatment

Understanding the dynamics of performance and bacterial community of biofilm under oligotrophic stress is necessary for the process optimization and risk management in biofilm systems for raw water pretreatment. In this study, biofilm obtained from a pilot-scale biofilm reactor was inoculated into a pilot-scale experimental tank for the treatment of oligotrophic raw water. Results showed that the removal of NH₄ ⁺–N was impaired in biofilm systems when influent NH₄ ⁺–N was less than 0.35 mg L^?1 or NH₄ ⁺–N loading rate of less than 7.51 mg L^?1 day^?1. The dominant bacteria detected in biofilm of different carrier were obvious distinct from phylum to genus level under oligotrophic stress. The dominant bacteria in elastic stereo media carrier changed from Proteobacteria (51.1%) to Firmicutes (32.7%), while Proteobacteria was always dominant in suspended ball carrier after long-term operation under oligotrophic conditions. Oligotrophic stress largely decreased the functional bacteria for the removal of nitrogen and organics including many genera in Proteobacteria and Nitrospirae, but increased several genera with spore forming organisms or potential bacterial pathogens in ESM carrier mainly including Bacillus, Mycobacterium, Pseudomonas, etc.     

Regulation of geochemical activity of microorganisms in a petroleum reservoir by injection of H<Subscript>2</Subscript>O<Subscript>2</Subscript> or water-air mixture

In the course of pilot trials of biotechnologies for the enhancement of oil recovery in formation waters of the Gangxi bed of the Dagang oil field (China), microbiological processes were investigated. The biotechnologies are based on injection into the petroleum reservoir of different oxygen sources (H₂O₂ solution or a water-air mixture) with nitrogen and phosphorus salts. The injection of water-air mixture with nitrogen and phosphorus salts resulted in an increase in the number of aerobic and anaerobic organotrophic bacteria, rates of sulfate reduction and methanogenesis in formation water and also the content of CO₂ (from 4.8–12 to 15–23.2%) and methane (from 86–88 to 91.8%) in the gas. The preferential consumption of isotopically light bicarbonate by methanogens resulted in a higher content of the light ¹²C in methane; the δ¹³C/CH₄ value changed from ?45.1…?48.3 to ?50.7…?59.3‰. At the same time, mineral carbonates of the formation water became isotopically heavier; the δ¹³C/Σcarbonates value increased from 3.4…4.0 to 5.4…9.6‰. Growth of hydrocarbon-oxidizing bacteria was accompanied by production of biosurfactants and decreased interfacial tension of formation water. Injection of H₂O₂ solution resulted in the activation of aerobic processes and in suppression of both sulfate reduction and methanogenesis. Methane content in the gas decreased from 86–88 to 75.7–79.8%, probably due to its consumption by methanotrophs. Due to consumption of isotopically light methane, the residual methane carbon became heavier, with the δ¹³C/CH₄ values from ?39.0 to ?44.3‰. At the same time, mineral carbonates of the formation water became isotopically considerably lighter; the δ¹³C/Σcarbonates value decreased from 5.4…9.6 to ?1.4…2.7‰. The additional amount of oil recovered during the trial of both variants of biotechnological treatment was 3819 t.     

Decreased Phototoxic Effects of TiO? Nanoparticles in Consortium of Bacterial Isolates from Domestic Waste Water

This study is aimed to explore the toxicity of TiO₂ nanoparticles at low concentrations (0.25, 0.50 & 1.00 μg/ml); on five bacterial isolates and their consortium in waste water medium both in dark and UVA conditions. To critically examine the toxic effects of nanoparticles and the response mechanism(s) offered by microbes, several aspects were monitored viz. cell viability, ROS generation, SOD activity, membrane permeability, EPS release and biofilm formation. A dose and time dependent loss in viability was observed for treated isolates and the consortium. At the highest dose, after 24h, oxidative stress was examined which conclusively showed more ROS generation & cell permeability and less SOD activity in single isolates as compared to the consortium. As a defense mechanism, EPS release was enhanced in case of the consortium against the single isolates, and was observed to be dose dependent. Similar results were noticed for biofilm formation, which substantially increased at highest dose of nanoparticle exposure. Concluding, the consortium showed more resistance against the toxic effects of the TiO₂ nanoparticles compared to the individual isolates.     

CO<Subscript>2</Subscript> enrichment affects eco-physiological growth of maize and alfalfa under different water stress regimes in the UAE

Water stress has been reported to alter morphology and physiology of plants affecting chlorophyll content, stomatal size and density. In this study, drought stress mitigating effects of CO₂ enrichment was assessed in greenhouse conditions in the hot climate of UAE. Commercially purchased maize (Zea mays L.) and alfalfa (Medicago sativa L.) were seeded in three different custom-built cage structures, inside a greenhouse. One cage was kept at 1000 ppm CO₂, the second at 700 ppm CO₂, and the third at ambient greenhouse CO₂ environment (i.e. 435 ppm). Three water stress treatments HWS (200 ml per week), MWS (400 ml per week), and CWS (600 ml per week) were given to each cage so that five maize pots and five alfalfa pots in each cage received same water stress treatments. In maize, total chlorophyll content was similar or higher in water stress treatments compared to control for all CO₂ concentrations. Stomatal lengths were higher in enriched CO₂ environments under water stress. At 700 ppm CO₂, stomatal widths decreased as water stress increased from MWS to HWS. At both enriched CO₂ environments, stomatal densities decreased compared to ambient CO₂ environment. In alfalfa, there was no significant increase in total chlorophyll content under enriched CO₂ environments, even though a slight increase was noticed.     

A Pilot Study of Bacteriological Population Changes through Potable Water Treatment and Distribution

This pilot study compares the compositions of bacterial biofilms in pipe networks supplied with water containing either high levels of biodegradable organic matter (BOM) or low levels of BOM (conventionally or biologically treated, respectively). The Microbial Identification System for fatty acid analysis was utilized in this study to identify a large number of organisms (>1,400) to determine population changes in both conventionally and biologically treated water and biofilms. Data generated during this study indicated that suspended bacteria have little impact on biofilms, and despite treatment (conventional or biological), suspended microbial populations were similar following disinfection. Prechlorination with free chlorine resulted not only in reduced plate count values but also in a dramatic shift in the composition of the bacterial population to predominately gram-positive bacteria. Chlorination of biologically treated water produced the same shifts toward gram-positive bacteria. Removal of assimilable organic carbon by the biologically active filters slowed the rate of biofilm accumulation, but biofilm levels were similar to those found in conventionally treated water within several weeks. Iron pipes stimulated the rate of biofilm development, and bacterial levels on disinfected iron pipes exceeded those for chlorinated polyvinyl chloride pipes. The study showed that the iron pipe surface dramatically influenced the composition, activity, and disinfection resistance of biofilm bacteria.     

A pilot study of bacteriological population changes through potable water treatment and distribution

This pilot study compares the compositions of bacterial biofilms in pipe networks supplied with water containing either high levels of biodegradable organic matter (BOM) or low levels of BOM (conventionally or biologically treated, respectively). The Microbial Identification System for fatty acid analysis was utilized in this study to identify a large number of organisms (>1,400) to determine population changes in both conventionally and biologically treated water and biofilms. Data generated during this study indicated that suspended bacteria have little impact on biofilms, and despite treatment (conventional or biological), suspended microbial populations were similar following disinfection. Prechlorination with free chlorine resulted not only in reduced plate count values but also in a dramatic shift in the composition of the bacterial population to predominately gram-positive bacteria. Chlorination of biologically treated water produced the same shifts toward gram-positive bacteria. Removal of assimilable organic carbon by the biologically active filters slowed the rate of biofilm accumulation, but biofilm levels were similar to those found in conventionally treated water within several weeks. Iron pipes stimulated the rate of biofilm development, and bacterial levels on disinfected iron pipes exceeded those for chlorinated polyvinyl chloride pipes. The study showed that the iron pipe surface dramatically influenced the composition, activity, and disinfection resistance of biofilm bacteria.