The continuum heterogeneous biofilm model with multiple limiting substrate Monod kinetics.

We describe a novel procedure to estimate the net growth rate of biofilms on multiple substrates. The approach is based on diffusion-reaction mass balances for chemical species in a continuum biofilm model with reaction kinetics corresponding to a Double-Monod expression. This analytical model considers a heterogeneous biofilm with variable distributions of biofilm density, activity, and effective diffusivity as a function of depth. We present the procedure to estimate the effectiveness factor analytically and compare the outcome with values obtained by the application of a rigorous numerical computational method using several theoretical examples and a test case. A comparison of the profiles of the effectiveness factor as a function of the Thiele modulus, φ, revealed that the activity of a homogeneous biofilm could be as much as 42% higher than that of a heterogeneous biofilm, under the given conditions. The maximum relative error between numerical and estimated effectiveness factor was 2.03% at φ near 0.7 (corresponding to a normalized Thiele modulus φ* = 1). For φ < 0.3 or φ > 1.4, the relative error was less than 0.5%. A biofilm containing aerobic ammonium oxidizers was chosen as a test case to illustrate the model's capability. We assumed a continuum heterogeneous biofilm model where the effective diffusivities of oxygen and ammonium change with biofilm position. Calculations were performed for two scenarios; Case I had low dissolved oxygen (DO) concentrations and Case II had high DO concentrations, with a concentration at the biofilm-fluid interface of 10 g O2 /m(3) . For Case II, ammonium was the limiting substrate for a biofilm surface concentration, CNs , ≤13.84 g of N/m(3) . At these concentrations ammonium was limiting inside the biofilm, and oxygen was fully penetrating. Conversely, for CNs > 13.84 g of N/m(3) , oxygen became the limiting substrate inside the biofilm and ammonium was fully penetrating. Finally, a generalized procedure to estimate the effectiveness factor for a system with multiple (n > 2) limiting substrates is given.

Monitoring the removal of nitrogen by applying a nitrification-denitrification process in a Sequencing Batch Reactor (SBR).

In this study the evaluation of nitrogen removal in wastewater from a meat products processing company was performed, using a Sequencing Batch Reactor (SBR) at pilot scale. The phases of the SBR operation were: filling, reaction (aeration and intermittent anoxia), sedimentation and discharge. In each of these phases analyses of ammonium (NH(4)(+)), nitrite (NO(2)(-)), nitrate (NO(3)(-)), pH and dissolved oxygen (DO) were carried out to monitor the process of nitrification-denitrification. The results showed that stage IV had the best performance (2.49 g COD(F)/Ld and 1.02 g NH(4)(+)-N/Ld) with a NH(4)(+)-N removal of 71%. The transformation of much of the NH(4)(+)-N to gaseous nitrogen was confirmed, with the concentration of NO(2)(-)-N and NO(3)(-)-N increasing during the reaction phase but decreasing in the effluent due to its transformation to gaseous nitrogen.

Changes in the aerobic vaginal bacterial mucous load after treatment with intravaginal sponges in anoestrous ewes: effect of medroxiprogesterone acetate and antibiotic treatment use.

Intravaginal sponges (IS) impregnated with progestagens are widely used for oestrous synchronization in ewes. As progestogens depress the immuno response, the first aim was to determine whether medroxiprogesterone acetate (MAP) content affects the vaginal bacteria number (VBN) in IS-treated anoestrous ewes. The second aim was to compare the effectiveness of different antibiotic treatments to control the VBN increase caused by IS. In both experiments, IS were inserted during 14 days in anoestrous ewes. In the first, 11 ewes received commercial sponges (50 mg MAP), and 10 ewes received placebo sponges. For the second experiment, IS were inserted in three groups (n = 12/group), containing oxytetracycline im (20 mg/kg); injected into the sponge (0.02 mg), or control (no antibiotic). At sponge withdrawal, all ewes received 300 UI eCG. Mucous samples were collected from the vagina before sponge insertion, at sponge withdrawal, 24, 48 and 72 h later, and the VBN (colony-forming units per ml; CFU/ml) was counted after 48-h incubation. Medroxiprogesterone content did not affect VBN (log CFU/ml: 4.3 ± 0.2 vs 4.4 ± 0.2 with and without MAP, respectively). Bacterial number increased from 3.5 ± 0.2 at sponge insertion to 6.9 ± 0.1 at sponge withdrawal (p < 0.0001) and decreased the following day to 4.3 ± 0.2 (p < 0.0001). In the second experiment, VBN increased at sponge withdrawal (p < 0.0001) in all groups and decreased the following day (p < 0.0001). The CFU/ml at sponge withdrawal was lower in ewes treated with antibiotics (p < 0.0001), being even lower when local rather than systemic antibiotic was administered (log CFU/ml: 3.3 ± 1.8 vs 7.2 ± 1.8). The day of oestrous VBN was similar for all treatments and similar to that observed before sponge insertion. We concluded that MAP does not influence the increase in VBN, as the main effect is provoked by the sponge device itself, and local antibiotic treatment resulted in a lower bacterial growth than systemic treatments.

Modeling for the optimal biodegradation of toxic wastewater in a discontinuous reactor.

The degradation of toxic compounds in Sequencing Batch Reactors (SBRs) poses inhibition problems. Time Optimal Control (TOC) methods may be used to avoid such inhibition thus exploiting the maximum capabilities of this class of reactors. Biomass and substrate online measurements, however, are usually unavailable for wastewater applications, so TOC must use only related variables as dissolved oxygen and volume. Although the standard mathematical model to describe the reaction phase of SBRs is good enough for explaining its general behavior in uncontrolled batch mode, better details are needed to model its dynamics when the reactor operates near the maximum degradation rate zone, as when TOC is used. In this paper two improvements to the model are suggested: to include the sensor delay effects and to modify the classical Haldane curve in a piecewise manner. These modifications offer a good solution for a reasonable complexification tradeoff. Additionally, a new way to look at the Haldane K-parameters (micro(o),K(I),K(S)) is described, the S-parameters (micro*,S*,S(m)). These parameters do have a clear physical meaning and, unlike the K-parameters, allow for the statistical treatment to find a single model to fit data from multiple experiments.

Inhibition of the growth of Paenibacillus larvae, the causal agent of American foulbrood of honeybees, by selected strains of aerobic spore-forming bacteria isolated from apiarian sources.

The bacterium Paenibacillus larvae, the causative agent of American foulbrood disease of honeybee larvae, occurs throughout the world and is found in many beekeeping areas of Argentina. The potential as biocontrol agents of antagonic aerobic spore-forming bacteria isolated from honey samples and other apiarian sources were evaluated. Each isolate was screened against one strain of Paenibacillus larvae (ATCC 9545) by using a perpendicular streak technique. Ten randomly selected bacterial strains from the group that showed the best antagonistic effect to P. larvae ATCC 9545 were selected for further study. These were identified as Bacillus subtilis (m351), B. pumilus (m350), B. licheniformis (m347), B. cereus (mv33), B. cereus (m387), B. cereus (m6c), B. megaterium (m404), Brevibacillus laterosporus (BLAT169), B. laterosporus (BLAT170), and B. laterosporus (BLAT171). The antagonistic strains were tested against 17 P. larvae strains from different geographical origins by means of a spot test in wells. The analysis of variance and posterior comparison of means by Tukey method (P < 0.01) showed that the best antagonists were B. megaterium (m404), B. licheniformis (m347), B. cereus (m6c), B. cereus (mv33), and B. cereus (m387).

Performance evaluation of an UASB reactor used for combined treatment of domestic sewage and excess aerobic sludge from a trickling filter.

This work aimed at evaluating the influence of the excess sludge produced in a trickling filter (TF) on the performance of a UASB reactor used for the combined treatment of domestic sewage and aerobic sludge. During phase 1 of the research, the UASB reactor/TF system was fed with domestic sewage pumped directly from the sewer collector of Arrudas stream, in Belo Horizonte-Brazil. During phase 2, besides feeding the reactor with domestic sewage, the UASB reactor was also fed with the aerobic sludge from the trickling filter. The UASB reactor, with a volume of 420 litres, was operated at a mean hydraulic detention time of 5.6 hours in both operational phases. After 133 days of continuous monitoring, no detrimental effect was noticed on the performance of the UASB reactor regarding the return of the aerobic sludge produced in the TF. On the contrary, the COD results indicated a higher percentage of compliance with the discharge standards set forth by the Brazilian environmental legislation. During phase 2 of the research, when the UASB reactor was used for combined treatment of domestic sewage and excess aerobic sludge from the TF, the anaerobic effluent presented mean concentrations of 108 mgCOD x L(-1), 57 mgBOD x L(-1) and 18 mgTSS x L(-1).

Characterization and dewaterability of raw and stabilized sludge using different treatment methods.

A comparison of the characteristics and stabilization potential of the four most used sludge treatment systems in Mexico was made. A pilot plant constituted by separate systems for anaerobic and aerobic digestion, lime stabilization, conditioning and dewatering, was built and operated during four months in one of the biological wastewater treatment plants in Acapulco, Mexico. Composting of sludge was also made. An aerobic static pile was built using bulking materials available in the region. A turbine centrifuge was used for dewatering the stabilized sludge and results showed good performance of the device. The main problem for the beneficial use of treated sludge was its pathogenicity. The composting process allowed us to obtain a product with approximately 20 fecal coliform density (MPN/g); with lime stabilization, the sludge produced had a fecal coliform density of 2 MPN/g. From these results, it is concluded that both the composting process and the alkaline stabilization with lime produce a well stabilized sludge, bacteriologically safe that accomplishes the requirements for its use on soil without restrictions. Related to parasitological removal, the best helminth egg removals were obtained also using these two processes. Ascaris sp. densities in raw sludge (309-430 eggs/g) were reduced to a final density of 3-14 eggs/g in the aerobic composting process and to 4-18 eggs/g in the lime stabilized sludge. Removal is not high enough to reach the recommended level for unrestricted use of stabilized sludge.

Sludge bed development in denitrifying reactors using different inocula-performance and microbiological aspects.

Aerobic and methanogenic consortia were evaluated as inocula for laboratory scale denitrifying reactors, fed with a synthetic wastewater with acetate as the main electron donor. The denitrifying microflora of inocula and reactors was evaluated by specific denitrifying activity, enumeration and isolation of denitrifiers, which were screened by amplified ribosomal DNA restriction analysis. Reactor performance was monitored by COD and nitrate removal efficiencies and granule size. The aerobic sludge failed to form granules, probably due to the development of a filamentous, nitrate-reducing organism which was characterised by 16SrDNA sequencing as Bacillus cereus. The methanogenic sludge showed denitrifying activity and adapted very rapidly to denitrifying conditions in the two reactors seeded with granules of different sizes. Denitrifiers grew around the granules, increasing the specific denitrifying activity of the sludge over 10-fold. Exopolymer-forming organisms, belonging to the same species, were isolated from both reactors. Granule size increased during operation, but flotation of the aggregates, related to gas retention was observed.

[Mitochondria and apoptosis]. / Mitocondria y apoptosis.

It is now accepted that mitochondria are endosymbionts, originated in aerobic bacteria which were integrated by the ancestor of eukaryotic cells. A part of the apoptotic machinery could exist in unicellular eukaryotic and some controlling apoptosis components might be present in prokaryotes. It is therefore possible that the mechanism originally involved in the maintenance of the symbiosis between the bacterial ancestor of the mitochondria and the host cell precursor of eukaryotes, provided the basis for the actual mechanism controlling cell survival. Metazoans would have improved this possibility by connecting to the mitochondria as principal effector of cellular death to the pathways of signal transduction. A variety of events appoint to the mitochondria as principal effector of the apoptosis. This including the release caspase activators (cytochrome c), changes in electron transport, loss of mitochondrial transmembrane potential, altered cellular oxidation-reduction, and participation of pro and antiapoptotic Bcl-2 proteins. The different signals that converge on mitochondria for activation or inhibition of these events, delineate several pathways in the physiology of the cellular death.

Biodegradation of disperse blue 79 using sequenced anaerobic/aerobic biofilters.

A sequential anaerobic/aerobic treatment process was used to biodegrade the azo dye disperse blue 79 (DB79). The integrated process was successfully tested and operated for the mineralization of the DB79 dye until a concentration of 120 mg/l in 96 h. In the first stage, the anaerobic biofilter biotransformed the DB79 to amines with efficiencies of decolorization higher than 95% in 72 h. The amines produced in the first stage were degraded in the aerobic biofilter with efficiencies of 65% in 24 h. It was observed that the use of a co-substrate on the anaerobic biofilter influenced the performance of the bioreactor only when the concentration of the DB79 was higher than 48 mg/l. It was found that the residual dye in the effluent of the anaerobic stage inhibits the performance of the aerobic microorganisms.

Removal of organic carbon, nitrogen and phosphorus in sequential batch reactors integrating the aerobic/anaerobic processes.

The performance of a bench-scale apparatus composed of two sequential batch reactors (SBR), forming an anaerobic/aerobic treatment system, was evaluated as to its potential use for biological removal of organic matter and nutrients. Both the reactors with 12.5 L of useful volume each were operated for the batch cycles of 12 hours receiving 8.0 L of substrate in each cycle. The first reactor (SBRAn) fed with synthetic substrate simulating domestic sewage was meant to remove the largest fraction of carbonic matter and to promote the substrate ammonification. The second reactor (SBRAe) was operated under alternating aerobic and anoxic conditions to establish conditions for achieving nitrification; denitrification and biological phosphate removal in the same batch cycle. Sodium acetate was used as an external carbon source for phosphate removal. Processes monitoring included the analyses of: COD, NTK-N, NH4(+)-N, NO2(-)-N, NO3(-)-N, PO4(3-)-P, alkalinity, volatile acids, pH, redox potential total, fixed and volatile solids. Under the operating conditions imposed, the system exhibited high performance in removing organic matter (COD), nitrogen and phosphorus, producing effluent with COD, NTK-N and PO4(3-)-P concentrations lower than 50.0 mg/L, 4.0 mg/L and 1.0 mg/L, respectively.

Disruption of the intestinal barrier and bacterial translocation in an experimental model of intestinal obstruction

Clinical evidence and the use of experimental models in laboratory animals indicate that the intestine is a reservoir of microorganisms that can cause systemic infection in the human. The purpose of this work was to study the possible effect of intestinal obstruction (IO) on the mechanical and chemical barriers that bring protection against microorganisms crossing from the intestinal lumen towards the systemic tissues. We demonstrated that 24 hours after IO, histological and ultrastructural alterations do occur, seriously compromising the structure of the intestinal barrier in 100 per cent of the studies animals. Likewise, it was observed that during the same period, microorganisms translocation from intestine to the peritoneal cavity and liver (100 and 80 per cent respectively) occurred. The lungs were spared. Changes observed in the intestinal epithelium are related to a process similar to that produced by intestinal ischemia: mitochondrial destruction, with subsequent decrease of its capacity to supply eb

Variation in sessile microflora during biofilm formation on AISI-304 stainless steel coupons.

Coupons of stainless steel type AISI-304 were exposed to the industrial cooling system of a petrochemical plant fed by seawater from the Guanabara Bay, Rio de Janeiro, Brazil, in order to study the in situ formation of biofilms. Bacteria, microalgae and fungi were detected on the coupons as soon as 48 h after exposure. Their respective numbers were determined at times 48, 96 and 192 h and over the following 8 weeks. Aerobic, anaerobic and sulfate-reducing bacteria were quantified according to the technique of the most probable number, and fungi by the pour plate technique. The number of microorganisms present in the forming biofilm varied over the experimental period, reaching maximal levels of 14 x 10(11) cells cm-2, 30 x 10(13) cells cm-2, 38 x 10(11) cells cm-2 and 63 x 10(5) cells cm-2, respectively, for aerobic bacteria, anaerobic bacteria, sulfate-reducing bacteria and fungi, and the dynamics of this variation depended on the group of microorganisms. Bacillus sp, Escherichia coli, Serratia sp and Pseudomonas putrefaciens were identified among the aerobic bacteria isolated. Additionally, microalgae and bacteria of the genus Gallionella were also detected. Nonetheless, no evidence of corrosion was found on the stainless steel type AISI-304 coupons over the experimental period.

Microbiota aeróbia e anaeróbi a normal da conjuntiva e borda palpebral de indivíduos hígidos / Aerobic and anaerobic normal microbiota of conjunctiva and lid margin of healthy subjects

Foram obtidos raspados da conjuntiva (CON) e bordo palpebral (BP) de ambos os olhos de 100 indivíduos hígidos para a pesquisa da microbiota aeróbia e anaeróbia normal do olho. O estudo foi realizado durante as 4 estaçöes do ano para a verificaçäo da relaçäo da frequência destes microorganismos coma a sazonalidade. Todas as amostras de BP apresentaram crescimento bacteriano, assim como 90 (45 por cento) de CON. A bactéria aeróbia mais frequentemente isolada, tanto em BP quanto em CON, foi Staphylococcus epidermidis. Outros aeróbios isolados foram Staphylococcus aureus, difteróides, Streptococcus spp., Micrococcus sp.,Staphylococcus saprophyticus, Acinetobacter Iwoffii e Bacillus spp. Eubacterium sp. foi o anaeróbio mais frequente em BP e Propionibacteriumspp. o ónico em CON. Além desses, identificaram-se Bacteroides fragilis, Clostridium innocuum e Peptococcus sp.. Microorganismos nos quais foi possível testar a relaçäo entre sua frequência, em BP ou em CON, com a sazonalidade foram Staphylococcus epidermis com 1 p<0,001 em BP e p<0,050 em CON, Staphylococcus aureus com um p<0,001em BP, e difteróides com um p<0,010 em BP e p<0,050 em CON. Streptococcus spp. em BP apresentou um p>0,002 o que näo é estatisticamente significativo. O presente estudo identifica a microbiota aeróbia e anaeróbia normal em CON e BP existente no nosso meio, alóem de comprovar estatisticamente a variaçäo sazonal de parte da mesma.

Aerobic sulfate reduction in microbial mats.

Measurements of bacterial sulfate reduction and dissolved oxygen (O2) in hypersaline bacterial mats from Baja California, Mexico, revealed that sulfate reduction occurred consistently within the well-oxygenated photosynthetic zone of the mats. This evidence that dissimilatory sulfate reduction can occur in the presence of O2 challenges the conventional view that sulfate reduction is a strictly anaerobic process. At constant temperature, the rates of sulfate reduction in oxygenated mats during daytime were similar to rates in anoxic mats at night: thus, during a 24-hour cycle, variations in light and O2 have little effect on rates of sulfate reduction in these mats.

Influencia de la dieta en la flora bacteriana duodenal en niños desnutridos con diarrea crónica / Influence of the diet in the duodenum bacterial flora in childrens malnutritions with chronic diarrhea

En 22 niños con diarrea crónica de causa no establecida con percentil <5 para peso/talla y sin edemas. Se estudió el contenido bacteriano duodenal aeróbico y anaeróbico antes y 15 días después de tres diferentes regímenes dietéticos. Leche de vaca una dieta semielemental sin sacarosa y otra en la cual 10 g de maltodextrina fueron sustituídos por 12 g de sacarosa. En el grupo de niños que recibió dieta semielemental sin sacarosa hubo una reducción del número de colonias bacterianas, en cambio con la dieta semielemental con sacarosa hubo un incremento de la flora bacteriana. Dado que la única diferencia entre estas dos dietas era la sacarosa se puede especular que este último carbohidrato puede favorecer la proliferación bacteriana duodenal. Esto puede tener implicaciones nutricionales como hemos evidenciado en otros estudios