B. Rodelas

The regulatory locus cinRI in Rhizobium leguminosarum controls a network of quorum-sensing loci.

N‐(3‐hydroxy‐7‐cis‐tetradecenoyl)‐l‐homoserine lactone (3OH,C14:1‐HSL) is a quorum‐sensing signalling molecule produced by Rhizobium leguminosarum. It is unusual in that it inhibits the growth of several strains of R. leguminosarum and was previously known as ‘small bacteriocin’. The cinRI locus responsible for the production of 3OH,C14:1‐HSL has been characterized; it is predicted to be on the chromosome, based on DNA hybridization. The cinR and cinI genes are in different transcriptional units, separated by a predicted transcription terminator. CinR regulates cinI expression to a very high level in a cell‐density dependent manner, and cinI expression is positively autoregulated by 3OH,C14:1‐HSL, the only identified N‐acyl homoserine lactone (AHL) produced by CinI. No other AHLs were identified that strongly induced cinI expression. Mutation of cinI or cinR abolishes the production of 3OH,C14:1‐HSL and also reduces the production of several other AHLs. This is thought to result from the expression of three other AHL production loci being affected by the absence of 3OH,C14:1‐HSL. AHLs produced by these other loci include N‐hexanoyl‐ and N‐octanoyl‐l‐homoserine lactones and, unexpectedly, N‐heptanoyl‐l‐homoserine lactone (C7‐HSL). The expression of the rhiI gene on the symbiotic plasmid is greatly reduced in a cinI mutant, and the major regulatory effect appears to be mediated at least in part as a result of an effect on expression of RhiR, the regulator of rhiI. Thus, cinR and cinI appear to be at the top of a regulatory cascade or network that influences several AHL‐regulated quorum‐sensing loci. The expression of cinI–lacZ fusions is significantly reduced (but not abolished) when the symbiosis plasmid pRL1JI is present, resulting in a reduction in the level of 3OH,C14:1‐HSL produced. Mutation of cinI had little effect on growth or nodulation. However, plasmid transfer was affected, and the results obtained indicate that 3OH,C14:1‐HSL produced by either the donor or the recipient in mating experiments can stimulate transfer of pRL1JI.

Analysis of microbial communities developed on the fouling layers of a membrane-coupled anaerobic bioreactor applied to wastewater treatment.

The structure of the biofouling layers formed on a pilot-scale membrane-coupled upflow anaerobic sludge blanket bioreactor (UASB) used to treat urban wastewater was analyzed by scanning electron microscopy and electron-dispersive X-ray microanalysis. For comparison, control samples of the membranes were fed either UASB effluent or raw wastewater in a laboratory-scale experiment. Microbial diversity in the fouling materials was analyzed by temperature gradient gel electrophoresis (TGGE) combined with sequence analysis of partial 16S rRNA. Significant differences in structure of the Bacteria communities were observed amongst the different fouling layers analyzed in the UASB membranes, particularly following a chemical cleaning step (NaClO), while the Archaea communities retained more similarity in all samples. The main Bacteria populations identified were evolutively close to Firmicutes (42.3%) and Alphaproteobacteria (30.8%), while Archaea were mostly affiliated to the Methanosarcinales and Methanospirillaceae. Sphingomonadaceae-related bacteria and methanogenic Archaea were persistently found as components of biofouling, regardless of chemical cleaning.

Effects of culture conditions on the production of polyhydroxyalkanoates by Azotobacter chroococcum H23 in media containing a high concentration of alpechín (wastewater from olive oil mills) as primary carbon source.

Large amounts of homopolymers containing beta-hydroxybutyrate (PHB) and copolymers containing beta-hydroxyvalerate (P[HB-co-HV]) are produced by Azotobacter chroococcum strain H23 when growing in culture media amended with alpechín (wastewater from olive oil mills) as the sole carbon source. Copolymer was formed when valerate (pentanoate) was added as a precursor to the alpechín medium, but it was not formed with the addition of propionate as a precursor. A. chroococcum formed homo- and copolymers of polyhydroxyalkanoates (PHAs) up to 80% of the cell dry weight, when grown on NH(4)(+)-medium supplemented with 60% (v/v) alpechín, after 48 h of incubation at 100 rev min(-1) and 30 degrees C. Production of PHAs by strain H23 using alpechín looks promising, as the use of a cheap substrate for the production of these materials is essential if bioplastics are to become competitive products.

Comparative analysis of the bacterial diversity in a lab-scale moving bed biofilm reactor (MBBR) applied to treat urban wastewater under different operational conditions

Different types of carriers were tested as support material in a lab-scale moving bed biofilm reactor (MBBR) used to treat urban wastewater under three different conditions of hydraulic retention time (HRT) and carrier filling ratios (FR). The bacterial diversity developed on the biofilms responsible of the treatment was studied using a cultivation-independent approach based on the polymerase chain reaction-temperature gradient gel electrophoresis technique (PCR-TGGE). Cluster analysis of TGGE fingerprints showed significant differences of community structure dependent upon the different operational conditions applied. Redundancy analysis (RDA) was used to determine the relationship between the operational conditions (type of carrier, HRT, FR) and bacterial biofilm diversity, demonstrating a significant effect of FR=50%. Phylogenetic analysis of PCR-reamplified and sequenced TGGE bands revealed that the prevalent Bacteria populations in the biofilm were related to Betaproteobacteria (46%), Firmicutes (34%),Alphaproteobacteria (14%) and Gammaproteobacteria (9%).

Microbial community structure and dynamics in a pilot-scale submerged membrane bioreactor aerobically treating domestic wastewater under real operation conditions.

A pilot scale submerged ultra-filtration membrane bioreactor (MBR) was used for the aerobic treatment of domestic wastewater over 9 months of year 2006 (28th March to 21st December). The MBR was installed at a municipal wastewater facility (EMASAGRA, Granada, Spain) and was fed with real wastewater. The experimental work was divided in 4 stages run under different sets of operation conditions. Operation parameters (total and volatile suspended solids, dissolved oxygen concentration) and environmental variables (temperature, pH, COD and BOD(5) of influent water) were daily monitored. In all the experiments conducted, the MBR generated an effluent of optimal quality complying with the requirements of the European Law (91/271/CEE 1991). A cultivation-independent approach (polymerase chain reaction-temperature gradient gel electrophoresis, PCR-TGGE) was used to analyze changes in the structure of the bacterial communities in the sludge. Cluster analysis of TGGE profiles demonstrated significant differences in community structure related to variations of the operation parameters and environmental factors. Canonical correspondence analysis (CCA) suggested that temperature, hydraulic retention time and concentration of volatile suspended solids were the factors mostly influencing community structure. 23 prominent TGGE bands were successfully reamplified and sequenced, allowing gaining insight into the identities of predominantly present bacterial populations in the sludge. Retrieved partial 16S-rRNA gene sequences were mostly related to the alpha-Proteobacteria, beta-Proteobacteria and gamma-Proteobacteria classes. The community established in the MBR in each of the four stages of operation significantly differed in species composition and the sludge generated displayed dissimilar rates of mineralization, but these differences did not influence the performance of the bioreactor (quality of the permeate). These data indicate that the flexibility of the bacterial community in the sludge and its ability to get adapted to environmental changes play an important role for the stable performance of MBRs.

Production of B-group vitamins by two Azotobacter strains with phenolic compounds as sole carbon source under diazotrophic and adiazotrophic conditions

Azotobacter vinelandii strain ATCC 12837 and A. chroococcum strain H23 (CECT 4435) were able to grow on N‐free or NH4Cl‐amended chemically‐defined (Burks) media, with protocatechuic acid (1–2 mmol l−1) or sodium p‐hydroxybenzoate (1–10 mmol l−1) as sole carbon (C) sources. At a concentration of 2 mmol l−1, both substrates supported nitrogen fixation (acetylene reduction assay) at similar or higher rates than bacteria grown in control media amended with 2 mmol l−1 sodium succinate as C source. The two strains produced the B‐group vitamins niacin, pantothenic acid, thiamine, riboflavin and biotin after 72 h of growth in chemically‐defined media with 2 mmol l−1 protocatechuic acid, sodium p‐hydroxybenzoate or sodium succinate as sole C source, either in N‐free media or in media amended with 0·1% NH4Cl. Quantitative production of all vitamins was affected by the use of the different C and N substrates.

Effects of the fungicide Captan on some functional groups of soil microflora

Abstract The effects of Captan at rates of 2.0, 3.5, 5.0 and 10.0 kg ha−1 on microbial function were studied in four agricultural soils under aerobic conditions. Parameters monitored included total culturable populations, numbers of aerobic N2-fixing bacteria, denitrifying bacteria, nitrifying bacteria and nitrogenase activity. Total culturable fungal populations, nitrifying bacteria, aerobic N2-fixing bacteria and nitrogenase activity were significantly decreased at dose rates of 2.0 to 10.0 kg ha−1. However, the presence of Captan enhanced denitrifying and total culturable bacteria, showing that some microbial groups can tolerate high doses of this fungicide.

Microbial enzymatic activities in a pilot-scale MBR experimental plant under different working conditions.

Phosphatases, glucosidase, protease, esterase and dehydrogenase activities in a MBR (membrane bioreactor) system equipped with ultrafiltration membranes for the treatment of real urban wastewater were measured at different volatile suspended solid (VSS) concentrations, total suspended solid (TSS) concentrations, hydraulic retention times (HRT), temperatures and inflow rates. The results showed the capacity of the MBR system to remove COD and BOD(5) at TSS between 7200 and 13,300 mg/L; HRT values of 8.05 and 15.27 h; inflow rates of 14.67 and 27.81 L/h; and temperatures between 4 and 27 degrees C. The enzymatic activities are influenced by increases in VSS and TSS concentrations. These results suggest that the ability to get adapted to environmental changes of the bacterial populations and their microbial enzymatic activities is essential to understand the biological processes that occur in MBR systems and crucial for proper urban wastewater treatment when using MBR technologies.

Production of vitamins by Azospirillum brasilense in chemically-defined media

The production of vitamins by Azospirillum brasilense was studied in chemically-defined media amended with malate, gluconate and fructose. The liberation of vitamins was significantly affected by the presence of different carbon sources and the age of the culture. Thiamine, niacin and pantothenic acid were produced in large amounts. Thiamine and riboflavin were produced only in culture containing malate or fructose. Biotin was not detected in the supernatants of the culture media.

Influence of Rhizobium/Azotobacter and Rhizobium/Azospirillum combined inoculation on mineral composition of faba bean (Vicia faba L.)

Abstract Mixed inoculation of Vicia faba L. with four different Rhizobium/Azospirillum and Rhizobium/Azotobacter combinations led to changes in total content, concentration and/or distribution of the mineral macro- and micronutrients, K, P, Ca, Mg, Fe, B, Mn, Zn and Cu, when compared with plants inoculated with Rhizobium only. The effects varied to a great extent among the Azotobacter and Azospirillum strains selected for combined inoculation.