The effect of biological sulfate reduction on anaerobic color removal in anaerobic-aerobic sequencing batch reactors.

Combination of anaerobic-aerobic sequencing processes result in both anaerobic color removal and aerobic aromatic amine removal during the treatment of dye-containing wastewaters. The aim of the present study was to gain more insight into the competitive biochemical reactions between sulfate and azo dye in the presence of glucose as electron donor source. For this aim, anaerobic-aerobic sequencing batch reactor fed with a simulated textile effluent including Remazol Brilliant Violet 5R (RBV 5R) azo dye was operated with a total cycle time of 12 h including anaerobic (6 h) and aerobic cycles (6 h). Microorganism grown under anaerobic phase of the reactor was exposed to different amounts of competitive electron acceptor (sulfate). Performance of the anaerobic phase was determined by monitoring color removal efficiency, oxidation reduction potential, color removal rate, chemical oxygen demand (COD), color, specific anaerobic enzyme (azo reductase) and aerobic enzyme (catechol 1,2-dioxygenase), and formation of aromatic amines. The presence of sulfate was not found to significantly affect dye decolorization. Sulfate and azo dye reductions took place simultaneously in all operational conditions and increase in the sulfate concentration generally stimulated the reduction of RBV 5R. However, sulfate accumulation under anaerobic conditions was observed proportional to increasing sulfate concentration.

Bacterial consortium proteomics under 4-chlorosalicylate carbon-limiting conditions.

In this study, the stable consortium composed by Pseudomonas reinekei strain MT1 and Achromobacter xylosoxidans strain MT3 (cell numbers in proportion 9:1) was under investigation to reveal bacterial interactions that take place under severe nutrient-limiting conditions. The analysis of steady states in continuous cultures was carried out at the proteome, metabolic profile, and population dynamic levels. Carbon-limiting studies showed a higher metabolic versatility in the community through upregulation of parallel catabolic enzymes (salicylate 5-hydroxylase and 17-fold on 2-keto-4-pentenoate hydratase) indicating a possible alternative carbon routing in the upper degradation pathway highlighting the effect of minor proportions of strain MT3 over the major consortia component strain MT1 with a significant change in the expression levels of the enzymes of the mainly induced biodegradation pathway such as salicylate 1-hydroxylase and catechol 1,2-dioxygenase together with important changes in the outer membrane composition of P. reinekei MT1 under different culture conditions. The study has demonstrated the importance of the outer membrane as a sensing/response protective barrier caused by interspecies interactions highlighting the role of the major outer membrane proteins OprF and porin D in P. reinekei sp. MT1 under the culture conditions tested.

Optimal microbial adaptation routes for the rapid degradation of high concentration of phenol.

Pseudomonas fluorescence KNU417 was able to degrade up to 700 mg/L of phenol in 65 h but could not degrade 1,000 mg/L of phenol. Phenol degradation rate was noticeably enhanced by pre-adaptation. In addition, the cell was able to degrade up to 1,300 mg/L of phenol by pre-adapting to 700 mg/L of phenol. Repeated adaptations to the same concentration of phenol showed negligible increase in degradation rate. Also, relatively low concentration of phenol (100-700 mg/L) required only one pre-adaptation while high concentration (1,000 mg/L) did two consecutive stepwise pre-adaptations for rapid degradation. Optimal adaptation routes were suggested for the fast phenol degradation. For example, 1,000 mg/L of phenol was degraded as fast as in 48 h when the cell was pre-adapted to 100 and 300 mg/L of phenol sequentially. The mechanism of adaptation was explained in terms of catechol 1,2-dioxygenase induction, related to aromatic ring cleavage.

Study of factors which negatively affect expression of the phenol degradation operon pheBA in Pseudomonas putida.

Transcription of the plasmid-borne phenol catabolic operon pheBA in Pseudomonas putida is activated by the LysR-family regulator CatR in the presence of the effector molecule cis,cis-muconate (CCM), which is an intermediate of the phenol degradation pathway. In addition to the positive control of the operon, several factors negatively affect transcription initiation from the pheBA promoter. First, the activation of the pheBA operon depends on the extracellular concentration of phenol. The pheBA promoter is rapidly activated in the presence of micromolar concentrations of phenol in minimal growth medium, but the initiation of transcription from this promoter is severely delayed after sudden exposure of bacteria to 2.5 mM phenol. Second, the transcriptional activation from this promoter is impeded when the growth medium of bacteria contains amino acids. The negative effects of amino acids can be suppressed either by overproducing CatR or by increasing, the intracellular amount of CCM. However, the intracellular amount of CCM is a major limiting factor for the transcriptional activation of the pheBA operon, as accumulation of CCM in a P. putida catB-defective strain, unable to metabolize CCM (but expressing CatR at a natural level), almost completely relieves the negative effects of amino acids. The intracellular amount of CCM is negatively affected by the catabolite repression control protein via downregulating at the post-transcriptional level the expression of the pheBA-encoded catechol 1,2-dioxygenase and the phenol monooxygenase, the enzymes needed for CCM production.

Constitutive expression of catABC genes in the aniline-assimilating bacterium Rhodococcus species AN-22: production, purification, characterization and gene analysis of CatA, CatB and CatC.

The aniline-assimilating bacterium Rhodococcus sp. AN-22 was found to constitutively synthesize CatB (cis,cis-muconate cycloisomerase) and CatC (muconolactone isomerase) in its cells growing on non-aromatic substrates, in addition to the previously reported CatA (catechol 1,2-dioxygenase). The bacterium maintained the specific activity of the three enzymes at an almost equal level during cultivation on succinate. CatB and CatC were purified to homogeneity and characterized. CatB was a monomer with a molecular mass of 44 kDa. The enzyme was activated by Mn2+, Co2+ and Mg2+. Native CatC was a homo-octamer with a molecular mass of 100 kDa. The enzyme was stable between pH 7.0 and 10.5 and was resistant to heating up to 90 degrees C. Genes coding for CatA, CatB and CatC were cloned and named catA, catB and catC respectively. The catABC genes were transcribed as one operon. The deduced amino acid sequences of CatA, CatB and CatC showed high identities with those from other Gram-positive micro-organisms. A regulator gene such as catR encoding a regulatory protein was not observed around the cat gene cluster of Rhodococcus sp. AN-22, but a possible relic of catR was found in the upstream region of catA. Reverse transcriptase-PCR and primer extension analyses showed that the transcriptional start site of the cat gene cluster was located 891 bp upstream of the catA initiation codon in the AN-22 strain growing on both aniline and succinate. Based on these data, we concluded that the bacterium constitutively transcribed the catABC genes and translated its mRNA into CatA, CatB and CatC.