Inner Layer Of Biofilm Research Articles

Sub-inhibitory concentrations of colistin and imipenem impact the expression of biofilm-associated genes in Acinetobacter baumannii.

Acinetobacter baumannii is an opportunistic pathogen that is responsible for nosocomial infections. Imipenem and colistin are drugs that are commonly used to treat severe infections caused by A. baumannii, such as sepsis, ventilator-associated pneumonia, and bacteremia. However, some strains of A. baumannii have become resistant to these drugs, which is a concern for public health. Biofilms produced by A. baumannii increase their resistance to antibiotics and the cells within the inner layers of biofilm are exposed to sub-inhibitory concentrations (sub-MICs) of antibiotics. There is limited information available regarding how the genes of A. baumannii are linked to biofilm formation when the bacteria are exposed to sub-MICs of imipenem and colistin. Thus, this study's objective was to explore this relationship by examining the genes involved in biofilm formation in A. baumannii when exposed to low levels of imipenem and colistin. The study found that exposing an isolate of A. baumannii to low levels of these drugs caused changes in their drug susceptibility pattern. The relative gene expression profiles of the biofilm-associated genes exhibited a change in their expression profile during short-term and long-term exposure. This study highlights the potential consequences of overuse and misuse of antibiotics, which can help bacteria become resistant to these drugs.

Advanced nitrogen removal in a fixed-bed anaerobic ammonia oxidation reactor following an anoxic/oxic reactor: Nitrogen removal contributions and mechanisms

This study demonstrated the feasibility of anaerobic ammonia oxidation (anammox) served as tertiary nitrogen removal process. An upflow fixed-bed reactor (UFBR) pre-inoculated with anammox bacteria (AnAOB) followed an anoxic/oxic (A/O) reactor treating magnetic-coagulation pretreated municipal wastewater. When bypassing 15% of influent into UFBR, UFBR removed 5.37 mg-TN/L contributing to 23.4% on total TN removal, in which the combination of partial nitritation and partial denitrification with anammox was main nitrogen removal pathway. Relatively low concentrations of NH4+-N and anaerobic environment promoted the growth of ammonia oxidizing archaea (AOA) in the inner-layer of biofilm in UFBR. The cooperation of AOA and ammonia-oxidizing bacteria (AOB) with AnAOB was achieved, with AOA, AOB, and AnAOB abundances of 0.01–0.32%, 0.25–0.44%, and 0.77–2.18% on the biofilm, respectively. Metagenomic analysis found that although AOB was the main NH4+-N oxidizer, archaeal amo gene on biofilm increased threefold during 90 days’ treatment.

Stratified microbial structure and activity within anode biofilm during electrochemically assisted brewery wastewater treatment.

In a bioelectrochemical system (BES), microbial community of anode biofilm is crucial to BES performance. In this study, the stratified pattern of community structure and activity of an anode-respiring biofilm in a BES fueled with brewery wastewater was investigated over time. The anode biofilm exhibited a superior performance in the removal of ethanol to that of an open-circuit system. The electrical current density reached a high level of 0.55mA/cm2 with a Coulombic efficiency of 71.4%, but decreased to 0.18mA/cm2 in the late stage of operation. A mature biofilm developed a more active outer layer covering a less active inner core, although the activities of the outer and inner layers of biofilm were similar in the early stage. More Geobacter spp., typical exoelectrogens, were enriched in the outer layer than in the inner layer of biofilm in the early stage, while more Geobacter spp. were distributed in the inner layer than in the outer layer in the late stage. The inactive and Geobacter-occupied inner layer of biofilm might be responsible for the decreased electricity generation from wastewater in the late stage of operation. This study provides better understanding of the effect of anode biofilm structure on BES performance.

The effect of biofilm thickness on electrochemical activity of Geobacter sulfurreducens

It is widely believed that the high electrochemical performance of Geobacter sulfurreducens relies on its thick and conductive biofilms in bioelectrochemical systems. However, in this study, the G. sulfurreducens biofilm reached the highest electrochemical activity with a biofilm thickness of ∼20 μm, and then the electrochemical activity decreased with increasing thickness until the biofilm growth ceased at a thickness of ∼45 μm. The electrochemical analysis and the metabolic spatial variability showed that in the first 5 cycles the live cells grew fast, which led to a rapid drop of charge transfer resistance and further contributed to high current generation, however, from cycle 5 to 12, a great many inactive cells accumulated in the inner layer of biofilm, which resulted in high diffusion resistance. Thus, although the G. sulfurreducens can always form thick biofilms, its highest electrochemical activity reached at a much thinner thickness, suggesting that the live-cell mass rather than the biofilm thickness is responsible for the high current generation.

Reuse of treated wastewater using sequencing batch bioreactor for the improvement of wheat growth

Reclaimed wastewater reuse for irrigation to crop plants is evaluated in a laboratory-scale experiment to assess growth and water saving potential from natural resources. A prototype laboratory-scale treatment plant was established for this purpose with suspended and attached growth configurations. Chakwal wheat variety was selected to examine growth parameters. The removal of chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP) were evaluated to check the quality of treated water. It was found that a suspended growth sequencing batch bioreactor (SGSBBR) achieved 97% ± 2 removal efficiency over a 4 h hydraulic retention time (HRT). For an attached growth sequencing batch bioreactor (AGSBBR) results showed 98% ± 2 removal efficiencies with polyurethane. TN and TP removal efficiency was 58.7 ± 3% and 64 ± 4.8% in SGSBBR, 53 ± 0.17% and 67 ± 2.7% in polyurethane. AGSBBR enhanced performance with AGSBBR may be due to enforced anoxic/aerobic conditions in the inner layers of biofilm formed on biocarriers which facilitate the required metabolic conditions for treating high strength wastewater. Plant growth was visibly greater in SGSBBR treated wastewater than AGSBBR because of less nutrient removal.

Differential biofilms characteristics of Shewanella decolorationis microbial fuel cells under open and closed circuit conditions

Biofilms formation capacities of Shewanella species in microbial fuel cells (MFCs) and their roles in current generation have been documented to be species-dependent. Understandings of the biofilms growth and metabolism are essential to optimize the current generation of MFCs. Shewanella decolorationis S12 was used in both closed-circuit and open-circuit MFCs in this study. The anodic S. decolorationis S12 biofilms could generate fivefold more current than the planktonic cells, playing a dominant role in current generation. Anodic biofilms viability was sustained at 98±1.2% in closed-circuit while biofilms viability in open-circuit decreased to 72±7% within 96h. The unviable domain in open-circuit MFCs biofilms majorly located at the inner layer of biofilm. The decreased biofilms viability in open-circuit MFCs could be recovered by switching into closed-circuit, indicating that the current-generating anode in MFCs could serve as a favorable electron acceptor and provide sufficient energy to support cell growth and metabolism inside biofilms.

Effect of substrate COD/N ratio on performance and microbial community structure of a membrane aerated biofilm reactor

Two parallel carbon-membrane aerated biofilm reactors were operated at well-defined conditions to investigate the effect of substrate COD/N ratios on the performance and microbial community structure of the bioreactor. Results showed that at substrate COD/Nof5, organic and nitrogen could be eliminated simultaneously, and COD removal degree, nitrification and denitrification efficiency reached 85%, 93% and 92%, respectively. With increasing substrate COD/N ratios, the specific oxygen utilization rates of nitrifying bacteria in biofilm were found to decrease, indicating that nitrifying population became less dominant. At substrate COD/N ratio of 6, excessive heterotrophs inhibited the activity of nitrifying bacteria greatly and thus led to poor nitrification process. With the help of fluorescence in situ hybridization (FISH), Nitrosomonas and Nitrosospira were identified as dominant ammonia-oxidizing bacteria in the biofilm at substrate COD/N of 0, whereas only Nitrosospira were detected in the biofilm at COD/N ratio of 5. Nitrospira were present as dominant nitrite-oxidizing bacteria in our study. Confocal laser scanning microscopy images revealed that at substrate COD/N ratio of 0 nitrifying bacteria existed throughout the biofilm and that at COD/N ratio of 5 they were mainly distributed in the inner layer of biofilm.