Antibiofilm activity of Bacillus pumilus SW9 against initial biofouling on microfiltration membranes

Predatory Bdellovibrio-and-like organism mixtures on efficient MBR in-situ membrane fouling diminishment and mechanisms

Membrane fouling is a major hindrance that restricts the application of membrane bioreactors (MBRs). Bdellovibrio-and-like organisms (BALOs), as obligatory parasitic bacteria, prey upon various bacteria. In this study, the BALO mixtures were screened and found more effective in membrane fouling mitigation compared to the single BALO species and extended the membrane filtration period by as long as 33.3%. The higher BALO diversity reduced the potential foulants generation in the activated sludge by decreasing the sludge viscosity as high as 13.8 ± 0.6% than the pure culture of BALO. Meanwhile, the mixed BALOs demonstrated superior biofilm predation capabilities, with the content of soluble microbial products and extracellular polymeric substances on the biofilm decreasing by 26.1 ± 0.5% and 38.3 ± 0.2% as the most compared to the single BALO species involved system. Additionally, the BALO mixtures expanded the single strains' host lysis spectrum of both the activated sludge and biofilm. The abundance of membrane-fouling-related bacteria such as Flavobacterium, Rhodobacter, and Labilithrix and pioneer bacteria such as Sphingorhabdus and Pseudomonas was significantly reduced. In summary, this study disclosed the significantly better membrane fouling mitigation effects of the BALOs with higher diversity, suggesting that the expansion of the host range is crucial for the further application of BALOs to enhance the anti-fouling performance of the MBR system.

Elucidation of auxotrophic deficiencies of Bacillus pumilus DSM 18097 to develop a defined minimal medium

Background

Culture media containing complex compounds like yeast extract or peptone show numerous disadvantages. The chemical composition of the complex compounds is prone to significant variations from batch to batch and quality control is difficult. Therefore, the use of chemically defined media receives more and more attention in commercial fermentations. This concept results in better reproducibility, it simplifies downstream processing of secreted products and enable rapid scale-up. Culturing bacteria with unknown auxotrophies in chemically defined media is challenging and often not possible without an extensive trial-and-error approach. In this study, a respiration activity monitoring system for shake flasks and its recent version for microtiter plates were used to clarify unknown auxotrophic deficiencies in the model organism Bacillus pumilus DSM 18097.

Results

Bacillus pumilus DSM 18097 was unable to grow in a mineral medium without the addition of complex compounds. Therefore, a rich chemically defined minimal medium was tested containing basically all vitamins, amino acids and nucleobases, which are essential ingredients of complex components. The strain was successfully cultivated in this medium. By monitoring of the respiration activity, nutrients were supplemented to and omitted from the rich chemically defined medium in a rational way, thus enabling a systematic and fast determination of the auxotrophic deficiencies. Experiments have shown that the investigated strain requires amino acids, especially cysteine or histidine and the vitamin biotin for growth.

Conclusions

The introduced method allows an efficient and rapid identification of unknown auxotrophic deficiencies and can be used to develop a simple chemically defined tailor-made medium. B. pumilus DSM 18097 was chosen as a model organism to demonstrate the method. However, the method is generally suitable for a wide range of microorganisms. By combining a systematic combinatorial approach based on monitoring the respiration activity with cultivation in microtiter plates, high throughput experiments with high information content can be conducted. This approach facilitates media development, strain characterization and cultivation of fastidious microorganisms in chemically defined minimal media while simultaneously reducing the experimental effort.

Electronic supplementary material

The online version of this article (10.1186/s12934-018-0956-1) contains supplementary material, which is available to authorized users.

Membrane fouling induced by AHL-mediated soluble microbial product (SMP) formation by fouling-causing bacteria co-cultured with fouling-enhancing bacteria

Membrane fouling still remains a major obstacle for wider applications of membrane bioreactor (MBR), which is mainly caused by soluble microbial products (SMP). Identification of key bacteria responsible for SMP production is essential for mitigation of membrane fouling. Here, we investigated the effect of microbial interaction on membrane fouling. We measured the membrane fouling potentials of 13 bacterial strains isolated from a pilot-scale MBR treating domestic wastewater when they were cultivated as single-culture and co-culture. We found that fouling-causing bacteria (FCB) displayed much higher fouling potential when co-cultured even with non-FCB and mixed population (activated sludge). In particular, the fouling potential of strain S26, one of FCB, increased 26.8 times when cultivated with strain S22 (fouling-enhancing bacteria, FEB). The secretion of N-octanoyl-L-homoserine lactone (C8-HSL) was increased by co-cultivating S22 and S26 as compared with cultivating as single culture, which stimulated the production of fouling-causing SMP by S26 and consequently resulted in severe membrane fouling. This result suggests that AHL-mediated quorum-sensing (QS) regulatory system was involved in secretion of fouling-causing SMP.

The lipopeptide 6-2 produced by Bacillus amyloliquefaciens anti-CA has potent activity against the biofilm-forming organisms

Both the whole cells and protoplasts of Pseudomonas aeruginosa PAO1 and Bacillus cereus, two biofilm-forming bacteria, were disrupted by the lipopeptide 6-2 produced by Bacillus amyloliquefaciens anti-CA. The lipopeptide 6-2 could also effectively inhibit the formation of biofilms and disperse pre-formed biofilms. Live/dead staining of the biofilms grown in the absence or presence of the lipopeptide 6-2 showed that more dead bacterial cells in the presence of the lipopeptide than those in the absence of the lipopeptide and biofilm formation was greatly reduced by the lipopeptide 6-2. Expression of the PslC gene related to exopolysaccharides in P. aeruginosa PAO1 was also inhibited. All these results demonstrated that the lipopeptide 6-2 produced by B. amyloliquefaciens anti-CA had a high activity against biofilm-forming bacteria. The lipopeptide 6-2 also killed the larvae of Balanus amphitrite and inhibit the germination of Laminaria japonica spore and growth of protozoa, all of which were the fouling organisms in marine environments.

N-acyl homoserine lactone-mediated quorum sensing with special reference to use of quorum quenching bacteria in membrane biofouling control

Membrane biofouling remains a severe problem to be addressed in wastewater treatment systems affecting reactor performance and economy. The finding that many wastewater bacteria rely on N-acyl homoserine lactone-mediated quorum sensing to synchronize their activities essential for biofilm formations; the quenching bacterial quorum sensing suggests a promising approach for control of membrane biofouling. A variety of quorum quenching compounds of both synthetic and natural origin have been identified and found effective in inhibition of membrane biofouling with much less environmental impact than traditional antimicrobials. Work over the past few years has demonstrated that enzymatic quorum quenching mechanisms are widely conserved in several prokaryotic organisms and can be utilized as a potent tool for inhibition of membrane biofouling. Such naturally occurring bacterial quorum quenching mechanisms also play important roles in microbe-microbe interactions and have been used to develop sustainable nonantibiotic antifouling strategies. Advances in membrane fabrication and bacteria entrapment techniques have allowed the implication of such quorum quenching bacteria for better design of membrane bioreactor with improved antibiofouling efficacies. In view of this, the present paper is designed to review and discuss the recent developments in control of membrane biofouling with special emphasis on quorum quenching bacteria that are applied in membrane bioreactors.

Antibiofilm activity, compound characterization, and acute toxicity of extract from a novel bacterial species of paenibacillus

The effectiveness of many antimicrobial agents is currently decreasing; therefore, it is important to search for alternative therapeutics. Our study was carried out to assess the in vitro antibiofilm activity using microtiter plate assay, to characterize the bioactive compounds using Ultra Performance Liquid Chromatography-Diode Array Detection and Liquid Chromatography-Mass Spectrometry and to test the oral acute toxicity on Sprague Dawley rats of extract derived from a novel bacterial species of Paenibacillus strain 139SI. Our results indicate that the crude extract and its three identified compounds exhibit strong antibiofilm activity against a broad range of clinically important pathogens. Three potential compounds were identified including an amino acid antibiotic C8H20N3O4P (MW 253.237), phospholipase A2 inhibitor C21H36O5 (MW 368.512), and an antibacterial agent C14H11N3O2 (MW 253.260). The acute toxicity test indicates that the mortality rate among all rats was low and that the biochemical parameters, hematological profile, and histopathology examination of liver and kidneys showed no significant differences between experimental groups (P > 0.05). Overall, our findings suggest that the extract and its purified compounds derived from novel Paenibacillus sp. are nontoxic exhibiting strong antibiofilm activity against Gram-positive and Gram-negative pathogens that can be useful towards new therapeutic management of biofilm-associated infections.