Salinity-Mediated Increment in Sulfate Reduction, Biofilm Formation, and Quorum Sensing: A Potential Connection Between Quorum Sensing and Sulfate Reduction?

Biocorrosion in marine environment is often associated with biofilms of sulfate reducing bacteria (SRB). However, not much information is available on the mechanism underlying exacerbated rates of SRB-mediated biocorrosion under saline conditions. Using Desulfovibrio (D.) vulgaris and Desulfobacterium (Db.) corrodens as model SRBs, the enhancement effects of salinity on sulfate reduction, N-acyl homoserine lactone (AHL) production and biofilm formation by SRBs were demonstrated. Under saline conditions, D. vulgaris and Db. corrodens exhibited significantly higher specific sulfate reduction and specific AHL production rates as well as elevated rates of biofilm formation compared to freshwater medium. Salinity-induced enhancement traits were also confirmed at transcript level through reverse transcription quantitative polymerase chain reaction (RT-qPCR) approach, which showed salinity-influenced increase in the expression of genes associated with carbon metabolism, sulfate reduction, biofilm formation and histidine kinase signal transduction. In addition, by deploying quorum sensing (QS) inhibitors, a potential connection between sulfate reduction and AHL production under saline conditions was demonstrated, which is most significant during early stages of sulfate metabolism. The findings collectively revealed the interconnection between QS, sulfate reduction and biofilm formation among SRBs, and implied the potential of deploying quorum quenching approaches to control SRB-based biocorrosion in saline conditions

Quorum Sensing and the Use of Quorum Quenchers as Natural Biocides to Inhibit Sulfate-Reducing Bacteria

Sulfate-reducing bacteria (SRB) are one of the main protagonist groups of biocorrosion in the seawater environment. Given their principal role in biocorrosion, it remains a crucial task to develop strategies to reduce the abundance of SRBs. Conventional approaches include the use of biocides and antibiotics, which can impose health, safety, and environmental concerns. This review examines an alternative approach to this problem. This is achieved by reviewing the role of quorum sensing (QS) in SRB populations and its impact on the biofilm formation process. Genome databases of SRBs are mined to look for putative QS systems and homologous protein sequences representative of autoinducer receptors or synthases. Subsequently, this review puts forward the potential use of quorum quenchers as natural biocides against SRBs and outlines the potential strategies for the implementation of this approach

Valutazione della pericolosita' connessa alla lavorazione di rocce contenenti amianto: relazione tra indice di rilascio e analisi d'immagine

Il tema amianto riunisce dentro di sé numerosi aspetti che vanno da quello sociale a quello scientifico, passando inevitabilmente da quello legato alla salute delle persone. Nonostante l’estrazione dei minerali del gruppo dell’amianto sia vietata, in Italia, non è vietata l’estrazione e l’utilizzo di litotipi che possono contenere minerali asbestiformi nella loro struttura interna (vene). Questi materiali vengono utilizzati per una grande varietà di fini: pietrisco nella linea ferroviaria, asfalti, lastre, materiale inerte nelle discariche; Inoltre, la presenza di numerosi manufatti di Eternit ancora esistenti su tutto il territorio, rende questa tematica ancora più importante e delicata. I litotipi che contengono minerali di amianto e che vengono estratti ed utilizzati in Italia sono: • Basalti • Peridotiti • Gabbri Lo sfruttamento e l’estrazione di queste rocce può liberare in atmosfera le fibre dei minerali asbestiformi e quindi causare gravi patologie come asbestosi, cancro polmonare e mesotelioma pleurico. Dal punto di vista mineralogico l’amianto è un insieme di minerali composto dal gruppo degli Anfiboli (inosiicati) e dal gruppo dei Serpentini (fillosilicati) che differiscono per la natura chimica e la struttura cristallina, ma sono accumunati da una struttura ricca in fibre che crescono parallele all’asse di stress principale durante la deformazione in condizioni metamorfiche. Lo sfruttamento e l’estrazione di rocce contenenti questi minerali può liberare in atmosfera le fibre e quindi causare gravi patologie come asbestosi, cancro polmonare e mesotelioma pleurico. Per questo la legislazione Italiana ha stabilito, col DM 14/05/96, la caratterizzazione delle rocce contenti amianto mediante un indice di rilascio che dia indicazione della propensione delle rocce di liberare le fibre. L’indice di rilascio viene calcolato come rapporto tra la percentuale di fibre liberate durante il processo di automacinazione e la densità relativa percentuale del materiale in blocchi. Il Decreto Ministeriale impone come soglia di rischio determinato dallo sfruttamento di un determinato affioramento un indice di rilascio di 0,1; nel caso in cui il valore dell’indice risulti maggiore, l’affioramento non può essere sfruttato per gli scopi indicati in precedenza. La procedura per il calcolo dell’indice di rilascio risulta, però, piuttosto lunga e complicata e prevede di simulare la lavorazione della roccia attraverso l’automacinazione di una certa quantità di volume roccioso per poi misurare la quantità di fibre d’amianto che sono state liberate. Oltre alla non dimostrabilità che la prova di automacinazione riesca a simulare in maniera efficace la lavorazione della roccia, alcuni aspetti molto importanti vengono tralasciati, come quello riferito alla possibilità di rilascio di fibre durante il trasporto del materiale e del suo accatastamento durante le fasi di lavorazione. Il decreto, inoltre, non fornisce delle indicazioni esaustive circa la procedura e gli strumenti da utilizzare per ottenere l’indice di rilascio, rendendo difficile la confrontabilità di risultati ottenuti mediante procedure diverse. Da questo contesto prende spunto il seguente studio il cui obiettivo finale è quello di evidenziare una correlazione tra il valore dell’indice di rilascio riferito ad un affioramento e la stima della densità di fibre d’amianto in una sezione sottile derivante dallo stesso affioramento. A questo scopo sono stati selezionati alcuni affioramenti in Toscana dei quali è stato calcolato l’indice di rilascio nell’ambito del progetto CaMAm; le sezioni sottili provenienti dagli stessi affioramenti sono state analizzate, in questo studio, mediante un’analisi d’immagine, selezionando tutti gli elementi composti da minerali d’amianto per confrontare la densità in fibre d'amianto con i valori dell'indice di rilascio

Quorum Sensing and the Use of Quorum Quenchers as Natural Biocides to Inhibit Sulfate-Reducing Bacteria

Sulfate-reducing bacteria (SRB) are one of the main protagonist groups of biocorrosion in the seawater environment. Given their principal role in biocorrosion, it remains a crucial task to develop strategies to reduce the abundance of SRBs. Conventional approaches include the use of biocides and antibiotics, which can impose health, safety, and environmental concerns. This review examines an alternative approach to this problem. This is achieved by reviewing the role of quorum sensing (QS) in SRB populations and its impact on the biofilm formation process. Genome databases of SRBs are mined to look for putative QS systems and homologous protein sequences representative of autoinducer receptors or synthases. Subsequently, this review puts forward the potential use of quorum quenchers as natural biocides against SRBs and outlines the potential strategies for the implementation of this approach

Bacteriophage Infectivity Against Pseudomonas aeruginosa in Saline Conditions

Pseudomonas aeruginosa is a ubiquitous member of marine biofilm, and reduces thiosulfate to produce toxic hydrogen sulfide gas. In this study, lytic bacteriophages were isolated and applied to inhibit the growth of P. aeruginosa in planktonic mode at different temperature, pH, and salinity. Bacteriophages showed optimal infectivity at a multiplicity of infection of 10 in saline conditions, and demonstrated lytic abilities over all tested temperature (25, 30, 37, and 45°C) and pH 6–9. Planktonic P. aeruginosa exhibited significantly longer lag phase and lower specific growth rates upon exposure to bacteriophages. Bacteriophages were subsequently applied to P. aeruginosa-enriched biofilm and were determined to lower the relative abundance of Pseudomonas-related taxa from 0.17 to 5.58% in controls to 0.01–0.61% in treated microbial communities. The relative abundance of Alphaproteobacteria, Pseudoalteromonas, and Planococcaceae decreased, possibly due to the phage-induced disruption of the biofilm matrix. Lastly, when applied to mitigate biofouling of ultrafiltration membranes, bacteriophages were determined to reduce the transmembrane pressure increase by 18% when utilized alone, and by 49% when used in combination with citric acid. The combined treatment was more effective compared with the citric acid treatment alone, which reported ca. 30% transmembrane pressure reduction. Collectively, the findings demonstrated that bacteriophages can be used as a biocidal agent to mitigate undesirable P. aeruginosa-associated problems in seawater applications

Additional file 1: of Application of hierarchical oligonucleotide primer extension (HOPE) to assess relative abundances of ammonia- and nitrite-oxidizing bacteria

Target coverage for the different primers used in this study. (PDF 1668 kb

Image_9_Bacteriophage Infectivity Against Pseudomonas aeruginosa in Saline Conditions.TIF

<p>Pseudomonas aeruginosa is a ubiquitous member of marine biofilm, and reduces thiosulfate to produce toxic hydrogen sulfide gas. In this study, lytic bacteriophages were isolated and applied to inhibit the growth of P. aeruginosa in planktonic mode at different temperature, pH, and salinity. Bacteriophages showed optimal infectivity at a multiplicity of infection of 10 in saline conditions, and demonstrated lytic abilities over all tested temperature (25, 30, 37, and 45°C) and pH 6–9. Planktonic P. aeruginosa exhibited significantly longer lag phase and lower specific growth rates upon exposure to bacteriophages. Bacteriophages were subsequently applied to P. aeruginosa-enriched biofilm and were determined to lower the relative abundance of Pseudomonas-related taxa from 0.17 to 5.58% in controls to 0.01–0.61% in treated microbial communities. The relative abundance of Alphaproteobacteria, Pseudoalteromonas, and Planococcaceae decreased, possibly due to the phage-induced disruption of the biofilm matrix. Lastly, when applied to mitigate biofouling of ultrafiltration membranes, bacteriophages were determined to reduce the transmembrane pressure increase by 18% when utilized alone, and by 49% when used in combination with citric acid. The combined treatment was more effective compared with the citric acid treatment alone, which reported ca. 30% transmembrane pressure reduction. Collectively, the findings demonstrated that bacteriophages can be used as a biocidal agent to mitigate undesirable P. aeruginosa-associated problems in seawater applications.</p

Table_1_Bacteriophage Infectivity Against Pseudomonas aeruginosa in Saline Conditions.DOCX

<p>Pseudomonas aeruginosa is a ubiquitous member of marine biofilm, and reduces thiosulfate to produce toxic hydrogen sulfide gas. In this study, lytic bacteriophages were isolated and applied to inhibit the growth of P. aeruginosa in planktonic mode at different temperature, pH, and salinity. Bacteriophages showed optimal infectivity at a multiplicity of infection of 10 in saline conditions, and demonstrated lytic abilities over all tested temperature (25, 30, 37, and 45°C) and pH 6–9. Planktonic P. aeruginosa exhibited significantly longer lag phase and lower specific growth rates upon exposure to bacteriophages. Bacteriophages were subsequently applied to P. aeruginosa-enriched biofilm and were determined to lower the relative abundance of Pseudomonas-related taxa from 0.17 to 5.58% in controls to 0.01–0.61% in treated microbial communities. The relative abundance of Alphaproteobacteria, Pseudoalteromonas, and Planococcaceae decreased, possibly due to the phage-induced disruption of the biofilm matrix. Lastly, when applied to mitigate biofouling of ultrafiltration membranes, bacteriophages were determined to reduce the transmembrane pressure increase by 18% when utilized alone, and by 49% when used in combination with citric acid. The combined treatment was more effective compared with the citric acid treatment alone, which reported ca. 30% transmembrane pressure reduction. Collectively, the findings demonstrated that bacteriophages can be used as a biocidal agent to mitigate undesirable P. aeruginosa-associated problems in seawater applications.</p

Image_10_Bacteriophage Infectivity Against Pseudomonas aeruginosa in Saline Conditions.TIF

<p>Pseudomonas aeruginosa is a ubiquitous member of marine biofilm, and reduces thiosulfate to produce toxic hydrogen sulfide gas. In this study, lytic bacteriophages were isolated and applied to inhibit the growth of P. aeruginosa in planktonic mode at different temperature, pH, and salinity. Bacteriophages showed optimal infectivity at a multiplicity of infection of 10 in saline conditions, and demonstrated lytic abilities over all tested temperature (25, 30, 37, and 45°C) and pH 6–9. Planktonic P. aeruginosa exhibited significantly longer lag phase and lower specific growth rates upon exposure to bacteriophages. Bacteriophages were subsequently applied to P. aeruginosa-enriched biofilm and were determined to lower the relative abundance of Pseudomonas-related taxa from 0.17 to 5.58% in controls to 0.01–0.61% in treated microbial communities. The relative abundance of Alphaproteobacteria, Pseudoalteromonas, and Planococcaceae decreased, possibly due to the phage-induced disruption of the biofilm matrix. Lastly, when applied to mitigate biofouling of ultrafiltration membranes, bacteriophages were determined to reduce the transmembrane pressure increase by 18% when utilized alone, and by 49% when used in combination with citric acid. The combined treatment was more effective compared with the citric acid treatment alone, which reported ca. 30% transmembrane pressure reduction. Collectively, the findings demonstrated that bacteriophages can be used as a biocidal agent to mitigate undesirable P. aeruginosa-associated problems in seawater applications.</p