Microbiologically influenced corrosion-more than just microorganisms.

Microbiologically influenced corrosion (MIC) is a phenomenon of increasing concern that affects various materials and sectors of society. MIC describes the effects, often negative, that a material can experience due to the presence of microorganisms. Unfortunately, although several research groups and industrial actors worldwide have already addressed MIC, discussions are fragmented, while information sharing and willingness to reach out to other disciplines are limited. A truly interdisciplinary approach, which would be logical for this material/biology/chemistry-related challenge, is rarely taken. In this review, we highlight critical non-biological aspects of MIC that can sometimes be overlooked by microbiologists working on MIC but are highly relevant for an overall understanding of this phenomenon. Here, we identify gaps, methods, and approaches to help solve MIC-related challenges, with an emphasis on the MIC of metals. We also discuss the application of existing tools and approaches for managing MIC and propose ideas to promote an improved understanding of MIC. Furthermore, we highlight areas where the insights and expertise of microbiologists are needed to help progress this field.

From laboratory tests to field trials: a review of cathodic protection and microbially influenced corrosion.

Cathodic protection (CP), an electrochemical method for managing corrosion, is widely used in many industries in both marine and buried environments. However, literature surrounding cathodic protection and its ability to prevent microbially influenced corrosion (MIC) is mixed. This review describes the mechanics of CP, how CP may influence MIC, and collates and summarises tests on CP and MIC reported in literature. The aim of the review is to identify any trends and knowledge gaps requiring further study. While the outcomes of CP testing are generally mixed, some trends can be seen and, overall, MIC is detrimental to the protective effects of CP, with CP being less effective when used according to current international standards. Tests conducted in the field or with mix communities of microbes showed that CP could be effective at preventing MIC, while tests with sulfate-reducing bacteria generally proved CP to be highly ineffective. It was commonly seen that the effectiveness of CP can be improved by increasing polarization, to potentials as low as -1000 mV (Ag/AgCl). However, a balance does need to be met via careful monitoring to ensure negative side effects of over protection do not become a major problem.

High Taxonomic Diversity in Ship Bilges Presents Challenges for Monitoring Microbial Corrosion and Opportunity To Utilize Community Functional Profiling.

One of the key areas in which microbially influenced corrosion (MIC) has been found to be a problem is in the bilges of maritime vessels. To establish effective biological monitoring protocols, baseline knowledge of the temporal and spatial biological variation within bilges, as well as the effectiveness of different sampling methodologies, is critical. We used 16S rRNA gene metabarcoding of pelagic and sessile bacterial communities from ship bilges to assess the variation in bilge bacterial communities to determine how the inherent bilge diversity could guide or constrain biological monitoring. Bilge communities exhibited high levels of spatial and temporal variation, with >80% of the community able to be turned over in the space of 3 months, likely due to disturbance events such as cleaning and maintenance. Sessile and pelagic communities within a given bilge were also inherently distinct, with dominant exact sequence variants (ESVs) rarely shared between the two. Taxa containing KEGG orthologies (KOs) associated with dissimilatory sulfate reduction and biofilm production, functions typically associated with MIC, were generally more prevalent in sessile communities. Collectively, our findings indicate that neither bilge water nor an unaffected bilge from within the same vessel would constitute an appropriate reference community for MIC diagnosis. Optimal sampling locations and strategies that could be incorporated into a standardized method for monitoring bilge biology in relation to MIC were identified. Finally, taxonomic and functional comparisons of bilge diversity highlight the potential of functional approaches in future biological monitoring of MIC and MIC mitigation strategies in general. IMPORTANCE Microbially influenced corrosion (MIC) has been estimated to contribute 20 to 50% of the costs associated with corrosion globally. Diagnosis and monitoring of MIC are complex problems requiring knowledge of corrosion rates, corrosion morphology, and the associated microbiology to distinguish MIC from abiotic corrosion processes. Historically, biological monitoring of MIC utilized a priori knowledge to monitor sulfate-reducing bacteria; however, it is becoming widely accepted that a holistic or community-level understanding of corrosion-associated microbiology is needed for MIC diagnosis and monitoring. Before biology associated with MIC attack can be identified, standardized protocols for sampling and monitoring must be developed. The significance of our research is in contributing to the development of robust and repeatable sampling strategies of bilges, which are required for the development of standardized biological monitoring methods for MIC. We achieve this via a biodiversity survey of bilge communities and by comparing taxonomic and functional variation.

An efficient, cost-effective method for determining the growth rate of sulfate-reducing bacteria using spectrophotometry.

The use of sulfate reducing bacteria (SRBs) in laboratory studies is a common approach for investigating microbially influenced corrosion (MIC). The characteristic formation of black iron sulfide precipitates during SRB growth, however, preclude the use of traditional spectrophotometric approaches for capturing growth data instead necessitating labour-intensive or technically specialized approaches. As such, an understanding of SRB growth responses to experimental conditions is often missing from MIC studies. Bernardez and de Andrade Lima (2015) have outlined a spectrophotometric approach for estimating SRB cell mass via the addition of HCl. This method has potential for the study SRB growth however its applicability is currently limited by the use of large aliquot volumes (45 mL), which restrict the number of timepoints that can sampled from one culture, and the extensive time devoted to cell preparation prior to OD readings. •We demonstrate an improved method for capturing SRB growth data via spectrophotometry following acidification. We incorporate lower sample volumes and adapt the method described in Bernardez and de Andrade Lima (2015) to a high throughput microtiter plate approach that increases the efficiency of this method and its applicability to growth rate studies.•Our results allay theoretical concerns that acidification may distort growth rate analysis by impacting cells differently depending on their metabolic state.•We further demonstrate that this method (acid-amended OD measurements) is more accurate and far more cost efficient than traditional methods (dilution spread-plate counting) and popular molecular methods (quantitative PCR) currently in use in SRB growth research.

Influence of carbon steel grade on the initial attachment of bacteria and microbiologically influenced corrosion.

The influence of the composition and microstructure of different carbon steel grades on the initial attachment (≤ 60 min) of Escherichia coli and subsequent longer term (28 days) corrosion was investigated. The initial bacterial attachment increased with time on all grades of carbon steel. However, the rate and magnitude of bacterial attachment varied on the different steel grades and was significantly less on the steels with a higher pearlite phase content. The observed variations in the number of bacterial cells attached across different steel grades were significantly reduced by applying a fixed potential to the steel samples. Longer term immersion studies showed similar levels of biofilm formation on the surface of the different grades of carbon steel. The measured corrosion rates were significantly higher in biotic conditions compared to abiotic conditions and were found to be positively correlated with the pearlite phase content of the different grades of carbon steel coupons.

The effect of metal microstructure on the initial attachment of Escherichia coli to 1010 carbon steel.

Metallurgical features have been shown to play an important role in the attachment of microorganisms to metal surfaces. In the present study, the influence of the microstructure of as-received (AR) and heat-treated (HT) 1010 carbon steel on the initial attachment of bacteria was investigated. Heat treatment was carried out with the aim of increasing the grain size of the carbon steel coupons. Mirror-polished carbon steel coupons were immersed in a minimal medium inoculated with Escherichia coli (ATCC 25922) to investigate the early (15, 30 and 60 min) and relatively longer-term (4 h) stages of bacterial attachment. The results showed preferential colonisation of bacteria on the grain boundaries of the steel coupons. The bacterial attachment to AR steel coupons was relatively uniform compared to the HT steel coupons where an increased number of localised aggregates of bacteria were found. Quantitative analysis showed that the ratio of the total number of isolated (i.e., single) bacteria to the number of bacteria in aggregates was significantly higher on the AR coupons than the HT coupons. Longer-term immersion studies showed production of extracellular polymeric substances by the bacteria and corrosion at the grain boundaries on both types of steel coupon tested.

Fiber Bragg grating tether used to measure drag forces in neutral buoyancy flow tank tests.

The drag exerted on neutrally buoyant tethered spheres in a flow tank was measured as a function of flow rate. A unique solution to the problem was achieved using an optical fiber including a Bragg grating sensor as part of the tether. Measurements of the strain on the tether taken at flow rates between 0.14 and 0.33 m/s, were used to determine drag forces for spheres with diameters ranging from 40 to 100 mm. Vortex-induced vibration was observed in tests performed at Reynolds numbers from 5 x 10(3) to 4.5 x 10(4). The drag coefficients for these tests were found to range from 0.51 to 0.77.

Strain-independent temperature measurement by use of a fluorescence intensity ratio technique in optical fiber.

The strain sensitivity of the fluorescence intensity ratio temperature-sensing technique has been measured to be (2 +/- 3) x 10(-4)%/muepsilon in Yb3+-doped fiber, implying a temperature-to-strain cross sensitivity of (2 +/- 3) x 10(-4) degrees C/muepsilon. The near-zero strain sensitivity means that this optical-fiber sensor technique is well suited for temperature measurement in strain-affected environments.

Self-referenced point temperature sensor based on a fluorescence intensity ratio in Yb(3+)-doped silica fiber.

An optical fiber temperature sensor, based on the fluorescence intensity ratio from the (2)F (5/2)(a) and (2)F(5/2)(b) Stark sublevels in ytterbium-doped silica fiber, has been investigated. Results of a sensor prototype demonstrate an accuracy near 1 degrees C in a 600 degrees C temperature range. Changes in the fluorescence intensity ratio because of variation in pump power, pump wavelength, and induced fiber bending loss are demonstrated to be small, supporting development of a practical sensor based on the technique described.

Influence of vascular and lumen flow on sodium movements across anuran intestine in vitro.

There is a positive linear relation between the vascular flow rate and the magnitudes of the unidirectional fluxes of Na in either direction in the steady state across the small intestine of the frog. Both unidirectional Na fluxes increase to the same extent with an increase in vascular flow so there is no apparent effect of flow on net Na movement. Raising the vascular flow rate in individual experiments increases the lumen-blood Na flux proportionately, but reducing the flow from an initially high value reduces the lumen-blood flux only slowly at first then more rapidly. The unidirectional Na fluxes increase linearly as the lumen flow rate is increased. In the colon increasing the vascular flow rate also increases the lumen-blood Na flux but changing the vascular flow rate has little effect on the blood-lumen flux, the net absorption of Na is invariably increased as the vascular flow increases. Using 14C-labelled sucrose as a marker for the extracellular space of the small intestine, it can be shown that the increases in Na flux found with increased vascular flow rates are associated with an increase in this sucrose space. An increase in sucrose space, therefore, seems to enhance the accessibility of the low resistance, paracellular pathways for Na to and from the blood across the epithelium.

Sodium movements across the vascularly perfused anuran small intestine and colon.

Values of unidirectional Na fluxes measured across the vascularly perfused small intestine of three anuran species are higher than those found in other preparations in vitro. In Rana ridibunda and R. pipiens no net movement of Na across the small intestine can be detected. In contrast, the unidirectional fluxes of Na across the colon of R. ridibunda and R. pipiens are lower than across the small intestine and a significant net absorption is found. Apparent loading and unloading pools for Na within the small intestine, as measured with tracer Na under standard experimental conditions, consist largely of extracellular Na presumably within the bulk phase of the lumen. The size of these pools can be greatly reduced by the rapid addition to or removal from the lumen of tracer. The loading pool appears to occupy not more than about 9% of the total tissue water, equivalent to about 20% of the extracellular water of the tissue. The washout of tracer Na from preloaded small intestine into the vascular bed is bi-exponential and appears from a pool, or pools, of apparent greater size than that of the loading pool. The results show that Na can move very rapidly across the small intestine and suggest that a high proportion of this movement occurs possibly via paracellular shunt pathways.