From laminar to turbulent: how methanogen and srb mic pathways shape their response to flow dynamics

npj | materials degradation Article Published in partnership with CSCP and USTB https://doi.org/10.1038/s41529-026-00795-8 From laminar to turbulent: how methanogen and srb mic pathways shape their response to flow dynamics Check for updates 1,4 1,4 2 2 3 1234567890():,; 1234567890():,; Eric Deland , Sara Taghavi Kalajahi , Fábio M. Carvalho , Luciana C. Gomes , Torben Lund Skovhus , Filipe Mergulhão2 & Andrea Koerdt1 Hydrodynamic conditions play a central role in microbiologically influenced corrosion (MIC) by regulating nutrient transport, metabolite removal, shear stress, and biofilm stability. As industrial systems operate across laminar and turbulent flow regimes, understanding MIC under controlled hydrodynamics is essential. In this study, the corrosion behavior of carbon steel was examined in the presence of Methanobacterium aff. IM1 and Desulfovibrio ferrophilus IS5 under laminar and turbulent flow. Corrosion rates were quantified by weight loss, and surface morphology was characterized using microscopy and tomography. Flow regime significantly influenced corrosion behavior for both microorganisms. Turbulent flow increased corrosion rates compared to laminar and abiotic controls, with Methanobacterium aff. IM1 exhibiting the highest overall corrosivity. Biotic conditions promoted more severe localized corrosion, with the deepest and widest pits observed for Methanobacterium aff. IM1. Under turbulent flow, Desulfovibrio ferrophilus IS5 developed significantly thicker and more heterogeneous biofilm–corrosion layers, whereas Methanobacterium aff. IM1 exhibited corrosion layers of comparable thickness to abiotic samples but with markedly increased surface roughness. These results demonstrate that biofilm thickness alone does not reflect corrosion severity and identify hydrodynamic regime as a key driver of MIC intensity and morphology. Microbiologically influenced corrosion (MIC) refers to a phenomenon in which microorganisms affect the corrosion process, either indirectly through produced metabolites or directly through electron uptake from the metal surface1. MIC can significantly compromise the integrity of industrial assets by initiating and/or accelerating material degradation once microorganisms establish biofilms on metal surfaces, leading to substantial economic losses and environmental risks2. To develop, validate, and implement new materials and effective mitigation strategies against MIC, it is essential to accurately predict corrosion rates under conditions that realistically reflect microbial activity and environmental constraints. Among the environmental parameters influencing MIC, hydrodynamics play a particularly complex role3. Industrial systems such as pipelines, cooling circuits, and offshore structures are continuously exposed to flow regimes ranging from laminar to turbulent, which highlights the need to investigate MIC under controlled hydrodynamic conditions. Biofilm development follows a dynamic life cycle (attachment, microcolony formation, maturation, and dispersion), and each step can be modulated by hydrodynamic forces and microbial responses mediated through extracellular polymeric substances (EPS)4,5. Pan et al., 20226 showed that under laminar flow, biofilms developed as thick but loosely structured layers with pronounced heterogeneity. EPS, particularly soluble EPS (S-EPS), were relatively abundant and more uniformly distributed throughout the biofilm, while loosely bound (LB-EPS) and tightly bound EPS (TB-EPS) accumulated more slowly. This loose structure made biofilms more susceptible to detachment at later growth stages. In contrast, turbulent flow promoted the formation of thin, dense, and mechanically stable biofilms capable of resisting shear stress. Turbulent conditions significantly increased total EPS production, with enhanced accumulation of LB-EPS and TB-EPS, which strengthened cell–cell aggregation and surface adhesion. Extracellular polysaccharides preferentially enveloped cells and proteins, contributing to a compact biofilm matrix that minimized detachment Bundesanstalt für Materialforschung und -prüfung (BAM), Berlin, Germany. 2LEPABE – Laboratory for Process Engineering, Environment, Biotechnology and Energy, ALiCE – Associate Laboratory in Chemical Engineering, Faculty of Engineering, University of Porto, Porto, Portugal. 3Research Centre for Built Environment, Climate and Water Technology, VIA University College, Horsens, Denmark. 4These authors contributed equally: Eric Deland, Sara Taghavi Kalajahi. e-mail: 1 npj Materials Degradation | (2026)10:56 1 Article https://doi.org/10.1038/s41529-026-00795-8 despite elevated shear forces. Overall, increasing shear stress shifted biofilm development toward higher EPS investment and structural compactness, highlighting the active role of hydrodynamics in shaping biofilm stability and resilience. Because biofilms play a central role in MIC1, changes in flow regime that alter microbial metabolism and biofilm architecture can directly affect MIC, corrosion rate, and the composition of corrosion products on metal surfaces. Liduino et al.7,8, examined how laminar and turbulent flow regimes affect MIC behaviour of welded carbon steel in dynamic seawater systems. Laminar flow promoted rapid oxygen depletion and the establishment of anaerobic, sulfate-reducing bacteria (SRB), leading to high sulfide production and deep localized pitting, particularly in heat-affected zones. In contrast, turbulent flow altered microbial community structure, limited sulfide accumulation, and reduced pit depth, while increasing pit density in hydrodynamically sheltered regions. Similar results were reported by Liu et al.5, who investigated the influence of fluid flow on microbial community development on X70 steel exposed to oilfield produced water. A low flow velocity of 0.2 m s⁻¹ promoted thicker biofilms, higher corrosion rates, and deep, narrow pits, whereas a higher flow velocity of 1.0 m s⁻¹ inhibited biofilm persistence, reduced overall corrosion severity, and produced wider, shallower pits. Together, these findings demonstrate that hydrodynamic regime controls microbial community structure, corrosion rate, and pit morphology by regulating biofilm stability at the metal surface. Moreover, single-species biofilms have been shown to alter their metabolism in response to shear stress, dissipating more energy and strengthening the binding of adhesive proteins involved in surface attachment when formed under higher shear9. Such adaptive responses indicate that microorganisms can sense and actively respond to hydrodynamic stress. These observations underscore the importance of assessing MIC across varying hydrodynamic regimes and microbial functional groups, as differences in corrosion behavior are closely linked to strain-specific MIC mechanisms. MIC mechanisms are now broadly classified into two categories: (i) metabolite-mediated MIC (M-MIC), driven by corrosive metabolic products such as sulfide or organic acids, and (ii) e (...truncated)