Biocorrosion induced by red-tide alga-bacterium symbiosis and the biofouling induced by dissolved iron for carbon steel in marine environment

• Self-promoted biofouling in seawater was detected for the first time. • P. tricornutum and B. altitudinis formed an active symbiotic system. • The symbiotic system facilitated the corrosion of carbon steel. • Dissolved corrosion products from steel activated the symbiotic system. The assemblages of unicellular microalgae and bacteria in phytoplankton communities can generally result in biodeterioration of metals in marine environment. In this study, the self-promoted biofouling mechanism underneath red-tide alga Phaeodactylum tricornutum and its symbiotic bacterium Bacillus altitudinis was systematically revealed. The mutualistic interaction of the bacteria and algae quadrupled the corrosion rate in comparison to the individual effect of the bacterium or algal strain alone. Reversely, the corroded metal appeared to be an accelerator that can stimulate the activity of the P. tricornutum and aggravate the biological pollution based on the result of 62.3% up-regulation of the key photosynthesis genes. The corrosion-biofouling-accelerated corrosion-deteriorated biofouling formed a vicious cycle.