Marine bacteria inhibit corrosion of steel via synergistic biomineralization

Metal corrosion often results in incalculable economic loss and significant safety hazards. Although numerous traditional methods have been used to mitigate the issue, such as coating and corrosion inhibitors, they are environmentally unfriendly and difficult to maintain. Therefore, in this study, an environmental approach was taken to protect steels from corrosion in a multi-species bacterial environment via synergistic biomineralization. The marine bacterium Pseudoalteromonas lipolytica mixed with Bacillus subtilis or Pseudomonas aeruginosa strains offered extraordinary corrosion protection for steel.The surface characterization and electrochemical tests showed that the biomineralized film generated by the mixed bacteria was more compact and protective than that induced by a single bacterium. Herein,we found that the synergistic mechanisms were rather different for the different bacterial groups. For Pseudoalteromonas lipolytica and Bacillus subtilis group, the related mechanisms were due to the increase of pH in the medium, secretion of carbonic anhydrase. As for Pseudoalteromonas lipolytica and Pseudomonas aeruginosa group, the synergistic mechanism was attributed to the inhibiting corrosive bacteria in biofilm by the growth advantage of Pseudoalteromonas lipolytica. Therefore, this study may introduce a new perspective for future use of biomineralization in a real marine environment.

Antagonism between coral pathogen Vibrio coralliilyticus and other bacteria in the gastric cavity of scleractinian coral Galaxea fascicularis

Scleractinian corals host numerous microbial symbionts with different types of interactions. The gastric cavity of scleractinian coral, as a semiclosed subenvironment with distinct chemical characteristics(e.g., dissolved O2, pH, alkalinity, and nutrients), harbors a distinct microbial community and a diverse array of bacteria that can be pathogenic or beneficial. Galaxea fascicularis is one of the dominant massive scleractinian coral species on inshore fringing reefs in the northern South China Sea.Although the abundance of coral-associated bacteria has been investigated in G. fascicularis, less is known about the microorganisms in the gastric cavity. In this study, we specially isolated cultivable bacterial strains from the gastric cavity of G.fascicularis collected from Hainan Island using a noninvasive sampling approach. Among the 101 representative bacterial strains, one Vibrio coralliilyticus strain, SCSIO 43001, was found to be a temperature-dependent opportunistic pathogen of G.fascicularis. The antagonistic activity between the 100 strains and V. coralliilyticus SCSIO 43001 was tested using a modified Burkholder diffusion assay. Our results showed that V. coralliilyticus SCSIO 43001 inhibits the growth of Erythrobacter flavus and Sphingomonas yabuuchiae. Additionally, we found that three Pseudoalteromonas strains showed moderate to high antibacterial activity against V. coralliilyticus SCSIO 43001 and several other coral-associated Gram-negative bacterial strains.These results suggest that competition between the coral pathogen and other bacteria also occurs in the gastric cavity of coral, and Pseudoalteromonas strains in the gastric cavity of G. fascicularis may provide a protective role in the defense against coinhabiting coral pathogens at elevated temperature.