Two specific cases of applying molecular techniques for deciphering the role of microorganisms
in industrial processes are presented: an offshore seawater injection system and a wastewater treatment
plant. In the first case, deoxyribonucleic acid (DNA) was extracted from a water sample taken from an
offshore seawater injection system and from enrichment cultures from the same sample. The V3
hypervariable region of the 16S rDNA gene was amplified by the polymerase chain reaction (PCR) and
bacterial diversity was studied using denaturing gel gradient electrophoresis (DGGE). DGGE
monitoring of the system showed that persistent bacteria were present, mainly facultative anaerobic
bacteria as Shewanella and Vibrio. These bacteria are also suspected to resist the biocide treatment used
in this system. A second case was based on a study of wastewater treatment plants where massive
sulfide production generally occurs during organic matter mineralization.