IMPACTS OF OCEAN ACIDIFICATION ON BACTERIAL COMMUNITIES IN COASTAL MICROBIAL BIOFILMS

Microbial biofilms can positively or negatively affect the coastal ecosystems by several means. Microorganisms in biofilm can remove contaminants, such as oil spills, nitrogen compounds, metals and radio nuclides, through bioremediation. They also serve as underwater matrixes producing chemical and biological cues to trigger larval settlement of a number of marine invertebrate species. The formation and dynamics of marine biofilms are also determined by multiple environmental factors. We are particularly interested in the influences of acidified marine water caused by increased atmospheric CO₂ to the marine biofilms.

The CO₂ concentration in atmosphere has been dramatically increased since industrial revolution due to the anthropogenic activities in energy consumption. It results in the considerably decreased pH in marine water, which consequently effects the ecosystems in the ocean. Here we conducted a study in understanding the dynamic changes of the marine biofilms associated with the CO₂ initiated ocean acidification. The natural sea water from the coast of Louisiana was collected and maintained in the laboratory conditions. The formation of microbial biofilms was controlled under ambient (400 ppm, p400) and increased (1,000 ppm, p1000) paCO₂ levels in the atmosphere. Structures of the biofilms generated under stresses of the two paCO₂ levels were visualized with scanning electron microscopy (SEM). Bacterial populations from different biofilms were also characterized with BIOLOG analyses. The result demonstrated a significant difference in overall bacterial communities between the biofilms in ambient paCO₂ and increased paCO₂ conditions (A). Utilizations of organic compounds, such as 4-Hydroxy benzoic acid, putrescine, D-Malic acid, and D-Xylose were significantly increased by biofilms in p1000 compared to p400 (B and C), which suggested that paCO₂ level dramatically influenced the metabolic activities of bacteria in the biofilm. Characterization of bacterial communities in the biofilms was also performed using terminal restriction fragment length polymorphism (TRFLP) and denaturation gradient gel electrophoresis (DDGE).

Further studies on the paCO₂ stimulated marine biofilm alterations to the costal ecosystems are highly desired for the restoration of coastal ecosystem and resources of fisheries and aquaculture.