Development of Rhizophora mangle (Rhizophoraceae) and Avicennia schaueriana (Avicenniaceae) in the presence of a hydrocarbon-degrading bacterial consortium and marine diesel oil

The development of Rhizophora mangle and Avicennia schaueriana seedlings impacted by marine diesel oil (MDO) was evaluated in the presence or absence of a hydrocarbon-degrading bacterial consortium (HBC). The bioassays were conducted in a greenhouse during 6 months and consisted of three different treatments (control, MDO only and MDO + HBC). The bacterial consortium was mainly composed of Bacillus spp. (73%), but Rhizobium spp., Pseudomonas spp., Ochrobactrum spp., and Brevundimonas spp. were also present. After 6 months, A. schaueriana seedlings showed higher mortality compared to those of R. mangle; R. mangle exhibited 68% (control), 44% (MDO alone) and 50% (MDO + HBC) seedlings survivorship compared to 42% (control), 0% (MDO alone) and 4% (MDO + HBC) for A. schaueriana. This variability may be due to differences in species physiology. Stem growth, diameter and number of leaves remained constant during the 6 months of the experiment with marine diesel oil and hydrocarbon-degrading bacterial consortium (MDO + BBC). For both mangrove species, bacterial enzymatic activity in the sediments was sufficient to maintain cell counts of 107 cells cm−3 in the rhizospheric soil and possibly synthetize the extracellular polymeric substances (EPS) that may emulsify and solubilize oil products.