Abstract
Polycyclic aromatic hydrocarbons (PAHs) pollutions often occur in marine and other saline environment, largely due to anthropogenic activities. However, study of the PAHs-degradation genotypes in halophiles is limited, compared with the mesophilic terrestrial PAHs degraders. In this study, a bacterial consortium (CY-1) was enriched from saline soil contaminated with crude oil using phenanthrene as the sole carbon source at 10% salinity. CY-1 was dominated by the moderate halophilic Marinobacter species, and its dominant PAHs ring-hydroxylating dioxygenase (RHD) genotypes shared high identity to the classic nah-related RHDs found in the mesophilic species. Further cloning of a 5.6-kb gene cluster from CY-1 unveiled the existence of a new type of PAHs degradation gene cluster (hpah), which most probably evolves from the nah-related gene clusters. Expression of the RHD in this gene cluster in E. coli lead to the discovery of its prominent salt-tolerant properties compared with two RHDs from mesophiles. As a common structural feature shared by all halophilic and halotolerant enzymes, higher abundance of acidic amino acids was also found on the surface of this RHD than its closest nah-related alleles. These results suggest evolution towards saline adaptation occurred after horizontal transfer of this hpah gene cluster into the halophiles.
Highlights
Are expected to be existed in saline environments and their molecular mechanisms to salt adaption remain to be investigated
The presence of the nah gene clusters in the coastal marine environment makes it possible to study nah genes transfer between the terrestrial and marine lineages, as suggested by the pahAc fragment discovered in Marinobacter sp
We identified nah-related Polycyclic aromatic hydrocarbons (PAHs) dioxygenases as the dominant genotype in a halophilic phenanthrene-degrading bacterial consortium (CY-1), which is dominated by Marinobacter species
Summary
Polycyclic aromatic hydrocarbons (PAHs) pollutions often occur in marine and other saline environment, largely due to anthropogenic activities. As a common structural feature shared by all halophilic and halotolerant enzymes, higher abundance of acidic amino acids was found on the surface of this RHD than its closest nah-related alleles These results suggest evolution towards saline adaptation occurred after horizontal transfer of this hpah gene cluster into the halophiles. We identified nah-related PAHs dioxygenases as the dominant genotype in a halophilic phenanthrene-degrading bacterial consortium (CY-1), which is dominated by Marinobacter species. Further efforts were made to characterize the property of the PAHs dioxygenase in this halophilic consortium and explore the evolution scenario of the new pah gene cluster in this consortium To date, this is the first report on cloning and overexpression of a halotolerant nah-like dioxygenase and prediction of horizontal transfer of nah-like gene clusters between halophilic and non-halotolerant bacteria
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