Evaluation of the Different Nutritional and Environmental Parameters on Microbial Pyrene Degradation by Mangrove Culturable Bacteria

Abstract

Mangrove ecosystems play curial roles in providing many ecological services and alleviating global climate change. However, they are in decline globally, mainly threatened by human activities and global warming, and organic pollutants, especially PAHs, are among the crucial reasons. Microbial remediation is a cost-effective and environmentally friendly way of alleviating PAH contamination. Therefore, understanding the effects of environmental and nutritional parameters on the biodegradation of polycyclic aromatic hydrocarbons (PAHs) is significant for the bioremediation of PAH contamination. In the present study, five bacterial strains, designated as Bp1 (Genus Rhodococcus), Sp8 (Genus Nitratireductor), Sp13 (Genus Marinobacter), Sp23 (Genus Pseudonocardia), and Sp24 (Genus Mycolicibacterium), have been isolated from mangrove sediment and their ring hydroxylating dioxygenase (RHD) genes have been successfully amplified. Afterward, their degradation abilities were comprehensively evaluated under normal cultural (monoculture and co-culture) and different nutritional (tryptone, yeast extract, peptone, glucose, sucrose, and NPK fertilizer) and environmental (cetyl trimethyl ammonium bromide (CTAB), sodium dodecyl sulfate (SDS)) parameters, as well with different co-contaminants (phenanthrene and naphthalene) and heavy metals (Cd²⁺, Cu²⁺, Fe³⁺, Ni²⁺, Mg²⁺, Mn²⁺, and Co²⁺). The results showed that strain Sp24 had the highest pyrene degradation rate (85%) in the monoculture experiment after being cultured for 15 days. Adding nitrogen- and carbon-rich sources, including tryptone, peptone, and yeast extract, generally endorsed pyrene degradation. In contrast, the effects of carbon sources (glucose and sucrose) on pyrene degradation were distinct for different bacterial strains. Furthermore, the addition of NPK fertilizer, SDS, Tween-80, phenanthrene, and naphthalene enhanced the bacterial abilities of pyrene removal significantly (p < 0.05). Heavy metals significantly reduced all bacterial isolates' degradation potentials (p < 0.05). The bacterial consortia containing high bio-surfactant-producing strains showed substantially higher pyrene degradation. Moreover, the consortia of three and five bacterial strains showed more degradation efficiency than those of two bacterial strains. These results provide helpful microbial resources for mangrove ecological remediation and insight into optimized culture strategies for the microbial degradation of PAHs.

Keywords: co-contamination; co-culture; degradation; heavy metals; nutrient supplements; pyrene.

Figure 1

Pyrene degradation by individual bacterial strains. The % degradation of each bacterial strain is the subtracted value of “pyrene lost in experimental group–abiotic pyrene lost in the negative control group” at the corresponding time. The error bar represents the standard deviation.

Figure 2

Effect of additional nutrient sources on pyrene degradation: (A) tryptone, (B) yeast extract, (C) peptone, (D) glucose, and (E) sucrose. The % pyrene degradation represents the subtracted value of “pyrene lost in experimental group–abiotic pyrene lost in the negative control group”. The +Ve CRTL represent pyrene degradation by the corresponding strains without the addition of supplementary carbon and nitrogen source. The error bar represents the standard deviation.

Figure 3

Effect of surfactant on pyrene degradation. The % pyrene degradation represents the subtracted value of “pyrene lost in experimental group–abiotic pyrene lost in the negative control group”. The +Ve CRTL represents pyrene degradation by the corresponding bacterial strains without the addition of surfactants. The error bar represents the standard deviation.

Figure 4

Effect of heavy metal on pyrene degradation: (A) Pb²⁺, (B) Cu²⁺, (C) Zn²⁺, (D) Mn²⁺, (E) Mg²⁺, (F) Co²⁺, and (G) Fe³⁺. The % pyrene degradation represents the subtracted value of “pyrene lost in experimental group–abiotic pyrene lost in the negative control group”. The +Ve CRTL represents pyrene degradation by the corresponding bacterial strains without the addition of heavy metals. The error bar represents the standard deviation.

Figure 5

Pyrene degradation in the presence of low molecular weight phenanthrene and naphthalene provided with a concentration of 50 mg/L. The % pyrene degradation represents the subtracted value of “pyrene lost in experimental group–abiotic pyrene lost in the negative control group”. The +Ve CRTL represents pyrene degradation by the corresponding bacterial strains without the addition of phenanthrene and naphthalene. The error bar represents the standard deviations.

Figure 6

Effect of different NPK fertilizer concentrations on pyrene degradation. The % pyrene degradation represents the subtracted value of “pyrene lost in experimental group–abiotic pyrene lost in the negative control group.” The +Ve CRTL represents pyrene degradation by the corresponding bacterial strains without the addition of NPK fertilizer. The error bar represents the standard deviation.

Figure 7

Correlation analysis between bacterial cell growth in terms of OD values and % degradation of pyrene.

Figure 8

Pyrene degradation by the consortia of two, three, and five bacterial strains of the study isolates. Full (100%) degradation was considered for the treatment in which no pyrene was detected in the HPLC analysis. The % pyrene degradation represents the subtracted value of “pyrene lost in experimental group–abiotic pyrene lost in the negative control group”. The error bar represents the standard deviation.