Biological treatment of complex saline phenolic wastewater remains a great challenge due to the low activity of bacterial populations under stressful conditions. Acid mine drainage (AMD) as a typically extreme environment, shaped unique AMD microbial communities. Microorganisms survived in the AMD environment have evolved various mechanisms of resistance to low pH, high salinity and toxic heavy metals. The primary goal of this work was to determine whether a strain isolated from an AMD could degrade phenol under stressful conditions such as low pH, high salinity and heavy metals. The results suggested that the strain Cobetia sp. SASS1 isolated from AMD presented different physiological characteristics in comparison with five most closely related species. SASS1 can efficiently degrade phenol at wide ranges of pH (3.0–9.0) and NaCl concentration (0–40 g/L), as well as the existence of Cu2+ and Mn2+. Specifically, the SASS1 could completely degrade 1500 mg/L phenol in 80 h at 10 g/L NaCl. Meanwhile, mineralization of phenol was achieved with complete degradation of 900 mg/L phenol and simultaneously COD decreasing from 2239 mg/L to 181.6 mg/L in 36 h. Based on biodegradation metabolites identification and enzyme activities analysis, both ortho-cleavage pathway and benzoic acid pathway for phenol degradation were proposed. These findings suggested that SASS1 was an efficient phenol degrader under salinity and acidic conditions, and could be considered as key population for bioremediation of industrial phenolic wastewaters under stressful conditions.
Microbial degradation plays an important role in the environmental remediation. However, most microorganisms’ pollutant-degrading capability is weakened due to their entry into a viable but non-culturable (VBNC) state. Despite there is some evidence for the VBNC state of pollutant-degrading bacteria, limited studies have been conducted to investigate the VBNC state of pollutant degraders among fungi. In this work, the morphological, physiological and molecular changes of a phenol-degrading yeast strain LN1 exposed to high phenol concentrations were investigated. The results confirmed that Candida sp. strain LN1, which possessed highly efficient capability in degrading 1000 mg/L of phenol, as well as high potential for aromatic compounds degradation, entered into the VBNC state after 14 h of incubation at 6000 mg/L phenol. Resuscitation of VBNC cells can restore their phenol degradation performance. Compared to normal cells, significant dwarfing, surface damage and physiological changes of VBNC cells were observed. Molecular analysis indicated that the down-regulated genes were related to oxidative stress response, xenobiotics degradation, carbohydrate and energy metabolism, whereas the up-regulated genes were related to RNA polymerase, amino acid metabolism, DNA replication and repair. This report revealed that a pollutant-degrading yeast strain entered into the VBNC state under high concentrations of contaminants, providing new insights into its survival status and bioremediation potential under stress. Importance The viable but non-culturable (VBNC) state is known to affect the culturability and activity of microorganisms. However, limited studies have been conducted to investigate the VBNC state of other pollutant degraders such as fungi. In this study, the VBNC state of a phenol-degrading yeast strain was discovered. In addition, comprehensive analysis of the morphological, physiological and molecular changes of the VBNC cells were performed. This study provides new insight into the VBNC state of pollutant degraders, and how they restored the activities that was inhibited by stressful conditions. Enhanced bioremediation performance of indigenous microorganisms could be expected by preventing and controlling the formation of VBNC state.
A group of secreted proteins from M. luteus, recognized as resuscitation promoting factors (Rpf) can resuscitate the viable but non-culturable (VBNC) state bacteria which have the potential function of environmental bioremediation.
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