The Effect of Organic Carbon Addition on the Community Structure and Kinetics of Microcystin-Degrading Bacterial Consortia

Abstract

Microcystin (MC), a hepatotoxin that is associated with cyanobacterial blooms in freshwater lakes, threatens the quality of drinking water resources. Biodegradation of MC using biofiltration is emerging as a cost-effective solution for drinking water treatment. This study reports isolation of five MC-degrading microbial consortia and investigation of their community structure and kinetics in the presence or absence of a readily-bioavailable organic carbon source. The results indicated that the presence of a bioavailable organic carbon source caused: (1) the proliferation of community members previously unobserved in each consortium cultured without ethanol; (2) a shift in abundance of representative taxa; (3) a fluctuation in genera affiliated with MC-biodegradation; and, (4) a unique response in simulated diversity among consortia. These changes to each microbial consortium were paralleled by a significant decline in MC degradation kinetics. Overall, this study highlights the importance of integrating environmental conditions into the design and operation of biofiltration systems for MC biodegradation.Previous studies have demonstrated the complete biodegradation of MC-LR within laboratory scale biofiltration systems following a preliminary lag phase of removal [14][15][16][17]. However, the toxin removal efficiency and extent of this lag phase can vary significantly with bacterial composition, nutrient concentration, and other environmental parameters that are associated with the source water. Efforts to evolve biofiltration from a passive process into a more standardized, controlled, and perhaps "engineered", biological treatment process for targeted removal of pollutants will require a better understanding of the physiology and genetics of MC-degrading bacteria [12][13][14][18][19][20].Significant efforts have been made to isolate and characterize the specific MC-degrading bacterial populations during algal bloom events in the source water and sediments, and from full scale biological treatment units in drinking water treatment facilities [7][8][9]17,[21][22][23][24]. However, these studies have not fully explored how these isolates function in mixed bacterial communities, nor the influences of mutualistic or antagonistic interactions on biodegradation kinetics. Several previous studies, however, have considered the effects of environmental stimuli (i.e., varying organic carbon concentrations) on MC-degrading bacterial consortia under aerobic conditions [7,8,23,[25][26][27][28][29]. Research showed that addition of organic carbon sources (i.e., glucose, acetate, or uncharacterized dissolved organic carbon (DOC)) significantly inhibits MC degradation kinetics of bacterial consortia [7,23,25,29]. Catabolite repression is postulated as a mechanism underlying this inhibition, where MC-degrading populations may prefer more energetically-favorable (easily metabolized) over more energetically-intensive substrates, such as MC [30]. Other (fewer) studies have demonstrated that the addition of an alternative organic ca...

A Mini Review on Microcystins and Bacterial Degradation

“…and Steroidobacter sp. from drinking water reservoir in Southern California [126] successfully indicated complete MC-LR degradation. Moreover bacterial community isolated from natural waters with previous cyanobacterial contamination was noted to entirely removal MC-LR without lag phase, however, the composition of the bacterial community was not analyzed [134].…”

Gut Microbiota of Freshwater Gastropod (Bellamya aeruginosa) Assist the Adaptation of Host to Toxic Cyanobacterial Stress

“…The presence of MCs may be responsible for this contrasting outcome of intestinal microbiota succession between the two groups. Some Pseudomonas species and Ralstonia species have been reported to degrade MCs [38,39]. MCs, as an intracellular toxin, are released only after cell death or damage accompanied with cell structure disruption [40].…”

“…Many studies have found that host exposure to environmental stresses, such as toxic exposure and dietary alterations, does lead to more nodes or more complex interactions of gut flora and even to shifts in the positive and negative relationships between some key bacteria and other bacteria [43][44][45]. Pseudomonas and Ralstonia, as MC-degrading bacteria [38,39], may not only have the ability to increase host tolerance to MCs by themselves, but the co-occurrence network revealed that these bacteria may also influence host resistance to toxic cyanobacterial stress by affecting the entire bacterial community.…”

Immobilization of Microcystin by the Hydrogel–Biochar Composite to Enhance Biodegradation during Drinking Water Treatment

“…The bacterial biodegradation of MC-LR has the potential to be an environmentally friendly and cost-effective biotechnology that produces no harmful by-products. − Natural bacterial strains or consortia that can effectively degrade MC-LR have been isolated from the natural water. − However, biodegradation requires a minimum of 24 h retention time for the complete removal of the toxin, while the hydraulic retention time during biofiltration is much shorter . Therefore, the biodegradation is necessary to be facilitated by capturing toxins on the filtration media to increase the toxin retention time during biofiltration without slowing the water filtration efficiency.…”

“… 8 − 10 However, biodegradation requires a minimum of 24 h retention time for the complete removal of the toxin, while the hydraulic retention time during biofiltration is much shorter. 12 Therefore, the biodegradation is necessary to be facilitated by capturing toxins on the filtration media to increase the toxin retention time during biofiltration without slowing the water filtration efficiency.…”