“Rational” Management of Dichlorophenols Biodegradation by the Microalga Scenedesmus obliquus

Abstract

The microalga Scenedesmus obliquus exhibited the ability to biodegrade dichlorophenols (dcps) under specific autotrophic and mixotrophic conditions. According to their biodegradability, the dichlorophenols used can be separated into three distinct groups. Group I (2,4-dcp and 2,6 dcp – no meta-substitution) consisted of quite easily degraded dichlorophenols, since both chloride substituents are in less energetically demanding positions. Group II (2,3-dcp, 2,5-dcp and 3,4-dcp – one meta-chloride) was less susceptible to biodegradation, since one of the two substituents, the meta one, required higher energy for C-Cl-bond cleavage. Group III (3,5-dcp – two meta-chlorides) could not be biodegraded, since both chlorides possessed the most energy demanding positions. In general, when the dcp-toxicity exceeded a certain threshold, the microalga increased the energy offered for biodegradation and decreased the energy invested for biomass production. As a result, the biodegradation per cell volume of group II (higher toxicity) was higher, than group I (lower toxicity) and the biodegradation of dichlorophenols (higher toxicity) was higher than the corresponding monochlorophenols (lower toxicity). The participation of the photosynthetic apparatus and the respiratory mechanism of microalga to biodegrade the group I and the group II, highlighted different bioenergetic strategies for optimal management of the balance between dcp-toxicity, dcp-biodegradability and culture growth. Additionally, we took into consideration the possibility that the intermediates of each dcp-biodegradation pathway could influence differently the whole biodegradation procedures. For this reason, we tested all possible combinations of phenolic intermediates to check cometabolic interactions. The present contribution bring out the possibility of microalgae to operate as “smart” bioenergetic “machines”, that have the ability to continuously “calculate” the energy reserves and “use” the most energetically advantageous dcp-biodegradation strategy. We tried to manipulate the above fact, changing the energy reserves and as a result the chosen strategy, in order to take advantage of their abilities in detoxifying the environment.

Biodegradation of 2,4-dichlorophenol by Bacillus endophyticus strain: optimization of experimental parameters using response surface methodology and kinetic study

“…While in higher concentration the micro-organism directs energy to biodegradation instead of growth leading to higher DCP removal per cell. Such observation was also reported by Papazi and Kotzabasis that the degradation of high toxic dichlorophenol congener is higher as compared to low toxic dichlorophenol congener and monochlorophenol [22]. The micro-organism use a different bioenergetic strategy in such a way so that there is balance between the 2,4-DCP biodegradability, 2,4-DCP toxicity and growth.…”

Potassium deficiency, a “smart” cellular switch for sustained high yield hydrogen production by the green alga Scenedesmus obliquus

“…An extremely high yield in hydrogen productivity appeared in Scenedesmus obliquus cultures when one meta-substituted dichlorophenols (m-dcps) was added to the culture medium [6,7]. Reduced m-dcps, according to their redox potential, take the place of electron donors in the photosynthetic electron flow, close to the PQ-pool.…”

“…Additionally, the first step of m-dcps biodegradation (the reduction of m-dcps) supports a continuous circuit between oxidized and reduced m-dcps, which promotes strong electron flow to the PQ-pool, and in turn to Fd and to hydrogenase. Oxygen depletion was achieved not only by the inhibition of PSII activity, but was also induced by the combinational transfer of electrons from reduced m-dcps to the ubiquinone of the mitochondrial respiratory mechanism (cytochromic and alternative pathways) [6,7].…”

Biodegradation and Co‐Metabolism of Monochlorophenols and 2,4‐Dichlorophenol by Microbial Consortium

“…The toxicity of the MCPs increased in the order of 2‐CP < 4‐CP < 3‐CP. The dechlorination of the meta ‐chloride residue is a more energy demanding process than for the ortho ‐ and para ‐positions indicating the higher toxicity of 3‐CP . The substrate inhibition phase was reached at lower concentrations for 3‐CP due to its higher toxicity as compared to 4‐CP.…”