Abdelkrim Mouzdahir

Anaerobic biodegradation of squalene: Using DGGE to monitor the isolation of denitrifying Bacteria taken from enrichment cultures

Abstract The process of enrichment and subsequently isolation of squalene degrading denitrifying bacteria has been developed. The enrichment method used in this study targeted denitrifying bacteria, therefore an initial enrichment incubation using nitrate amendments under anaerobic conditions was performed before squalene amendment. Denaturant gradient gel electrophoresis (DGGE) analysis of polymerase chain reaction (PCR)-amplified DNA fragments prepared from extracted DNA was used to compare the composition of bacterial communities at various steps of enrichment cultures and the diversity of the 80 isolated strains obtained by classical culture methods. After 8 months of anaerobic incubation, the squalene biodegradation rate reached 80%. The community composition changed substantially during the incubation time. The enrichment cultures were dominated by 12 phylotypes, of which eight corresponded to cultivatable strains. Their identities were established by sequencing V3-V5 16SrRNA PCR fragments directly or after excision of DGGE bands and comparing the sequences with those available in GenBank. Most of the isolates were Proteobacteria of the gamma subgroup; among them, seven novel denitrifying bacteria which were capable of using squalene as the sole carbon source, were isolated and characterized.

Production of a polyunsaturated isoprenoid wax ester during aerobic metabolism of squalene by Marinobacter squalenivorans sp. nov.

ABSTRACT This paper describes the production of 5,9,13-trimethyltetradeca-4E,8E,12-trienyl-5,9,13-trimethyltetradeca-4E,8E,12-trienoate during the aerobic degradation of squalene by a Marinobacter strain, 2Asq64, isolated from the marine environment. A pathway involving initial cleavage of the C10-C11 or C14-C15 double bonds of the squalene molecule is proposed to explain the formation of this polyunsaturated isoprenoid wax ester. The isoprenoid wax ester content reached 1.1% of the degraded squalene at the mid-exponential growth phase and then decreased during the stationary phase. The wax ester content increased by approximately threefold in N-limited cultures, in which the ammonium concentration corresponds to conditions often found in marine sediments. This suggests that the bacterial formation of isoprenoid wax esters might be favored in such environments. The bacterial strain is then characterized as a member of a new species, for which we propose the name Marinobacter squalenivorans sp. nov.

The impact of industrial pollution on the Jorf Lasfar coastal zone (Morocco, Atlantic Ocean): the mussel as an indicator of metal contamination

Abstract The present study characterizes the effluents of the ‘Maroc Phosphore’ factories III and IV (of Jorf Lasfar coastal zone). The results show that the effluent (Cs/l) is very acid, very phosphate-rich, high in suspended matter and calcium-rich. Hydrological parameters indicate an important content of phosphates, especially in the stations located in the South of Cs/l. Tissues of mussel Mytilus galloprovincialis from the Jorf Lasfar zone present high concentrations of Cd and Cu.

Anaerobic biodegradation of pristane by a marine sedimentary bacterial and/or archaeal community

Pristane was incubated in anaerobic sediment slurries under conditions promoting or limiting nitrate reduction. Pristane was efficiently degraded (85% after 6 months) by the mixed microbial community when nitrate reducing processes were avoided. The biodegradation of pristane was accompanied by the abundant production of methane which indicated that methanogenic Archaea were involved in the degradation of the substrate. Comparison of the biodegradation rate of pristane with that of unsaturated isoprenoid alkenes indicated that, in Recent anoxic sediments, acyclic isoprenoid alkanes can also undergo relatively rapid biotransformations and, therefore, can no longer be considered as recalcitrant biomarkers.

Diagnosis on the state of healthiness, quality of the coast and biological resources 'case of the Moroccan Atlantic coast' (City of El Jadida).

In this study, we present a diagnosis concerning the state of healthiness of the coast of the city of El Jadida by: characterisation of the various collectors rejected in sea without any preliminary treatment, measure of the physicochemical parameters of seawater from sampling stations, evaluation of the concentration of certain heavy metals (Cd, Cu, Zn, Fe and Mn) in four species of algae, which shows that metal contents vary according to the species and the sampling stations, measure of the metal content in mussels, which varies according to the site. A comparative study with the data of the literature shows that algae and mussels generally present values that are weaker than those coming from other geographical areas.

Visible light-dependent degradation of long-chain alkenes in killed cells of Emiliania huxleyi and Nannochloropsis salina.

Photosensitized degradation rates of phytoplanktonic n-alkenes under visible light exposure were determined in laboratory experiments. Killed cells of Emiliania huxleyi and Nannochloropsis salina were used as source of biogenic alkenes. In E. huxleyi killed cells, minor C31 and C33 n-alkenes were strongly photodegraded, while the major C37 and C38 n-alkenes appeared particularly recalcitrant towards photochemical processes. This particular photochemical recalcitrance has been attributed to the chemical structure and localization of these hydrocarbons in the cells. Most of the n-alkenes of N. salina were strongly photodegraded in killed cells. The photodegradation of phytoplanktonic alkenes showed apparent second-order kinetics with respect to light exposure, and the half-life doses obtained logically decrease with increasing number of double bonds in these compounds. These results strongly suggest that significant amounts of phytoplanktonic n-alkenes must be photodegraded in the euphotic zone of the oceans during senescence.

Aerobic and anaerobic abiotic oxidation of squalene in the presence of hydroperoxides

Abiotic oxidation of squalene in the presence of hydroperoxysterols was studied in seawater under aerobic and anaerobic conditions. This ubiquitous isoprenoid alkene is quickly degraded in the presence of oxygen and its oxidation results mainly in the production of tertiary alcohols and to a lesser extent of epoxides and secondary alcohols. Although the degradation of squalene logically slows down under anaerobic conditions, a significant oxidation affording similar products than in the case of aerobic degradation has been observed. These results show that hydroperoxysterols, which seem to be well preserved in Recent sediments, could contribute to the oxidation of unsaturated lipids (such as squalene) in sedimentary environments under oxic and anoxic conditions.