Olivier Nercessian

Alteromonas genovensis sp. nov., isolated from a marine electroactive biofilm and emended description of Alteromonas macleodii Baumann et al. 1972 (approved lists 1980).

Thirty-five isolates obtained from a marine electroactive biofilm grown on a stainless steel cathode (Genoa, Italy) were investigated by a polyphasic taxonomic approach. Whole-cell fatty acid methyl ester analysis indicated that the isolates belonged to the class Gammaproteobacteria and were closely related or belonging to the genus Alteromonas. Genomic fingerprinting using the BOX-PCR primer delineated five clusters of isolates with similar BOX-PCR fingerprints. This study demonstrated that isolates from four of the BOX-PCR clusters belonged to Alteromonas macleodii and that the 14 isolates representing BOX-PCR cluster 1 constituted a novel species, which shared 98.4 % 16S rRNA gene sequence similarity with its nearest phylogenetic neighbour, Alteromonas hispanica. Both phenotypic and genotypic analyses enabled this novel species, for which the name Alteromonas genovensis sp. nov. is proposed, to be differentiated from established species of the genus Alteromonas. The DNA G+C content of Alteromonas genovensis sp. nov. is 44.5 mol% and the type strain is LMG 24078(T) (=CCUG 55340(T)).

Ruegeria scottomollicae sp. nov., isolated from a marine electroactive biofilm.

Seventy isolates were obtained from a marine electroactive biofilm that was generated on a cathodically polarized stainless steel electrode (Genoa, Italy). The genetic diversity was investigated by means of BOX-PCR fingerprinting and two clusters of isolates with similar BOX-PCR profiles were delineated. Whole-cell fatty acid methyl ester analysis and 16S rRNA gene sequence analysis showed that the isolates belonged to the Roseobacter lineage of the class Alphaproteobacteria. DNA-DNA hybridization experiments and a biochemical analysis demonstrated that four isolates belonged to the species Ruegeria mobilis. However, 66 isolates from the second BOX-PCR cluster constituted a novel species within the genus Ruegeria, for which the name Ruegeria scottomollicae sp. nov. is proposed. The DNA G+C content was 61.0+/-0.4 %. The type strain is LMG 24367(T) (=CCUG 55858(T)).

Bacterial diversity of the cultivable fraction of a marine electroactive biofilm

Stainless steel electrodes were cathodically polarized at -200 mV versus an Ag/AgCl reference electrode in natural seawater in order to produce current. The current increased and stabilized at 0.5 A/m(2) in less than 10 days. The cultivable fraction of the microbial biofilm population formed on the surface of the current harvesting cathodes was examined by culture dependent techniques. Three hundred fifty six isolates were obtained. They were primarily characterized by whole cell fatty acid methyl ester analysis followed by 16S rRNA gene sequencing. The results showed that the isolates represented different phylogenetic groups including members of the Alpha- and Gammaproteobacteria, the phylum Firmicutes, the family Flavobacteriacae and the phylum Actinobacteria. Denaturing gradient gel electrophoresis demonstrated that the microbial population of the biofilm formed on the cathode and of the surrounding seawater comprised the same dominant members. This study demonstrated that the cultivable microbial fraction of a marine electroactive biofilm is phylogenetically highly diverse.

Harvesting electricity with Geobacter bremensis isolated from compost.

Electrochemically active (EA) biofilms were formed on metallic dimensionally stable anode-type electrode (DSA), embedded in garden compost and polarized at +0.50 V/SCE. Analysis of 16S rRNA gene libraries revealed that biofilms were heavily enriched in Deltaproteobacteria in comparison to control biofilms formed on non-polarized electrodes, which were preferentially composed of Gammaproteobacteria and Firmicutes. Among Deltaproteobacteria, sequences affiliated with Pelobacter and Geobacter genera were identified. A bacterial consortium was cultivated, in which 25 isolates were identified as Geobacter bremensis. Pure cultures of 4 different G. bremensis isolates gave higher current densities (1400 mA/m2 on DSA, 2490 mA/m2 on graphite) than the original multi-species biofilms (in average 300 mA/m2 on DSA) and the G. bremensis DSM type strain (100–300 A/m2 on DSA; 2485 mA/m2 on graphite). FISH analysis confirmed that G. bremensis represented a minor fraction in the original EA biofilm, in which species related to Pelobacter genus were predominant. The Pelobacter type strain did not show EA capacity, which can explain the lower performance of the multi-species biofilms. These results stressed the great interest of extracting and culturing pure EA strains from wild EA biofilms to improve the current density provided by microbial anodes.

Electrochemical checking of aerobic isolates from electrochemically active biofilms formed in compost

Aims:  To design a cyclic voltammetry (CV) procedure to check the electrochemical activity of bacterial isolates that may explain the electrochemical properties of biofilms formed in compost.