Ado Van Assche

Peracetic acid oxidation as an alternative pre-treatment for the anaerobic digestion of waste activated sludge

Anaerobic digestion is generally considered to be an economic and environmentally friendly technology for treating waste activated sludge, but has some limitations, such as the time it takes for the sludge to be digested and also the ineffectiveness of degrading the solids. Various pre-treatment technologies have been suggested to overcome these limitations and to improve the biogas production rate by enhancing the hydrolysis of organic matter. This paper studies the use of peracetic acid for disintegrating sludge as a pre-treatment of anaerobic digestion. It has been proved that this treatment effectively leads to a solubilisation of organic material. A maximum increase in biogas production by 21% is achieved. High dosages of PAA lead to a decrease in biogas production. This is due to the inhibition of the anaerobic micro-organisms by the high VFA-concentrations. The evolution of the various VFAs during digestion is studied and the observed trends support this hypothesis.

Rosenbergiella australoborealis sp. nov., Rosenbergiella collisarenosi sp. nov. and Rosenbergiella epipactidis sp. nov., three novel bacterial species isolated from floral nectar

The taxonomic status of nine strains of the family Enterobacteriaceae isolated from floral nectar of wild Belgian, French, South African and Spanish insect-pollinated plants was investigated following a polyphasic approach. Confirmation that these strains belonged to the genus Rosenbergiella was obtained from comparative analysis of partial sequences of the 16S rRNA gene and other core housekeeping genes (atpD [ATP synthase β-chain], gyrB [DNA gyrase subunit B] and rpoB [RNA polymerase β-subunit]), DNA-DNA reassociation data, determination of the DNA G+C content and phenotypic profiling. Two strains belonged to the recently described species Rosenbergiella nectarea, while the other seven strains represented three novel species within the genus Rosenbergiella. The names Rosenbergiella australoborealis sp. nov. (with strain CdVSA 20.1(T) [LMG 27954(T)=CECT 8500(T)] as the type strain), Rosenbergiella collisarenosi sp. nov. (with strain 8.8A(T) [LMG 27955(T)=CECT 8501(T)] as the type strain) and Rosenbergiella epipactidis sp. nov. (with strain 2.1A(T) [LMG 27956(T)=CECT 8502(T)] as the type strain) are proposed. Additionally, the description of the genus Rosenbergiella is updated on the basis of new phenotypic and molecular data.

Acinetobacter dijkshoorniae sp. nov., a new member of the Acinetobacter calcoaceticus-Acinetobacter baumannii complex mainly recovered from clinical samples in different countries.

The recent advances in bacterial species identification methods have led to the rapid taxonomic diversification of the genus Acinetobacter. In the present study, phenotypic and molecular methods have been used to determine the taxonomic position of a group of 12 genotypically distinct strains belonging to the Acinetobacter calcoaceticus-Acinetobacter baumannii (ACB) complex, initially described by Gerner-Smidt and Tjernberg in 1993, that are closely related to Acinetobacter pittii. Strains characterized in this study originated mostly from human samples obtained in different countries over a period of 15 years. rpoB gene sequences and multilocus sequence typing were used for comparisons against 94 strains representing all species included in the ACB complex. Cluster analysis based on such sequences showed that all 12 strains grouped together in a distinct clade closest to Acinetobacter pittiithat was supported by bootstrap values of 99 %. Values of average nucleotide identity based on blast between the genome sequence of strain JVAP01T (NCBI accession no. LJPG00000000) and those of other species from the ACB complex were always <91.2 %, supporting the species status of the group. In addition, the metabolic characteristics of the group matched those of the ACB complex and the analysis of their protein signatures by matrix-assisted laser desorption ionization time-of-flight MS identified some specific peaks. Our results support the designation of these strains as representing a novel species, for which the name Acinetobacter dijkshoorniae sp. nov. is proposed. The type strain is JVAP01T (=CECT 9134T=LMG 29605T).

Phylogenetic signal in phenotypic traits related to carbon source assimilation and chemical sensitivity in Acinetobacter species

A common belief is that the phylogeny of bacteria may reflect molecular functions and phenotypic characteristics, pointing towards phylogenetic conservatism of traits. Here, we tested this hypothesis for a large set of Acinetobacter strains. Members of the genus Acinetobacter are widespread in nature, demonstrate a high metabolic diversity and are resistant to several environmental stressors. Notably, some species are known to cause opportunistic human infections. A total of 133 strains belonging to 33 species with validly published names, two genomic species and species of an as-yet unknown taxonomic status were analyzed using the GENIII technology of Biolog, which allows high-throughput phenotyping. We estimated the strength and significance of the phylogenetic signal of each trait across phylogenetic reconstructions based on partial RNA polymerase subunit B (rpoB) and core genome sequences. Secondly, we tested whether phylogenetic distance was a good predictor of trait differentiation by Mantel test analysis. And finally, evolutionary model fitting was used to determine if the data for each phenotypic character was consistent with a phylogenetic or an essentially random model of trait distribution. Our data revealed that some key phenotypic traits related to substrate assimilation and chemical sensitivity are linked to the phylogenetic placement of Acinetobacter species. The strongest phylogenetic signals found were for utilization of different carbon sources such as some organic acids, amino acids and sugars, thus suggesting that in the diversification of Acinetobacter carbon source assimilation has had a relevant role. Future work should be aimed to clarify how such traits have shaped the remarkable ability of this bacterial group to dominate in a wide variety of habitats.

Characterization of the bacterial community composition in water of drinking water production and distribution systems in Flanders, Belgium

The quality of drinking water is influenced by its chemical and microbial composition which in turn may be affected by the source water and the different processes applied in drinking water purification systems. In this study, we investigated the bacterial diversity in different water samples from the production and distribution chain of thirteen drinking water production and distribution systems from Flanders (Belgium) that use surface water or groundwater as source water. Water samples were collected over two seasons from the source water, the processed drinking water within the production facility and out of the tap in houses along its distribution network. 454‐pyrosequencing of 16S ribosomal RNA gene sequences revealed a total of 1,570 species‐level bacterial operational taxonomic units. Strong differences in community composition were found between processed drinking water samples originating from companies that use surface water and other that use groundwater as source water. Proteobacteria was the most abundant phylum in all samples. Yet, several phyla including Actinobacteria were significantly more abundant in surface water while Cyanobacteria were more abundant in surface water and processed water originating from surface water. Gallionella, Acinetobacter, and Pseudomonas were the three most abundant genera detected. Members of the Acinetobacter genus were even found at a relative read abundance of up to 47.5% in processed water samples, indicating a general occurrence of Acinetobacter in drinking water (systems).

Cupriavidus metallidurans Strains with Different Mobilomes and from Distinct Environments Have Comparable Phenomes

Cupriavidus metallidurans has been mostly studied because of its resistance to numerous heavy metals and is increasingly being recovered from other environments not typified by metal contamination. They host a large and diverse mobile gene pool, next to their native megaplasmids. Here, we used comparative genomics and global metabolic comparison to assess the impact of the mobilome on growth capabilities, nutrient utilization, and sensitivity to chemicals of type strain CH34 and three isolates (NA1, NA4 and H1130). The latter were isolated from water sources aboard the International Space Station (NA1 and NA4) and from an invasive human infection (H1130). The mobilome was expanded as prophages were predicted in NA4 and H1130, and a genomic island putatively involved in abietane diterpenoids metabolism was identified in H1130. An active CRISPR-Cas system was identified in strain NA4, providing immunity to a plasmid that integrated in CH34 and NA1. No correlation between the mobilome and isolation environment was found. In addition, our comparison indicated that the metal resistance determinants and properties are conserved among these strains and thus maintained in these environments. Furthermore, all strains were highly resistant to a wide variety of chemicals, much broader than metals. Only minor differences were observed in the phenomes (measured by phenotype microarrays), despite the large difference in mobilomes and the variable (shared by two or three strains) and strain-specific genomes.