Microbiota adaptation after an alkaline pH perturbation in a full-scale UASB anaerobic reactor treating dairy wastewater.

The aim of this study was to understand how the microbial community adapted to changes, including a pH perturbation, occurring during the start-up and operation processes in a full-scale methanogenic UASB reactor designed to treat dairy wastewater. The reactor performance, prokaryotic community, and lipid degradation capacity were monitored over a 9-month period. The methanogenic community was studied by mcrA/mrtA gene copy-number quantification and methanogenic activity tests. A diverse prokaryotic community characterized the seeding sludge as assessed by sequencing the V4 region of the 16S rRNA gene. As the feeding began, the bacterial community was dominated by Firmicutes, Synergistetes, and Proteobacteria phyla. After an accidental pH increase that affected the microbial community structure, a sharp increase in the relative abundance of Clostridia and a decrease in the mcrA/mrtA gene copy number and methanogenic activity were observed. After a recovery period, the microbial population regained diversity and methanogenic activity. Alkaline shocks are likely to happen in dairy wastewater treatment because of the caustic soda usage. In this work, the plasticity of the prokaryotic community was key to surviving changes to the external environment and supporting biogas production in the reactor.

Phylotype diversity in a benthic cyanobacterial mat community on King George Island, maritime Antarctica.

Cyanobacterial 16S ribosomal RNA gene diversity was examined in a benthic mat on Fildes Peninsula of King George Island (62º09'54.4''S, 58º57'20.9''W), maritime Antarctica. Environmental DNA was isolated from the mat, a clone library of PCR-amplified 16S rRNA gene fragments was prepared, and amplified ribosomal DNA restriction analysis (ARDRA) was done to assign clones to seven groups. Low cyanobacterial diversity in the mat was suggested in that 83% of the clones were represented by one ARDRA group. DNA sequences from this group had high similarity with 16S rRNA genes of Tychonema bourrellyi and T. bornetii isolates, whose geographic origins were southern Norway and Northern Ireland. Cyanobacterial morphotypes corresponding to Tychonema have not been reported in Antarctica, however, this morphotype was previously found at Ward Hunt Lake (83ºN), and in western Europe (52ºN). DNA sequences of three of the ARDRA groups had highest similarity with 16S rDNA sequences of the Tychonema group accounting for 9.4% of the clones. Sequences of the remaining three groups (7.6%) had highest similarity with 16S rRNA genes of uncultured cyanobacteria clones from benthic mats of Lake Fryxell and fresh meltwater on the McMurdo Ice Shelf.

Cellular and biochemical response to Cr(VI) in Stenotrophomonas sp.

Chromium (Cr)-resistant bacteria isolated from a soil with 6 g kg(-1) of Cr were identified based on 16S rRNA gene sequence analysis as a Stenotrophomonas, and designated as JD1. Growth of JD1 was accompanied by transformation of Cr(VI) to Cr(III) in liquid medium initially containing 300 mg L(-1) Cr(VI), the maximum concentration allowing growth. JD1 produced the highest levels of a Cr(VI)-binding exopolysaccharide when grown in medium with 100 mg L(-1) Cr(VI). The relative exopolysaccharide monosaccharide composition was analysed by HPLC, which showed that rhamnose+galactose was the major component, and that its relative level increased when cells were grown with Cr(VI). JD1 grew as a biofilm on various inert surfaces. Biofilm macromolecular composition analysis indicated that the relative levels of exopolysaccharide and protein were more abundant in biofilms grown in 100 mg L(-1) Cr(VI), whereas relative uronic acid levels remained constant. Biofilm cells exposed to Cr(VI) were elongated, grouped in clusters and exopolysaccharide obtained from the biofilm extracellular matrix had an enhanced capacity to bind Cr(VI). Exopolysaccharide production and composition, and biofilm growth are discussed as a mechanism of protection that allows survival during Cr(VI) stress.