Microbial Community Evolution Is Significantly Impacted by the Use of Calcium Isosaccharinic Acid as an Analogue for the Products of Alkaline Cellulose Degradation

The evolution of alkaliphilic biofilm communities in response to extreme alkaline pH values

Extremes of pH present a challenge to microbial life and our understanding of survival strategies for microbial consortia, particularly at high pH, remains limited. The utilization of extracellular polymeric substances within complex biofilms allows micro‐organisms to obtain a greater level of control over their immediate environment. This manipulation of the immediate environment may confer a survival advantage in adverse conditions to biofilms. Within the present study alkaliphilic biofilms were created at pH 11.0, 12.0, or 13.0 from an existing alkaliphilic community. In each pH system, the biofilm matrix provided pH buffering, with the internal pH being 1.0–1.5 pH units lower than the aqueous environment. Increasing pH resulted in a reduced removal of substrate and standing biomass associated with the biofilm. At the highest pH investigated (pH 13.0), the biofilms matrix contained a greater degree of eDNA and the microbial community was dominated by Dietzia sp. and Anaerobranca sp.

Hydrogenotrophic Methanogenesis Under Alkaline Conditions

A cement-based geological disposal facility (GDF) is one potential option for the disposal of intermediate level radioactive wastes. The presence of both organic and metallic materials within a GDF provides the opportunity for both acetoclastic and hydrogenotrophic methanogenesis. However, for these processes to proceed, they need to adapt to the alkaline environment generated by the cementitious materials employed in backfilling and construction. Within the present study, a range of alkaline and neutral pH sediments were investigated to determine the upper pH limit and the preferred route of methane generation. In all cases, the acetoclastic route did not proceed above pH 9.0, and the hydrogenotrophic route dominated methane generation under alkaline conditions. In some alkaline sediments, acetate metabolism was coupled to hydrogenotrophic methanogenesis via syntrophic acetate oxidation, which was confirmed through inhibition studies employing fluoromethane. The absence of acetoclastic methanogenesis at alkaline pH values (>pH 9.0) is attributed to the dominance of the acetate anion over the uncharged, undissociated acid. Under these conditions, acetoclastic methanogens require an active transport system to access their substrate. The data indicate that hydrogenotrophic methanogenesis is the dominant methanogenic pathway under alkaline conditions (>pH 9.0).

Genomic Insights Into A Novel, Alkalitolerant Nitrogen Fixing Bacteria, Azonexus sp. Strain ZS02

Alkaline environments represent a significant challenge to the growth of micro-organisms. Despite this, there are a number of alkaline environments which contain active microbial communities. Here we describe the genome of a diazotrophic, alkalitolerant strain of Azonexus, which was isolated from a microcosm seeded with hyperalkaline soils resulting from lime depositions. The isolate has a genome size 3.60 Mb with 3431 protein coding genes. The proteome indicated the presence of genes associated with the cycling of nitrogen, in particular the fixation of atmospheric nitrogen. Although closely related to Azonexus hydrophilus strain d8-1 by both 16S (97.9%) and in silico gDNA (84.1%) relatedness, the isolate demonstrates a pH tolerance above that reported for this strain. The proteome contained genes for the complete Na⁺/H⁺ antiporter (subunits A to G) for cytoplasmic pH regulation; this may account for the phenotypic characteristics of this strain which exhibited optimal growth conditions of pH 9 and 30°C.

Anaerobacillus isosaccharinicus sp. nov., an alkaliphilic bacterium which degrades isosaccharinic acid

Strain NB2006^T was isolated from an isosaccharinate-degrading, nitrate-reducing enrichment culture in minimal freshwater medium at pH 10. Analysis of the 16S rRNA gene sequence indicated that this strain was most closely related to species of the newly established genus Anaerobacillus. This was supported by phenotypic and metabolic characterisation that showed that NB2006^T was rod-shaped, Gram-stain-positive, motile and formed endospores. It was an aerotolerant anaerobe and an obligate alkaliphile that grew at pH 8.5-11, could tolerate up to 6 % (w/v) NaCl, and grew at a temperature between 10 and 40 °C. In addition, it could utilise a number of organic substrates, and was able to reduce nitrate and arsenate. The predominant cellular fatty acids were C_16 : 0, C_16 : 1ω11c, anteiso-C_15 : 0, iso-C_15 : 0, C_16 : 1ω7c/iso-C_15 : 0 2-OH and C_14 : 0. The cell wall peptidoglycan contained meso-diaminopimelic acid and the DNA G+C content was 37.7 mol%. In silico DNA-DNA hybridization with the four known species of the genus Anaerobacillus showed 21.8, 21.9, 22.4, and 21.5 % relatedness to Anaerobacillusarseniciselenatis DSM 15340^T, Anaerobacilus alkalidiazotrophicus DSM 22531^T, Anaerobacillusalkalilacustris DSM 18345^T, and Anaerobacillus macyae DSM 16346^T, respectively. NB2006^T differed from strains of other species of the genus Anaerobacillus in its ability to metabolise isosaccharinate, an alkaline hydrolysis product of cellulose. On the basis of the consensus of phylogenetic and phenotypic analyses, this strain represents a novel species of the genus Anaerobacillus, for which the name Anaerobacillus isosaccharinicus sp. nov. is proposed. The type strain is NB2006^T (=DSM 100644^T=LMG 30032^T).