The use of response surface analysis to study the growth of Bacillus acidocaldarius throughout the growth range of temperature and pH

Alicyclobacillus curvatus sp. nov. and Alicyclobacillus mengziensis sp. nov., two acidophilic bacteria isolated from acid mine drainage

Two acidophilic strains, designated as ALEF1^T and S30H14^T, were isolated from acid mine drainage sediment. Cells of both strains were Gram-stain-positive, aerobic, endospore-forming rods. Strains ALEF1^T and S30H14^T were acidophilic and mesophilic, the former grew at 20–40 °C (optimum, 30 °C) and pH 2.5–4.5 (optimum, pH 3.5), while the latter grew at 20–45 °C (optimum, 30 °C) and pH 2.0–5.5 (optimum, pH 4.5). The 16S rRNA gene-based sequence analysis revealed that strains ALEF1^T and S30H14^T belonged to the genus Alicyclobacillus, and were phylogenetically close to Alicyclobacillus ferrooxydans TC-34^T with 97.1 and 97.4% similarity, respectively. The similarity between the two novel strains was 98.6 %. The average nucleotide identity value between the genome sequences of ALEF1^T and S30H14^T was 79.5 %, and that between each of the two isolates and A. ferrooxydans TC-34^T were 72.0 and 74.3 %. In addition, the digital DNA–DNA hybridization value between ALEF1^T and S30H14^T was 24.9 %, between strain ALEF1^T and A. ferrooxydans TC-34^T was 21.7 %, and between S30H14^T and A. ferrooxydans TC-34^T was 26.3 %, far below the interspecies threshold. Both strains could utilize diverse carbon sources for heterotrophic growth; strain ALEF1^T could utilize ferrous iron as the energy source for autotrophic growth. Menaquinone 7 was the only quinone detected in either strain. Both strains contained anteiso-C_15 : 0 and anteiso-C_17 : 0, while ω-alicyclic fatty acids were not detected. Based on their phylogenetic positions, as well as phenotypic and genomic data, it is considered that strains ALEF1^T and S30H14^T represent two novel species within the genus Alicyclobacillus, for which the names Alicyclobacillus curvatus sp. nov. (type strain ALEF1^T=CGMCC 1.17055^T=KCTC 43124^T) and Alicyclobacillus mengziensis sp. nov. (S30H14^T=CGMCC 1.17050^T=KCTC 43125^T) are proposed.

Metabolic Efficiency of Sugar Co-Metabolism and Phenol Degradation in Alicyclobacillus acidocaldarius for Improved Lignocellulose Processing

Substrate availability plays a key role in dictating metabolic strategies. Most microorganisms consume carbon/energy sources in a sequential, preferential order. The presented study investigates metabolic strategies of Alicyclobacillus acidocaldarius, a thermoacidophilic bacterium that has been shown to co-utilize glucose and xylose, as well as degrade phenolic compounds. An existing metabolic model was expanded to include phenol degradation and was analyzed with both metabolic pathway and constraint-based analysis methods. Elementary flux mode analysis was used in conjunction with resource allocation theory to investigate ecologically optimal metabolic pathways for different carbon substrate combinations. Additionally, a dynamic version of flux balance analysis was used to generate time-resolved simulations of growth on phenol and xylose. Results showed that availability of xylose along with glucose did not predict enhanced growth efficiency beyond that of glucose alone, but did predict some differences in pathway utilization and byproduct profiles. In contrast, addition of phenol as a co-substrate with xylose predicted lower growth efficiency. Dynamic simulations predicted co-consumption of xylose and phenol in a similar pattern as previously reported experiments. Altogether, this work serves as a case study for combining both elementary flux mode and flux balance analyses to probe unique metabolic features, and also demonstrates the versatility of A. acidocaldarius for lignocellulosic biomass processing applications.

Alicyclobacillusspp. in the Fruit Juice Industry: History, Characteristics, and Current Isolation/Detection Procedures

The first Alicyclobacillus spp. was isolated in 1982, and was originally thought to be strictly limited to thermophilic and acidic environments. Two years later, another Alicyclobacillus sp., A. acidoterrestris, was identified as the causative agent in spoilage of commercially pasteurized apple juice. Subsequent studies soon found that Alicyclobacillus spp. are soilborne bacteria, and do not strictly require thermophilic and acidic environments. Alicyclobacillus spp. posess several distinct characteristics; the major one is their ability to survive commercial pasteurization processes and produce off-flavors in fruit juices. The fruit juice industry has acknowledged Alicyclobacillus spp. as a major quality control target microorganism. Guaiacol and halophenols were identified as the offensive smelling agent in many Alicyclobacillus spp. related spoilage. Though the exact formation pathway of these off-flavors by Alicyclobacillus spp. are not yet identified, studies report that the presence of Alicyclobacillus spp. in the medium may be a major contributor to the formation of these off-flavors. Many identification methods and isolation media were developed in the last two decades. However, most of these methods were developed specifically for A. acidoterrestris, which was the first identified off-flavor producing Alicyclobacillus. However, recent studies indicate that other species of Alicyclobacillus may also produce guaiacol or the halophenols. In this respect, all Alicyclobacillus spp. should be monitored as potential spoilage bacteria in fruit juices. This article includes an overall review of the history of Alicyclobacillus spp., characteristics, suggested off-flavor production pathways, and commonly used identification methods for the currently identified Alicyclobacillus spp.

Evaluation of direct plating methods to enumerate Alicyclobacillus in beverages

Ten agar media were evaluated for their suitability to support spore germination and colony development by six strains of Alicyclobacillus acidoterrestris, three strains of Alicyclobacillus acidocaldarius, and one strain of Alicyclobacillus cycloheptanicus. The influence of plating method (pour versus spread), incubation temperature (43 degrees C and 50 degrees C), and incubation time (up to 10 days) on colony development were determined. K agar, Alicyclobacillus medium (ALI agar), and Bacillus acidoterrestris thermophilic (BAT) agar recovered the highest numbers of spores. Orange serum agar and Hiraishi glucose yeast extract agar were the least suitable. Overall, surface plating was superior to pour plating and, with the exception of one strain of A. acidocaldarius which grew better at 50 degrees C, incubation of K agar, ALI agar, and BAT agar plates at 43 degrees C or 50 degrees C resulted in recovery of equivalent numbers of spores. Essentially all viable spores were detected on media incubated for 3 days at 43 degrees C. The ability of one strain of each Alicyclobacillus species to grow in ten non-carbonated commercially manufactured beverages at 30 degrees C and 43 degrees C was markedly affected by the composition of the beverages. Results show that surface plating samples on BAT agar, followed by incubating plates at 43 degrees C for 3 days provide the most suitable conditions to enumerate ten strains of three species of Alicyclobacillus most commonly responsible for spoilage of beverages.