Parageobacillus caldoxylosilyticus , or previously identified as Geobacillus caldoxylosilyticus , is a thermophilic Gram-positive bacterium which can easily withstand growth temperatures ranging from 40 °C to 70 °C. Here, we present the first complete genome sequence of Parageobacillus caldoxylosilyticus ER4B which was isolated from an empty oil palm fruit bunch compost in Malaysia. Whole genome sequencing was performed using the PacBio RSII platform. The genome size of strain ER4B was around 3.9Mbp, with GC content of 44.31%. The genome consists of two contigs, in which the larger contig (3,909,276bp) represents the chromosome, while the smaller one (54,250bp) represents the plasmid. A total of 4,164 genes were successfully predicted, including 3,972 protein coding sequences, 26 rRNAs, 91 tRNAs, 74 miscRNA, and 1 tmRNA. The genome sequence data of strain ER4B reported here may contribute to the current molecular information of the species. It may also facilitate the discovery of molecular traits related to thermal stress, thus, expanding our understanding in the acclimation or adaptation towards extreme temperature in bacteria.
Microorganisms have acquired both common and unique abilities to withstand cold stress on Earth. Many studies on bacterial cold shock have been conducted, however, the majority of the studies were focused on mesophiles and psychrophiles. To date, limited information is available on the response of thermophilic bacteria to cold stress and therefore, it is not known how thermophilic bacteria would respond to different cold shocks. To address this question, the cold shock responses of a thermophilic Parageobacillus caldoxylosilyticus ER4B which has an optimal growth temperature at 64 °C were determined using Real-Time PCR (RT-qPCR). When the bacterium was exposed to mild cold shock at 54 °C, the expressions of gene encoding for pyruvate kinase and acetolactate synthase were significantly upregulated, suggesting that more pyruvate molecules were produced to synthesize branched-chain amino acids that could alter the fatty acid profile on the cell membrane. Accumulation of pyruvate in the bacterium could also help to scavenge cold-induced reactive oxygen species (ROS). Meanwhile, exposing the bacterium to extreme cold shock at 10 °C resulted in significant upregulation of genes encoding for γ-glutamylcyclotransferase, cold shock protein B and competence protein ComEA. An increase in these enzymes expression indicated more extreme measures including apoptosis and transformation were adopted during extreme cold shock.
Parageobacillus caldoxylosilyticus is a rod-shaped thermophilic bacterium that can grow optimally at high temperatures. The thermophilicity of the bacterium is expected to be largely accounted for by the production of thermostable enzymes which has valuable applications in many fields. However, the species is poorly studied, hence, the growth conditions at high temperatures remained unclear until today. Therefore, this study aimed to determine the growth characterization of P. caldoxylosilyticus, including growth media preferences, optimal growth temperature, as well as minimum and maximum growth temperature. P. caldoxylosilyticus strain ER4B isolated from oil palm empty fruit bunch compost was used in this study. The bacterial strain was first identified using 16S rRNA sequencing, and the subsequent BLAST result showed that it is closest to P. caldoxylosilyticus strain UTM6. It is found that ER4B grew best in LB as compared to R2A, TSB, and NB medium. Further temperature tests determined the optimum growth temperature of the strain to be at 64°C Besides, the bacterium forms mucoid circular punctiform colonies that are yellowish in color on an agar plate, and the colony is usually 2 mm to 4 mm in diameter. The microscopic analysis also revealed that strain ER4B is a Gram-positive rod-shaped bacterium that has a length ranging from 3 µm to 6 µm, with a diameter of around 0.5 µm.
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