Rapid polymerase chain reaction assays for Brevibacillus laterosporus detection

Inoculating exogenous bacterium Brevibacillus laterosporus ZR-11 at maturity stage accelerates composting maturation by regulating physicochemical parameters and indigenous bacterial community succession

Brevibacillus laterosporus ZR-11, a bio-control strain, was innovatively inoculated at maturity stage of composting to clarify its effect on physicochemical parameters and indigenous bacterial community structure in compost pile. Results revealed that ZR-11 inoculum rapidly increased pile temperature to 52 ºC and raised germination index (GI) value to beyond 85% on day 3, thereby achieving higher pile temperature and GI in the inoculated group than the non-inoculated group almost along maturity stage, and also decreased C/N ratio of the inoculated group to below 20 by composting end (day 8). Also, ZR-11 succeeded in colonizing compost pile along maturity stage. These suggested that ZR-11 as inoculum at maturity stage could accelerate compost maturation and have a potential to participate in bio-fertilizer production. High-throughput sequencing indicated that bacterial community structure experienced substantial succession in the inoculated and non-inoculated groups, and Firmicutes, Proteobacteria, and Actinobacteria were the dominant phyla in the two groups during maturity stage, with their abundances higher in the inoculated group. Saccharomonospora and Ammoniibacillus abundance increased on day 3 while Actinomadura abundance increased on day 6 in the inoculated group. As verified statistically, pile temperature and pH were key factors closely linked to dominant genera abundance, where Saccharomonospora and Ammoniibacillus abundance were positively correlated to pile temperature, while Actinomadura abundance was positively correlated to pile pH. Thus, it was inferred that ZR-11 inoculum could improve parameters such as temperature and pH to modify dominant genera abundance, thus regulating indigenous bacterial community succession, which might in turn promote compost maturation.

Structural Diversity, LC-MS-MS Analysis and Potential Biological Activities of Brevibacillus laterosporus Extract

Lake Mariout is Egypt's degraded coastal marine habitat that encompasses a variety of wastes. The biodiversity and hard environmental conditions allow the co-existence of organisms with high resistance and rich metabolism, making them potential candidates for screening and isolating novel microbial strains. A bacterial isolate (BF202) cultured from the marine sediments of Alexandria's Mariout Lake (Egypt) was tested for its antimicrobial and anticancer potential. The phylogenetic analysis of the isolated strain's 16S rDNA and gyrB revealed that BF202 belongs to Brevibacillus laterosporus (B. laterosporus). Antibiosis of B. laterosporus was confirmed against microbial pathogens including Escherichia coli, Klebsiella pneumoniae, Salmonella typhi, and Staphylococcus aureus. The highest antibacterial activity was detected on glucose peptone medium after 18 h of incubation at 35 °C, and at pH of 7.0 in the presence of mannose and ammonium carbonate as carbon and nitrogen sources, respectively. The cytotoxicity of the methanolic extract against breast cancer (MCF-7) and normal Vero cell lines, using the MTT test, revealed IC50 values of 7.93 and 23.79 µg/mL, respectively. To identify apoptotic and necrotic cells, a flow cytometric analysis using annexin V-FITC/PI dual-labeling was utilized and recorded a higher number of necrotic cells compared to apoptotic ones. Similarly, the cell cycle S-phase arrest was reported. The LC-MS-MS investigation of B. laterosporus extract and the molecular networking database analysis demonstrated five strategic diketopiperazine compounds with antimicrobial and anticancer activities. Taken together, this research shows that the crude extract of B. laterosporus might be an effective agent against drug-resistant bacteria and malignant disorders due to its richness in diketopiperazines.

A simple colorimetric method for viable bacteria detection based on cell counting Kit-8

In this study, Cell Counting Kit-8 (CCK-8) was introduced to detect the concentration of live bacteria for the first time depending on the redox reaction between CCK-8 solution and dehydrogenase. CCK-8 solution can be reduced to form water soluble orange-yellow formazan by the dehydrogenase present in bacterial cells, and the concentration of live bacteria is proportional to the absorbance value of formazan at 450 nm. Based on this principle, Staphylococcus aureus and Escherichia coli were chosen as the model bacteria. The optimal detection conditions were investigated and a good linear relationship was obtained in the concentration range from 2.600 × 10² to 1.160 × 10⁹ CFU mL^-1 with a linear equation of Y = 0.06305 log₁₀ X-0.1153 (X in CFU mL^-1, R² = 0.9747) for S. aureus and 9.750 × 10² to 6.000 × 10⁸ CFU mL^-1 with a linear equation of Y = 0.06122 log₁₀ X-0.1358 (X in CFU mL^-1, R² = 0.9958) for E. coli. The CCK-8 based viable bacteria detection method can be completed within 2 h with a wide bacterial detection concentration range. Satisfactory results were obtained when applied to an actual sample analysis and there is a good consistency between the proposed CCK-8 based method and the traditional plate counting method. More importantly, this method can realize the one-time detection of a large number of samples with high sensitivity, which suggests its great potential in high-throughput bacterial detection.

Identification of a Novel Brevibacillus laterosporus Strain With Insecticidal Activity Against Aedes albopictus Larvae

Bacterial species able to produce proteins that are toxic against insects have been discovered at the beginning of the last century. However, up to date only two of them have been used as pesticides in mosquito control strategies targeting larval breeding sites: Bacillus thuringensis var. israelensis and Lysinibacillus sphaericus. Aiming to expand the arsenal of biopesticides, bacterial cultures from 44 soil samples were assayed for their ability to kill larvae of Aedes albopictus. A method to select, grow and test the larvicidal capability of spore-forming bacteria from each soil sample was developed. This allowed identifying 13 soil samples containing strains capable of killing Ae. albopictus larvae. Among the active isolates, one strain with high toxicity was identified as Brevibacillus laterosporus by 16S rRNA gene sequencing and by morphological characterization using transmission electron microscopy. The new isolate showed a larvicidal activity significantly higher than the B. laterosporus LMG 15441 reference strain. Its genome was phylogenomically characterized and compared to the available Brevibacillus genomes. Thus, the new isolate can be considered as a candidate adjuvant to biopesticides formulations that would help preventing the insurgence of resistance.