Preservation of Paenibacillus polymyxa BTK01 and Bacillus subtilis BTK07 as lignocellulolytic bacterial starters for industrial applications: Physicochemical conditions, enzyme stability, freeze-drying processes and cryoprotection

Effect of Lyoprotective Agents on the Preservation of Survival of a Bacillus cereus Strain PBG in the Freeze-Drying Process

Lyophilization is a widely employed long-term preservation method in which the bacterial survival rate largely depends on the cryoprotectant used. Bacillus cereus strain PBC was selected for its ability to thrive in environments contaminated with arsenic, lead, and cadmium, tolerate 500 ppm of free cyanide, and the presence of genes such as ars, cad, ppa, dap, among others, associated with the bioremediation of toxic compounds and enterotoxins (nheA, nheB, nheC). Following lyophilization, the survival rates for Mannitol 2.5%, Mannitol 10%, and Glucose 1% were 98.02%, 97.12%, and 96.30%, respectively, with the rates being lower than 95% for other sugars. However, during storage, for the same sugars, the survival rates were 78.71%, 97.12%, and 99.97%, respectively. In the cake morphology, it was found that the lyophilized morphology showed no relationship with bacterial survival rate. The best cryoprotectant for the PBC strain was 1% glucose since it maintained constant and elevated bacterial growth rates during storage, ensuring that the unique characteristics of the bacterium were preserved over time. These findings hold significant implications for research as they report a new Bacillus cereus strain with the potential to be utilized in bioremediation processes.

Effects of Reductive Soil Disinfestation Combined with Liquid-Readily Decomposable Compounds and Solid Plant Residues on the Bacterial Community and Functional Composition

Reductive soil disinfestation (RSD) incorporated with sole plant residues or liquid-readily decomposable compounds is an effective management strategy to improve soil health. However, the synthetic effects of RSD incorporated with liquid-readily decomposable compounds and solid plant residues on soil ecosystem services remain unclear. Field experiments were carried out to investigate the effects of untreated soil (CK), RSD incorporated with sawdust (SA), molasses (MO), and their combinations (SA + MO) on the bacterial community and functional composition. The results showed that RSD treatments significantly altered soil bacterial community structure compared to CK treatment. The bacterial community structure and composition in MO and SA + MO treatments were clustered compared to SA treatment. This was mainly attributed to the readily decomposable carbon sources in molasses having a stronger driving force to reshape the soil microbial community during the RSD process. Furthermore, the functional compositions, such as the disinfestation efficiency of F. oxysporum (96.4 - 99.1%), abundances of nitrogen functional genes, soil metabolic activity, and functional diversity, were significantly increased in all of the RSD treatments. The highest disinfestation efficiency and abundances of denitrification (nirS and nrfA) and nitrogen fixation (nifH) genes were observed in SA + MO treatment. Specifically, SA + MO treatment enriched more abundant beneficial genera, e.g., Oxobacter, Paenibacillus, Cohnella, Rummeliibacillus, and Streptomyces, which were significantly and positively linked to disinfestation efficiency, soil metabolic activity, and denitrification processes. Our results indicated that combining RSD practices with liquid-readily decomposable compounds and solid plant residues could effectively improve soil microbial community and functional composition.

Assessing oxygen limiting fermentation conditions for 2,3-butanediol production from Paenibacillus polymyxa

2,3-butanediol (2,3-BDO) is a platform chemical that can be converted to a wide array of products ranging from bio-based materials to sustainable aviation fuel. This chemical can be produced by a variety of microorganisms in fermentation processes. Challenges remain for high titer 2,3-BDO production during fermentation due to several parameters, but controlling oxygen is one of the most relevant processing parameters to ensure viable product output. This work investigated the fermentation of plant biomass sugars by the 2,3-BDO producer Paenibacillus polymyxa. Aerobic and oxygen limited fermentation conditions were initially evaluated using molasses-based media to determine cell growth and 2,3-BDO output. Similar conditions were then evaluated on hydrolysate from pretreated sweet sorghum bagasse (SSB) that contained fermentable sugars from structural polysaccharides. Fermentations in molasses media under aerobic conditions found that 2,3-BDO could be generated, but over time the amount of 2,3-BDO decreased due to conversion back into acetoin. Oxygen limited fermentation conditions exhibited improved biomass growth, but only limited suppression of 2,3-BDO conversion to acetoin occurred. Glucose depletion appeared to have a greater role influencing 2,3-BDO conversion back into acetoin. Further improvements in 2,3-BDO yields were found by utilizing detoxified SSB hydrolysate.