Effects of Different Culture Conditions on the Biofilm Formation of Bacillus pumilus HR10

Biocontrol of fungal phytopathogens by Bacillus pumilus

Plant growth-promoting bacteria are one of the most interesting methods of controlling fungal phytopathogens. These bacteria can participate in biocontrol via a variety of mechanisms including lipopeptide production, hydrolytic enzymes (e.g., chitinase, cellulases, glucanase) production, microbial volatile organic compounds (mVOCs) production, and induced systemic resistance (ISR) triggering. Among the bacterial genera most frequently studied in this aspect are Bacillus spp. including Bacillus pumilus. Due to the range of biocontrol traits, B. pumilus is one of the most interesting members of Bacillus spp. that can be used in the biocontrol of fungal phytopathogens. So far, a number of B. pumilus strains that exhibit biocontrol properties against fungal phytopathogens have been described, e.g., B. pumilus HR10, PTB180, B. pumilus SS-10.7, B. pumilus MCB-7, B. pumilus INR7, B. pumilus SE52, SE34, SE49, B. pumilus RST25, B. pumilus JK-SX001, and B. pumilus KUDC1732. B. pumilus strains are capable of suppressing phytopathogens such as Arthrobotrys conoides, Fusarium solani, Fusarium oxysporum, Sclerotinia sclerotiorum, Rhizoctonia solani, and Fagopyrum esculentum. Importantly, B. pumilus can promote plant growth regardless of whether it alters the native microbiota or not. However, in order to increase its efficacy, research is still needed to clarify the relationship between the native microbiota and B. pumilus. Despite that, it can already be concluded that B. pumilus strains are good candidates to be environmentally friendly and commercially effective biocontrol agents.

Isolation of Potential Probiotic Bacillus spp. from the Intestine of Nile Tilapia to Construct Recombinant Probiotic Expressing CC Chemokine and Its Effectiveness on Innate Immune Responses in Nile Tilapia

This study aimed to investigate the potential probiotic Bacillus spp. from the intestine of Nile tilapia in order to construct a recombinant probiotic for the enhancement of the Nile tilapia immune response. One hundred bacterial isolates from the intestine of Nile tilapia were characterized for species identification using the 16s ribosomal RNA (rRNA). Only Bacillus isolates with exhibited antagonistic activity were investigated for their biological functions, which included protease-producing capacity, bile salts and pH tolerance, antibiotic susceptibility, and pathogenicity tests. According to the best results, Bacillus isolate B29, as closely related to B. subtilis, was selected to construct a recombinant probiotic for the delivery of CC chemokine protein (pBESOn-CC). The existence of recombinant probiotics was confirmed by Western blotting before the feeding trial. In addition, the CC chemokine mRNA level was quantified in the intestine of fish fed probiotics after 30 days of feeding. Total immunoglobulin, lysozyme activity, alternative complement 50 activity (ACH50), and phagocytic activity of fish fed either wild-type or recombinant probiotics were significantly increased, indicating that probiotics could stimulate the Nile tilapia immune system through different processes. Interestingly, the dietary supplementation of recombinant probiotics has a stronger immune response enhancement than the wild-type strain.

Smoothie Drinks: Possible Source of Resistant and Biofilm-Forming Microorganisms

Smoothie drinks are currently very popular drinks sold especially in fast food establishments. However, smoothies are a significant source of microorganisms. The aim of this study was to evaluate the microbiological quality of smoothies purchased in Eastern Bohemia. A higher prevalence of mesophilic aerobic bacteria (5.4-7.2 log CFU/mL), yeast (4.4-5.9 log CFU/mL) and coliform bacteria (3.1-6.0 log CFU/mL) was observed in vegetable smoothies, in which even the occurrence of enterococci (1.6-3.3 log CFU/mL) was observed. However, the occurrence of S. aureus, Salmonella spp. and Listeria spp. was not observed in any samples. Nevertheless, antimicrobial resistance was observed in 71.8% of the isolated strains. The highest level of resistance was found in isolates from smoothie drinks with predominantly vegetable contents (green smoothie drinks). Considerable resistance was observed in Gram-negative rods, especially to amoxicillin (82.2%) and amoxicillin with clavulanic acid (55.6%). Among enterococci, only one vancomycin-resistant strain was detected. The vast majority of isolated strains were able to form biofilms at a significant level, which increases the clinical importance of these microorganisms. The highest biofilm production was found in Pseudomonas aeruginosa, Kocuria kristinae and Klebsiella pneumoniae. Overall, significant biofilm production was also noted among isolates of Candida spp.

A manganese-oxidizing bacterium-Enterobacter hormaechei strain DS02Eh01: Capabilities of Mn(II) immobilization, plant growth promotion and biofilm formation

While biogenic Mn oxides (BioMnO_x) generated by Mn(II)-oxidizing bacteria (MOB) have attracted increasing attention, a MOB strain isolated from Mn-polluted sediments was identified and assigned as Enterobacter hormaechei DS02Eh01. Its Mn(II) immobilization activity, plant growth-promoting traits, and biofilm formation capability were investigated. The results showed that strain DS02Eh01 was found to be able to tolerate Mn(II) up to 122 mM. The strain immobilized Mn(II) in aquatic media mainly through extracellular adsorption, bio-oxidation and pH-induced precipitation as well as manganese oxidation. DS02Eh01-derived BioMnO_x are negatively charged and have a larger specific surface area (86.70 m²/g) compared to the previously reported BioMnO_x. The strain can immobilize Mn(II) at extreme levels, for instance, when it was exposed to 20 mM Mn(II), about 59% of Mn(II) were found immobilized and 17% of Mn(II) were converted to MnO_x. The SEM and TEM observation revealed that the DS02Eh01-derived BioMnO_x were aggregates doped with granules and microbial pellets. The precipitated Mn(II) and the Mn(III)/Mn(IV) oxides co-existed in BioMnO_x, in which Mn(II) and Mn(IV) were found dominant with Mn(II) accounting for 49.6% and Mn(IV) accounting for 41.3%. DS02Eh01 possesses plant growth-promoting traits and biofilm formation capacity even under Mn(II) exposure. Mn(II) exposure at 5 mM was found to stimulate strain DS02Eh01 to form biofilms, from which, the extracted EPS was mainly composed of aromatic proteins. This study reveals that E. hormaechei strain DS02Eh01 possesses the potential in environmental ecoremediation via coupling processes of macrophytes extraction, biochemical immobilization and biosorption.

Biofilm formation and extracellular polymeric substance (EPS) production by Bacillus haynesii and influence of hexavalent chromium

Biofilm-forming bacteria play a key role in the removal of heavy metals including hexavalent chromium [Cr(VI)] from contaminated sites. In this study, biofilm-forming B. haynesii was examined for extracellular polymeric substances (EPS) production and hexavalent chromium [Cr(VI)] reduction potential. Exposure of B. haynesii with Cr(VI) (12.5-100 mg L^-1) for 48 h enhanced pellicle dry weight (20-24%), cell-size (5.1-23.2%) and cell granularity (8.5-19.2%). Also, EPS production was increased by 10-35% by promoting the synthesis of protein (94-119%) and polysaccharide (2-33%) components in EPS. Further, the reduction (27.7 %) and distribution (15.87%) of Cr(VI) were mainly mediated by EPS than the other cellular fractions. Findings of the study suggest that the EPS from B. haynesii was efficiently reduced to Cr(VI) present in aqueous medium and the potential of the organism can be further explored for the mitigation of Cr(VI) contamination.