Isolation and screening of probiotic candidates from marron, Cherax cainii (Austin, 2002) gastrointestinal tract (GIT) and commercial probiotic products for the use in marron culture

Bacillus genus industrial applications and innovation: First steps towards a circular bioeconomy

In recent decades, environmental concerns have directed several policies, investments, and production processes. The search for sustainable and eco-friendly strategies is constantly increasing to reduce petrochemical product utilization, fossil fuel pollution, waste generation, and other major ecological impacts. The concepts of circular economy, bioeconomy, and biorefinery are increasingly being applied to solve or reduce those problems, directing us towards a greener future. Within the biotechnology field, the Bacillus genus of bacteria presents extremely versatile microorganisms capable of producing a great variety of products with little to no dependency on petrochemicals. They are able to grow in different agro-industrial wastes and extreme conditions, resulting in healthy and environmentally friendly products, such as foods, feeds, probiotics, plant growth promoters, biocides, enzymes, and bioactive compounds. The objective of this review was to compile the variety of products that can be produced with Bacillus cells, using the concepts of biorefinery and circular economy as the scope to search for greener alternatives to each production method and providing market and bioeconomy ideas of global production. Although the genus is extensively used in industry, little information is available on its large-scale production, and there is little current data regarding bioeconomy and circular economy parameters for the bacteria. Therefore, as this work gathers several products' economic, production, and environmentally friendly use information, it can be addressed as one of the first steps towards those sustainable strategies. Additionally, an extensive patent search was conducted, focusing on products that contain or are produced by the Bacillus genus, providing an indication of global technology development and direction of the bacteria products. The Bacillus global market represented at least $18 billion in 2020, taking into account only the products addressed in this article, and at least 650 patent documents submitted per year since 2017, indicating this market's extreme importance. The data we provide in this article can be used as a base for further studies in bioeconomy and circular economy and show the genus is a promising candidate for a greener and more sustainable future.

Characterization of Potential Probiotic Activity of Lactic Acid Bacteria Isolated from Camel Colostrum by Biochemical and Molecular Methods

A total of 60 isolates of lactic acid bacteria (LAB) were isolated from Jordanian camel colostrum using biochemical and molecular methods. Two dominant species were identified, and they were Lactobacillus salivarius and Enterococcus faecium. The entire 60 isolated LAB were tested for their acidity and bile tolerance, antimicrobial activity, and antibiotic sensitivity to test their potential probiotic activity. All 60 isolates were tolerant to different pH concentrations (2, 3, 4, 5, 6, 7, 8, 9, and 10) with different survival rates (%). The entire isolates were also tolerant to different bile salt concentrations (0.2, 0.4, 0.6, 0.8, 1, 2, and 3) with different bile resistance (%). All isolates have a different range of antimicrobial activity against Staphylococcus aureus, E. coli, and Salmonella typhimurium. The 60 isolates were almost sensitive to ampicillin, amoxicillin, and clarithromycin when different concentrations were used except some isolates of intermediate resistance. Only 6% of the isolates were resistant to clarithromycin at a concentration of 15 µg per disc.

Evaluation of probiotic properties of Lysinibacillus macroides under in vitro conditions and culture of Cyprinus carpio on growth parameters

Cyprinus carpio is an important freshwater fish in aquaculture. It was used for the isolation of potential probiotic strain for aquaculture applications. The most dominant strain was isolated on MRS agar from the gastrointestinal (GI) of C. carpio and identified as Lysinibacillus macroides using molecular marker 16S rRNA gene. Various probiotic properties such as acid and bile tolerance and antibiotic susceptibility were analysed under in vitro conditions. Further, formulate pelletized feed using probiotic (L. macroides) in different concentrations (2, 4, 6 and 8%). Rearing of C. carpio was carried out 45 days and fed with formulated feed. The highest length (5.14 ± 0.07 cm) and weight (3.56 ± 0.07 g) of C. carpio fingerlings was recorded in the 8% LM probiotic pelletized feed, while in fingerlings fed with control showed lower in the length (3.02 ± 0.13 cm) and the weight (0.92 ± 0.04 g) on the 45th day of the experiment. Both percentage of weight gain (PWG) and specific growth rate (SGR) were significantly increased (P < 0.05) of C. carpio fingerlings fed with probiotic feed compared to control feed. Hence, the use of probiotic bacteria could be an encouraging alternative feed for future endeavours in the field of aquaculture. In conclusion, L. macroides can serve as probiotic for sustainable, competitive and promising beneficial bacteria to aquaculture industry.

Bacillus velezensis WLYS23 strain possesses antagonistic activity against hybrid snakehead bacterial pathogens

AIM

The aims of this study were to screen an antagonistic probiotic for the prevention and control of bacterial diseases in snakehead fish and to evaluate the antimicrobial activities, biosafety and biocontrol effect of the antagonistic strain.

METHODS AND RESULTS

In this study, the WLYS23 strain exhibiting the most effective antagonistic properties against several fish pathogens was selected from the intestine of healthy snakehead fish. The strain was identified as Bacillus velezensis based on morphological, physiological and biochemical characteristics, and phylogenetic analysis. This strain showed amylase, cellulase, protease and lipase activities according to extracellular enzyme activity assays. Moreover, the cell-free extract of the WLYS23 strain exhibited strong antibacterial activity, with MICs of ≤64 μg ml^-1 for most fish pathogens. Additionally, the cell-free extract was heat and pH stable, and resistant to protease, whereas their antimicrobial activities were significantly influenced by metal ions at high concentration. The WLYS23 strain and its cell-free extract were safe for snakehead and zebrafish. The disease resistance of snakehead fish was significantly increased following administration of the WLYS23 strain and its cell-free extract respectively. The complete genome of the WLYS23 strain was sequenced and found to harbour seven gene clusters encoding secondary metabolites with antimicrobial activity.

CONCLUSION

The WLYS23 strain possesses great potential as a biocontrol agent, which can be commercially developed to improve disease control in freshwater aquaculture.

SIGNIFICANCE AND IMPACT OF THE STUDY

Snakehead fish are important commercially farmed fish worldwide. However, the bacterial diseases caused by Aeromonas sp. and Nocardia seriolae in farmed snakehead fish lead to huge economic losses. Safe, economical and efficient probiotics are limited to prevent and control these diseases. Here, we provide a promising biocontrol agent with antagonistic activity against bacterial diseases of snakehead.

Microbial pathogens of freshwater crayfish: A critical review and systematization of the existing data with directions for future research

Despite important ecological role and growing commercial value of freshwater crayfish, their diseases are underresearched and many studies examining potential crayfish pathogens do not thoroughly address their epizootiology, pathology or biology. This study reviews over 100 publications on potentially pathogenic viruses, bacteria, fungi and fungal-like microorganisms reported in crayfish and systematizes them based on whether pathogenicity has been observed in an analysed species. Conclusions on pathogenicity were based on successful execution of infectivity trials. For 40.6% of examined studies, microbes were successfully systematized, while for more than a half (59.4%) no conclusion on pathogenicity could be made. Fungi and fungal-like microorganisms were the most studied group of microbes with the highest number of analysed hosts, followed by bacteria and viruses. Our analysis demonstrated the need for: (a) inclusion of higher number of potential host species in the case of viruses, (b) research of bacterial effects in tissues other than haemolymph, and (c) more research into potential fungal and fungal-like pathogens other than Aphanomyces astaci. We highlight the encountered methodological challenges and biases and call for a broad but standardized framework for execution of infectivity trials that would enable systematic data acquisition on interactions between microbes and the host.

Community Structure of Protease-Producing Bacteria Cultivated From Aquaculture Systems: Potential Impact of a Tropical Environment

Protease-producing bacteria play vital roles in degrading organic matter of aquaculture system, while the knowledge of diversity and bacterial community structure of protease-producing bacteria is limited in this system, especially in the tropical region. Herein, 1,179 cultivable protease-producing bacterial strains that belonged to Actinobacteria, Firmicutes, and Proteobacteria were isolated from tropical aquaculture systems, of which the most abundant genus was Bacillus, followed by Vibrio. The diversity and relative abundance of protease-producing bacteria in sediment were generally higher than those in water. Twenty-one genera from sediment and 16 genera from water were identified, of which Bacillus dominated by Bacillus hwajinpoensis in both and Vibrio dominated by Vibrio owensii in water were the dominant genera. The unique genera in sediment or water accounted for tiny percentage may play important roles in the stability of community structure. Eighty V. owensii isolates were clustered into four clusters (ET-1-ET-4) at 58% of similarity by ERIC-PCR (enterobacterial repetitive intergenic consensus-polymerase chain reaction), which was identified as a novel branch of V. owensii. Additionally, V. owensii strains belonged to ET-3 and ET-4 were detected in most aquaculture ponds without outbreak of epidemics, indicating that these protease-producing bacteria may be used as potential beneficial bacteria for wastewater purification. Environmental variables played important roles in shaping protease-producing bacterial diversity and community structure in aquaculture systems. In sediment, dissolved oxygen (DO), chemical oxygen demand (COD), and salinity as the main factors positively affected the distributions of dominant genus (Vibrio) and unique genera (Planococcus and Psychrobacter), whereas temperature negatively affected that of Bacillus (except B. hwajinpoensis). In water, Alteromonas as unique genus and Photobacterium were negatively affected by NO₃ ^--N and NO₂ ^--N, respectively, whereas pH as the main factor positively affected the distribution of Photobacterium. These findings will lay a foundation for the development of protease-producing bacterial agents for wastewater purification and the construction of an environment-friendly tropical aquaculture model.

Bacillus velezensis LF01: in vitro antimicrobial activity against fish pathogens, growth performance enhancement, and disease resistance against streptococcosis in Nile tilapia (Oreochromis niloticus)

Streptococcus agalactiae is a major pathogen causing streptococcosis. To prevent and control this bacterial disease, antagonistic bacteria have become a new research hotspot. This study evaluated the probiotic potential of Bacillus velezensis LF01 strain, which is antagonistic to S. agalactiae. The active compounds produced by LF01 showed antimicrobial activity against a broad spectrum of fish pathogens, including S. agalactiae, Streptococcus iniae, Aeromonas hydrophila, Edwardsiella tarda, Edwardsiella ictaluri, Aeromonas schubertii, Aeromonas veronii, Aeromonas jandaei, and Vibrio harveyi. The antimicrobial compounds were heat stable, pH stable, UV stable, resistant to proteases, and could be stored for a long time. To evaluate the probiotic function of LF01 in Nile tilapia, juveniles were divided into three treatment groups: a control group, an interval feeding group, and a continuous feeding group. Tilapia fed with LF01-supplemented diets (1.0 × 10⁹ CFU/g) showed significantly better growth performances than those of the control group (P < 0.05). Tilapia fed with LF01-supplemented diets significantly increased lysozyme (LZY) and superoxide dismutase (SOD) activities. The expression of three immune-related genes (C3, lyzc, and MHC-IIβ) was higher in the intestine, head kidney, and gill of tilapia from the continuous feeding group than in those from the control group (P < 0.05). Tilapia fed with LF01-supplemented diets showed remarkably improved survival rates after S. agalactiae infection, and analysis of their intestinal tract pathogens revealed that the abundance of Edwardsiella and Plesiomonas had significantly decreased compared with the control group. Our findings demonstrate that LF01 is an effective antagonist against various fish pathogens and has potential for controlling infections by Streptococcus spp. and other pathogens in tilapia.

Isolation and characterization of Bacillus spp. strains as potential probiotics for poultry

Probiotics have become one of the potential solutions to global restriction on antibiotic use in food animal production. Bacillus species have been attractive probiotics partially due to their long-term stability during storage. In this study, 200 endospore-forming bacteria isolates were recovered from sourdough and the gastrointestinal tract (GIT) of young broiler chicks. Based on the production of a series of exoenzymes and survivability under stress conditions similar to those in the poultry GIT, 42 isolates were selected and identified by 16S rRNA gene sequencing. Seven strains with a profile of high enzymatic activities were further evaluated for sporulation efficiency, biofilm formation, compatibility among themselves (Bacillus spp.), and antagonistic effects against three bacteria pathogenic to poultry and humans: Enterococcus cecorum, Salmonella enterica, and Shiga-toxin-producing Escherichia coli. The strains from sourdough were identified as Bacillus amyloliquefaciens whereas the ones from the chicks' GIT were Bacillus subtilis. These strains demonstrated remarkable potential as probiotics for poultry.

Dietary supplementation of black soldier fly (Hermetica illucens) meal modulates gut microbiota, innate immune response and health status of marron (Cherax cainii, Austin 2002) fed poultry-by-product and fishmeal based diets

The present study aimed to evaluate the dietary supplementary effects of black soldier fly (Hermetia illucens) (BSF) meal on the bacterial communities in the distal gut, immune response and growth of freshwater crayfish, marron (Cherax cainii) fed poultry-by-product meal (PBM) as an alternative protein source to fish meal (FM). A total of 64 marron were randomly distributed into 16 different tanks with a density of four marron per tank. After acclimation, a 60-days feeding trial was conducted on marron fed isonitrogenouts and isocalorific diets containing protein source from FM, PBM, and a combination of FM + BSF and PBM + BSF. At the end of the trial, weight gain and growth of marron were found independent of any dietary treatment, however, the two diets supplemented with BSF significantly (P < 0.05) enhanced haemolymph osmolality, lysozyme activity, total haemocyte counts, and protein and energy contents in the tail muscle. In addition, the analysis of microbiota and its predicted metabolic pathways via 16s rRNA revealed a significantly (P < 0.05) higher bacterial activity and gene function correlated to biosynthesis of protein, energy and secondary metabolites in PBM + BSF than other dietary groups. Diets FM + BSF and PBM + BSF were seen to be associated with an up-regulation of cytokine genes in the intestinal tissue of marron. Overall, PBM + BSF diet proved to be a superior diet in terms of improved health status, gut microbiota and up-regulated expression of cytokine genes for marron culture.

In Vitro Selection and Identification of Potential Probiotics Isolated from the Gastrointestinal Tract of Nile Tilapia, Oreochromis niloticus

Fish gut bacteria can be used as probiotics for aquaculture. The aim of this study is to screen and identify beneficial probiotic bacteria from the gut of Nile tilapia, Oreochromis niloticus. Nine out of one hundred thirty-five isolates were non-pathogenic through intraperitoneal injection and had antibacterial activities with at least a strain from the five isolated fish pathogens, Aeromonas sobria, Aeromonas hydrophila, Pseudomonas aeruginosa, Pseudomonas putida, and Staphylococcus aureus. Further tests showed that such isolates can survive in the presence of high bile concentration (10%) and at different acidic pH values. A strains (14HT) was sensitive to all selected antibiotics, two strains were (9HT and 11HT) resistant to streptomycin and three strains (9HT, 11HT and 38HT) had resistance to two antibiotics. Four isolates (11HT, 33HT, 38HT and 41HT) had an amylase and a protease activities and one strain (47HT) showed only amylase activity. Based on 16S rRNA gene analysis, the isolated strains were identified as follows: Lactococcus lactis (8HT, 9HT, 11HT and 33HT); Enterococcus faecalis (14HT), Lysinibacillus sp. (38HT) and Citrobacter freundii (39HT, 41HT and 47HT).