Systems biology of recombinant protein production in Bacillus megaterium

Effects of Bacillus megatherium 1259 on Growth Performance, Nutrient Digestibility, Rumen Fermentation, and Blood Biochemical Parameters in Holstein Bull Calves

Simple Summary

This study was conducted to investigate the effects of dietary supplementation with Bacillus megaterium 1259 (BM1259) on growth performance, nutrient digestibility, rumen fermentation, and blood biochemical parameters in Holstein bull calves. The results demonstrated that the addition of BM1259 to the diets can significantly improve the growth performance and elevate the apparent digestibility of crude protein and neutral detergent fiber. Moreover, supplementation with BM1259 ameliorated rumen fermentation and reduced the emission of both ammoniacal nitrogen and sulfuretted hydrogen in feces and urine. In addition, adding 12 g/head/day of BM1259 had no adverse effect on blood biochemical parameters and the health status of Holstein bull calves. This study demonstrates that BM1259 can be applied as a potential microecologics to improve production performance and nitrogen utilization in Holstein bull calves.

Abstract

Bacillus megaterium is an ideal microecologics in the feed industry. BM1259 was already isolated from chicken manure and the whole-genome sequencing was also analyzed in our previous study. However, few studies concentrated on dietary supplementation with BM1259 in young ruminants and especially its effect on Holstein bull calves have not been reported. Hence, this experiment was conducted with the aim to evaluate the effects of BM1259 on growth performance, nutrient digestibility, rumen fermentation, and blood biochemical parameters in Holstein bull calves. Twenty-four healthy Holstein bull calves with the initial age of 90 days old and a similar body weight (115 ± 6.5 kg) were selected and randomly allocated into two groups with one Holstein bull calf in each pen (2.5 m × 2.2 m). Holstein bull calves in the control group (COG) were fed a basal total mixed ration (TMR), while experimental treatments (BMG) were fed with the TMR diet supplemented with 12 g/head/day of BM1259 powder (1 × 10¹⁰ cfu/g) separately. Results showed that (1) the average daily gain and dry matter intake of the BMG were significantly higher than those of the COG (p < 0.01), increased by 12.5% and 8.79%, respectively, during the 4–8 weeks after the addition of 12 g/head/day of BM1259; from 0 to 8 weeks, ADG (p < 0.05) and DMI (p < 0.05) in the BMG were significantly higher than those in the COG, increased by 14.9% and 6.04%, respectively. (2) At the end of the fourth week, the apparent digestibility of crude protein and neutral detergent fiber in the BMG was significantly higher than that in the COG (p < 0.05), increased by 5.97% and 6.70%, respectively; at the end of the eighth week, the apparent digestibility of crude protein and neutral detergent fiber was significantly higher than that of the COG (p < 0.01), increased by 5.88% and 10.26%, respectively. (3) At the end of the eighth week, the rumen fluid pH (p < 0.05), MCP (p < 0.05), and acetate (p < 0.05) in the BMG were significantly higher than those in the COG, increased by 9.03%, 19.68%, and 12.74%, respectively; at the end of the fourth and eighth week, NH₃-N concentration in the BMG was significantly lower than that in the COG, with a decrease of 21.81% and 16.40%, respectively. (4) At the end of the fourth (p < 0.05) and eighth week (p < 0.05), the glutamate content of the rumen fluid of the Holstein bull calves in the BMG was significantly higher than that in the COG, increased by 13.21% and 14.32%, respectively; at the end of the fourth week, the contents of glutamate in the serum (p < 0.05), urine (p < 0.05), and feces (p < 0.05) of the Holstein bull calves in the BMG were significantly lower than those in the COG, decreased by 25.76%, 33.87%, and 9.23%, respectively; at the end of the eighth week, the contents of glutamate in the serum, urine, and feces of the Holstein bull calves in the BMG were significantly lower than those in the COG (p < 0.01), decreased by 26.69%, 27.94%, and 11.11%, respectively. (5) After adding 12 g/head/day of BM1259, the urine ammonia–nitrogen content of the BMG was extremely significantly lower than that of the COG at the end of the fourth and eighth week (p < 0.01), decreased by 54.60% and 40.31%, respectively. (6) After adding 12 g/head/day of BM1259, there was no significant effect on the level of blood biochemical parameters of the Holstein bull calves. This study demonstrates that BM1259 can be applied as a potential microecologics to improve growth performance, nutrient digestibility, rumen fermentation, and nitrogen utilization in Holstein bull calves.

Flux Connections Between Gluconate Pathway, Glycolysis, and Pentose-Phosphate Pathway During Carbohydrate Metabolism in Bacillus megaterium QM B1551

Bacillus megaterium is a bacterium of great importance as a plant-beneficial bacterium in agricultural applications and in industrial bioproduction of proteins. Understanding intracellular processing of carbohydrates in this species is crucial to predicting natural carbon utilization as well as informing strategies in metabolic engineering. Here, we applied stable isotope-assisted metabolomics profiling and metabolic flux analysis to elucidate, at high resolution, the connections of the different catabolic routes for carbohydrate metabolism immediately following substrate uptake in B. megaterium QM B1551. We performed multiple 13C tracer experiments to obtain both kinetic and long-term 13C profiling of intracellular metabolites. In addition to the direct phosphorylation of glucose to glucose-6-phosphate (G6P) prior to oxidation to 6-phosphogluconate (6P-gluconate), the labeling data also captured glucose catabolism through the gluconate pathway involving glucose oxidation to gluconate followed by phosphorylation to 6P-gluconate. Our data further confirmed the absence of the Entner-Doudoroff pathway in B. megaterium and showed that subsequent catabolism of 6P-gluconate was instead through the oxidative pentose-phosphate (PP) pathway. Quantitative flux analysis of glucose-grown cells showed equal partition of consumed glucose from G6P to the Embden-Meyerhof-Parnas (EMP) pathway and from G6P to the PP pathway through 6P-gluconate. Growth on fructose alone or xylose alone was consistent with the ability of B. megaterium to use each substrate as a sole source of carbon. However, a detailed 13C mapping during simultaneous feeding of B. megaterium on glucose, fructose, and xylose indicated non-uniform intracellular investment of the different carbohydrate substrates. Flux of glucose-derived carbons dominated the gluconate pathway and the PP pathway, whereas carbon flux from both glucose and fructose populated the EMP pathway; there was no assimilatory flux of xylose-derived carbons. Collectively, our findings provide new quantitative insights on the contribution of the different catabolic routes involved in initiating carbohydrate catabolism in B. megaterium and related Bacillus species.

Regulated ploidy of Bacillus subtilis and three new isolates of Bacillus and Paenibacillus

Bacteria were long assumed to be monoploid, maintaining one copy of a circular chromosome. In recent years it became obvious that the majority of species in several phylogenetic groups of prokaryotes are oligoploid or polyploid. The present study aimed at investigating the ploidy in Gram-positive aerobic endospore-forming bacteria. First, the numbers of origins and termini of the widely used laboratory strain Bacillus subtilis 168 were quantified. The strain was found to be mero-oligoploid in exponential phase (5.9 origins, 1.2 termini) and to down-regulate the number of origins in stationary phase. After inoculation of fresh medium with stationary-phase cells the onset of replication preceded the onset of mass increase. For the analysis of the ploidy in fresh isolates, three strains were isolated from soil, which were found to belong to the genera of Bacillus and Paenibacillus. All three strains were found to be mero-oligoploid in exponential phase and exhibit a growth phase-dependent down-regulation of the ploidy level in stationary phase. Taken together, these results indicate that mero-oligoploidy as well as growth phase-dependent copy number regulation might be widespread in and typical for Bacillus and related genera.

Combinatorial promoter engineering of glucokinase and phosphoglucoisomerase for improved N-acetylglucosamine production in Bacillus subtilis

In previous work, a recombinant Bacillus subtilis strain was successfully constructed for microbial production of N-acetylglucosamine (GlcNAc). In this study, GlcNAc titer was further improved by combinatorial promoter engineering of key genes glck encoding glucokinase and pgi encoding phosphoglucoisomerase. First, three promoters including constitutive promoter P₄₃, xylose inducible promoter P_xylA, and isopropyl-β-d-thiogalactoside inducible P_grac were used to replace the native promoters of glcK and pgi, yielding 12 recombinant strains. It was found that when glcK and pgi were both under the control of promoter P_xylA, the highest GlcNAc titer in 3-L fed-batch bioreactor reached 35.12g/L, which was 52.6% higher than that of the initial host. Next, the transcriptional levels of the related genes in glycolysis, GlcNAc synthesis pathway, peptidoglycan synthesis pathway, and pentose phosphate pathway were investigated by quantitative real-time PCR analysis. Fine-tuning upper GlcNAc synthesis pathway by combinatorial promoter substitution significantly enhanced GlcNAc production in engineered B. subtilis.

Genome sequences of the biotechnologically important Bacillus megaterium strains QM B1551 and DSM319

Bacillus megaterium is deep-rooted in the Bacillus phylogeny, making it an evolutionarily key species and of particular importance in understanding genome evolution, dynamics, and plasticity in the bacilli. B. megaterium is a commercially available, nonpathogenic host for the biotechnological production of several substances, including vitamin B(12), penicillin acylase, and amylases. Here, we report the analysis of the first complete genome sequences of two important B. megaterium strains, the plasmidless strain DSM319 and QM B1551, which harbors seven indigenous plasmids. The 5.1-Mbp chromosome carries approximately 5,300 genes, while QM B1551 plasmids represent a combined 417 kb and 523 genes, one of the largest plasmid arrays sequenced in a single bacterial strain. We have documented extensive gene transfer between the plasmids and the chromosome. Each strain carries roughly 300 strain-specific chromosomal genes that account for differences in their experimentally confirmed phenotypes. B. megaterium is able to synthesize vitamin B(12) through an oxygen-independent adenosylcobalamin pathway, which together with other key energetic and metabolic pathways has now been fully reconstructed. Other novel genes include a second ftsZ gene, which may be responsible for the large cell size of members of this species, as well as genes for gas vesicles, a second β-galactosidase gene, and most but not all of the genes needed for genetic competence. Comprehensive analyses of the global Bacillus gene pool showed that only an asymmetric region around the origin of replication was syntenic across the genus. This appears to be a characteristic feature of the Bacillus spp. genome architecture and may be key to their sporulating lifestyle.