Characteristics and biological control functions of Bacillus sp.PM8313 as a host-associated probiotic in red sea bream(Pagrus major)aquaculture

Host-associated probiotics(HAPs)are bacteria originally isolated from rearing water or the host's gastrointestinal tract in order to enhance the host's growth and health.This study investigated the HAP potential of Bacillus sp.PM8313,isolated from wild red sea bream(Pagrus major),through characterization and feeding trials.Results based on in vitro tests showed that PM8313 is safe,confirming its hemolytic,cytotoxic,and antibiotic resistance.In addition,PM8313 showed advantages as a probiotic with high viability in the gastrointestinal model and a high cell adhesion rate.Whole-genome sequencing demonstrated that PM8313 has a 4,615,871 bp single circular chromosome and a guaninecytosine content of 45.25%.It also showed the absence of genes encoding virulence factors,such as cytotoxin,enterotoxin,hemolysin,sphingomyelinase,and phospholipase.In the feeding trial,a supplemental diet of 1×10^(8)CFU/g PM8313 positively altered the weight gain,digestive enzyme activity,and intestinal microbiota composition of red sea bream.Analysis of nonspecific immune parameters and immune-related gene expression,and a challenge test showed that PM8313 supplementation increases immunity and pathogenic bacteria resistance.Our findings suggest that PM8313 should be considered for application as a novel HAP to red sea bream aquaculture.

Host-Associated Quantitative Abundance Profiling Reveals the Microbial Load Variation of Root Microbiome

Plant-associated microbes are critical for plant growth and survival under natural environmental conditions.To date,most plant microbiome studies involving high-throughput amplicon sequencing have focused on the relative abundance of microbial taxa.However,this technique does not assess the total microbial load and the abundance of individual microbes relative to the amount of host plant tissues.Here,we report the development of a host-associated quantitative abundance profiling(HA-QAP)method that can accurately examine total microbial load and colonization of individual root microbiome members relative to host plants by the copy-number ratio of microbial marker gene to plant genome.We validate the HAQAP method using mock experiments,perturbation experiments,and metagenomic sequencing.The HA-QAP method eliminates the generation of spurious outputs in the classical method based on microbial relative abundance,and reveals the load of root microbiome to host plants.Using the HA-QAP method,we found that the copy-number ratios of microbial marker genes to plant genome range from 1.07 to 6.61 for bacterial 16S rRNA genes and from 0.40 to 2.26 for fungal internal transcribed spacers in the root microbiome samples from healthy rice and wheat.Furthermore,using HA-QAP we found that an increase in total microbial load represents a key feature of changes in root microbiome of rice plants exposed to drought stress and of wheat plants with root rot disease,which significantly influences patterns of differential taxa and species interaction networks.Given its accuracy and technical feasibility,HA-QAP would facilitate our understanding of genuine interactions between root microbiome and plants.

Host gut-derived Bacillus probiotics supplementation improves growth performance, serum and liver immunity, gut health, and resistive capacity against Vibrio harveyi infection in hybrid grouper(♀Epinephelus fuscoguttatus × ♂Epinephelus lanceolatus)

Several reports have revealed the vital role that probiotics play in fish growth and health.However,few works are available for host gut-derived probiotics on the growth,immunity,and gut microbiota of fish,especially in hybrid grouper (♀Epinephelus fuscoguttatus×♂Epinephelus lanceolatus) due to their isolation difficulty and functional verification.This study aimed at assessing 3 host gut-derived Bacillus species?effects on the growth,immune and antioxidant-biochemical responses,haematological parameters,intestinal morphology,immune-related gene expression,gut microbiota,and disease resistance against Vibrio harveyi in hybrid grouper.A total of 480 hybrid grouper (initial weight=9.03±0.02 g) were randomly allotted into 4 groups,namely,the group fed a basal diet without probiotic inclusion (control,B0),the group fed the basal diet with Bacillus velezensis GPSAK4 (BV),the group fed the basal diet with Bacillus subtilis GPSAK9 (BS),and the group fed the basal diet with Bacillus tequilensis GPSAK2 (BT) strains at 1.0×10^(9)CFU/g.After a 6-week feeding trial,the results revealed significant improvements (P<0.05) in the growth performance,whole fish-body proximate composition,blood haematological parameters,serum,liver,and intestinal biochemical indexes,intestinal morphology,and protection against V.harveyi pathogen in the probiotic-treated groups compared with the untreated.Additionally,the expressions of intestinal tight junction genes (occludin and ZO1),pro-and anti-inflammatory genes,including IL1β,IL6,IL8,TNFa,MyD88,IL10,and TGFβ,were upregulated (P<0.05) after Bacillus species administration.Host gut-derived Bacillus supplementation shaped the gut microbiota by significantly increasing (P<0.05) the relative abundance of Proteobacteria,Bacteroidetes,Actinobacteria (except the BS group),Acidobacteria(except the BT group),Cyanobacteria (except the BV and BT groups),and Verrucomicrobia phyla,as well as known beneficial genera (Romboutsia,Turicibacter,Epulopiscium,Clostridium_sensu_stricto 1 and 13,Lactobacillus,and Bacillus),but significantly decreased (P<0.05) the abundance of Firmicutes,Chloroflexi,and Fusobacteria phyla,and purported pathogenic genera (Staphylococcus and Photobacterium) compared with the control group.Collectively,the results suggest that B.velezensis GPSAK4,B.subtilis GPSAK9(especially this strain),B.tequilensis GPSAK2 dietary supplementation at 1.0×10^(9)CFU/g has positive effects on the intestinal health of hybrid grouper via microbial composition modulation,thus enhancing the assimilation and absorption of nutrients to boost fish growth,immunity,and disease resistance.

Landscape genetic analyses reveal host association of mitochondrial haplotypes in the Asian corn borer,Ostrinia furnacalis

Crop expansion often leads to high pest pressure.These pests may have fitness trade-offs related to host use,and some host-associated genotypes may benefit and increase in frequency.However,evidence concerning the effect of host availability on spatial distribution and frequency of mitochondrial haplotypes is scarce.We studied genetic variation of the Asian corn borer,Ostrinia furnacalis(Guenée),across a large area during 2 years(2016 and 2017).Mitochondrial sequence data were obtained from 530 individuals collected from 79 locations in Shandong Province,China.In total,155 haplotypes were found based on the combined cytochrome oxidase subunit 1(COI)and COII genes.Three haplotypes(H2,H12,and H23)were dominant,whereas most of the other haplotypes occurred in low frequency.A haplotype network showed that the 155 haplotypes can be grouped into three clusters.Haplotype clusters seemed to be randomly distributed.The frequency of H12(in Cluster 1)was positively correlated with maize crop proportion,but negatively correlated with other crops(primarily vegetables,oilseed crops,and cotton)at all spatial scales(1-,3-,and 5-km radius).Cluster 2 had haplotype H23,and this cluster was negatively correlated with semi-natural habitats.Cluster 3 had no dominant haplotype and was not affected by landscape factors.We conclude that H12 may be a maize-associated haplotype.Further study is needed to verify the possibility that the carriers of this haplotype may possess some fitness trade-offs.Our study highlights the importance of host availability in O.furnacalis haplotype distribution and frequency.