Production of Hydrolases by N2-fixing Microorganisms

Stress-Responsive Gene Expression, Metabolic, Physiological, and Agronomic Responses by Consortium Nano-Silica with Trichoderma against Drought Stress in Bread Wheat

The exploitation of drought is a critical worldwide challenge that influences wheat growth and productivity. This study aimed to investigate a synergistic amendment strategy for drought using the single and combined application of plant growth-promoting microorganisms (PGPM) (Trichoderma harzianum) and biogenic silica nanoparticles (SiO2NPs) from rice husk ash (RHA) on Saudi Arabia's Spring wheat Summit cultivar (Triticum aestivum L.) for 102 DAS (days after sowing). The significant improvement was due to the application of 600 ppm SiO2NPs and T. harzianum + 600 ppm SiO2NPs, which enhanced the physiological properties of chlorophyll a, carotenoids, total pigments, osmolytes, and antioxidant contents of drought-stressed wheat plants as adaptive strategies. The results suggest that the expression of the studied genes (TaP5CS1, TaZFP34, TaWRKY1, TaMPK3, TaLEA, and the wheat housekeeping gene TaActin) in wheat remarkably enhanced wheat tolerance to drought stress. We discovered that the genes and metabolites involved significantly contributed to defense responses, making them potential targets for assessing drought tolerance levels. The drought tolerance indices of wheat were revealed by the mean productivity (MP), stress sensitivity index (SSI), yield stability index (YSI), and stress tolerance index (STI). We employed four databases, such as BAR, InterPro, phytozome, and the KEGG pathway, to predict and decipher the putative domains in prior gene sequencing. As a result, we discovered that these genes may be involved in a range of important biological functions in specific tissues at different developmental stages, including response to drought stress, proline accumulation, plant growth and development, and defense response. In conclusion, the sole and/or dual T. harzianum application to the wheat cultivar improved drought tolerance strength. These findings could be insightful data for wheat production in Saudi Arabia under various water regimes.

Plant-associated halotolerant bacteria improving growth of Vicia faba L. Mariout-2 under salinity conditions

In this comprehensive investigation, we successfully isolated and characterized 40 distinct plant-associated halotolerant bacteria strains obtained from three halophytic plant species: Tamarix nilotica, Suaeda pruinosa, and Arthrocnemum macrostachyum. From this diverse pool of isolates, we meticulously selected five exceptional plant-associated halotolerant bacteria strains through a judiciously designed seed biopriming experiment and then identified molecularly. Bacillus amyloliquefaciens DW6 was isolated from A. macrostachyum. Three bacteria (Providencia rettgeri DW3, Bacillus licheniformis DW4, and Salinicoccus sesuvii DW5) were isolated for the first time from T. nilotica, S. pruinosa and S. pruinosa, respectively. Paenalcaligenes suwonensis DW7 was isolated for the first time from A. macrostachyum. These plant-associated halotolerant bacteria exhibited growth-promoting activities, including phosphate solubilization, nitrogen fixation, and production of bioactive compounds, i.e., ammonia, phytohormones, hydrogen cyanide, siderophores, and exopolysaccharides. A controlled laboratory experiment was conducted to reduce the detrimental impact of soil salinity. Vicia faba seedlings were inoculated individually or in mixtures by the five most effective plant-associated halotolerant bacteria to reduce the impact of salt stress and improve growth parameters. The growth parameters were significantly reduced due to the salinity stress in the control samples, compared to the experimental ones. The unprecedented novelty of our findings is underscored by the demonstrable efficacy of co-inoculation with these five distinct bacterial types as a pioneering bio-approach for countering the deleterious effects of soil salinity on plant growth. This study thus presents a remarkable contribution to the field of plant science and offers a promising avenue for sustainable agriculture in saline environments.

Synergistic effects of Azospirillum brasilense and Bacillus cereus on plant growth, biochemical attributes and molecular genetic regulation of steviol glycosides biosynthetic genes in Stevia rebaudiana

The current study aimed to scale up the favorable bio-stimulants for enhancing the growth and breeding strategies of Stevia rebaudiana to increase sugar productivity. Inoculation of 45-day-old S. rebaudiana plantlets with Bacillus cereus and Azospirillum brasilense alone or in combination for 30 days allowed comparisons among their effects on enhancement and improvement of plant growth, production of bioactive compounds and expression of steviol glycoside genes. B. cereus SrAM1 isolated from surface-sterilized Stevia rebaudiana leaves was molecularly identified using 16s rRNA and tested for its ability to promote plant growth. Beneficial endophytic B. cereus SrAM1 induced all plant growth-promoting traits, except solubilization of phosphate, therefore it showed high effectiveness in the promotion of growth and production of bioactive compounds. Treatment of plants with B. cereus SrAM1 alone revealed carbohydrates content of 278.99 mg/g, total soluble sugar of 114.17 mg/g, total phenolics content of 34.05 mg gallic acid equivalent (GAE)/g dry weight) and total antioxidants activity of 32.33 mg (A.A)/g dry weight). Thus, plantlets inoculated with B. cereus SrAM1 alone exhibited the greatest responses in physiological and morphological parameters, but plantlets inoculated with B. cereus SrAM1 + A. brasilense showed a maximal upregulation of genes responsible for the biosynthesis of steviol glycosides (Kaurene oxidase, ent-KO; UDP-dependent glycosyl transferases of UGT85C2, UGT74G1, UGT76G1). Taken together, the used bacterial strains, particularly B. cereus SrAM1 could significantly improve the growth of S. rebaudiana via dynamic interactions in plants.

Enzymatic characterization of the saliva of the eriophyid mite, Aceria pongamiae Keifer1966 (Acari: Eriophyidae) and the bacterial endobiome of the galls induced on Pongamia pinnata (L.) Pierre (Fabaceae)

Galls, like other regular plant organs, possess their own histological and physiological features. A high degree of specificity is maintained between the host and the inducer, and hence gall morphogenesis is highly conserved and would help trace gall lineages and cell fate. The present study highlights the induction and subsequent development of leaf galls on the Indian Beech tree, Pongamia pinnata (L) Pierre (Fabaceae), mediated through the active participation of a gall-inducing species of eriophyid mite, Aceria pongamiae Keifer and gall-associated bacterial endobiome. The saliva of A. pongamiae and selected strains of gall-associated bacterial endobiome were characterized in part during the study. Three strains of Staphylococcus arlettae (PGP1-3) and one strain of Bacillus flexus (PGP4) were identified from the leaf galls through 16S rDNA sequencing. The mite saliva displayed tryptophanase activity, and the bacterial strains showed differential enzyme activities (protease, amylase, cellulase, DNAse, pectinase, tryptophanase, and catalase). All four strains of bacterial endobiome exhibited unique metal tolerance as well as pH and temperature regulating activity. Evaluation of the potential role of the mite saliva and the gall associated bacterial endobiome in gallogenesis was done by monitoring the plant growth-promoting activity of the salivary extract and the isolated bacterial strains through in vitro seed (Vigna radiata) germination assay. Salivary extract of the mite showed the highest rate of plant growth-promoting activity compared with that of the isolated strains of bacterial endobiome. The present study forms the first attempt that illustrates the characteristic features of the saliva of the gall inducer and the gall associated bacterial endobiome. Based on the results of the current study, we suggest that eriophyid mite saliva and the gall-associated microbes play significant roles in the induction of cecidia.

Multifaceted intervention of Bacillus spp. against salinity stress and Fusarium wilt in tomato

AIM

This study aimed to screen halotolerant Bacillus strains able to promote growth and protect tomato plants against salt stress and Fusarium wilt (Fusarium oxysporum f. sp. lycopersici).

METHODS AND RESULTS

We evaluated some halotolerant strains of Bacillus spp. (Bacillus velezensis (AP-3) and Bacillus spp. (AP-6, AP-85 and AP-100)) to promote growth of tomato plants grown under salinity stress conditions and to protect them against Fusarium wilt disease. Such strains had been previously selected among 154 bacterial strains through biochemical tests (siderophores and indoleacetic acid productions, cellulase and catalase activity, nitrogen fixation and phosphate solubilization) in the presence of 100-mmol l^-1 NaCl. Besides the above-mentioned strains, B. subtilis QST-713 (Serenade^TM ) was also evaluated. Compared to control plants, aboveground dry weight increased in plants inoculated with AP-6, AP-85, AP-3, AP-100 and QST-713 strains developed in the absence of salt stress. The same tendency occurred for root dry weight; however, AP-3 strain was more effective, promoting an increase of 163%, when compared to control. Chlorophyll index and height increased >40 and 53%, respectively, for all Bacillus strains. Saline stress reduced plant growth regardless of the presence of Bacillus. Height, stem diameter, and aboveground and root dry weights increased in plants treated with Bacillus strains grown under saline conditions when compared to control. Bacillus velezensis AP-3 reduced the severity of Fusarium wilt in tomato by 50% when compared to control.

CONCLUSION

Halotolerant Bacillus strains controlled tomato Fusarium wilt, increased growth as well as tolerance to salt stress.

SIGNIFICANCE AND IMPACT OF THE STUDY

We demonstrated the efficacy of halotolerant Bacillus strains to control Fusarium wilt and improve tomato growth. We also demonstrated that these Bacillus strains protect tomato plants against salt stress. Bacillus can be used in an eco-friendly way because they are considered Generally Recognized As Safe.

Rhizospheric bacterial isolates of grass pea (Lathyrus sativus L.) endowed with multiple plant growth promoting traits

AIM

The main aim of this work was to examine the plant growth promoting, biocontrol activities and stress competency of grass pea rhizobacterial strains from Ethiopia.

METHODS AND RESULTS

Serial dilutions were carried out to isolate rhizobacterial strains from the rhizosphere soil samples. The isolates were characterized for their plant growth promoting, biocontrolling and stress tolerance potential. The isolates that showed better performance in the tested parameters were identified by 16S rRNA gene sequencing. Among the isolates tested on Pikovskaya agar medium, 22 isolates that showed solubilization index of >2·41 cm were selected for further screening tests. Isolate AAUGPR-53 identified as Enterococcus species, Enterococcus casseliflavus strain showed the highest phosphate solubilization index and indole-3-acetic acid production efficiency of 4·81 ± 0·02 (μg ml-1 ) and 56·55 ± 0·45 (μg ml-1 ), respectively. Sixteen (72·7%) of the isolates showed in vitro antifungal inhibition against Fusarium oxysporum f. sp. lentis with isolates AAUGPR-92 and AAUGPR-91 identified as Enterococcus species, E. casseliflavus strain and Enterococcus gallinarum strain exhibiting the highest inhibition of 83 and 78%, respectively. Likewise, 68·2%, 91·30%, 45·5%, 77·3% and 100% of the isolates produced chitinase, protease, cellulase, HCN and NH3 , respectively. Most of the isolates showed good tolerance to the tested stress factors. The 16S rRNA partial sequencing of the rhizobacterial isolates proved their taxonomic position in the existing bacterial isolates.

CONCLUSION

The results indicated that three strains, AAUGPR-53, 91 and 92, that showed maximum sequence identity (99%) to Enterococcus species, E. casseliflavus and E. gallinarum were recommended as microbial inoculants for trials under greenhouse and field conditions.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study illustrates an effective alternative to conventional fertilizers that may contribute to crop disease reduction. Our results provide a foundation for future research that will lead to identifying potentially useful biocontrol strains found in the rhizosphere of grass pea.