Bacterial Diversity and Community in Response to Long-Term Nitrogen Fertilization Gradient in Citrus Orchard Soils

Citrus orchards receive increasing amounts of nitrogen fertilizer for the purpose of optimal yields and good quality of citrus fruits. Although the effects of increased nitrogen fertilizer on citrus fruit trees have been reasonably well studied, few comparable studies have examined impacts on soil bacterial communities and diversity, even though they play critical roles in orchard ecosystem functioning. In our study, Illumina MiSeq sequencing was used to investigate bacterial community structure and diversity under 5-years long-term nitrogen fertilization gradients (N0, N1, N2, N3, N4, and N5) in citrus orchard soils. The sequencing result showed that nitrogen fertilizer addition increased bacterial diversity along the N0 to N3 gradient but decreased bacterial diversity along the N3 to N5 gradient. The increase in the nitrogen fertilizer rate altered bacterial community composition by increasing the relative abundance of Delta-proteobacteria, Nitrospirae, SBR1093, and Latescibacteria and decreasing the relative abundance of Alpha-proteobacteria. Finally, regression analysis revealed that bacterial diversity and the relative abundance of Nitrosomonadales, Rhodobiaceae, Gemmatimonas, and Variibacter exhibited a significant positive correlation with citrus yield. The study revealed that a reasonable nitrogen fertilizer rate applied to citrus orchards could improve bacterial community structure and diversity and increase citrus yield.

Molecular Diversity of Chlorpyrifos Degrading Bacteria Isolated from Apple Orchard Soils of Himachal Pradesh

A total of seventy-two bacterial isolates were obtained employing enrichment culture technique from apple orchard soils contaminated with chlorpyrifos. Pure cultures of bacterial isolates were obtained using streak plate method on mineral salt medium. Bacterial isolates were characterized on the basis of morphology, culture and biochemical properties. Six bacterial isolates exhibited high extracellular organophosphorus hydrolase activity along with high tolerance towards high concentrations of chlorpyrifos. Genomic DNA extraction from bacterial isolates was done with phenol/chloroform method. Molecular Diversity of six chlorpyrifos degrading bacterial isolates was done employing RAPD-PCR technique by using 25 decamer primers, where amplification was showed by only 20 primers. A total of 337 amplified bands and 64 unique bands ranging in size from 100 to 4900bps were produced after RAPD analysis. The similarity coefficient estimated by Jaccard’s coefficient for these bacterial isolates was found to range between 31 to 64 percent.

No-Till and Solid Digestate Amendment Selectively Affect the Potential Denitrification Activity in Two Mediterranean Orchard Soils

Improved soil managements that include reduced soil disturbance and organic amendment incorporation represent valuable strategies to counteract soil degradation processes that affect Mediterranean tree cultivations. However, changes induced by these practices can promote soil N loss through denitrification. Our research aimed to investigate the short-term effects of no-tillage and organic amendment with solid anaerobic digestate on the potential denitrification in two Mediterranean orchard soils showing contrasting properties in terms of texture and pH. Denitrifying enzyme activity (DEA) and selected soil variables (available C and N, microbial biomass C, basal respiration) were monitored in olive and orange tree orchard soils over a five-month period. Our results showed that the application of both practices increased soil DEA, with dynamics that varied according to the soil type. Increased bulk density, lowered soil aeration, and a promoting effect on soil microbial community growth were the main DEA triggers under no-tillage. Conversely, addition of digestate promoted DEA by increasing readily available C and N with a shorter effect in the olive grove soil, due to greater sorption and higher microbial efficiency, and a long-lasting consequence in the orange orchard soil related to a larger release of soluble substrates and their lower microbial use efficiency.

Isolation and identification of guaiacol producing Alicyclobacillus fastidiosus strains from orchards in Poland

The genus Alicyclobacillus comprises a group of Gram-positive, thermo-acidophilic bacteria that are capable of producing highly resistant endospores during unfavorable environmental conditions. The members of this genus inhabit natural environments, including hot springs and soils. The main reason behind the spoilage of final commercial fruit products by Alicyclobacillus is the contamination of fruits with soil at the time of harvesting. Some of the Alicyclobacillus species, including Alicyclobacillus acidoterrestris, are categorized as spoilage bacteria due to their ability to produce off-flavor compounds (e.g., guaiacol and halophenols) that adversely affect the taste and aroma of beverages. In our study, Alicyclobacillus species were isolated from Polish orchard soils and fruits and were subjected to 16S rDNA sequencing. The results of the analysis showed that the isolated strains belonged to A. acidoterrestris and Alicyclobacillus fastidiosus species. All the three isolated strains of A. fastidiosus (f1, f2, f3) exhibited similar morphological and biochemical properties as the strain described in the literature. However, these isolated strains were able to produce guaiacol at temperatures of 20°C, 25°C, and 45°C. Thus, the strains of A. fastidiosus discovered in the present study can be included in the group of spoilage species as they possessed the gene responsible for the production of guaiacol.