Soil microbial biomass interactions influencing the mineralisation of N in biosolids‐amended agricultural soil were investigated under field conditions in two soil types, a silty clay and a sandy silt loam, with contrasting organic matter contents. Soil treatments included: dewatered raw sludge (DRAW); dewatered and thermally dried, mesophilic anaerobically digested biosolids (DMAD and TDMAD, respectively); lime‐treated unstabilised sludge cake (LC); and NH4Cl as a mineral salt control for measuring nitrification kinetics. Soil mineral N and microbial biomass N (MBN) concentrations were determined over 90 days following soil amendment. Despite its lower total and mineral N contents, TDMAD had a larger mineralisable pool of N than DMAD, and was an effective rapid release N source. Increased rates of mineralisation and nitrification of biosolids‐N were observed in the silty clay soil with larger organic matter content, implying increased microbial turnover of N in this soil type compared with the sandy silt loam, but no significant difference in microbial immobilisation of biosolids‐N was observed between the two soil types. Thus, despite initial differences observed in the rates of N mineralisation, the overall extent of N release for the different biosolids tested was similar in both soil types. Therefore, the results suggest that fertiliser guidelines probably do not need to consider the effect of soil type on the release of mineral N for crop uptake from different biosolids products applied to temperate agricultural soils.
The difficulties in developing novel classes of antibacterials is leading to a resurgence of interest in bacteriophages as therapeutic agents, and in particular engineered phages that can be optimally designed. Here, pre-clinical microbiology assessment is presented of a Staphylococcus aureus phage engineered to deliver a gene encoding an antibacterial small acid soluble spore protein (SASP) and further, rendered non-lytic to give product SASPject PT1.2. PT1.2 has been developed initially for nasal decolonisation of S. aureus, including methicillin-resistant S. aureus. Time-kill curve assays were conducted with PT1.2 against a range of staphylococcal species, and serial passaging experiments were conducted to investigate the potential for resistance to develop. SASPject PT1.2 demonstrates activity against 100% of 225 geographically diverse S. aureus isolates, exquisite specificity for S. aureus, and a rapid speed of kill. The kinetics of S. aureus/PT1.2 interaction is examined together with demonstrating that PT1.2 activity is unaffected by the presence of human serum albumin. SASPject PT1.2 shows a low propensity for resistance to develop with no consistent shift in sensitivity in S. aureus cells passaged for up to 42 days. SASPject PT1.2 shows promise as a novel first-in-class antibacterial agent and demonstrates potential for the SASPject platform.
BackgroundSoda lakes are unique environments in terms of their physical characteristics and the biology they harbour. Although well studied with respect to their microbial composition, their viral compositions have not, and consequently few bacteriophages that infect bacteria from haloalkaline environments have been described.MethodsBacteria were isolated from sediment samples of lakes Magadi and Shala. Three phages were isolated on two different Bacillus species and one Paracoccus species using agar overlays. The growth characteristics of each phage in its host was investigated and the genome sequences determined and analysed by comparison with known phages.ResultsPhage Shbh1 belongs to the family Myoviridae while Mgbh1 and Shpa belong to the Siphoviridae family. Tetranucleotide usage frequencies and G + C content suggests that Shbh1 and Mgbh1 do not regularly infect, and have therefore not evolved with, the hosts they were isolated on here. Shbh1 was shown capable of infecting two different Bacillus species from the two different lakes demonstrating its potential broad-host range. Comparative analysis of their genome sequence with known phages revealed that, although novel, Shbh1 does share substantial amino acid similarity with previously described Bacillus infecting phages (Grass, phiNIT1 and phiAGATE) and belongs to the Bastille group, while Mgbh1 and Shpa are highly novel.ConclusionThe addition of these phages to current databases should help with metagenome/metavirome annotation efforts. We describe a highly novel Paracoccus infecting virus (Shpa) which together with NgoΦ6 and vB_PmaS_IMEP1 is one of only three phages known to infect Paracoccus species but does not show similarity to these phages.Electronic supplementary materialThe online version of this article (doi:10.1186/s12985-016-0656-6) contains supplementary material, which is available to authorized users.
Interest in phage-based therapeutics is increasing, at least in part due to the need for new treatment options for infections caused by antibiotic-resistant bacteria. It is possible to use wild-type (WT) phages to treat bacterial infections, but it is also possible to modify WT phages to generate therapeutics with improved features. Here, we will discuss features of Phico Therapeutics’ SASPject technology, which modifies phages for use as targetable nano-delivery vehicles (NDV), to introduce antibacterial Small Acid Soluble Spore Protein (SASP) genes into specific target bacteria.
Centrifuge dewatering digested sewage sludge has been reported to significantly increase numbers of Escherichia coli, potentially exceeding the UK microbiological standards of 10 3 or 10 5 E. coli/g dry solids (DS) for enhanced or conventional treatment for agricultural use, respectively. Here, we report an investigation of the effects of different types of dewatering process on E. coli enumeration in conventionally treated, anaerobically digested sludge (primary and secondary liquid digestion), as well as raw sludge at eight wastewater treatment works in the United Kingdom. The dewatering methods evaluated included: centrifuge conditioning and filter-belt and filter-plate pressing. The results demonstrated that conventional treatment by primary and secondary liquid digestion and dewatering conditioning produces biosolids compliant with UK maximum microbiological limits for agricultural application.
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