Alleviating arsenic stress affecting the growth of Vigna radiata through the application of Klebsiella strain ASBT-KP1 isolated from wastewater.

Arsenic contamination of soil and water is a major environmental issue. Bioremediation through plant growth-promoting bacteria is viable, cost-effective, and sustainable. Along with arsenic removal, it also improves plant productivity under stressful conditions. A crucial aspect of such a strategy is the selection of bacterial inoculum. The described study demonstrates that the indigenous wastewater isolate, ASBT-KP1, could be a promising candidate. Identified as Klebsiella pneumoniae, ASBT-KP1 harbors genes associated with heavy metal and oxidative stress resistance, production of antimicrobial compounds and growth-promotion activity. The isolate efficiently accumulated 30 µg/g bacterial dry mass of arsenic. Tolerance toward arsenate and arsenite was 120 mM and 70 mM, respectively. Plant biomass content of Vigna radiata improved by 13% when grown in arsenic-free soil under laboratory conditions in the presence of the isolate. The increase became even more significant under the same conditions in the presence of arsenic, recording a 37% increase. The phylogenetic analysis assigned ASBT-KP1 to the clade of Klebsiella strains that promote plant growth. Similar results were also observed in Oryza sativa, employed to assess the ability of the strain to promote growth, in plants other than V. radiata. This study identifies a prospective candidate in ASBT-KP1 that could be employed as a plant growth-promoting rhizoinoculant in agricultural practices.

Mitigation of biogenic methanethiol using bacteriophages in synthetic wastewater augmented with Pseudomonas putida.

Wastewater malodour is the proverbial 'elephant in the room' notwithstanding its severe implications on sanitation, health, and hygiene. The predominant malodorous compounds associated with wastewater treatment plants and toilets are volatile organic compounds, such as hydrogen sulphide, ammonia, methanethiol, and organic acids. Among them, methanethiol warrants more attention owing to its relatively low olfactory threshold and associated cytotoxicity. This requires an efficient odour-abatement method since conventional techniques are either cost-prohibitive or leave recalcitrant byproducts. Bacteriophage-based methodology holds promise, and the described work explores the potential. In this study, a non-lysogenous Pseudomonas putida strain is used as a model organism that produces methanethiol in the presence of methionine. Two double-stranded DNA phages of genome sizes > 10 Kb were isolated from sewage. ɸPh_PP01 and ɸPh_PP02 were stable at suboptimal pH, temperature, and at 10% chloroform. Moreover, they showed adsorption efficiencies of 53% and 89% in 12 min and burst sizes of 507 ± 187 and 105 ± 7 virions per cell, respectively. In augmented synthetic wastewater, ɸPh_PP01 and ɸPh_PP02 reduced methanethiol production by 52% and 47%, respectively, with the concomitant reduction in P. putida by 3 logs in 6 h. On extension of the study in P. putida spiked-sewage sample, maximum reduction in methanethiol production was achieved in 3 h, with 49% and 48% for ɸPh_PP01 and ɸPh_PP02, respectively. But at 6 h, efficiency reduced to 36% with both the phages. The study clearly demonstrates the potential of phages as biocontrol agents in the reduction of malodour in wastewater.

Escherichia coli ST155 as a production-host of three different polyvalent phages and their characterisation with a prospect for wastewater disinfection.

Bacteriophages are generally specific, and a cocktail of phages is needed to combat different bacterial targets. Their production usually requires pathogenic isolation hosts. We identified a novel strain, Escherichia coli ST155, that could serve as a production host for three different polyvalent phages (ϕPh_SE03, ϕPh_SD01, and ϕPh_EC01), thus superseding the use of individual isolation hosts. Upon propagation in E. coli ST155, the phages demonstrated differential intergeneric infectivity against Salmonella enterica, E. coli OP50, Shigella dysenteriae, E. coli MDR, and Acinetobacter baumannii. Phages were characterised based on morphology, latent period, burst size, the efficiency of plating, and restriction enzyme profile. Survival assay on Caenorhabditis elegans, the absence of Shiga toxin, and enterotoxigenic E. coli virulence genes indicated that E. coli ST155 could be non-pathogenic. Lack of antibiotic resistance and absence of functional prophages rendered the host suitable for environmental applications. As a proof-of-concept, phage ϕPh_SE03 was produced in ST155 by employing a unique Bacteriophage Amplification Reactor-Lytics Broadcasting System and was simultaneously disseminated into S. enterica augmented wastewater, which resulted in a 3-log reduction in 24 h. The study establishes the potential of E. coli ST155 as a phage production host thereby minimising the possibility of accidental release of pathogenic hosts into wastewater.