Editorial: Soil-microbial interactions Dlamini, Phesheya; Sekhohola-Dlamini, Lerato M; Cowan, A Keith
Frontiers in microbiology,
05/2023, Letnik:
14
Journal Article
Appropriate wastewater technologies and sound management are crucial to global water quality and conservation. The integrated algal pond system (IAPS), considered an efficient, passive and low‐cost ...wastewater treatment technology for peri‐urban spaces, is perceived to yield a final effluent unsuitable for discharge. Experiments were carried out to challenge the prevailing perception that algal‐based wastewater treatment processes and in particular IAPS produce an effluent that does not always meet national and/or regional regulatory standards. Formation of a microalgal–bacterial floc (MaB‐flocs) and settleability together with biomass removal from algal settling ponds (ASPs) is shown to reduce total suspended solids (TSS) from >50 to <20 mg L−1. Thus, production of a readily settleable MaB‐floc coupled with removal of settled biomass from ASP ensures that final effluent TSS remains below the general limit of 25 mg L−1 and yields an effluent suitable for either irrigation or discharge.
Seven-carbon (7-C) sugars and sugar alcohols are common in higher plants, algae, fungi and bacteria. The biochemical origin and physiological function of these monosaccharides in plants and algae ...however is not well understood and has not been fully investigated. Here the occurrence, metabolism, and transport of heptuloses, heptitols, and heptoses are integrated in accordance with function to emphasise the importance of these apparently neglected sugars. This therefore is the first comprehensive synthesis of knowledge about 7-C sugar biochemistry, a relatively underexplored area of carbohydrate biology that needs to be integrated into mainstream sugar research. Available information on the metabolism of heptuloses, heptitols, and heptoses in
Medicago sativa
(alfalfa),
Persea americana
(avocado),
Primula
sp.,
Kalanchoë pinnata
, and the red alga
Porphyridium
sp. was thoroughly investigated and evaluated. Results indicate that 7-C sugars share a common precursor and are products of a TKT-dependent heptulose shunt in which Suc-derived Fru 6-P is converted either to Sed 7-P or mannoheptulose 7-P or both in competent tissues and species. In plants, free heptuloses probably arise as a consequence of phosphatase activity, whereas heptoses appear to be formed by isomerisation of the corresponding phloem translocated heptuloses following import into non-photosynthetic tissue. It is proposed that the major physiological function of 7-C sugars and heptitols, in addition to serving as a carbon sink, involves metal ion chelation, translocation and remobilisation to fulfil nutrient requirements essential for growth and development.
The integrated algal pond system (IAPS) is a passive wastewater treatment technology that can be used to remediate liquid waste from domestic, industrial and agricultural sources. The system exploits ...the mutualistic interaction between microalgae and bacteria to generate water of a quality suitable for discharge and/or reuse. During the treatment process, biomass in the form of microalgal–bacterial flocs (MaB-flocs) is generated, and this can be harvested and beneficiated in downstream processing. Here, we review literature on MaB-floc and extracellular polymeric substance (EPS) formation and discuss how essential microalgal–bacterial mutualism is at effecting IAPS-based wastewater treatment. Aggregation of microalgae and bacteria into MaB-flocs is clearly an outcome of EPS production by these microorganisms and arises for purposes of chemical and developmental interaction, protection, communication, aggregation and adhesion. The polymeric compounds which form the scaffold of this extracellular matrix comprise polysaccharides, proteins, uronic acid and nucleic acid. Natural EPS can be used as bioflocculant in water purification and in the dewatering and settling of sludge and is therefore an ideal natural replacement for commercially available synthetic polymers. Additionally, EPS are considered high value and can be used in many commercial applications. Thus, and to ensure sustained MaB-floc production in IAPS-based wastewater treatment plants, it is important that correct levels of EPS are maintained to facilitate settling and biomass recovery. Furthermore, it is the associated environmental and operational conditions that most impact EPS production and in turn, MaB-floc formation, and quality of the final IAPS-treated water.
Integrated algal pond systems (IAPSs) combine anaerobic and aerobic bioprocesses to affect sewage treatment. The present work describes the isolation and partial characterisation of soluble ...extracellular polymeric substances (EPSs) associated with microalgal bacterial flocs (MaB-flocs) generated in high rate algal oxidation ponds (HRAOPs) of an IAPS treating domestic sewage. Productivity and change in MaB-flocs concentration, measured as mixed liquor suspended solids (MLSS) between morning (MLSS
) and evening (MLSS
) were monitored and the substructure of the MaB-flocs matrix examined by biochemical analysis and Fourier transform infrared spectroscopy (FT-IR). Results show that MaB-flocs from HRAOPs are assemblages of microorganisms produced as discrete aggregates as a result of microbial EPS production. Formation and accumulation of the EPS was stimulated by light. Analysis by FT-IR revealed characteristic carbohydrate enrichment of these polymeric substances. In contrast, FT-IR spectra of EPSs from dark-incubated MaB-flocs confirmed that these polymers contained increased aliphatic and aromatic functionalities relative to carbohydrates. These differences, it was concluded, were due to dark-induced transition from phototrophic to heterotrophic metabolism. The results negate microalgal cell death as a contributor to elevated chemical oxygen demand of IAPS treated water.
This review focuses on ligninolytic fungi, soil bacteria, plants and root exudates in the degradation and solubilisation of low grade and waste coal and the interaction between these mutualistic ...biocatalysts. Coal represents a considerable portion of the total global fossil fuel reserve and continued demand for, and supply of this resource generates vast quantities of spoil and low grade waste. Large scale bioremediation technologies for the beneficiation of waste coal have unfortunately not yet been realised despite the many discoveries of microorganisms capable of lignite, lignin, and humic acid breakdown. Even so, solubilisation and depolymerization of low grade coal appears to involve either ligninolytic enzyme action or the production of alkaline substances or both. While the precise mechanism of coal biosolubilisation is unclear, a model for the phyto-biodegradation of low rank coal by mutualistic interaction between ligninolytic microorganisms and higher plants is proposed. Based on accumulated evidence this model suggests that solubilisation and degradation of lignite and waste coals commences upon plant root exudate and ligninolytic microorganism interaction, which is mutualistic, and includes soil bacteria and both mycorrhizal and non-mycorrhizal fungi. It is envisaged that this model and its further elaboration will aid in the development of functional technologies for commercial bioremediation of coal mine spoils, contribute to soil formation, and the overall biogeochemistry of organic carbon in the global ecosystem.
Increasing pressure is being exerted on the peri‐urban space that has elevated the demand for electricity, affects the global water resource, and impacts the potential to produce food, fiber, and ...commodity products. Algae‐based technologies and in particular algae‐based sewage treatment provides an opportunity for recovery of water for recycle and re‐use, sequestration of greenhouse gases, and generation of biomass. Successful coupling of municipal sewage treatment to an algae‐to‐energy facility depends largely on location, solar irradiance, and temperature to achieve meaningful value recovery. In this paper, an algae‐to‐energy sewage treatment system for implementation in southern Africa is elaborated. Using results from the continued operation of an integrated algal pond system (IAPS), it is shown that this 500‐person equivalent system generates 75 kL per day water for recycle and re‐use and, ∼9 kg per day biomass that can be converted to methane with a net energy yield of ∼150 MJ per day, and ∼0.5 kL per day of high nitrogen‐containing liquid effluent (>1 g/L) with potential for use as organic fertilizer. It is this opportunity that IAPS‐based algae‐to‐energy sewage treatment provides for meaningful energy and co‐product recovery within the peri‐urban space and, which can alleviate pressure on an already strained water–energy–food nexus.
Exploring plant growth-promoting (PGP) bacterial activity of microbial components aggregated by wastewater treatment can reduce dependence on fossil fuel-derived fertilisers. This study describes the ...isolation and identification of bacteria from microalgae-bacteria flocs (MaB-flocs) generated in high-rate algal oxidation ponds (HRAOP) of an integrated algal pond system (IAPS) remediating municipal wastewater. Amplified 16S rRNA gene sequence analysis determined the molecular identity of the individual strains. Genetic relatedness to known PGP rhizobacteria in the NCBI GenBank database was by metagenomics. Isolated strains were screened for the production of indoles (measured as indole-3-acetic acid; IAA) and an ability to mineralise
,
, and K
+
. Of the twelve bacterial strains isolated from HRAOP MaB-flocs, four produced indoles, nine mineralised
, seven solubilised P, and one K. Potential of isolated strains for PGP activity according to one-way ANOVA on ranks was: ECCN 7b > ECCN 4b > ECCN 6b > ECCN 3b = ECCN 10b > ECCN 1b = ECCN 5b > ECCN 8b > ECCN 2b > ECCN 12b > ECCN 9b = ECCN 11b. Further study revealed that cell-free filtrate from indole-producing cultures of Aeromonas strain ECCN 4b, Enterobacter strain ECCN 7b, and Arthrobacter strain ECCN 6b promoted mung bean adventitious root formation suggestive of the presence of auxin-like biological activity.
Escherichia
coli
isolates, commonly found as gut microflora in warm-blooded animals, are classified into the major phylogroups, A, B1, B2 and D, and further divided into subgroups: A0, A1, B1, B2
2
, ...B2
3
, D1 and D2. This study tracks and classifies
E
.
coli
strains along an integrated algal pond system (IAPS) during municipal sewage treatment. PCR-confirmed
E
.
coli
isolates were delineated into phylogroup by targeting genes
chuA
,
yjaA
and TSPE4.C2 using the triplex PCR assay. Antimicrobial susceptibility testing was by disk diffusion assay. A total of 120
E. coli
isolates were confirmed by analysis of the
uidA
gene. Phylogenetic analysis revealed 57 isolates were group A with others in groups B2 (35), B1 (16) and D (12). Isolate susceptibility to antibiotics was norfloxacin > florfenicol > gatifloxacin > streptomycin > gentamicin. Nearly all isolates (117, 98%) were sulphamethoxazole- and penicillin G-resistant (115, 96%). Thus, resistance was manifest by all phylogroups and to 3–17 of drugs tested. These findings confirm presence of various multidrug-resistant
E
.
coli
phylogroups throughout the IAPS wastewater treatment process and emphasize the usefulness of multidrug resistance profiling as a tool for microbial source tracking and, with which to determine origin of faecal pollution.
Humans are dependent upon soil which supplies food, fuel, chemicals, medicine, sequesters pollutants, purifies and conveys water, and supports the built environment. In short, we need soil, but it ...has little or no need of us. Agriculture, mining, urbanization and other human activities result in temporary land-use and once complete, used and degraded land should be rehabilitated and restored to minimize loss of soil carbon. It is generally accepted that the most effective strategy is phyto-remediation. Typically, phytoremediation involves re-invigoration of soil fertility, physicochemical properties, and its microbiome to facilitate establishment of appropriate climax cover vegetation. A myco-phytoremediation technology called Fungcoal was developed in South Africa to achieve these outcomes for land disturbed by coal mining. Here we outline the contemporary and expanded rationale that underpins Fungcoal, which relies on in situ bio-conversion of carbonaceous waste coal or discard, in order to explore the probable origin of humic substances (HS) and soil organic matter (SOM). To achieve this, microbial processing of low-grade coal and discard, including bio-liquefaction and bio-conversion, is examined in some detail. The significance, origin, structure, and mode of action of coal-derived humics are recounted to emphasize the dynamic equilibrium, that is, humification and the derivation of soil organic matter (SOM). The contribution of plant exudate, extracellular vesicles (EV), extra polymeric substances (EPS), and other small molecules as components of the dynamic equilibrium that sustains SOM is highlighted. Arbuscular mycorrhizal fungi (AMF), saprophytic ectomycorrhizal fungi (EMF), and plant growth promoting rhizobacteria (PGPR) are considered essential microbial biocatalysts that provide mutualistic support to sustain plant growth following soil reclamation and restoration. Finally, we posit that de novo synthesis of SOM is by specialized microbial consortia (or ‘humifiers’) which use molecular components from the root metabolome; and, that combinations of functional biocatalyst act to re-establish and maintain the soil dynamic. It is concluded that a bio-scaffold is necessary for functional phytoremediation including maintenance of the SOM dynamic and overall biogeochemistry of organic carbon in the global ecosystem
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