Another microbial paper, this time looking at aquaponics and iron availability

[dw1305]

Hi all,
I've got even less idea of where to put this one, so I'll leave it in "substrates", even though they are the component that is entirely lacking in this study.

Bartelme RP, Oyserman BO, Blom JE, Sepulveda-Villet OJ, Newton RJ. (2018) "Stripping Away the Soil: Plant Growth Promoting Microbiology Opportunities in Aquaponics." Front Microbiol. 2018 22;9:8. doi: 10.3389/fmicb.2018.00008. PMID: 29403461; PMCID: PMC5786511. <"Stripping Away the Soil: Plant Growth Promoting Microbiology Opportunities in Aquaponics">. It is open-source so every-one should have access.

Why it maybe of interest to us, is that it is a paper that looks at:

.......... how microbes enrich plant growth through various mechanisms, such as enhancing resistance to disease and drought, producing beneficial molecules, and supplying nutrients and trace metals to the plant rhizosphere. Previous studies of plant growth promoting microorganisms (PGPM) have focused primarily on soil-based crops. In contrast, aquaponics is a water-based agricultural system, in which production relies upon internal nutrient recycling to co-cultivate plants with fish. This arrangement has management benefits compared to soil-based agriculture, as system components may be designed to directly harness microbial processes that make nutrients bioavailable to plants..........

......... Regardless of the agricultural system, root health is essential to the survival of plants; so one focus area for aquaponic plant growth promoting microorganisms (PGPM) research should be microbial root colonization. Arbuscular mycorrhizal fungi are well-documented plant growth promoting fungi that colonize plant roots. In traditional soil-based agriculture, arbuscular mycorrhizal fungi promote phosphorus uptake and enhance biomass production (Govindasamy et al., 2011). Arbuscular mycorrhizal fungi also appear to be important for plant health in hydroponics. For example, in one hydroponic system study, arbuscular mycorrhizal fungi inhibited Fusarium spp. from inducing root rot in tomatoes grown under near-commercial conditions (Utkhede, 2006). While arbuscular mycorrhizal fungi are a commonly cited PGPM, many different microorganisms are thought to be PGPMs. One such group, rhizobia, were discovered in the 19th Century (Beijerinck, 1888), and now these diazotrophic bacteria are recognized as essential agents in promoting growth among crops such as legumes, rice, and wheat (Govindasamy et al., 2011; Ji et al., 2014; Majeed et al., 2015). Interestingly, iron siderophores facilitate the formation of rhizobium diazotrophic nodules (Barton et al., 1996; Brear et al., 2013), suggesting micronutrients may play a role in PGPM colonization in other agricultural systems, such as hydroponics/aquaponics.

........ PGPM research in soilless engineered environments has the potential to advance the fundamental understanding of rhizosphere microorganism associations. It is clear plants recruit PGPMs to their rhizosphere, but the mechanisms driving plant growth promoting rhizosphere interactions are difficult to disinter from soil-based studies (DeVries and Wallenstein, 2017). Soil matrices are chemically complex and heterogeneous, exhibiting immensely diverse microbial communities. Additionally, given the large variability among soil and crop types (DeVries and Wallenstein, 2017), rhizosphere recruitment of PGPMs in this environment remains mainly theoretical and often limited to a case-by-case basis. The complexity of the soil matrix also adds technological hurdles to studying PGPMs. The soil matrix often hinders nucleic acid extraction and, subsequently, sequence-based analyses of microorganisms, thus inhibiting the exploration of microbial community structure......

TBC. .. the iron (Fe) bit

cheers Darrel

 

[dw1305]

Hi all,
This is the bit that maybe of most interest to us and it talks about the difficulties of keeping iron (Fe) in solution.

Iron Limitation: a Case Study for Pgpm Research in Aquaponic Plant Production <Stripping Away the Soil: Plant Growth Promoting Microbiology Opportunities in Aquaponics>.

....... Herein we review what is known about iron requirements in aquaponics and discuss possible iron supplementation strategies that do not require industrially produced chelated iron. Iron is an essential molecule for a multitude of metalloprotein structures........... often fish iron needs are met or frequently exceeded, with commercial feeds (Watanabe et al., 1997), so little attention is paid to this component of aquaculture operations. In contrast, although undigested fish feed contains excess iron, plant grow beds in aquaponics are often limited by bioavailable iron (Fe2+). This nutrient deficiency is a known cause of chlorosis in the hydroponic subsystem crops, ............. chelated iron is added at a concentration of 2 mg/L per day to prevent chlorosis (Rakocy et al., 2004). One major factor driving iron deficiency is that soluble ferrous iron (2+) easily crosses the rhizoplane of the roots, but ferric iron (3+) is insoluble. Consequently, the competing chemical reactions driving Fe2+ to Fe3+ (i.e., the speciation of iron in natural water systems by hydroxyl radicals and ionic interactions) and pH dependency complicate the mass balance of iron in aquaponic systems (Rose and Waite, 2002; Waite, 2002).....

...... Published literature on the role of siderophores in soil-based agriculture point to both an enhancement of growth and a link to pathogenesis (Kloepper et al., 1980; Neilands and Leong, 1986). Pseudomonas fluorescens Pf-5 is one PGPM known to increase the bioavailability of iron through siderophore production in iron deficient soils (Loper and Henkels, 1997). ............. Furthermore, genomic analyses of Pseudomonas spp. indicate a distinct ability to modulate the surrounding rhizosphere community through antifungal and bacteriocin production, in addition to siderophore production (Loper et al., 2012). In soil-based agriculture, other bacterial species such as, Bacillus and Paenibacillus spp. exhibit similar PGPM characteristics (Govindasamy et al., 2011). All of the aforementioned PGPM microbes found in soil studies may allow aquaponics practitioners to biologically remediate regularly occurring nutrient deficiencies. Since there is evidence PGPM ecophysiologies work to overcome micronutrient deficiencies in engineered environments (Villarroel et al., 2011), there is ample opportunity to research their usefulness for aquaponic system design and management........

.......Though the resiliency of aquaponic systems to phytopathogen infection requires experimental study, other groups of PGPM’s (such as Bacillus spp. and Paenibacillus spp.) may be linked to plant resilience (Govindasamy et al., 2011; Loper et al., 2012). In hydroponics, PGPM species have been identified from the bacterial genera Pseudomonas, Bacillus, Enterobacter, Streptomyces, Gliocladium, and Trichoderma; many of which produce siderophores (Lee and Lee, 2015). It also has been demonstrated that siderophore production by a Chryseobacterium spp. alleviates iron starvation in tomato plants (Radzki et al., 2013). It is likely that other syntrophic or symbiotic relationships between plants and rhizoplane microbiomes exist, but as of now remain undiscovered or underutilized. As more PGPM’s are discovered, operators may potentially integrate batch-culturing devices to facilitate the growth of PGPM’s producing siderophores.........

TBC

cheers Darrel

 

[dw1305]

Hi all,
Nitrification and synergistic effects
<Stripping Away the Soil: Plant Growth Promoting Microbiology Opportunities in Aquaponics>

.......must carefully balance the pH requirements of fish, nitrifying microorganisms, and plants by identifying a mean pH that facilitates biological growth throughout all components, even if it is not optimal for any one component. Typically this means aquaponic operation at a pH of 7.0, whereas plants grown hydroponically prefer a lower pH, from 5.5 to 6.5 (Rakocy et al., 2006). However, pH balancing does not follow a concrete rule for operation, as a review of aquaponic crop production (Tyson et al., 2011) suggests normal total crop yields may be obtained at pH levels above those recommended for traditional production. Recent research into nitrifying microorganisms suggests that certain species of nitrite-oxidizing bacteria become more competitive at lower pH levels (Hüpeden et al., 2016), .....

....... There is also evidence of overlap between fish gut microbiomes and rhizosphere microbiomes (Hacquard et al., 2015), which could indicate microbial-based health benefits of fish-plant co-cultivation and an opportunity to use PGPM manipulation to benefit both plant and fish growth. Root-associated microorganisms are also known to influence plant phenology, such as flowering time (Wagner et al., 2014; Pérez-Jaramillo et al., 2016), and thus, in theory, could be used to manipulate desired plant biological characteristics in controlled settings such as those found in aquaponics......

cheers Darrel