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The grazing activity of Acrobeloides sp. drives phytate mineralisation within its trophic relationship with bacteria

Mercedes García-Sánchez

Mercedes García-Sánchez

Eco&Sols, INRAE, Université de Montpellier, CIRADMontpellier, France
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García-Sánchez, Mercedes
, 
Mathilde Souche

Mathilde Souche

Eco&Sols, INRAE, Université de Montpellier, CIRADMontpellier, France
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Souche, Mathilde
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Carlos Trives-Segura

Carlos Trives-Segura

Eco&Sols, INRAE, Université de Montpellier, CIRADMontpellier, France
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Trives-Segura, Carlos
 et 
Claude Plassard

Claude Plassard

Eco&Sols, INRAE, Université de Montpellier, CIRADMontpellier, France
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Plassard, Claude
  
01 janv. 2021
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Publié en ligne: 01 janv. 2021
Pages: 1 - 13
DOI: https://doi.org/10.21307/jofnem-2021-021
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© 2021 Authors, published by Sciendo.
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Figure 1:

Scheme of the experimental design used to follow the effect of bacterial grazer displacement. Petri dishes (90 mm diameter) were filled with agarose medium containing 1 mM of sodium phytate or inorganic phosphate. The inoculum (100 µL) was placed at a single point of the dish, marked ‘x’. After three weeks, Petri dishes were open and the agarose was separated in two parts called zones 1 and 2.
Scheme of the experimental design used to follow the effect of bacterial grazer displacement. Petri dishes (90 mm diameter) were filled with agarose medium containing 1 mM of sodium phytate or inorganic phosphate. The inoculum (100 µL) was placed at a single point of the dish, marked ‘x’. After three weeks, Petri dishes were open and the agarose was separated in two parts called zones 1 and 2.

Figure 2:

Bacterial grazer populations of Acrobeloides sp. previously fed on B. subtilis 168 or Bradyrhizobium sp. measured throughout the zones 1 and 2 after inoculation at a single point located at the top of zone 1 and grown either with phytate (A) or Pi (B) as the P source. Data are means (±SE, n = 5). The same lowercase letters indicate a lack of significance (p < 0.05) within the same zone of the Petri dish. Stars above a bar indicate a significant difference between the two P sources (*p < 0.05; **p < 0.01) for the same zone.
Bacterial grazer populations of Acrobeloides sp. previously fed on B. subtilis 168 or Bradyrhizobium sp. measured throughout the zones 1 and 2 after inoculation at a single point located at the top of zone 1 and grown either with phytate (A) or Pi (B) as the P source. Data are means (±SE, n = 5). The same lowercase letters indicate a lack of significance (p < 0.05) within the same zone of the Petri dish. Stars above a bar indicate a significant difference between the two P sources (*p < 0.05; **p < 0.01) for the same zone.

Figure 3:

Effect of grazing activities by Acrobeloides sp. nematodes on phytate mineralization catalyzed either by B. subtilis 168 or Bradyrhizobium sp. Shown are the free Pi amounts extracted from zones 1 or 2 after three weeks of incubation with phytate as the sole source of P in absence (A) or in presence (B) of nematodes. Bacteria (A) or nematodes (B) were inoculated at a single point located at the top of zone 1 with nematodes previously fed on each bacterial strain. Control treatment (Ctrl) consisted of water deposit instead of bacteria or nematodes. Data are means (±SE, n = 5). The same lowercase letters indicate a lack of significance (p < 0.05) within the same zone of the Petri dish. Stars above a bar indicate a significant difference between the absence/presence of Acrobeloides sp. (*p < 0.05; **p < 0.01) within each zone and bacterial strain.
Effect of grazing activities by Acrobeloides sp. nematodes on phytate mineralization catalyzed either by B. subtilis 168 or Bradyrhizobium sp. Shown are the free Pi amounts extracted from zones 1 or 2 after three weeks of incubation with phytate as the sole source of P in absence (A) or in presence (B) of nematodes. Bacteria (A) or nematodes (B) were inoculated at a single point located at the top of zone 1 with nematodes previously fed on each bacterial strain. Control treatment (Ctrl) consisted of water deposit instead of bacteria or nematodes. Data are means (±SE, n = 5). The same lowercase letters indicate a lack of significance (p < 0.05) within the same zone of the Petri dish. Stars above a bar indicate a significant difference between the absence/presence of Acrobeloides sp. (*p < 0.05; **p < 0.01) within each zone and bacterial strain.

Total bacterial cells according to the P source (phytate or Pi) and the absence (−N) or the presence (+N) of Acrobeloides sp_

Bacterial strains
Parameters P source Bacterial grazers B. subtilis 168 Bradyrhizobium sp.
Numbers Phytate −N 9.67 × 106 (1.81 × 106)a 6.62 × 106 (2.13 × 106)b
Phytate +N 8.92 × 106 (1.01 × 106)a 3.28 × 106 (0.43 × 106)b
Grazing effect NS NS
Pi −N 28.1 × 106 (13.7 × 106)a 42.2 × 106 (8.87 × 106)a
Pi +N 5.44 × 106 (0.51 × 106)a 2.84 × 106 (0.46 × 106)b
Grazing effect * ***
Ratio Phytate/Pi −N 0.20 ± 0.06b 0.11 ± 0.04b
Phytate/Pi +N 1.63 ± 0.12a 1.35 ± 0.04a
Grazing effect *** **

Ratio of multiplication of Acrobeloides sp_ fed on B_ subtilis 168 or Bradyrhizobium sp_ and grown with phytate or Pi as the sole source of P, calculated by dividing the total numbers of nematodes counted after three weeks by the initial number inoculated in zone 1 (100 individuals)_

Source of P
Bacterial strains Phytate Pi
B. subtilis 168 379.9 ± 28.4b 459 ± 22.9b
Bradyrhizobium sp. 396.9 ± 14.2b 621 ± 40.2a
Bacterial effect ***

Total amounts of free Pi mineralized by each bacterial strain and expressed in µg of free Pi per million of bacterial cells grown in absence (−N) or in presence (+N) of nematodes_

Bacterial strains
Bacterial grazers B. subtilis 168 Bradyrhizobium sp.
−N 0.95 ± 0.21a 3.71 ± 1.73a
+N 31.26 ± 3.67a 18.96 ± 0.86b
Grazing effect *** ***

The total numbers of Acrobeloides sp_ individuals according to the co-inoculated bacterial species, B_ subtilis 168 or Bradyrhizobium sp_, and the source of P supplied into the medium, phytate or Pi_

Bacterial strains
Parameters Source of P B. subtilis 168 Bradyrhizobium sp.
Numbers Phytate 38.0 × 103 ± 2.84 × 103bA 39.7 × 103 ± 1.42 × 103bB
Pi 45.9 × 103 ± 2.28 × 103bA 62.1 × 103 ± 4.02 × 103aA
Ratio Phy/Pi 0.83 ± 0.07a 0.64 ± 0.03b

Evolution of bacterial populations of B_ subtilis 168 or Bradyrhizobium sp_ throughout the zones 1 and 2 after inoculation at a single point located at the top of zone 1 either in absence (−N) or in presence (+N) of bacterial grazers_

B. subtilis 168 Bradyrhizobium sp.
P source Bacterial grazers Zone 1 Zone 2 Zone 1 Zone 2
Phytate −N 9.08 × 106 (1.90 × 106)a 0.60 × 106 (0.04 × 106)b** 6.42 × 106 (2.90 × 106)a 0.20 × 106 (0.09 × 106)b**
Phytate +N 5.50 × 106 (0.85 × 106)a 3.45 × 106 (0.61 × 106)ab 1.80 × 106 (0.30 × 106)b 1.52 × 106 (0.20 × 106)b
Pi −N 27.2 × 106 (12 × 106)a 0.07 × 106 (0.04 × 106)b** 41.9 × 106 (7 × 106)a** 0.20 × 106 (0.15 × 106)b**
Pi +N 3.40 × 106 (0.38 × 106)a 2.20 × 106 (0.41 × 106)ab 1.59 × 106 (0.18 × 106)b 1.59 × 106 (0.29 × 106)b
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