samples in Spain. In treated sludge samples, oocysts have been observed in all
WWTPs analyzed (25 samples) with different stabilization treatment (83.3%). This
study provides evidence that oocysts are present in sewage sludge end products from
WW treatment processes with the negative consequences for public health [60].
4.2 Prokaryotic Components
The predominant prokaryotic phyla are affiliated mainly with Hydrobacteria
represented
by
Proteobacteria,
Bacteroidetes,
Planctomycetes,
and
Verrucomicrobia and Terrabacteria represented by Chloroflexi, Firmicutes, and
Actinobacteria (Fig. 3b). Archaea domain is accounting for 0.02% of the total 18S
rDNA reads, represented by 70% of human intestinal methanogens (Morin et al.,
2020).
Prokaryotes and eukaryotes are involved in important biogeochemical processes
such as carbon, nitrogen, sulfur, or phosphorus biogeochemical cycles of which a
large number of microorganisms are always represented by so-called candidate
species (Fig. 3b) [52]. These microbial phyla would be of great importance for the
transformation of chemical elements, making them available to plants, thus contributing to soil fertility. Some of these non-cultivable microbial lineages are affiliated
with obligate intracellular bacteria such as the Alphaproteobacteria and Rickettsiae
[61], while others are affiliated with Bacteroidetes [62] or close to Chlamydiae
[63]. Within this latter family, two new genera, Parachlamydia and Neochlamydia,
have been described [62, 64].
Although only 12–15% of the 16S rRNA gene sequences extracted from the
sludge microbiota are affiliated with the human gastrointestinal tract microbiota,
97% of the fecal taxa preserved in the sludge reflect the population structure of the
human or animal fecal microbiota [65, 66]. Among Proteobacteria and
Bacteroidetes phyla, members of the orders Aeromonadales, Alteromonadales,
Enterobacteriales,
Legionellales,
Pseudomonadales,
Vibrionales,
Xanthomonadales, Actinomycetales, Bacillales, Clostridiales, Lactobacillales, and
Bacteroidales are common members of the human microbiome (NIH Human
Microbiome Project catalogue, http://www.hmpdacc.org/catalog/) and described as
carriers of multiple determinants of antibiotic resistance [67]. Some human or animal
pathogens detected in the final effluent or constituting a part of the sludge generated
during WW purification process can survive the treatment process. This is also the
case for several commensal or saprophytic microorganisms that can adopt a pathogenic lifestyle in inappropriate ecological niche, or whenever the host defenses are
weakened or compromised. The possibility of a transfer of these microorganisms to
humans, animals, and plants through inappropriately treated WW or sludge use
cannot be ruled out [68].
It is well recognized that several plant pathogens, either bacteria, fungi, viruses,
parasitic nematodes, or oomycetes (e.g., Phytophthora and Pythium) are waterborne
[69, 70]. Phytopathogenic bacteria are present in treated WW used in irrigation
64
E. Ammar et al.
WWTPs analyzed (25 samples) with different stabilization treatment (83.3%). This
study provides evidence that oocysts are present in sewage sludge end products from
WW treatment processes with the negative consequences for public health [60].
4.2 Prokaryotic Components
The predominant prokaryotic phyla are affiliated mainly with Hydrobacteria
represented
by
Proteobacteria,
Bacteroidetes,
Planctomycetes,
and
Verrucomicrobia and Terrabacteria represented by Chloroflexi, Firmicutes, and
Actinobacteria (Fig. 3b). Archaea domain is accounting for 0.02% of the total 18S
rDNA reads, represented by 70% of human intestinal methanogens (Morin et al.,
2020).
Prokaryotes and eukaryotes are involved in important biogeochemical processes
such as carbon, nitrogen, sulfur, or phosphorus biogeochemical cycles of which a
large number of microorganisms are always represented by so-called candidate
species (Fig. 3b) [52]. These microbial phyla would be of great importance for the
transformation of chemical elements, making them available to plants, thus contributing to soil fertility. Some of these non-cultivable microbial lineages are affiliated
with obligate intracellular bacteria such as the Alphaproteobacteria and Rickettsiae
[61], while others are affiliated with Bacteroidetes [62] or close to Chlamydiae
[63]. Within this latter family, two new genera, Parachlamydia and Neochlamydia,
have been described [62, 64].
Although only 12–15% of the 16S rRNA gene sequences extracted from the
sludge microbiota are affiliated with the human gastrointestinal tract microbiota,
97% of the fecal taxa preserved in the sludge reflect the population structure of the
human or animal fecal microbiota [65, 66]. Among Proteobacteria and
Bacteroidetes phyla, members of the orders Aeromonadales, Alteromonadales,
Enterobacteriales,
Legionellales,
Pseudomonadales,
Vibrionales,
Xanthomonadales, Actinomycetales, Bacillales, Clostridiales, Lactobacillales, and
Bacteroidales are common members of the human microbiome (NIH Human
Microbiome Project catalogue, http://www.hmpdacc.org/catalog/) and described as
carriers of multiple determinants of antibiotic resistance [67]. Some human or animal
pathogens detected in the final effluent or constituting a part of the sludge generated
during WW purification process can survive the treatment process. This is also the
case for several commensal or saprophytic microorganisms that can adopt a pathogenic lifestyle in inappropriate ecological niche, or whenever the host defenses are
weakened or compromised. The possibility of a transfer of these microorganisms to
humans, animals, and plants through inappropriately treated WW or sludge use
cannot be ruled out [68].
It is well recognized that several plant pathogens, either bacteria, fungi, viruses,
parasitic nematodes, or oomycetes (e.g., Phytophthora and Pythium) are waterborne
[69, 70]. Phytopathogenic bacteria are present in treated WW used in irrigation
64
E. Ammar et al.