7.3 Arsenic-Transforming Bacteria and Its Diversity
with Genes Related to Arsenic and Enzymes Resulting
From Arsenic-Contaminated Aquatic Sediment
Bacteria are the most prerequisite in As cycling. However, only few studies have
reported 16S rRNA and functional genes which is related to arsenic-contaminated
tropical sediment.
Using culture-derived metagenomic and bioinformatic approaches, the variety in
microorganism especially bacteria, As III and As V transformation in freshwater
sediment process, was involved by bacterial genes and enzymes related and in
anaerobic As III- and As V-enrichment cultures (ECs) are reported. The taxonomic
profile reveals significant differences among these diverse communities.
Dechloromonas, Arcobacter, Clostridium thermopalmarium, and Sedimentibacter
were exclusively found in these contaminated sediments (EC); however,
Anaerobacillus was limited to AsV-EC. Novel microorganisms that are both As
V-reducers and As III-oxidizers were identified: Acidovorax facilis, Dechloromonas,
A. delafieldii, Shewanella, Aquabacterium, Macellibacteroides fermentans, and
C. thermopalmarium. Phylogenic variations were shown among the aioA, arsC,
and arrA genes and those of different species, which indicates horizontal gene
transfer. Structural and functional reliability and familial subgroups can be assessed
using ArsC and AioA sets of amino acids. The situations necessary for As V
reduction are conserved, proposing robust discriminating pressure for sustaining
the functionality of ArsC. Altogether, these findings highlight the role of freshwater
sediment bacteria in arsenic mobility and the untapped diversity of dissimilatory
arsenate-resistant and arsenate-reducing bacteria contributing to arsenic toxicity in
aquatic/marine environments (Suhadolnik et al. 2017) (Fig. 12.4).
The large set of effects reported on arsenic-exposed biofilms such as the reduction
of biomass and algal growth (especially diatoms), the reduction of the proportion of
autotrophic vs. heterotrophic organisms, or the lowering nutrient cycling and nitrogen content brings into question the arsenic concentration thresholds established by
the US EPA for freshwater systems. The toxicity results described was under arsenic
concentrations of 130 g L/1 and lower and concluded that recent studies do not
support either the criterion maximum concentration of 340 _g L
À1 (acute exposure),
proposed by the US EPA in freshwaters, or the criterion continuous concentration
(chronic exposure) of 150 _g L
À1 , and it was suggested that these thresholds should
be updated. It is also important to note that arsenic exposure thresholds for human
health (10 g L
À1 ) are 15 times lower than those established for environmental health
(Fig. 12.5 and Barral-Fraga et al. 2020) (Fig. 12.6).
250
P. Narayanasamy and R. K. Subramanian
with Genes Related to Arsenic and Enzymes Resulting
From Arsenic-Contaminated Aquatic Sediment
Bacteria are the most prerequisite in As cycling. However, only few studies have
reported 16S rRNA and functional genes which is related to arsenic-contaminated
tropical sediment.
Using culture-derived metagenomic and bioinformatic approaches, the variety in
microorganism especially bacteria, As III and As V transformation in freshwater
sediment process, was involved by bacterial genes and enzymes related and in
anaerobic As III- and As V-enrichment cultures (ECs) are reported. The taxonomic
profile reveals significant differences among these diverse communities.
Dechloromonas, Arcobacter, Clostridium thermopalmarium, and Sedimentibacter
were exclusively found in these contaminated sediments (EC); however,
Anaerobacillus was limited to AsV-EC. Novel microorganisms that are both As
V-reducers and As III-oxidizers were identified: Acidovorax facilis, Dechloromonas,
A. delafieldii, Shewanella, Aquabacterium, Macellibacteroides fermentans, and
C. thermopalmarium. Phylogenic variations were shown among the aioA, arsC,
and arrA genes and those of different species, which indicates horizontal gene
transfer. Structural and functional reliability and familial subgroups can be assessed
using ArsC and AioA sets of amino acids. The situations necessary for As V
reduction are conserved, proposing robust discriminating pressure for sustaining
the functionality of ArsC. Altogether, these findings highlight the role of freshwater
sediment bacteria in arsenic mobility and the untapped diversity of dissimilatory
arsenate-resistant and arsenate-reducing bacteria contributing to arsenic toxicity in
aquatic/marine environments (Suhadolnik et al. 2017) (Fig. 12.4).
The large set of effects reported on arsenic-exposed biofilms such as the reduction
of biomass and algal growth (especially diatoms), the reduction of the proportion of
autotrophic vs. heterotrophic organisms, or the lowering nutrient cycling and nitrogen content brings into question the arsenic concentration thresholds established by
the US EPA for freshwater systems. The toxicity results described was under arsenic
concentrations of 130 g L/1 and lower and concluded that recent studies do not
support either the criterion maximum concentration of 340 _g L
À1 (acute exposure),
proposed by the US EPA in freshwaters, or the criterion continuous concentration
(chronic exposure) of 150 _g L
À1 , and it was suggested that these thresholds should
be updated. It is also important to note that arsenic exposure thresholds for human
health (10 g L
À1 ) are 15 times lower than those established for environmental health
(Fig. 12.5 and Barral-Fraga et al. 2020) (Fig. 12.6).
250
P. Narayanasamy and R. K. Subramanian