Hydrochemical Characteristics
LGL is a sodium carbonate type lake that exhibits major water cations of Na+ (105.90–106.62 mg/L) and Ca2+ (84.24–85.80 mg/L), while the major anions are HCO3− (472.34–476.17 mg/L) and CO32− (75.97–76.43 mg/L). The average water temperature in mid-July was 16.7°C, while the pH of the water was alkaline, ranging from 8.54 to 8.62. The average values of TOC, TN, and TP were 6.21 mg/L, 104.21 mg/L and 1.91 mg/L, respectively (Table 1).
Table 1
Chemical characteristics of surface water and sediment samples from Langaco Lake.Table 2: Operational taxonomic unit (OTU) richness and diversity measures from Langaco Lake communities.Table 3: Hydrochemical characteristics and dominant genera within worldwide soda lakes.Table 1. Chemical characteristics of surface water and sediment samples from Langaco lake.
Samples
|
Temp
(°C )
|
pH
|
TOC
(%)
|
TN
(µg/L)
|
TS
(g/L)
|
TP
(µg/L)
|
|
Major ions (mg/L)
|
Na+
|
K+
|
Ca2+
|
Mg2+
|
Cl−
|
SO42−
|
CO32−
|
HCO3−
|
|
L1, L1a
|
16.70
|
8.62
|
6.20
|
102.70
|
1.00
|
1.92
|
106.24
|
15.24
|
85.08
|
74.34
|
56.08
|
75.73
|
76.30
|
475.56
|
|
L2, L2a
|
16.51
|
8.54
|
6.18
|
106.37
|
1.02
|
1.91
|
106.40
|
15.84
|
85.80
|
73.46
|
56.57
|
79.02
|
76.10
|
472.34
|
|
L3, L3a
|
16.32
|
8.61
|
6.22
|
107.56
|
1.03
|
1.93
|
105.90
|
16.24
|
84.24
|
75.13
|
55.89
|
76.35
|
75.97
|
476.17
|
|
L4, L4a
|
17.30
|
8.59
|
6.25
|
100.24
|
0.99
|
1.90
|
106.62
|
16.00
|
84.80
|
74.87
|
56.28
|
73.47
|
76.43
|
473.79
|
|
Note: TOC, total organic carbon; TN, total nitrogen; TP, total phosphorus.
|
Bacterial And Archaeal Community Diversity
Bacterial and archaeal community composition was investigated among the four LGL samples using high-throughput Illumina sequencing of community 16S rRNA genes (Table 2). A total of 5,879 OTUs were recovered that comprised 4,871 bacterial OTUs and 1,008 archaeal OTUs. Among bacterial samples, the richness and diversity of L2 and L4 were slightly higher than those of the L1 and L3 samples. The observed bacterial community OTU richness, Shannon index, and ACE values ranged from 1,025–1,293, 5.20–6.07, and 2,148.23–2,376.17, respectively. In contrast, archaeal diversity (221–269 observed OTUs, Shannon index values of 2.98–3.30, and ACE index values of 417.63–536.42) was significantly lower than that of the bacterial communities.
Table 2
Operational taxonomic unit (OTU) richness and diversity measures from Langaco Lake communities.
Sample-ID
|
Sequence reads
|
Richness and diversity metric
|
OTUs
|
Shannon
|
ACE
|
Chao1
|
Coverage
|
Simpson
|
Bacteria
|
|
|
|
|
|
|
|
L1
|
9,377
|
1,025
|
5.20
|
2,148.23
|
1,668.18
|
0.95
|
0.03
|
L2
|
9,424
|
1287
|
6.07
|
2,359.52
|
1,990.62
|
0.94
|
0.01
|
L3
|
9356
|
1266
|
5.92
|
2,243.30
|
1,912.93
|
0.94
|
0.01
|
L4
|
9354
|
1293
|
5.96
|
2,376.17
|
1,995.66
|
0.94
|
0.01
|
Archaea
|
|
|
|
|
|
|
|
L1a
|
16,316
|
269
|
2.98
|
536.42
|
390.27
|
0.99
|
0.12
|
L2a
|
16,465
|
221
|
3.16
|
417.63
|
336.62
|
0.99
|
0.09
|
L3a
|
16,415
|
250
|
3.27
|
434.32
|
395.25
|
0.99
|
0.10
|
L4a
|
16,403
|
268
|
3.30
|
497.65
|
418.19
|
0.99
|
0.09
|
Note: ACE, abundance-based coverage estimator.
|
Taxonomic Composition Of Lgl Microbial Communities
Venn diagrams were used to visualize the overlap in the OTUs among the lake water samples (Fig S1). Total unique bacterial genera observed in the four samples were 219 (L1), 270 (L2), 291 (L3), and 271 (L4), while unique archaeal genera were significantly lower at 77 (L1a), 56 (L2a), 72 (L3a), and 74 (L4a). There were 472 and 81 shared bacterial genera among the two communities. The most abundant sequences were selected as representative sequences of OTUs, and the relative abundances of bacterial and archaeal populations among communities were compared at the phylum, class, and genus taxonomic levels (Fig. 2 and Fig S2). In addition, community clustering based on community compositional differences indicated that there were three different bacterial community groups, with L3 and L1 each comprising single branches, and L4 and L2 clustering together. In contrast, the archaeal communities comprised two groups with L4 and L1 comprising one group, while L3 and L2 comprised the other group. Overall, twenty-four bacterial phyla were detected in the LGL microbial communities, comprising 50 classes and 327 genera. Additionally, eight archaeal phyla were detected that comprised nine classes and 29 genera (Table S1, S2, S3).
At the phylum level, the predominant bacteria (> 1% relative abundance) were Proteobacteria (42.79–53.70% relative abundance), Bacteroidetes (11.13–15.18%), Planctomycetes (4.20–12.82%), and Acidobacteria (5.91–9.50%), followed by Actinobacteria (2.60–5.80%), Verrucomicrobia (2.11–4.08%), Chloroflexi (2.00–2.54%), Parcubacteria (0.83–2.16%), Firmicutes (0.63–1.14%), and Nitrospirae (0.21–1.53%). The dominant archaeal phyla among all samples were Crenarchaeota (35.97–58.29%), Euryarchaeota (33.02–39.89%), and Woesearchaeota (6.50–21.57%). In addition, Pacearchaeota (0.63–1.13%) and Acidobacteria (0.01%) were detected in the L1a and L3a samples. The relative abundances of Woesearchaeota were greater than 20% in the L2a, L3a, and L4a samples, but only 6.50% in L1a.
At the class level, the dominant Bacteria (> 1% relative abundance) among the four samples were Betaproteobacteria (21.46–28.52%), followed by Alphaproteobacteria (9.13–12.34%), Gammaproteobacteria (7.91–10.70%), Sphingobacteriia (5.90–7.61%), Actinobacteria (2.60–5.76%), Deltaproteobacteria (1.87–2.95%), and Planctomycetia (3.97–12.00%). The dominant Archaea among the four samples were Thermoprotei (35.97–58.29%), Methanomicrobia (24.08–32.84%), Thermoplasmata (6.94–8.86%), and unclassified Woesearchaeota groups (6.50–21.57%).
At the genus level, the dominant bacterial genera (excluding unclassified genera) among the four samples were Thiobacillus (8.92–16.78%), Hydrogenophaga (1.76–3.71%), Gemmobacter (1.38–3.56%), Algoriphagus (0.87–3.15%), Pirellula (1.07–2.44%), Parcubacteria-genera-incertae-sedis (0.83–2.16%), Ilumatobacter (1.25–1.70%), Sphingorhabdus (0.69–1.74%), Phaeodactylibacter (1.07–1.40%), and the acidobacterial groups GP16, GP6, GP3, and GP7 (0.67–2.42%). In addition to the above bacterial genera, other Bacteria exhibited higher abundances in individual samples including Lacibacter (1.15%) in L1, Saccharibacterial genera incertae-sedis (0.59–0.80%) in L2 and L3, Thermomonas (1.03–3.21%) in L1 and L3, and Litorilinea (0.55–0.68%) in the L2 and L4 samples. The dominant archaeal genera were Methanoregula (21.40–28.29%), Thermocladium (4.17–12.75%), Methanomassiliicoccus (6.92–8.77%), Woesearchaeota incertae-sedis-AR16 group (2.46–5.96%), and Methanothrix (1.02–1.91%). Each of the four samples exhibited unique archaeal genera including Aridibacter (0.01%) in L1a, Aquisphaera (0.01%) in L4a, and Halovenus (0.01%) in L3a and L4a.
Associations Between Environmental Factors And Dominant Genera
Differences in abundances among samples were investigated (Fig. 3) while considering the twelve and nine most abundant bacterial and archaeal phyla, respectively. The most abundant (> 1% relative abundance) bacterial genera among the four communities were the betaproteobacterial genera Thiobacillus and Hydrogenophaga, the alphaproteobacterial genus Gemmobacter, and the gammaproteobacterial genus Thermomonas. In addition, Methanoregula was the most abundant archaeal genus, and other archaeal genera exhibited higher abundances in individual samples including Thermocladium and Methanomassiliicoccus.
CCA was conducted to evaluate the relationships among community structures and environmental parameters, yielding numerous associations of overall community composition with several environmental parameters. Consequently, environmental parameters were analyzed in context of representative genera (Fig. 4). The abundances of the dominant bacterial genus Thiobacillus were most correlated with TP, followed by pH, CO32− concentrations, and temperature. The abundances of the next most dominant bacterial genera Hydrogenophaga and Gemmobacter were associated with TP and HCO3− concentrations. The Moderately abundant (1.50–4.00%) bacterial genera Thermomonas, Algoriphagus, and Sphingorhabdus in the L1 samples were correlated with TP, pH, and HCO3− concentrations. The abundances of the Parcubacteria genera incertae sedis and GP16 groups were strongly correlated with pH and Cl− concentrations, respectively. The minorly abundant (1.5–2.5%) genera of Rheinheimera, Nitrospira, and Gp6 in the L2 samples were significantly correlated with TN, in addition to the concentrations of Ca2+, SO42−, and Cl−. Furthermore, the abundances of the genera Pirellula, Gimesia, and Spartobacteria genera incertae sedis were related to K+, and Na+ concentrations, in addition to TOC and TS in the L3 and L4 samples. The abundances of the dominant (> 20%) archaeal genera Methanoregula, Methanothrix, Methanomassiliicoccus, Pacearchaeota incertae sedis-AR13, and Woesearchaeota incertae sedis-AR16 were highly correlated with TOC and TS in addition to the concentrations of K+, and Na+. In addition, Thermocladium abundances were particularly highly associated with HCO3− concentrations.