heavy metal tolerant microalgae

Overview

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humans and other (micro)organisms, even at low part per billion (ppb) concentrations1. They can enter the
for HMs in drinking water exemplarily shown for cadmium at 0.003 mg/L, arsenic at 0.01 mg/L, lead at 0.01
mg/L, chromium at 0.05 mg/L, and copper at 2 mg/L12. Higher limits may apply to industrial effluents and
mg/L, cadmium at 0.8 mg/L, copper at 9.2 mg/L, lead at 0.36 mg/L, and zinc at 4.09 mg/L15. In contrast, the
pollution. Wastewater from an electroplating factory contained copper concentrations up to 15,560 mg/L,
along with significant levels of nickel (245 mg/L) and zinc (505 mg/L). Additionally, the lead concentration in
a wastewater from an industrial area in Delhi was found to be 326 mg/L while the cadmium concentration was
promising candidates for a deep physiological and HM tolerance analysis. As shown in Table 1, most of the
isolates exhibited tolerance to As(V) at 100 mg/L and Pb at 20 mg/L. However, Cd, Cu, and Cr(VI) were highly
strain Ehr15-5 showed a high tolerance to Cr(VI), maintaining growth even exposed to 15 mg/L. These five
Molecularly identified species and their morphological descriptions are given in Table 2.
Table 1. Algal tolerance to heavy metals. For green algae, the growth in the media containing heavy metals
nt sequence SSU genes were compared using BLAST. The SSU rRNA genes were found to be 98.96% similar to
result, the ITS sequence was most similar to Chlamydomonas inflexa CCAP 11/42 (FR865584.1) (99.16%)
followed by Chlamydomonas ulvaensis SAG2.72 (AJ749612.1) (99.07%). However, these two sequences were
100% identical to each other. Only a few sequences of these two species were available in the GenBank database.
Chlamydomonas pulvinata and the CCAP strains 11/166, 11/154 and 11/158. These isolates were 98.32–98.48%
merged sequence was 99.5–100% similar to Tetradesmus obliquus strains. Moreover, the isolate Ehr33-9 belongs
wide), which is slightly wider than Pseudanabaena limnetica, which shows a width range of 1.2 to 1.5 μm. Based
appeared in 25–50% of certain locations, alongside frequent occurrences of Chlamydomonas microalgae35. C.
Microalgal growth was evaluated at HM concentrations of 0 to 10 mg/L, with cultures exposed up to 20 mg/L.
lower metal concentrations, such as 0.5 mg/L of Cu and up to 2 mg/L of Cd for C. vulgaris RG1-4, growth was
increased growth at 0.4 mg/L of CdCl2, but growth declined at higher concentrations37. Among the tested
copper, even at concentrations up to 20 mg/L. In contrast, P. catenata Ehr15-5, a cyanobacterium, died after 4
days at a concentration of 0.5 mg/L of copper. The microalga most tolerant to Cd exposure was L. segnis Ehr31-
1; minimal adverse effects on growth were observed, even when Cd concentrations were elevated to 20 mg/L.
C. ulvaensis Ehr33-6, and T. obliquus Ehr33-9, with EC50 values of 22.13 ± 2.07 mg/L, 20.11 ± 0.32 mg/L, and
20.88 ± 0.52 mg/L, respectively. These values are significantly higher than the average EC50 value of 4.53 mg/L
found in the literature (Supplementary Table S8). In contrast, the diatom isolate Navicula permitis demonstrated
the highest EC50 value at 29.41 mg/L under similar conditions38. Notably, the same species of C. vulgaris and T.
obliquus exhibited much lower tolerance to Cu, with EC50 values of only 0.1 mg/L39 and 5.84 mg/L40, respectively.
In another study, T. obliquus showed an even lower EC50 value of 0.05 mg/L41. Other copper-tolerant microalgae
with corresponding EC50 values of 19.97 mg/L, 23.30 mg/L42, and 18.14 mg/L43, respectively.
Two isolates demonstrated higher tolerance to Cd than the average EC50 value of 6.24 mg/L reported in the
literature (Fig. 2). The isolate L. segnis Ehr31-1 showed no growth inhibition at a Cd concentration of 20 mg/L,
segnis Ehr31-1 can tolerate Cd concentrations exceeding 20 mg/L. The isolate C. vulgaris RG1-4 showed an EC50
value of 9.73 ± 0.19 mg/L, which is lower than the reference strain C. vulgaris SAG211-11b, which exhibited an
EC50 of 12.70 ± 2.58 mg/L. One study reported that two strains of cyanobacteria could tolerate 40 mg/L of Cd44,
but previously reported EC50 values were lower than the current results (Supplementary Table S9).
except for strains C. ulvaensis Ehr33-6 and T. obliquus Ehr33-9, which grew at 2 mg/L without significant
the reference strain. The growth rate inhibition experiments were done in three biological replicates (n = 3) and
minor effects at up to 10 mg/L, with an EC50 of 14.34 ± 5.06 mg/L. However, it could not tolerate Cu or Cd at

Methods (brief)

A total of 51 microalgae cultures were isolated from the collected samples, consisting of 44 green microalgae
The raw data from the ICP-MS measurements, including HM concentrations, dry biomass, and the calculated
Samples were taken from three locations, Roter Graben near Freiberg (50°56’24.1”N 13°22’20.1”E), three
(Environmental Systems Research Institute, Inc. (Esri))101. Sample collection was conducted in accordance with
To enrich the microalgae from the samples, they were cultured in both solid media containing 1.5% agar and
colonies were collected with a fine needle and streak-plated onto new solid media for isolation. However,
bacteria were reduced, but not eliminated. Thus, from each treatment, 20 µL samples were streaked onto suitable
27’s tolerance to high concentration of heavy HM(oid)s: As(III) – 100 mg/L (NaAsO2), As(V) – 100 mg/L
degradation. From the fresh liquid culture, 3 mL samples were taken and centrifuged using refrigerated
assessed at both the beginning and the end of the test. Furthermore, 10 mL of filtered samples were collected at
Each day, a 1 mL sample was collected and thoroughly mixed with a pipette if necessary. The sample was then
the method in reference128. A 1 mL of the sample was transferred to a 2 mL tube and centrifuged at 14,000 g for
concentrated HNO3 (~ 65%) and stored at -20 °C for further analysis of HM concentrations. Samples’ metal
concentration were analysed by an inductively coupled plasma mass spectrometer (iCAP™ RQ ICP-MS, Thermo
The details of ICP-MS calibration procedures were: Scandium (Sc) and rhodium (Rh) were used as internal
concentrations for the calculation were the ICP-MS measured concentrations. And they were calculated
tissue and blood samples using Chelex 100 resin. Biol. Proced. Online. 20, 12 (2018).
the collection of microalgal samples from mining areas. We also appreciate our colleagues Rustiana Yuliasni,

Implications

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Update history

The five most recent substantive edits to this page, classified major (evidence or structure moved), correction (a published value or statement was wrong and has been fixed), or minor (narrative rewritten without changing the underlying evidence). Each description is derived from what the edit did to this page; the linked commit is the authoritative record, routine regeneration passes are excluded, and the full version history lives in git. When DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.

Commit	Date	Change	Description
b01ec52c	2026-08-04	major	2 sections added
d49e450f	2026-08-03	major	5 sections added; narrative text revised