**3.2 Articles description**

**Table 3** shows the detailed information of each of the articles: year of publication, authors, journal in which it was published, the molecular method applied for the identification of picocyanobacteria, and type of water body where the research was carried out.

#### **Figure 1.**

*Flowchart of the research search strategy. Source: own elaboration through the application diagrams.net.*







#### **Table 3.**

*Summary of the results of each article selected for the research.*

The number of publications per year ranged from 2001 to 2021. Of the 34 articles analyzed, it was found that 2019 was the year with the highest number of publications recorded on the subject, followed by 2017, which had five and four publications, respectively (**Table 3**) see annex. This is evidence that research on picocyanobacteria has increased in recent years.

In addition, **Figure 2** (see annex) shows the countries with the greatest number of research projects developed for the study and identification of picocyanobacteria in the environments described above. Thus, the country where the institute or center where the research was carried out is located was identified. It is important to clarify that these countries corresponded to the sampling sites.

The countries with the highest number of research studies were China (7), United States (6), and United Kingdom (3). The countries with at least two publications were: Brazil, Canada, Spain, Italy, Japan, and Russia. Germany, Argentina, Switzerland, Sweden, Austria, and Poland had only one publication.

**Figure 3** (see annex) shows the picocyanobacteria identified in the articles analyzed, showing that *Synechococcus* was the predominant genus in surface water bodies, with a frequency of 24 articles, followed by *Cyanobium* with a frequency of 4 articles.

#### **Figure 2.**

*Countries where research studies on picocyanobacteria molecularly identified in surface waters have been carried out.Source: own elaboration through the software program Microsoft Excel.*

#### **Figure 3.**

*Predominant picocyanobacteria in freshwater bodies. Source: own elaboration through the statistical tool RStudio.*

As shown in **Figure 4** (see annex), oligotrophic lakes were the most studied for the identification of picocyanobacteria with a relative frequency of 32%, followed by oligomesotrophic lakes with 18.6% and mesotrophic and eutrophic lakes with 14% each.

#### **3.3 Research topics on picocyanobacteria**

The keyword mapping shows that the words: Cyanobacterium, Cyanobacteria, *Synechococcus*, Lake, Microbiology, 16S RNA, and Picocyanobacteria are the ones that

#### **Figure 4.**

*Trophic state of the lakes studied in the articles of interest. Source: own elaboration through the statistical tool RStudio.*

**Figure 5.** *Keyword mapping used in the search. Source: own elaboration through the application VOSviewer.*

show the highest tendency in the present research with a frequency in the number of articles of 22, 18, 16, 14, 11, 11 and 10, respectively (**Figure 5**) see annex.
