Reduction of Spermidine Content Resulting from Inactivation of Two Arginine Decarboxylases Increases Biofilm Formation in Synechocystis sp. Strain PCC 6803

Abstract

The phototropic bacterium sp. strain PCC 6803 is able to adapt its morphology in order to survive in a wide range of harsh environments. Under conditions of high salinity, planktonic cells formed cell aggregates in culture. Further observations using crystal violet staining, confocal laser scanning microscopy, and field emission-scanning electron microscopy confirmed that these aggregates were biofilms. Polyamines have been implicated in playing a role in biofilm formation, and during salt stress the content of spermidine, the major polyamine in , was reduced. Two putative arginine decarboxylases, Adc1 and Adc2, in were heterologously expressed in and purified. Adc2 had high arginine decarboxylase activity, whereas Adc1 was much less active. Disruption of the genes in resulted in decreased spermidine content and formation of biofilms even under nonstress conditions. Based on the characterization of the mutants, Adc2 was the major arginine decarboxylase whose activity led to inhibition of biofilm formation, and Adc1 contributed only minimally to the process of polyamine synthesis. Taken together, in the shift from planktonic lifestyle to biofilm formation was correlated with a decrease in intracellular polyamine content, which is the inverse relationship of what was previously reported in heterotroph bacteria. There are many reports concerning biofilm formation in heterotrophic bacteria. In contrast, studies on biofilm formation in cyanobacteria are scarce. Here, we report on the induction of biofilm formation by salt stress in the model phototrophic bacterium sp. strain PCC 6803. Two arginine decarboxylases (Adc1 and Adc2) possess function in the polyamine synthesis pathway. Inactivation of the and genes leads to biofilm formation even in the absence of salt. The shift from planktonic culture to biofilm formation is regulated by a decrease in spermidine content in This negative correlation between biofilm formation and polyamine content, which is the opposite of the relationship reported in other bacteria, is important not only in autotrophic but also in heterotrophic bacteria.

Cyanophycin and arginine metabolism in cyanobacteria

“…Arginine decarboxylase (speA gene product, All3401) is the first enzyme in a polyamine biosynthesis pathway that in Anabaena produces sym-homospermidine [72]. On the other hand, two arginine decarboxylase-encoding genes and their encoded proteins (Slr1312 and Slr0662) have recently been characterized to be involved in spermidine synthesis in Synechocystis [73]. The different polyamines accumulated in Anabaena and Synechocystis reflect the observation that heterocystous cyanobacteria specifically accumulate sym-homospermidine that is needed for heterocyst differentiation [72,74], whereas in Synechocystis spermidine content negatively correlates with biofilm formation [73].…”

Homospermidine biosynthesis in the cyanobacterium Anabaena requires a deoxyhypusine synthase homologue and is essential for normal diazotrophic growth

“…In particular, homospermidine can be synthesized from putrescine that is produced from decarboxylation of ornithine or indirectly from the decarboxylation of arginine, e.g., via arginine decarboxylase and agmatinase (Michael, ). Whereas cyanobacterial genomes generally appear to lack a gene encoding ornithine decarboxylase, they contain genes putatively encoding arginine decarboxylase and agmatinase (https://genome.annotation.jp/cyanobase), and these genes or enzymes have been characterized in a few cases (Schriek et al, ; Burnat and Flores, ; Kera et al, ). The cyanobacteria do not appear to have, however, a typical homospermidine synthase, and a DHS‐like protein has instead been suggested as a possible alternative homospermidine synthesizing enzyme (Shaw et al, ).…”

Polyamine‐independent growth and biofilm formation, and functional spermidine/spermine N‐acetyltransferases in Staphylococcus aureus and Enterococcus faecalis

“…The spirochaete and agent of Lyme Disease Borrelia burgdorferi does not synthesize polyamines but it is absolutely dependent on the spermidine uptake transporter potABCD for growth (Bontemps-Gallo et al, 2018). Polyamines are also essential for robust biofilm formation in Y. pestis (Patel et al, 2006), Vibrio cholerae (Karatan et al, 2005;Lee et al, 2009) and Bacillus subtilis (Burrell et al, 2010;Hobley et al, 2014;Hobley et al, 2017), whereas endogenous polyamines inhibit biofilm formation in Shewanella oneidensis (Ding et al, 2014), A. tumefaciens and Synechocystis (Kera et al, 2018). It has been known for more than 50 years that many Gram-positive species do not contain spermidine or tetraamine spermine ( Fig.…”