In the case of PssT, deleting its C-terminal part made the protein more prone to homointeractions, but lack of the same domain made its interactions with PssP impossible. Deleting the C-terminal part of PssT in the RtAH1 mutant resulted in production of EPS with prevalence of HMW fractions. The results obtained in this work indicate functional interconnection between the PssP2 protein encoded within the Pss-II polysaccharide synthesis region with the EPS polymerization system encoded by the genes in the Pss-I region:Demeclocycline hydrochloride glycosyltransferase PssC active at the EPS unit assembly step and proteins PssP and PssT involved in polymerization/transport outside the cell. The mutant with a disrupted pssP2 gene and encoding a protein lacking 153 amino acids from its C-terminal cytoplasmic domain produced more EPS than the wild type strain, and in addition to a quantitative increase, domination of HMW fractions containing chains with molecular masses higher than in the wild type was observed. In line with this was the significant change in the autoaggregation properties of the mutant. The pssP2 integration mutant induced fewer, but all pink nodules and the fresh masses of clover plant shoots were higher than in plants infected with the wild type. LMW EPS in S. meliloti was shown to be important for nodule invasion,A23187 and HMW EPS is symbiotically inactive. It was shown that HMW EPS preserve Rhizobium sullae from desiccation. The data concerning the role of HMW EPS in R. leguminosarum is scarce, however certain pieces of data indicate that it may be advantageous to rhizobia during the infection step. The phenotypes of pssP2::pKP2 and pssT::pAH1 mutants support this idea. Both produce more HMW EPS, induce fewer but all effective nodules than the wild type, and the average green masses of plants inoculated with these strains is higher than for RtTA1. In other bacteria LMW and HMW polysaccharides play different roles in infection, virulence and persistence. In S. flexneri, the Stype Oag contribute to virulence, and VL-type Oag chains to bacterial resistance to complement. In Pseudomonas aeruginosa, LPS with long -type Oag chains contributes to greater resistance to complement and virulence in mice. In Salmonella typhimurium, both L-type and VL-type Oag chains have been shown to confer resistance to complement. The S-type and L-type LPS Oag chains of S. flexneri confer colicin E2 resistance. PssP2 was shown to interact with PssP, PssT, and one of the studied glycosyltransferases involved in synthesis of the octasaccharide EPS subunit, i.e. PssC, which acts by adding a glucuronosyl residue to the growing chain.