Biofilm effect of Lactobacillus plantarum

The decarboxylation of tricarboxylic L-malic acid to dicarboxylic L-lactic acid and CO2 consists of malolactic fermentation (MLF). This bioconversion, referred to as secondary fermentation, is highly desirable in red wines or some white wines and is typically carried out by indigenous lactic acid (LAB) bacteria or selected LAB cultures. 

Many species belonging to the genera Lactobacillus, Pediococcus, Leuconostoc, and Oenococcus are capable of converting L-malic acid into L-lactic acid, but the most common malolactic starter cultures are generally only selected strains of Oenococcus oeni. Several studies have based their attention on this subject in the past decade, and LAB species. Oeni was studied for use in wine making and in the MLF method. In particular due to its enzyme pathway, strains belonging to the Lactobacillus genus may also play an important role in extreme environments.

In this study the effect of incubation times (24 and 72 h) on the development of the biofilm was assessed. The study highlighted that the capacity to form biofilm was strain-dependent, regardless of the source of isolation and stress conditions. Specifically, two clusters were established, produced by high and low biofilm producer strains. 

Among high strains of producer, L. Plantarum Lpls22 was selected as the highest producer strain and was cultivated using oak supports in planktonic form or in biofilm. In order to evaluate planktonic and biofilm cell survival and to evaluate the impact of biofilm on L-malic acid conversion, model wines were used at 12 percent ethanol and pH 3.5 or 3.2. A significant survival decay was observed for cells in planktonic form. In comparison, cells showed high resistance in the biofilm life-style, ensuring a prompt and complete conversion of L-malic acid.

The biofilm life style of strains of Lactobacillus plantarum (L. plantarum) was evaluated in vitro as a new and effective biotechnological technique to ensure the conversion of L-malic acid under conditions of wine stress. Almost 68 L. plantarum in acid (pH 3.5 or 3.2) or ethanol (12 percent or 14 percent) stress conditions,  were isolated from different sources were evaluated for their ability to form biofilm.

this work was publish  in foods under title "Effect of Biofilm Formation by Lactobacillus plantarum on the Malolactic Fermentation in Model Wine" 

Currently, L. Plantarum strains, which have genes that encode enzymes such as Citrate lyase, phenolic acid decarboxylase, esterase, and glucosidase can have a positive effect on the taste of MLF and wine. MLF's effectiveness depends primarily on the concentration of the starter community as well as its ability to thrive in prohibitive wine conditions.

Culturable biofilm cells generated by L. Plantarum high producer strains were evaluated at the early stage (24 h) and late stage (72 h). Regardless of the stress conditions (p> 0.05), a sum of approximately 8.5 log CFU/mL was detected in the biofilms at the early stage. Similarly, no major differences (p> 0.05) between control and stress conditions were observed in late-stage biofilms as well.

The identified but cultivable cells listed in the biofilm were significantly lower (p< 0.05) than the early biofilm cells. After 72 h of incubation, a decrease of approximately 1 log CFU/mL was recognised. The decay of cultured cells may be the result of numerous causes, such as their entry into a viable but non-culturable state (VBNC), biofilm cell activity, and their particular aggregations. In fact, the formation of aggregates of bacterial cells could give rise to a single plate colony, resulting in an underestimation of cultured cells.

In addition, cells may also enter a VBNC state in a mature biofilm, resulting in the failure to develop in routine bacteriological culture media while retaining their metabolic activity. For several Lactobacillus species, including L. Plantarum is widely known, in some extreme conditions,

Enzymatic processes such as the conversion of L-malic acid to L-lactic acid may be adversely affected by the decrease number for cells in planktonic form. Indeed, MLF begins when the LAB population exceeds 6 Log CFU/mL, as stated by earlier research

The research team observed other results also along with the survival of L. plantarum. It was a high ethanol level (12 percent) with a low pH level (both pH 3.2 and pH 3.5). The biofilm life-style, on the other hand, is commonly accepted as an appropriate method to protect bacteria from harsh environmental conditions. In line with these results, the levels of culturable cells attached to biofilm were not significantly affected in this work (p> 0.05) in MW at pH 3.5 and pH 3.2, illustrating that cells were not significantly affected (p> 0.05). The biofilm type of L. plantarum was substantially more resistant than other planktonic.